Some standard content:
Standard of the Ministry of Electronics Industry of the People's Republic of China Antenna Test Method
Polarization Measurement
This standard applies to the polarization measurement of antennas. Definition of polarization and its description method
1.1 Overview
1.1.1 Definition of polarization
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Polarization is a characteristic of a single-frequency electromagnetic field, which describes the shape and orientation of the trajectory of the vector endpoints changing with time. By convention, when only plane waves or local plane waves are considered, it is only necessary to specify the polarization of the electric field vector E, because for plane waves with known propagation directions, the magnetic field vector H has a simple relationship with the electric field vector E: H=Y.(SxE)
Where: Y. ——The characteristic admittance of the medium, in vacuum Y. —Unit vector in the propagation direction,
eThe dielectric constant of the medium;
——The magnetic permeability of the medium.
377=2.66×10-S,
The far field radiated by the antenna is usually observed in a small area, in which the field can be approximately regarded as a plane wave propagating radially away from the antenna. The electric field is in a plane perpendicular to the propagation direction. Its endpoint trajectory is generally an ellipse, and the ellipse may degenerate into a straight line or a circle. Accordingly, the polarization is called elliptical polarization, linear polarization or circular polarization. 1.1.2 Handing of the polarization ellipse
The direction of rotation of the endpoint of the electric field vector that depicts a circle or ellipse in the polarization plane (perpendicular to the propagation direction) is called the polarization direction or handing. If the observer looks in the direction of propagation and the rotation direction is clockwise (counterclockwise), then this handing is called right-handed (left-handed), see Figure 1.
The Ministry of Electronics Industry of the People's Republic of China Issued on January 5, 1985 Implemented on July 1, 1986
Clockwise
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Figure 1 Description of handedness
Direction of propagation
Direction of propagation
1.1.3 Method of describing polarization ellipse
Elliptical polarization is characterized by the axis ratio, handedness and inclination of the polarization ellipse. The inclination is the angle between the major axis of the ellipse and a reference direction in the plane in which it lies. For plane waves, when looking at the polarization plane in the direction of propagation, the inclination is measured clockwise from the reference direction. 1.1.4 Polarization of the antenna
The polarization of an antenna in a given direction is defined as the polarization of the electric field vector E, radiated by the antenna in the far field in that direction. In the spherical coordinate system, its polarization in the (, in) direction is shown in Figure 2. 0=0-
antenna position,
8-90°
$=90°
Figure 2 Polarization ellipse relative to the antenna coordinate system 1.1.5 Selection of reference direction
The reference direction for the orientation of the polarization ellipse is arbitrarily selected, but the u axis is usually taken as the reference direction. For most antenna pattern measurements2
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, it is appropriate to establish a local coordinate system in a plane perpendicular to the line connecting the antenna under test and the source antenna. One axis of the coordinate system is parallel to the surface of the test field, and the other axis is perpendicular to it. The horizontal axis is usually selected as the reference direction. This standard adopts this provision. 1.1.6 Orientation of the local coordinate system
When examining the antenna receiving an incident plane wave from a given direction, it should be noted that the wave emitted by the antenna has a different propagation direction from the incident plane wave. Since the polarization direction is relative to the propagation direction, in order to be consistent with the definition of wave polarization, the local coordinate system related to each wave should be oriented as follows. See Figure 3. Antenna
Figure 3 Relationship between the polarization characteristics of an antenna when transmitting and receiving E, the far-field loss of an antenna; E, the loss of a radiated wave that matches the antenna polarization, E, the loss of a radiated wave with arbitrary polarization 1.1.7 Antenna Receiving Polarization
When the power density of a plane wave radiated from a given direction is constant, the polarization of the incident wave that produces the maximum response (open-circuit voltage, short-circuit current or effective power) at the antenna terminal is called the antenna receiving polarization. The receiving polarization of the antenna is the same as the polarization of the antenna. 1.1.8 Polarization EfficiencyWww.bzxZ.net
If the polarization of the incident plane wave is different from the receiving polarization of the antenna, then polarization loss will occur due to this mismatch. Polarization mismatch is usually calculated using polarization efficiency*p.
Polarization efficiency is defined as the ratio of the power actually received by the antenna when the intensity of the radio wave is the same to the power received when polarization matching occurs in the same direction.
1.1.9 Co-polarization and cross-polarization
If the polarization of the radio wave and the receiving polarization of the antenna have the same axial ratio, the same polarization rotation direction and the same long axis spatial orientation, the polarization efficiency reaches the maximum value. At this time, the incident wave is called co-polarized for the receiving polarization of the antenna. If the axial ratio of the two waves is the same, the long axes are orthogonal and the rotation directions are opposite, the polarization efficiency is zero. At this time, the incident wave is called cross-polarized for the receiving polarization of the antenna. 1.2 Poncalai Sphere
1.2.1 Geometric Representation of Polarization
The Poncalai Sphere is a useful and intuitive geometric representation for describing polarization effects. The basis for establishing the Poncalai Sphere is that any wave can be decomposed into two orthogonal components (they can be two orthogonal linear polarizations, elliptical polarizations or circular polarizations). Points on the sphere correspond to all possible polarizations.
The Poincare sphere is shown in Figure 4. Any point W on the sphere uniquely represents the polarization state of the wave. Point W can be represented by the coordinates 2 on the sphere:
*This factor is also called the polarization mismatch factor and the polarization reception factor. 3
135° linear polarization
Horizontal linear polarization
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Left-hand circular polarization
Right-hand circular polarization
Vertical linear polarization
-45° linear polarization
Figure 4-Poncali sphere representation of the polarization state of a plane wave W When W is decomposed into E (horizontal linear polarization) and E (vertical linear polarization) t=a
When W is decomposed into E45- (45° linear polarization) and E13 (135° linear polarization) 5=8
When W is decomposed into E, (left-hand circular polarization) and E (right-hand circular polarization) s=y
The correspondence between the points on the Poncali sphere and all possible polarizations is shown in Figure 5. Left-hand circular polarization
A pole represents circular polarization
Latitude represents axial ratio
Equator represents linear polarization H
Right-hand direction in the lower hemisphere
Right-hand circular polarization
Left-hand direction in the upper hemisphere
45° linear polarization
Longitude represents inclination
Figure 5 represents polarization state on the Poncalai sphere
1.2.2 Complex polarization ratio
The complex polarization ratio is given by the following formula:
p,=prejot
p,=ppejso
pc=pcej8c
（3）
（5）
Where PEtga=Ev/Ew
Pp= tgB=E135*/E4s'1
pc=tgV=Er/ELo
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8, 8 and 6c are the relative phases between the corresponding orthogonal components. The relative phase 0c of the circularly polarized component is defined by the angle between the instantaneous electric field vector of the right-handed circularly polarized component and the horizontal direction at the moment when the electric field vector of the left-handed circularly polarized component is in the horizontal direction, as shown in Figure 6. Therefore, when the electric field vectors of the two waves are in the same horizontal direction at the same time, the two circularly polarized components are in phase. Vertical
Figure 6 Definition of the phase reference line for orthogonal circular components 1.2.2.1 The axis ratio of the ellipse can be expressed as the circular polarization ratio: pe+1
The sign of the denominator indicates the polarization rotation. Right-hand circular polarization is positive and left-hand circular polarization is negative. Its inclination angle is given by the following formula: t=dc/2
1.2.3 Numerical expression of polarization efficiency
(8)
If the point on the Poncalei sphere corresponding to the polarization of the receiving antenna is Ar, and the point corresponding to the polarization of the transmitted wave is W, then the polarization efficiency can be determined by the following formula:
p=cos-
where 2 is the angle between A and W in Figure 7. P can also be expressed by polarization ratio: left-hand circular polarization
horizontal linear polarization
right-hand circular polarization
45° linear polarization
Figure 7 shows the polarization state p of the incident wave W and the receiving antenna A drawn on the Poncalai sphere
[1+pwpr2
(1+p)(1+p)
（10）
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Where: w and, are any one of the three polarization ratios, and c. It can be seen that this formula is similar to the mismatch loss formula of a lossless transmission line. The reflection coefficients of the signal source and the load are similar to Pw and P, respectively. Using the relationship between the circular polarization ratio and the axial ratio, the polarization efficiency can also be written as: =(1+ pw)(1+y,) +4yw),+(1- ve)(1- p,)cos42(1+w2)(1+y,2)
（11）
wherein the axis ratio takes a positive value for right-hand circular polarization and a negative value for left-hand circular polarization, and the angle 4 is the relative phase difference (oc) between the two polarizations W and A, w.,
1.3 Relationship between polarization box and Poncalai sphere
Poncalai sphere and polarization box are a graphical method for describing Stokes parameters, which can be used to convert one set of polarization parameters into another set of polarization parameters. Figure 8 shows the relationship between the polarization box and the Poncalai sphere. It can be proved that the sides and diagonals of the polarization box have the following relationship:
Diagonal of side
Y,=cos2a
Y,=cos2β
Yc=cos2y
X,=sin2a
Xp=sin2β
Xc=sin2y
The following example illustrates the conversion between polarization parameters. Assume that pt and S are known from measurement, and pc, c, > and inclination are the quantities to be determined. From the polarization box, we can see that:
Ye=X,sind,
left-hand circular polarization
linear polarization
horizontal linear polarization
so we have:
From the definition of e, we can calculate:
Figure 8 Polarization box and its relationship with the Poncalai spherecos2y=sin2asind,
a=arctgpy
so we can determine", from which Pc can be calculated by the following formula:pc=tgy
oc=arc cos
=arccos
（12）
（14)
Thus, checking the polarization box eliminates the ambiguity of c defined only by its cosine. Once Pc and 8c are determined, the axial ratio> and the inclination angle can be obtained from the following formula:
1.4 Unit vector representation of polarization
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T=0c/2
1.4.1 A general form of representing the polarization unit vector as a matrix (17)
For some applications, it is advantageous to represent the polarization of the field as a unit vector. For example, the wave W can be represented by two orthogonal Elliptical polarization is expressed as: W
Egeide
sinpeide
When E and E are (H, V), (45, 135°) or (L, R), p and are (a,), (B,.oD) or (V, 8c).
To illustrate the application of polarization loss, the transmitting wave W and the receiving polarization A of the antenna are expressed in circular polarization components: W
The normalized voltage response of the antenna to the wave is: OSyH
(sinywej(oc)w
siny.ej()
Vi+pewl
=(A, W)=Atw
where the superscript + indicates the complex conjugate of the transpose (note that V is a phasor). Matrix operations yield: =cosywcosy,(1 + pcwpe,*)
=cosy.cosyw+siny,sinywei4,
where Pc, * is the complex conjugate of Pc. And
4= (dc)w-(8c), =2(Tw-T,)
The polarization efficiency is given by the following formula!
where * is the complex conjugate of.
p=00*= [[2
（20）
The process of determining the polarization efficiency by the loss method is as follows: the power density of the incoming wave and the effective aperture of the antenna are each decomposed into two components corresponding to two orthogonal polarizations, so that each component of the incoming wave is polarization-matched with the corresponding component of the antenna effective aperture. Generally speaking, the partial responses generated by paired polarization-matched components do not necessarily add up to obtain the maximum value. The condition for polarization matching is \, =vw and 4=0, at which time: p =|3=(cos-y+siny)2=1.
·（26)
2 Polarization measurement
2.1 Overview
2.1.1 Necessity of polarization measurement
The radiation pattern of an antenna designed for a specified polarization is usually described by the field component of that polarization. This description is not comprehensive because cross-polarization components may also exist. To fully describe, the polarization must be measured with direction as a variable. Especially in the direction deviating from the main beam peak, the polarization may be very different from the design value, and even on the main beam, its change may be quite large. 2.1.2 Classification of polarization measurement methods
The measurement methods of antenna polarization can be roughly divided into three categories: a. Obtain partial data of the antenna polarization characteristics; b.
Obtain complete polarization data, but need to be compared with a polarization standard; obtain complete polarization data, but do not need a polarization standard, or know the polarization characteristics of the measurement antenna in advance. c.
The second method is called the transfer method or comparison method, and the third method is called the absolute method. The choice of method depends on the type of antenna being measured, the required accuracy, the amount of polarization data required, the time available for measurement, and the allowable cost. 2.1.3 Specific methods of polarization measurement
Specific polarization measurement methods include the following: a. Polarization pattern method; b. Rotating source method; c. Multiple amplitude component method; SJ2534.9--85; d. Phase amplitude method.
To fully describe the polarization characteristics of the antenna, the polarization ellipse (axis ratio and inclination) of the wave radiated by the antenna and the handedness of the electric field vector must be determined. The polarization state of the wave can be represented by a unique point on the Poncalai sphere. Some measurement methods cannot obtain sufficient data to fully describe the polarization state of the wave, so the unique point on the Poncalai sphere cannot be determined. For example, when the axis ratio and inclination have been determined, but the handedness has not been determined, it is unclear which point is the one of the two conjugate points in the upper and lower hemispheres of the Poncalai sphere. When the handedness is known, or the polarization is close to linear polarization, that is, the two conjugate points are close to each other, the data is sufficient. 2.1.4 System Stability
It should be noted that some of the methods discussed below require sequential measurements; for the second measurement, one or more antennas need to be rotated. The stability of the system is therefore a question, since any change in frequency or gain in the system will produce measurement errors. Measurement errors are particularly severe when the antenna must be calibrated over a large field of view, as in the near-field detection method. For these methods, an extremely stable signal source is essential. To achieve the required frequency stability, frequency synthesizers and phase-locking techniques can be used. For polarization measurement methods where multiple measurements are made simultaneously, such high frequency stability is not required. 2.2 Measurement of Polarization Pattern
2.2.1 Measurement Method
The polarization pattern method can determine the tilt angle and the axis ratio, but not the handedness of the polarization. For this measurement, the antenna under test can be operated in either receiving or transmitting mode. If working in the transmitting mode, the method is essentially to rotate the dipole or other linear polarization detector in a plane perpendicular to the direction of human transmission and measure its relative voltage response. When the system is polarization matched, the value is 1. 2.2.2 Definition of polarization pattern
The curve of the value drawn with the receiving polarization of the linear polarization detection antenna as the inclination angle is called the polarization pattern (see Figure 9). The polarization pattern is tangent to the polarization ellipse of the field at the endpoints of the major axis and the minor axis, thus determining the axis ratio and inclination of the incident wave. Polarization pattern
Polarization circle
Figure 9 Polarization pattern of wave
2.2.3 Explanation of the method
It can be explained as follows using the Poncalli sphere. For example, as shown in Figure 10, the polarization of the incident wave W is located on the sphere. Rotate the linear polarization detection antenna The receiving polarization A, is always located on the equator of the sphere. The square root of the relative response! | is equal to the cosine of half the angle between W and 4, as shown in Figure 10. When the inclination of A, rotates, the position of A, on the sphere moves at the equator, causing the value of! | to change. Plotting the function relationship of "" against the inclination angle, the polarization direction diagram is obtained. It should be noted that if W is located at the conjugate point W, in the lower hemisphere, the same polarization direction diagram is obtained. To avoid confusion, the polarization rotation direction should be measured. 8
Due to the response
(oc),=2r.
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Left-hand circular polarization
Right-hand circular polarization
Figure 10 Polarization direction diagram method represented by the Poncalei sphere4=(0c)w-(c),
=cosy,cos yw+ siny,sinywei4
4 = (8c)w-(dc),=2(TW-T,)
So the polarization direction diagram can also be obtained from the polarization loss formula. This can be explained by the phasor diagram in Figure 11. When t, changes, the value of "" also changes accordingly. Draw the function relationship of ! to t, and you will get the polarization direction diagram. Complex plane
Cosy,Co5YW
Figure 11 Polarization pattern s = (oc)w-(oc) obtained using the polarization matrix result,
The polarization efficiency of the system is equal to 1, so the polarization efficiency can be obtained directly from the polarization pattern. This is a useful result if the antenna under test is intended to be used in a system that is equipped with a linearly polarized antenna with a known spatial orientation. The disadvantage of the polarization pattern method is that when the antenna under test is fixed, the detector antenna must rotate 360°, so it is not convenient to obtain polarization data as a function of direction. 2.3 Rotating source method
2.3.1 Measurement method
The rotating source method can determine the function of axis (rather than rotation or tilt) to direction. This method is that the linearly polarized source antenna is continuously rotated when the observation direction of the antenna under test changes. This method is of great value for measuring near-circularly polarized antennas. The rotation of the source antenna causes the tilt angle Tw of the incident field to rotate at the same rate. When cutting and recording according to 6 or, the rotation rate Tw should be much higher than 6 or. The time response of the recording system should be able to keep up with the changes of 1. This method can be extended to the spiral cutting mode of the radiation pattern (in this case tw, and are all 9
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in change. And TwΦ6), so that the axial ratio of the antenna in all directions can be recorded on an axial ratio radiation pattern. 2.3.2 Example
The radiation pattern of an elliptically polarized antenna obtained by the rotating source method is shown in Figure 12. If the amplitude change is expressed in decibels, the axial ratio (also expressed in decibels) recorded in any direction on the radiation pattern is the width of the amplitude deviation envelope. This particular antenna is basically circularly polarized in the axial direction (6=0°) and elliptically polarized in the direction of the maximum value of the side lobe. 10
2.3.3 Measurement error
Angle (9)
Figure 12 Continuously scanned polarization radiation pattern as a function of angle Reflection and multipath effects of the source antenna will introduce measurement errors. For example, when the reflected wave intensity is 40 dB lower than the direct wave intensity, the introduced axial ratio measurement error is about 0.17 dB.
2.4, Multiple Amplitude Component Method
2.4.1 Measurement Method
The multiple amplitude component method can be used to completely determine the polarization without measuring the phase. It has been proven that the polarization of the wave can be determined by the response amplitude of 4 antennas with different but known polarizations. For the sampling antenna polarization, it is most convenient to choose horizontal or vertical linear polarization, 45° or 135° linear polarization, left-hand or right-hand circular polarization and any fourth component different from this set of 6 components. These sampling antennas should have known gains and the measurement equipment should be properly calibrated to compensate for the difference in gain. From these data, the polarization of the wave, that is, the polarization of the antenna under test, can be completely determined. The Stokes parameters can be obtained by graphical methods or linear equations. 2.4.2 Description of the method
It is usually more convenient to measure the value of the polarization ratio, so all six components are used. This method can be illustrated by the Poncalai sphere shown in Figure 13. The linear polarization ratio, diagonal polarization ratio and circular polarization ratio (Pz, Pp, Pc, respectively) are measured. From these data, the angles 2α, 2β and 2V are determined. These angles define the loci on the Poncalai sphere corresponding to all possible polarizations with polarization ratios PL, P, and Pc. The common intersection of the three loci determines the polarization of the wave. 10
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Left-hand circular polarization
Right-hand circular polarization
Figure 13 Multiple amplitude component method of polarization measurement If > is positive, the handedness is right-handed, and if √ is negative, the handedness is left-handed. Complex c+
Use pc to determine the axial ratio and handedness, because =
The phase angle of the circular polarization ratio is calculated as follows:Y,
Be=arctg
where Y, and Y are obtained from the polarization box:
Since the tilt angle is half of c, the polarization is completely determined. 2.4.3 Improved method
(1-pp\)
(1+pp\)
(1-pr)
(1+p,2)
If the handedness is not required, a modified method of the multiple amplitude component method (which only requires a single linearly polarized antenna for measurement) can be used to determine the axial ratio and tilt angle within the entire radiation pattern of the antenna under test. The radiation pattern of the antenna under test is measured with the source antenna oriented at 0° (horizontal), 45°90° (vertical) and 135°. From these data, p and pD are calculated, and thus c is obtained, and the inclination angle can be determined. From the polarization box, it can be seen that the axial ratio is:
y=-ctga
where:
arc.cos(Y+Y)%
For high-precision results, a linearly polarized antenna should be a polarization standard. 2.5 Phase-amplitude method
2.5.1 Overview of measurement method
With the phase-amplitude method, all the data required to define the complete polarization can be measured simultaneously. By cutting through the entire set of directional patterns, the entire polarization pattern and radiation pattern of the antenna can be measured in one operation. The required measurement equipment is shown in Figure 14. The field of the antenna under test is sampled with a dual-polarized receiving antenna, and the antenna under test operates in the transmitting mode. The output of the receiver is the response amplitude of each polarization of the sampled antenna and its relative phase. If the two polarizations are orthogonal, the complex polarization ratio can be obtained. The polarization of the sampling antenna should be known. And the gains of the two antenna-receiver channels should be the same. 11
2.5.2 Automatic test
Antenna under test W
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Dual polarization sampling antenna
Mixer
Amplitude and phase receiver
Mixer
Figure 14 Test equipment for phase-amplitude method of polarization measurement Usually, it is not economically feasible to design a pure polarization sampling antenna with known polarization. If the test site is equipped with automatic test equipment with a computer, it is not necessary to use a precise linear polarization or circular polarization antenna. Because as long as the actual polarization of the sampling antenna is known, the measurement data can be corrected by calculation. For example, suppose the measurement requires an orthogonal circularly polarized sampling antenna, but the actual sampling antenna is only nearly circularly polarized, but not perfectly circularly polarized. As long as the polarization direction is known, the polarization of the sampling antenna can be measured by the improved multiple amplitude component method. By sending these data to the computer, the computer software can be designed to automatically compensate for the characteristics of the sampling antenna. 2.5.3 Polarization adjustment network
If the antenna test site is not automated and is not equipped with a computer, another method can be used, that is, a polarization adjustment network is used outside the sampling antenna to obtain the required polarization. A typical sampling antenna can be composed of two orthogonal linear polarization antennas. For example, they can feed the same reflector antenna. The antenna is connected to the input of the amplitude and phase receiver. The simplest polarization adjustment network is an attenuator and a phase shifter in series in each channel. These networks can be designed to work at radio frequency and connected in series between the sampling antenna and the mixer of the receiver. In addition, the network can also be designed to work at intermediate frequency, so that the same network can be used at any frequency covered by the receiver. If the measurement system is capable of digital data recording and a suitable computer is available, a digital polarization correction network can be used. If right-hand or left-hand circular polarization is required, the network can be adjusted using the polarization pattern method. A nominal linearly polarized reference antenna can be used. Usually the adjustment accuracy of circular polarization is limited by reflections and misalignment in the test field. When precise measurements are required, a polarization standard is needed to adjust the gain of the two channels. If a linear polarization standard is used, the output signals of the two channels are adjusted to be equal. For horizontal linear polarization, Sc is adjusted to zero degrees. The system can be checked by rotating the standard antenna 360°. The output level should remain unchanged, while the phase angle c should always be twice the standard rotation angle. The rotation angle is measured relative to the horizontal direction. 2.5.4 Measurement using a circularly polarized sampling antenna The measurement of the polarization of the antenna under test using a circularly polarized sampling antenna can be illustrated by the Poncalai sphere in Figure 15. The complex circular polarization ratio obtained by measurement is:
Left-hand circularly polarized sampling antenna
Measured antenna
Right-hand circularly polarized sampling antenna
Figure 15 Phase amplitude measurement using circularly polarized antenna tgy1 Measurement method
The function of axialization (rather than rotation or tilt) to direction can be determined by the rotating source method. This method is that when the observation direction of the antenna under test changes, the linear polarization source antenna rotates continuously. This method is of great value for measuring near-circular polarization antennas. The rotation of the source antenna causes the tilt angle Tw of the incident field to rotate at the same rate. When cutting and recording according to 6 or, the rotation rate Tw should be much higher than 6 or. The time response of the recording system should keep up with the changes of 1. This method can be extended to the spiral cutting mode of the radiation pattern (at this time tw, and are 9
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are changing. And TwΦ6), so that the axial ratio of the antenna in all directions can be recorded on an axial ratio radiation pattern. 2.3.2 Example
The radiation pattern of the elliptically polarized antenna obtained by the rotating source method is shown in Figure 12. If the amplitude variation is expressed in decibels, the axial ratio (also expressed in decibels) recorded in any direction on the pattern is the width of the amplitude deviation envelope. This particular antenna is essentially circularly polarized in the axial direction (6 = 0°) and elliptically polarized in the direction of the maximum sidelobe. 10
2.3.3 Measurement errors
Angle (9)
Figure 12 Polarization pattern of a continuous scan as a function of angle Reflections from the source antenna and multipath effects can introduce measurement errors. For example, when the reflected wave strength is 40 dB lower than the direct wave strength, the axial ratio measurement error introduced is about 0.17 dB.
2.4, Multiple Amplitude Component Method
2.4.1 Measurement Method
The multiple amplitude component method allows complete determination of polarization without measuring the phase. It has been shown that the polarization of a wave can be determined from the amplitude responses of four antennas with different but known polarizations. For the sampling antenna polarization, it is most convenient to choose horizontal or vertical linear polarization, 45° or 135° linear polarization, left-hand or right-hand circular polarization and any fourth component different from the set of six components. The sampling antennas should have known gains and the measuring equipment should be appropriately calibrated to compensate for differences in gain. From these data, the polarization of the wave can be fully determined, that is, the polarization of the antenna under test. The Stokes parameters can be obtained graphically or by a system of linear equations. 2.4.2 Description of the method
It is usually more convenient to measure the values of the polarization ratios, so all six components are used. The method can be illustrated by the Poncalai sphere shown in Figure 13. The linear polarization ratio, the diagonal polarization ratio and the circular polarization ratio (Pz, Pp, Pc respectively) are measured. From these data, the angles 2α, 2β and 2V are determined. These angles define the loci on the Poncalai sphere corresponding to all possible polarizations with polarization ratios PL, P, and Pc. The common intersection of the three loci determines the polarization of the wave. 10
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Left-hand circular polarization
Right-hand circular polarization
Figure 13 Multiple amplitude component method of polarization measurement If > is positive, the handedness is right-handed, and √ is negative, the handedness is left-handed. Complex c+
Use pc to determine the axis ratio and handedness, because =
The phase angle of the circular polarization ratio is calculated by the following formula: Y,
Be=arctg
Where Y, and Y are obtained from the polarization box:
Because the inclination angle is half of c, the polarization is completely determined. 2.4.3 Improvement of the method
(1-pp\)
(1+pp\)
(1-pr)
(1+p,2)
If the measurement of the handedness is not required, a modification of the multiple amplitude component method (which requires only a single linearly polarized antenna for measurement) can be used to determine the axial ratio and the tilt angle within the entire radiation pattern of the antenna under test. The pattern of the antenna under test is measured with the source antenna oriented at 0° (horizontal), 45° 90° (vertical) and 135°. From these data, p and pD are calculated, and thus c is obtained, from which the tilt angle can be determined. From the polarization box, the axial ratio is:
y=-ctga
where:
arc.cos(Y+Y)%
For high-precision results, the linearly polarized antenna should be a polarization standard. 2.5 Phase-amplitude method
2.5.1 Overview of measurement method
Using the phase-amplitude method, all the data required to define the complete polarization can be measured simultaneously. By cutting the entire set of directional patterns, all polarization patterns and radiation patterns of the antenna can be measured in one operation. The required measurement equipment is shown in Figure 14. The field of the antenna under test is sampled with a dual-polarized receiving antenna, and the antenna under test works in a transmitting mode. The output of the receiver is the response amplitude and relative phase of each polarization of the sampling antenna. If the two polarizations are orthogonal, the complex polarization ratio can be obtained. The polarization of the sampling antenna should be known. And the gain of the two antenna-receiver channels should be the same. 11
2.5.2 Automatic test
Antenna under test W
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Dual polarization sampling antenna
Mixer
Amplitude and phase receiver
Mixer
Figure 14 Test equipment for phase-amplitude method of polarization measurement Usually, it is not economically feasible to design a pure polarization sampling antenna with known polarization. If the test site is equipped with automatic test equipment with a computer, it is not necessary to use a precise linear polarization or circular polarization antenna. Because as long as the actual polarization of the sampling antenna is known, the measurement data can be corrected by calculation. For example, suppose that the measurement requires an orthogonal circular polarization sampling antenna, but the actual sampling antenna is only nearly circularly polarized, but not ideally circularly polarized. As long as the polarization rotation is known, the polarization of the sampling antenna can be measured by the improved multiple amplitude component method. By sending these data to the computer, the computer software can be designed to automatically compensate for the characteristics of the sampling antenna. 2.5.3 Polarization Adjustment Network
If the antenna test site is not automated and not equipped with a computer, another approach is to use a polarization adjustment network external to the sampling antenna to obtain the required polarization. A typical sampling antenna can be composed of two orthogonal linearly polarized antennas. For example, they can feed the same reflector antenna. The antennas are connected to the input of the amplitude and phase receiver. The simplest polarization adjustment network is an attenuator and a phase shifter in series in each channel. These networks can be designed to work at radio frequency and connected in series between the sampling antenna and the mixer of the receiver. In addition, the network can be designed to work at intermediate frequency, so that the same network can be used for any frequency covered by the receiver. If the measurement system is capable of digital data recording and a suitable computer is available, a digital polarization correction network can be used. If right-handed or left-handed circular polarization is required, the network can be adjusted by the polarization pattern method. A nominal linearly polarized reference antenna can be used. Usually the adjustment accuracy of circular polarization is limited by reflections, misalignment, etc. in the test site. When precision measurements are required, a polarization standard is needed to adjust the gain of the two channels. If a linear polarization standard is used, the output signals of the two channels are adjusted to be equal. For horizontal linear polarization, Sc is adjusted to zero degrees. The system can be tested by rotating the standard antenna 360°. The output level should remain unchanged, while the phase angle c should always be twice the standard rotation angle. The rotation angle is measured relative to the horizontal direction. 2.5.4 Measurement using a circularly polarized sampling antenna The measurement of the polarization of the antenna under test using a circularly polarized sampling antenna can be illustrated by the Poncalei sphere in Figure 15. The complex circular polarization ratio obtained from the measurement is:
Left-hand circularly polarized sampling antenna
Antenna under test
Right-hand circularly polarized sampling antenna
Figure 15 Phase amplitude measurement tgy using a circularly polarized antenna1 Measurement method
The function of axialization (rather than rotation or tilt) to direction can be determined by the rotating source method. This method is that when the observation direction of the antenna under test changes, the linear polarization source antenna rotates continuously. This method is of great value for measuring near-circular polarization antennas. The rotation of the source antenna causes the tilt angle Tw of the incident field to rotate at the same rate. When cutting and recording according to 6 or, the rotation rate Tw should be much higher than 6 or. The time response of the recording system should keep up with the changes of 1. This method can be extended to the spiral cutting mode of the radiation pattern (at this time tw, and are 9
SJ2534.9—85
are changing. And TwΦ6), so that the axial ratio of the antenna in all directions can be recorded on an axial ratio radiation pattern. 2.3.2 Example
The radiation pattern of the elliptically polarized antenna obtained by the rotating source method is shown in Figure 12. If the amplitude variation is expressed in decibels, the axial ratio (also expressed in decibels) recorded in any direction on the pattern is the width of the amplitude deviation envelope. This particular antenna is essentially circularly polarized in the axial direction (6 = 0°) and elliptically polarized in the direction of the maximum sidelobe. 10
2.3.3 Measurement errors
Angle (9)
Figure 12 Polarization pattern of a continuous scan as a function of angle Reflections from the source antenna and multipath effects can introduce measurement errors. For example, when the reflected wave strength is 40 dB lower than the direct wave strength, the axial ratio measurement error introduced is about 0.17 dB.
2.4, Multiple Amplitude Component Method
2.4.1 Measurement Method
The multiple amplitude component method allows complete determination of polarization without measuring the phase. It has been shown that the polarization of a wave can be determined from the amplitude responses of four antennas with different but known polarizations. For the sampling antenna polarization, it is most convenient to choose horizontal or vertical linear polarization, 45° or 135° linear polarization, left-hand or right-hand circular polarization and any fourth component different from the set of six components. The sampling antennas should have known gains and the measuring equipment should be appropriately calibrated to compensate for differences in gain. From these data, the polarization of the wave can be fully determined, that is, the polarization of the antenna under test. The Stokes parameters can be obtained graphically or by a system of linear equations. 2.4.2 Description of the method
It is usually more convenient to measure the values of the polarization ratios, so all six components are used. The method can be illustrated by the Poncalai sphere shown in Figure 13. The linear polarization ratio, the diagonal polarization ratio and the circular polarization ratio (Pz, Pp, Pc respectively) are measured. From these data, the angles 2α, 2β and 2V are determined. These angles define the loci on the Poncalai sphere corresponding to all possible polarizations with polarization ratios PL, P, and Pc. The common intersection of the three loci determines the polarization of the wave. 10
SJ2534.9—85
Left-hand circular polarization
Right-hand circular polarization
Figure 13 Multiple amplitude component method of polarization measurement If > is positive, the handedness is right-handed, and √ is negative, the handedness is left-handed. Complex c+
Use pc to determine the axis ratio and handedness, because =
The phase angle of the circular polarization ratio is calculated by the following formula: Y,
Be=arctg
Where Y, and Y are obtained from the polarization box:
Because the inclination angle is half of c, the polarization is completely determined. 2.4.3 Improvement of the method
(1-pp\)
(1+pp\)
(1-pr)
(1+p,2)
If the measurement of the handedness is not required, a modification of the multiple amplitude component method (which requires only a single linearly polarized antenna for measurement) can be used to determine the axial ratio and the tilt angle within the entire radiation pattern of the antenna under test. The pattern of the antenna under test is measured with the source antenna oriented at 0° (horizontal), 45° 90° (vertical) and 135°. From these data, p and pD are calculated, and thus c is obtained, from which the tilt angle can be determined. From the polarization box, the axial ratio is:
y=-ctga
where:
arc.cos(Y+Y)%
For high-precision results, the linearly polarized antenna should be a polarization standard. 2.5 Phase-amplitude method
2.5.1 Overview of measurement method
Using the phase-amplitude method, all the data required to define the complete polarization can be measured simultaneously. By cutting the entire set of directional patterns, all polarization patterns and radiation patterns of the antenna can be measured in one operation. The required measurement equipment is shown in Figure 14. The field of the antenna under test is sampled with a dual-polarized receiving antenna, and the antenna under test works in a transmitting mode. The output of the receiver is the response amplitude and relative phase of each polarization of the sampling antenna. If the two polarizations are orthogonal, the complex polarization ratio can be obtained. The polarization of the sampling antenna should be known. And the gain of the two antenna-receiver channels should be the same. 11
2.5.2 Automatic test
Antenna under test W
SJ2534.9--85
Dual polarization sampling antenna
Mixer
Amplitude and phase receiver
Mixer
Figure 14 Test equipment for phase-amplitude method of polarization measurement Usually, it is not economically feasible to design a pure polarization sampling antenna with known polarization. If the test site is equipped with automatic test equipment with a computer, it is not necessary to use a precise linear polarization or circular polarization antenna. Because as long as the actual polarization of the sampling antenna is known, the measurement data can be corrected by calculation. For example, suppose that the measurement requires an orthogonal circular polarization sampling antenna, but the actual sampling antenna is only nearly circularly polarized, but not ideally circularly polarized. As long as the polarization rotation is known, the polarization of the sampling antenna can be measured by the improved multiple amplitude component method. By sending these data to the computer, the computer software can be designed to automatically compensate for the characteristics of the sampling antenna. 2.5.3 Polarization Adjustment Network
If the antenna test site is not automated and not equipped with a computer, another approach is to use a polarization adjustment network external to the sampling antenna to obtain the required polarization. A typical sampling antenna can be composed of two orthogonal linearly polarized antennas. For example, they can feed the same reflector antenna. The antennas are connected to the input of the amplitude and phase receiver. The simplest polarization adjustment network is an attenuator and a phase shifter in series in each channel. These networks can be designed to work at radio frequency and connected in series between the sampling antenna and the mixer of the receiver. In addition, the network can be designed to work at intermediate frequency, so that the same network can be used for any frequency covered by the receiver. If the measurement system is capable of digital data recording and a suitable computer is available, a digital polarization correction network can be used. If right-handed or left-handed circular polarization is required, the network can be adjusted by the polarization pattern method. A nominal linearly polarized reference antenna can be used. Usually the adjustment accuracy of circular polarization is limited by reflections, misalignment, etc. in the test site. When precision measurements are required, a polarization standard is needed to adjust the gain of the two channels. If a linear polarization standard is used, the output signals of the two channels are adjusted to be equal. For horizontal linear polarization, Sc is adjusted to zero degrees. The system can be tested by rotating the standard antenna 360°. The output level should remain unchanged, while the phase angle c should always be twice the standard rotation angle. The rotation angle is measured relative to the horizontal direction. 2.5.4 Measurement using a circularly polarized sampling antenna The measurement of the polarization of the antenna under test using a circularly polarized sampling antenna can be illustrated by the Poncalei sphere in Figure 15. The complex circular polarization ratio obtained from the measurement is:
Left-hand circularly polarized sampling antenna
Antenna under test
Right-hand circularly polarized sampling antenna
Figure 15 Phase amplitude measurement tgy using a circularly polarized antenna1 Measurement method
The polarization can be completely determined without measuring the phase by using the multiple amplitude component method. It has been shown that the polarization of a wave can be determined from the amplitude of the response of four antennas with different but known polarizations. For sampling antenna polarization, it is most convenient to choose horizontal or vertical linear polarization, 45° or 135° linear polarization, left-hand or right-hand circular polarization and any fourth component different from this set of six components. These sampling antennas should have known gains and the measurement equipment should be appropriately calibrated to compensate for the gain differences. From these data, the polarization of the wave can be completely determined, that is, the polarization of the antenna under test. The Stokes parameters can be obtained by graphical methods or by a system of linear equations. 2.4.2 Description of the method
It is usually more convenient to measure the value of the polarization ratio, so all six components are used. The method can be illustrated by the Poncalei sphere shown in Figure 13. The linear polarization ratio, diagonal polarization ratio and circular polarization ratio (Pz, Pp, Pc respectively) are measured. From these data the angles 2α, 2β and 2V are determined. These angles define the loci on the Poncalei sphere corresponding to all possible polarizations with polarization ratios PL, P, and Pc. The common intersection of the three loci determines the polarization of the wave. 10
SJ2534.9—85
Left-hand circular polarization
Right-hand circular polarization
Figure 13 Multiple amplitude component method for polarization measurement If > is positive, the handedness is right-handed, and √ is negative, the handedness is left-handed. Complex c+
Use pc to determine the axis ratio and handedness, because =
The phase angle of the circular polarization ratio is calculated as follows: Y,
Be=arctg
Where Y, and Y are obtained from the polarization box:
Since the inclination angle is half of c, the polarization is completely determined. 2.4.3 Improvement of the method
(1-pp\)
(1+pp\)
(1-pr)
(1+p,2)
If the measurement of the handedness is not required, a modification of the multiple amplitude component method (which requires only a single linearly polarized antenna for measurement) can be used to determine the axial ratio and the tilt angle within the entire radiation pattern of the antenna under test. The pattern of the antenna under test is measured with the source antenna oriented at 0° (horizontal), 45° 90° (vertical) and 135°. From these data, p and pD are calculated, and thus c is obtained, from which the tilt angle can be determined. From the polarization box, the axial ratio is:
y=-ctga
where:
arc.cos(Y+Y)%
For high-precision results, the linearly polarized antenna should be a polarization standard. 2.5 Phase-amplitude method
2.5.1 Overview of measurement method
Using the phase-amplitude method, all the data required to define the complete polarization can be measured simultaneously. By cutting the entire set of directional patterns, all polarization patterns and radiation patterns of the antenna can be measured in one operation. The required measurement equipment is shown in Figure 14. The field of the antenna under test is sampled with a dual-polarized receiving antenna, and the antenna under test works in a transmitting mode. The output of the receiver is the response amplitude and relative phase of each polarization of the sampling antenna. If the two polarizations are orthogonal, the complex polarization ratio can be obtained. The polarization of the sampling antenna should be known. And the gain of the two antenna-receiver channels should be the same. 11
2.5.2 Automatic test
Antenna under test W
SJ2534.9--85
Dual polarization sampling antenna
Mixer
Amplitude and phase receiver
Mixer
Figure 14 Test equipment for phase-amplitude method of polarization measurement Usually, it is not economically feasible to design a pure polarization sampling antenna with known polarization. If the test site is equipped with automatic test equipment with a computer, it is not necessary to use a precise linear polarization or circular polarization antenna. Because as long as the actual polarization of the sampling antenna is known, the measurement data can be corrected by calculation. For example, suppose that the measurement requires an orthogonal circular polarization sampling antenna, but the actual sampling antenna is only nearly circularly polarized, but not ideally circularly polarized. As long as the polarization rotation is known, the polarization of the sampling antenna can be measured by the improved multiple amplitude component method. By sending these data to the computer, the computer software can be designed to automatically compensate for the characteristics of the sampling antenna. 2.5.3 Polarization Adjustment Network
If the antenna test site is not automated and not equipped with a computer, another approach is to use a polarization adjustment network external to the sampling antenna to obtain the required polarization. A typical sampling antenna can be composed of two orthogonal linearly polarized antennas. For example, they can feed the same reflector antenna. The antennas are connected to the input of the amplitude and phase receiver. The simplest polarization adjustment network is an attenuator and a phase shifter in series in each channel. These networks can be designed to work at radio frequency and connected in series between the sampling antenna and the mixer of the receiver. In addition, the network can be designed to work at intermediate frequency, so that the same network can be used for any frequency covered by the receiver. If the measurement system is capable of digital data recording and a suitable computer is available, a digital polarization correction network can be used. If right-handed or left-handed circular polarization is required, the network can be adjusted by the polarization pattern method. A nominal linearly polarized reference antenna can be used. Usually the adjustment accuracy of circular polarization is limited by reflections, misalignment, etc. in the test site. When precision measurements are required, a polarization standard is needed to adjust the gain of the two channels. If a linear polarization standard is used, the output signals of the two channels are adjusted to be equal. For horizontal linear polarization, Sc is adjusted to zero degrees. The system can be tested by rotating the standard antenna 360°. The output level should remain unchanged, while the phase angle c should always be twice the standard rotation angle. The rotation angle is measured relative to the horizontal direction. 2.5.4 Measurement using a circularly polarized sampling antenna The measurement of the polarization of the antenna under test using a circularly polarized sampling antenna can be illustrated by the Poncalei sphere in Figure 15. The complex circular polarization ratio obtained from the measurement is:
Left-hand circularly polarized sampling antenna
Antenna under test
Right-hand circularly polarized sampling antenna
Figure 15 Phase amplitude measurement tgy using a circularly polarized antenna1 Measurement method
The polarization can be completely determined without measuring the phase by using the multiple amplitude component method. It has been shown that the polarization of a wave can be determined from the amplitude of the response of four antennas with different but known polarizations. For sampling antenna polarization, it is most convenient to choose horizontal or vertical linear polarization, 45° or 135° linear polarization, left-hand or right-hand circular polarization and any fourth component different from this set of six components. These sampling antennas should have known gains and the measurement equipment should be appropriately calibrated to compensate for the gain differences. From these data, the polarization of the wave can be completely determined, that is, the polarization of the antenna under test. The Stokes parameters can be obtained by graphical methods or by a system of linear equations. 2.4.2 Description of the method
It is usually more convenient to measure the value of the polarization ratio, so all six components are used. The method can be illustrated by the Poncalei sphere shown in Figure 13. The linear polarization ratio, diagonal polarization ratio and circular polarization ratio (Pz, Pp, Pc respectively) are measured. From these data the angles 2α, 2β and 2V are determined. These angles define the loci on the Poncalei sphere corresponding to all possible polarizations with polarization ratios PL, P, and Pc. The common intersection of the three loci determines the polarization of the wave. 10
SJ2534.9—85
Left-hand circular polarization
Right-hand circular polarization
Figure 13 Multiple amplitude component method for polarization measurement If > is positive, the handedness is right-handed, and √ is negative, the handedness is left-handed. Complex c+
Use pc to determine the axis ratio and handedness, because =
The phase angle of the circular polarization ratio is calculated as follows: Y,
Be=arctg
Where Y, and Y are obtained from the polarization box:
Since the inclination angle is half of c, the polarization is completely determined. 2.4.3 Improvement of the method
(1-pp\)
(1+pp\)
(1-pr)
(1+p,2)
If the measurement of the handedness is not required, a modification of the multiple amplitude component method (which requires only a single linearly polarized antenna for measurement) can be used to determine the axial ratio and the tilt angle within the entire radiation pattern of the antenna under test. The pattern of the antenna under test is measured with the source antenna oriented at 0° (horizontal), 45° 90° (vertical) and 135°. From these data, p and pD are calculated, and thus c is obtained, from which the tilt angle can be determined. From the polarization box, the axial ratio is:
y=-ctga
where:
arc.cos(Y+Y)%
For high-precision results, the linearly polarized antenna should be a polarization standard. 2.5 Phase-amplitude method
2.5.1 Overview of measurement method
Using the phase-amplitude method, all the data required to define the complete polarization can be measured simultaneously. By cutting the entire set of directional patterns, all polarization patterns and radiation patterns of the antenna can be measured in one operation. The required measurement equipment is shown in Figure 14. The field of the antenna under test is sampled with a dual-polarized receiving antenna, and the antenna under test works in a transmitting mode. The output of the receiver is the response amplitude and relative phase of each polarization of the sampling antenna. If the two polarizations are orthogonal, the complex polarization ratio can be obtained. The polarization of the sampling antenna should be known. And the gain of the two antenna-receiver channels should be the same. 11
2.5.2 Automatic test
Antenna under test W
SJ2534.9--85
Dual polarization sampling antenna
Mixer
Amplitude and phase receiver
Mixer
Figure 14 Test equipment for phase-amplitude method of polarization measurement Usually, it is not economically feasible to design a pure polarization sampling antenna with known polarization. If the test site is equipped with automatic test equipment with a computer, it is not necessary to use a precise linear polarization or circular polarization antenna. Because as long as the actual polarization of the sampling antenna is known, the measurement data can be corrected by calculation. For example, suppose that the measurement requires an orthogonal circular polarization sampling antenna, but the actual sampling antenna is only nearly circularly polarized, but not ideally circularly polarized. As long as the polarization rotation is known, the polarization of the sampling antenna can be measured by the improved multiple amplitude component method. By sending these data to the computer, the computer software can be designed to automatically compensate for the characteristics of the sampling antenna. 2.5.3 Polarization Adjustment Network
If the antenna test site is not automated and not equipped with a computer, another approach is to use a polarization adjustment network external to the sampling antenna to obtain the required polarization. A typical sampling antenna can be composed of two orthogonal linearly polarized antennas. For example, they can feed the same reflector antenna. The antennas are connected to the input of the amplitude and phase receiver. The simplest polarization adjustment network is an attenuator and a phase shifter in series in each channel. These networks can be designed to work at radio frequency and connected in series between the sampling antenna and the mixer of the receiver. In addition, the network can be designed to work at intermediate frequency, so that the same network can be used for any frequency covered by the receiver. If the measurement system is capable of digital data recording and a suitable computer is available, a digital polarization correction network can be used. If right-handed or left-handed circular polarization is required, the network can be adjusted by the polarization pattern method. A nominal linearly polarized reference antenna can be used. Usually the adjustment accuracy of circular polarization is limited by reflections, misalignment, etc. in the test site. When precision measurements are required, a polarization standard is needed to adjust the gain of the two channels. If a linear polarization standard is used, the output signals of the two channels are adjusted to be equal. For horizontal linear polarization, Sc is adjusted to zero degrees. The system can be tested by rotating the standard antenna 360°. The output level should remain unchanged, while the phase angle c should always be twice the standard rotation angle. The rotation angle is measured relative to the horizontal direction. 2.5.4 Measurement using a circularly polarized sampling antenna The measurement of the polarization of the antenna under test using a circularly polarized sampling antenna can be illustrated by the Poncalei sphere in Figure 15. The complex circular polarization ratio obtained from the measurement is:
Left-hand circularly polarized sampling antenna
Antenna under test
Right-hand circularly polarized sampling antenna
Figure 15 Phase amplitude measurement tgy using a circularly polarized antenna1 Overview of the measurement method
Using the phase-amplitude method, all the data required to define the complete polarization can be measured simultaneously. By cutting the entire set of directional patterns, all polarization patterns and radiation patterns of the antenna can be measured in one operation. The required measurement equipment is shown in Figure 14. The field of the antenna under test is sampled with a dual-polarized receiving antenna, and the antenna under test works in a transmitting mode. The output of the receiver is the response amplitude and relative phase of each polarization of the sampling antenna. If the two polarizations are orthogonal, the complex polarization ratio can be obtained. The polarization of the sampling antenna should be known. And the gain of the two antenna-receiver channels should be the same. 11
2.5.2 Automatic test
Antenna under test W
SJ2534.9--85
Dual polarization sampling antenna
Mixer
Amplitude and phase receiver
Mixer
Figure 14 Test equipment for phase-amplitude method of polarization measurement Usually, it is not economically feasible to design a pure polarization sampling antenna with known polarization. If the test site is equipped with automatic test equipment with a computer, it is not necessary to use a precise linear polarization or circular polarization antenna. Because as long as the actual polarization of the sampling antenna is known, the measurement data can be corrected by calculation. For example, suppose that the measurement requires an orthogonal circular
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