TWI540792B - A far-field calibration system of an antenna arrary system - Google Patents

Description

Far field calibration system for antenna systems

The invention relates to a test method, in particular to a far field calibration system for an antenna system.

Any antenna that has been properly operated can be successfully measured in the near or far field. However, due to cost, size and more complex details, the advantages of the near and far field range are different. In general, the far field range is suitable for lower frequency antennas, which require a single field type measurement; the near field range is suitable for higher frequency antennas, which require full field and polarization measurements.

Each measurement has additional subtypes, each of which has certain advantages and disadvantages, which makes the measurement techniques between the far and near fields difficult to compare. But the near-field measurement technology has a recognized advantage, that is, it can do complete measurements indoors, eliminating weather, electromagnetic interference, safety and other issues. However, the same advantages can be used in far field measurement techniques, which use a microwave darkroom and a standardized measurement space.

It has been shown that MIMO antenna systems require more detailed measurements than traditional passive antennas, and therefore require additional measurement equipment and complex test methods. Therefore, in the system development process, it is necessary to spend a lot of money to build complex and expensive test systems and instruments, such as near-field measurement systems or Over-the-Air (OTA) measurement systems.

However, once the input multiple output (MIMO) antenna array system is deployed at the antenna base (such as a military radar base or a base station of a wireless communication system), if some transmission/reception (T/R) modules fail or If the signal phase and amplitude settings are incorrect, how to perform re-correction of the amplitude and phase of the antenna unit is a very important issue because we cannot build complicated and expensive near-field quantities on the ground. Measurement system or Over-the-Air (OTA) measurement system. Therefore, a simple antenna self-calibration system must be developed. This system can detect the failed antenna unit and update it in time to maintain the MIMO antenna system to work properly.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a self-calibration system module of a linear antenna array and a reference antenna. The self-calibration system module 1 is composed of a multiple input multiple output (MIMO) linear antenna array 40 (consisting of equidistant and identical antenna elements) and a reference antenna 400. A module is placed behind each antenna element that can affect the amplitude and phase of the received signal. Through experimentation, amplitude and phase often change only in discrete steps. The output of this received signal on the array antenna is due to the arrival of plane waves from the ξ direction. The formula is as follows

Where S _e ( θ )=the field distribution function of the antenna element

d = spacing between adjacent antenna elements

λ = wavelength in free space

ξ = array to plane wave direction

= complex excitation coefficient of module m

In order to facilitate the calculation, the array to plane wave direction ξ = 0, then (1) can be simplified to

Please refer to FIG. 2. FIG. 2A and FIG. 2B are schematic diagrams of a conventional Van Hezewijk Element Excitations Method (EEM). This design (Van Hezewijk, JGFast Determination of the Element Excitation of an Active Phased Array Antenna, IEEE AP-S conf., vol. 3, pp. 1478-1481, 24-28 Jun, (1991)), with accuracy Bad question. Taking a 3-bits phase shifter as an example, S ₀ ,..., S _{7 are} represented as complex signals measured by phase settings 0,...,7 on the reference antenna. Figure 2A shows that when the mutual coupling is negligible and the amplitude of the element under test is unaffected by the phase setting, the measured signal is on the circle. Figure 2B is a more practical example. Since the signal measured by the non-ideal phase shifter (the amplitude varies with the phase state) is not exactly on the circle, the minimum mean error algorithm is used to calculate the measured signal S. _i .

In view of this, the present invention provides a phase rotation method (PRM) for a multiple input multiple output (MIMO) antenna array. This method uses the reference signal provided by the reference antenna for calibration and uses the test antenna module to measure the signal in the near-far range.

The present invention provides a far field calibration system for an antenna system comprising a multiple input multiple output (MIMO) active phased antenna array and one (or several) reference antennas. Basically, the array antenna is composed of a group of beam formers and M groups of antenna unit modules. One of the M antenna element modules is selected as an antenna unit to be tested (AUT), and the reference antenna is used to generate a standard radiation pattern. The far field calibration system of the antenna system of the present invention further includes a test antenna module, and the multi-input multi-output active phase antenna array is disposed on the same plane for measuring a radiation field type of the antenna unit; The reference antenna is coupled to a module, the module includes an amplifier and a phase shifter; the far-field calibration system of the antenna system further includes a metal reflective surface disposed in parallel with the normal vector extending direction of the plane for reflecting The antenna signal of the antenna unit (AUT) and the reference antenna and each antenna unit except the antenna unit (AUT) and the reference antenna are respectively coupled to a dummy load; the antenna unit to be tested The excitation coefficient of the (AUT) is adjusted according to the radiation pattern of the antenna unit (AUT) to be tested, so that the radiation pattern of the antenna unit (AUT) to be tested conforms to the standard radiation pattern; wherein the excitation coefficient includes one An amplitude coefficient and a phase coefficient, the excitation coefficient can be measured by a power meter, a reference antenna amplitude coefficient (A1), a reference antenna phase coefficient ( ψ _r ( j )), and an S-parameter simulated far field The approximation is adjusted.

In summary, the far field calibration system of the antenna system provided by the present invention can be borrowed The radiation pattern is optimized by adjusting the excitation coefficients of each antenna element on the antenna array one by one. After the multi-input multi-output (MIMO) antenna array system is installed in the antenna base, if the active components of the antenna unit fail due to aging or other reasons, it is extremely difficult to transport it back to the R&D unit for maintenance. Therefore, the far field calibration system of the antenna system provided by the present invention can detect the failed antenna unit and timely update and update the antenna base, and the self-calibration system can perform simple antenna system correction at the antenna base to maintain multiple inputs. The output (MIMO) antenna array system is working properly.

On the other hand, the present invention further enhances the intensity of the antenna radiation signal through the metal reflecting surface, so that the strength of the coupled signal of the antenna test is improved, and the test module does not need to be disposed directly in front of the array antenna. Therefore, the antenna system can achieve a single plane self-correction method, which greatly simplifies the system design difficulty.

The detailed description of the present invention and the accompanying drawings are to be understood by the claims The scope is subject to any restrictions.

1‧‧‧Self-school system module

4‧‧‧ Far field calibration system for antenna systems

40‧‧‧Active phased linear antenna array

41‧‧‧Test antenna module

400‧‧‧reference antenna

401‧‧‧ antenna unit to be tested

402‧‧‧Antenna unit

405‧‧‧Metal reflective surface

411‧‧‧Power measuring device

4000‧‧‧Amplifier

4001‧‧‧ phase shifter

4020‧‧‧Virtual load

A‧‧‧ plane

1 is a schematic diagram of a self-calibration system module of a linear antenna array and a reference antenna.

2A and 2B are schematic diagrams of a conventional Van Hezewijk Element Excitations Method (EEM).

3 is a schematic diagram of the use of Phase Rotation (PRM) in an embodiment of the present invention.

4A is a schematic diagram of a far field calibration system of an antenna system according to an embodiment of the present invention.

4B is an equivalent model diagram showing the interaction of electromagnetic fields between antennas using an S-parameters method in accordance with an embodiment of the present invention.

FIG. 5 is a schematic diagram of an S-parameters simulation architecture according to an embodiment of the present invention.

FIG. 6 is a schematic diagram showing simulation results of using GEMS EM simulation software according to an embodiment of the present invention.

7A and 7B are diagrams showing the use of GEMS EM simulation software (C201) according to an embodiment of the present invention. A comparison chart with far field approximation simulation (C202).

FIG. 8 is a schematic diagram of a comparison of analog field types of an antenna unit to be tested and a reference antenna according to an embodiment of the present invention.

9 is a flow chart showing the steps of a far field calibration system of an antenna system according to an embodiment of the present invention.

10A and 10B are schematic diagrams showing test results of 1000 samples according to an embodiment of the present invention.

Various illustrative embodiments are described more fully hereinafter with reference to the accompanying drawings. However, the inventive concept may be embodied in many different forms and should not be construed as being limited to the illustrative embodiments set forth herein. Rather, these exemplary embodiments are provided so that this invention will be in the In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Similar numbers always indicate similar components.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, such elements are not limited by the terms. These terms are used to distinguish one element from another. Thus, a first element discussed below could be termed a second element without departing from the teachings of the inventive concept. As used herein, the term "and/or" includes any of the associated listed items and all combinations of one or more.

[Embodiment of Far Field Calibration System for Antenna System]

Before introducing an embodiment of the present invention, please refer to FIG. 3. FIG. 3 is a schematic diagram of a phase rotation method (PRM) according to an embodiment of the present invention. Assuming that the phase setting of one module (i) is changed, and the amplitude and phase settings of other antenna elements are fixed, the received signal will be

In the right form of (3), the first term is constant for S(θ), and the last term depends on the variable ψ _i . Therefore, the field type excited by a single antenna element on module (i) is determined by the last term, and the relationship is written as

As shown in Figure 3, taking a 3-bits phase shifter as an example, E _r (1),..., E _r (8) are represented as complex signals measured by phase settings 1, ..., 8 on the reference antenna. . If the mutual coupling is negligible and the amplitude of the element under test (E _i ) is unaffected by the phase setting, the signal of the active module (E _i ) and the signal generated by the reference antenna (E _{r )} When combined, the signal measured in the far field range can be expressed as E _i and the signal centered on the center C (E _r (j), the jth phase state of the table), the vector sum of the two . Combining E _r (j) and E _i in the near-far field range, when ψ _r ( j ) and ψ _i are in phase/inverted, the maximum/minimum measured power can be obtained. However, due to the phase quantization of the phase shifter, there is a phase error ε between them.

Thus, with proper calibration procedures, the amplitude and phase of the active module (i) can be calculated via tuning. The excitation coefficients of each of the active antenna elements on the antenna array are determined one after another to obtain an optimum array radiation pattern. In order to make the accuracy of the correction higher, the E _r (center of the center C) signal can be compared with the signal size of E _i (the origin coordinate to the vector of the center C).

Please refer to FIG. 4A. FIG. 4A is a schematic diagram of a far field calibration system of an antenna system according to an embodiment of the present invention. The far field calibration system of the antenna system of the present embodiment includes a multiple input multiple output (MIMO) active antenna array 40, and the multiple input multiple output (MIMO) active antenna array (40) includes M equal distances (d Antenna unit 400, 401, 402, one of the antenna units is an antenna unit (AUT) 401 to be tested, one of the antenna units is a reference antenna 400, and the reference antenna is used to generate a standard radiation field type For correction purposes. The multiple input multiple output (MIMO) active antenna array 40 further includes a test antenna module 41 for measuring signals in a near far field range, and the test antenna module 41 and the multiple input multiple output active antenna array 40 are disposed on The same plane A. In addition, the far field calibration system 4 of the antenna system sets the normal vector of the metal reflecting surface 405 to the plane A. Extending direction and parallel to the plane A. The metal reflecting surface 405 is configured to reflect the electric wave signal of the antenna unit 401 to be tested and the reference antenna 400. The test antenna module 41 is disposed at the edge of the multi-input and multi-output active phase antenna array 40, so that the mechanism design of the antenna test system is relatively simple. However, in other embodiments, the test antenna module 41 can also be disposed in the active phase antenna array 40, and the invention is not limited thereto.

When performing the measurement, all the antenna elements are connected to the virtual load 4020 except for the Antenna under test (AUT) 401. The reference antenna 400 is coupled to a module which is composed of an amplifier 4000 (amplifying the signal to a specified value a _r ) and a phase shifter 4001 (controlling the reference antenna signal ψ _r ( j ), j=1, .. ., 8, with a 3-bits phase shifter as an example). The signal source transmits the signal to the antenna unit 401 to be tested through the amplifier 4000 and the phase shifter 4001, and the amplitude/phase ( a ₁ / ψ ₁ ) of the antenna unit 401 to be tested is unknown to the far field measurement. data. The excitation coefficient of the antenna unit 401 to be tested is adjusted according to the radiation pattern of the antenna unit 401 to be tested, so that the radiation field of the antenna unit 401 to be tested approximates the standard radiation pattern. And, the amplitude coefficient and the phase coefficient of the excitation coefficient can be measured by a power meter 411, a reference antenna amplitude coefficient (A ₂ ), and a reference antenna phase coefficient ( ψ _r ( j )). And the far field approximation of the S parameter simulation is adjusted.

4B is an equivalent model diagram showing the mutual coupling action of electromagnetic fields between antennas using the S-parameters method in the embodiment of the present invention. The phase rotation method (Phase Rotation Method) is introduced by numerical simulation verification obtained by a general execution-driven multiprocessor simulator (GEMS EM). Assume that all antennas are well matched (S ₁₁ = S ₂₂ = S ₃₃ =0) and the effects of mutual coupling are negligible. As shown in FIG. 4B, the measurement field type (b ₃ ) of the test antenna module 41 is located at (x _o , y _o , z _o ), which can be expressed as

And b ₃ '( j )= A ₁ + A ₂ e ^{jδ ( j )} (5.b)

_{Wherein, A 1 = a r | S} 31 |

A ₂ = a _i | S ₃₂ |

δ ( j )= ψ _i - ψ _r ( j )+∠ S ₃₂ -∠ S ₃₁

b ₃ = test the received signal on the antenna module 41 (or reflected voltage wave)

S ₃₁ = scattering parameter of the incident/reflected voltage wave on the reference antenna 400 / test antenna module 41

S ₃₂ = scattering parameter of the incident/reflective voltage wave on the antenna unit 401/test antenna module 41 to be tested

In FIG. 4A, the amplitude (A ₂ ) and phase ( ψ _r '( j )) of the reference antenna 400 at each phase state (j) can be noted, and the programmable read only memory can be pre-corrected and stored before the system is deployed. Body (PROM) correction amount. On the reference antenna 400, the phase state (j) of the 3-bits phase shifter can obtain the maximum value and the minimum value, and b ₃ ' is expressed as b ₃ ' _Max = A ₁ + A ₂ ^ejε b ₃ ' _Min = A ₁ - A ₂ e ^jε (6)

According to the hybrid circuit, when the system impedance R=1, the maximum/minimum power value is

As shown in FIG. 4A, (P ^Max , P ^Min ) is called a power coefficient, where P ^Max is the maximum cosine power value and P ^Min is the minimum cosine power value.

From (7), the amplitude of the excitation coefficient on the antenna unit (AUT) 401 to be tested can be derived as

Similarly, the phase of the excitation coefficient on the antenna unit (AUT) 401 to be tested can also be derived ψ _i = ε + ψ _r ( j ) - (∠ S ₃₂ - ∠ S ₃₁ ) (9.a)

In equations (8) and (9), the power coefficients (P ^Max , P ^Min ), a _{r ,} and ψ _r '( j ) are stored in advance in a modified programmable read only memory (Correction PROM). However, since the S-parameters measurement requires a coherent test mode, |S ₃₂ | (the amplitude of the antenna unit (AUT) 401 to be tested) and ∠ S ₃₁ -∠ S ₃₂ (the antenna unit to be tested) The measurement phase difference between the (AUT) 401 and the reference antenna 400 is difficult to know. Therefore, in this paper, the GO calculation method and the Far-field approximation method are applied to simulate the relevant S-parameters as follows:

among them, as well as

among them Measuring the field type of the antenna when transmitting the i-th antenna; The measurement field type of the test antenna for the reference antenna transmission.

Substituting (10.b)/(10.c) and (7) into equations (8)/(9), the amplitude coefficient a ₁ and the phase coefficient of the excitation coefficient on the antenna unit (AUT) 401 to be tested are obtained. ₁ . Thus, depending on the design specifications, the excitation coefficients of each of the antenna elements 402 on the active phased linear antenna array 40 can be optimized by adjusting one by one.

Next, we will use the GEMS EM simulation software to verify the PRM method. FIG. 5 is a schematic diagram of an S-parameters simulation architecture according to an embodiment of the present invention. An array of two antennas combined with a metal reflecting surface 405 having a distance of 400 millimeters (mm) from the antenna unit 401 to be tested in the z-axis direction. All of the antenna elements in this embodiment are formed on the FR4 substrate, and the FR4 substrate has a thickness of 1.6 millimeters (mm). FIG. 6 is a schematic diagram showing simulation results of using GEMS EM simulation software according to an embodiment of the present invention. At frequencies between 2.35 and 2.37 GHz, the reflection loss and isolation are below -10 dB, with a reflection loss of 20 log 10 (|S ₃₃ |) and an isolation of 20 log 10 (|S ₁₂ |). The simulation results are good and suitable for numerical verification. Since all resonant antennas have approximately the same frequency response at the resonant frequency, the antenna is equally effective as other frequencies when the antenna is resonant at other frequencies.

Next, the far field approximation is used to simulate |S ₃₁ | (the amplitude of the forward transmission gain) and ∠ S ₃₂ -∠ S ₃₁ (the phase difference between the antenna unit to be tested (AUT) and the reference antenna). 7A and 7B are comparison diagrams of the GEMS EM simulation software (C201) and the far field approximation simulation (C202) according to an embodiment of the present invention. The comparison results are good and continue to be further analyzed.

FIG. 8 is a schematic diagram of a comparison of analog field types of an antenna unit to be tested and a reference antenna according to an embodiment of the present invention. As shown in FIG. 8, in order to compensate the amplitude of |S ₃₁ | in the off-boresight direction, let the antenna unit field type S _e ( θ )=cos( θ ), and compare the antenna unit to be tested (AUT) And the analog field of the reference antenna, the result is within an acceptable range from 0 to 60 degrees in the non-far field angle.

Please refer to FIG. 10, which is a schematic diagram of test results of 1000 samples. Finally, the results of the far-field approximation are applied to equations (8) and (9) to adjust the excitation coefficients of amplitude (a1) and phase (ψ ₁ ) on the antenna element to be tested. In order to ensure sufficient signal strength and phase angle resolution on the reference antenna for detection, a 30 dBm amplifier and a 5-bit phase shifter were placed in the reference antenna in this study. Then, according to the calibration procedure, the excitation coefficients of the antenna unit to be tested are sequentially adjusted one by one to verify the far field calibration system of the antenna system of the present invention. FIG. 10 is a schematic diagram showing test results of 1000 samples according to an embodiment of the present invention. The numerical value shows that the average value of the phase/amplitude error between the far field approximation method and the precision value of the present invention is 1.39 ° / -0.44 dB.

Please also refer to Figures 4 and 9. 9 is a flow chart showing the steps of a far field calibration system of an antenna system according to an embodiment of the present invention.

First, one of the antenna units is selected as the antenna unit to be tested (step S901); thereafter, the amplitude coefficient of the antenna unit to be tested and the measured phase difference between the reference antenna and the antenna unit to be tested are calculated (step S903) Adjusting the amplitude coefficient and the phase coefficient of the antenna unit to be tested (step S905); and performing one of the antenna units has been adjusted through steps S901 to S905, and the above steps S901 to S905 may be repeated. Each of the antenna elements is tuned.

The above description is only an embodiment of the present invention, and is not intended to limit the scope of the invention.

4‧‧‧ Far field calibration system for antenna systems

40‧‧‧Active Linear Antenna Array

41‧‧‧Test antenna module

400‧‧‧reference antenna

401‧‧‧Antenna unit to be tested (AUT)

402‧‧‧Antenna unit

405‧‧‧Metal reflector

411‧‧‧Power measuring device

4000‧‧‧Amplifier

4001‧‧‧ phase shifter

4020‧‧‧Virtual load

A‧‧‧ plane

Claims (10)

A far field calibration system for an antenna system, comprising: a multiple input multiple output (MIMO) active phased antenna array, comprising a plurality of antenna elements, one of the antenna elements being an antenna unit to be tested (AUT) One of the antenna units is a reference antenna for generating a standard radiation field type, and a test antenna module is disposed on the same plane as the multiple input and multiple output active phase antenna array. The method for measuring the radiation field of the antenna elements; a metal reflecting surface disposed in parallel with the normal vector extending direction of the plane for reflecting a signal of the antenna to be tested (AUT) and the reference antenna; The reference antenna is coupled to a module, and the module includes an amplifier and a phase shifter. Each of the antenna units except the antenna unit (AUT) and the reference antenna are respectively coupled to the antenna unit. a virtual load; wherein an excitation coefficient of the antenna unit to be tested (AUT) is adjusted according to a radiation field type of the antenna unit (AUT) to be tested, so that a radiation field type of the antenna unit (AUT) to be tested conforms to the Quasi radiation pattern; wherein the excitation coefficients include a coefficient of a phase and amplitude coefficients, the coefficients may be excited by a power factor, a reference amplitude coefficient of the antenna (A _r), a reference antenna phase coefficients (ψ _r (j) ) and the far field approximation of an S-parameter simulation is adjusted. The far field calibration system of the antenna system according to claim 1, wherein the amplitude coefficient (A _r ) of the reference antenna and the phase coefficient ( ψ _r ( j )) are pre-corrected and stored before the system is deployed. Programmable read-only memory (PROM) correction. The far field calibration system of the antenna system of claim 1, wherein the power coefficient comprises a maximum cosine power value (P ^Max ) or a minimum cosine power value (P ^Min ). The far field calibration system of the antenna system according to claim 3, wherein the power coefficient includes the amplitude coefficient of the antenna unit (AUT) to be tested (|S ₃₂ |) and the reference antenna and the test One of the middle antenna units (AUT) measures the phase difference (∠ S ₃₁ -∠ S ₃₂ ). The far field calibration system of the antenna system according to claim 4, wherein the amplitude (A ₁ ) of the excitation coefficient of the antenna unit (AUT) to be tested is obtained by the following formula The far field calibration system of the antenna system according to claim 4, wherein the phase (ψ ₁ ) of the excitation coefficient of the antenna unit (AUT) to be tested is obtained by the following expression: ψ _i = ε + ψ _r ( j )-(∠ S ₃₂ -∠ S ₃₁ ), Wherein A _{2 is} the amplitude of the test antenna receiving the signal transmitted from the antenna unit in the test, and ψ _r ( j ) is the phase of the reference antenna transmit signal when the phase shifter state is j, where j is an integer. The far field calibration system of the antenna system according to claim 4, wherein the amplitude coefficient (|S ₃₂ |) of the antenna unit to be tested (AUT) and the reference antenna and the antenna unit under test (AUT) The measured phase difference (∠ S _{31 -} ∠ S ₃₂ ) can be obtained by a far field approximation method represented by the following formula. among them, ( θ ₀ , ) the measured field type of the test antenna when transmitting the i-th test antenna, Sr ( θ ₀ , The test field type of the test antenna is transmitted for the reference antenna. The far field calibration system of the antenna system of claim 3, wherein the maximum cosine power value (P ^Max ) or the minimum cosine power value (P ^Min ) is calculated when the system impedance is 1. Got it. The far field calibration system of the antenna system of claim 1, wherein the test antenna module is disposed at an edge of the multiple input multiple output active phase antenna array. The far field calibration system of the antenna system of claim 1, wherein the reference antenna has a distance of 400 mm (400 mm) from the metal reflecting surface.