High-precision real-time dynamic test method for radar antenna internal calibration network

Abstract

The invention provides a high-precision real-time dynamic test method for an internal calibration network of a radar antenna. The method uses a reflection method to perform a high-precision amplitude and phase change real-time test of an internal calibration network or a cable of a radar. A state switch is added in an antenna array surface to switch a reflection end to perform electromagnetic reflection. A calibration switch is used to switch between a plurality of internal calibration networks of a phased array antenna, and then amplitude and phase change tests of different internal calibration networks are performed. A circulator, a single machine with a circulator-like function, or a power divider is used to separate a reflected signal from a direct leakage signal. Various weighted algorithms are used to reduce the interference of source leakage signals. An internal calibration reflection method is inserted in a radar working mode to perform a real-time internal calibration network amplitude and phase test during the radar working process.

Description

Technical Field

[0001] The invention belongs to the technical field of antennas, and in particular relates to a high-precision real-time dynamic testing method for an internal calibration network of a radar antenna. Background Art

[0002] The internal calibration network is an important component of the radar antenna. Its main function is to provide support for the detection and monitoring of the radar antenna. Radar antennas, especially large phased array antennas, generally adopt modular design. The main link of this type of antenna often has a long electrical propagation path, and it is difficult to disassemble and test the modules. The performance of the antenna after operation needs long-term monitoring. The internal calibration network provides the possibility for long-term monitoring of the amplitude and phase characteristics of the radar main link.

[0003] The radiating unit or active single-unit coupling part of the radar antenna transmits the signal to the internal calibration network, which synthesizes all the coupling signals and sends them to the back-end for signal processing, and monitors the changes of the main transmission signal accordingly. The internal calibration network also provides the possibility for monitoring the receiving link. The back-end sends the RF signal to the internal calibration network, which distributes the signal to each radiating unit or active channel and transmits the signal to the receiving link of the antenna, and judges the amplitude and phase characteristics of the receiving link accordingly.

[0004] Large phased array antennas often have multiple panels. After the antenna is debugged and tested, the panels are removed and transported when it is delivered to the field, and reassembled after arriving at the destination. In this process, the phase of the antenna's main transmission and reception paths and the calibration network will change, ranging from tens of degrees to hundreds of degrees, which leads to an overall change in the phase between modules, so recalibration is required. The commonly used calibration method requires external calibration of the antenna array, using antennas such as probes or horns to retest each unit or module of the entire array, while field calibration often has limited accuracy, is difficult to operate, and takes a long time, with a huge workload, and even cannot be operated in some situations. If the antenna is calibrated regularly, special personnel and equipment are required to perform special field operations, and the real-time performance of field calibration is poor. It cannot be tested during the operation of the radar, and the real-time changes in the phase between modules cannot be observed.

[0005] Products on some platforms, such as spaceborne phased array antennas, are deployed after being launched into a predetermined orbit. The deployment of the antenna in space will cause the shape of the inter-board cable to change, which will lead to a change in the phase of the inter-board cable, which is about a few degrees to more than ten degrees. This phase change becomes unacceptable for systems with high multi-channel consistency requirements or low sidelobe antennas. If the on-orbit imaging external calibration method is used, the phase calibration accuracy is limited, and other errors are introduced incidentally, and it is impossible to distinguish various error sources.

[0006] In addition to the phase changes caused by the above-mentioned antenna assembly and deployment, the long-term operation of the antenna causes the antenna temperature to rise, which in turn causes phase changes within and between modules. Even if cables of the same batch and length are used, there will be differences in their phase changes, especially when the cables are very long, the phase changes of different modules may vary greatly. If the temperature of the X-band antenna cable rises from 10°C to 20°C, the phase change of a 5-meter-long RF cable is greater than 50°. The inconsistency of the temperature of the antenna array causes large differences in the phase changes of the modules on the antenna array, which in turn leads to deterioration of beam performance. Therefore, it is necessary to perform real-time phase calibration during the operation of the antenna, test the phase changes between modules in real time, and then compensate for the phase changes to prevent beam performance deterioration caused by phase change differences due to temperature rise.

[0007] In summary, due to the test, transportation, deployment and temperature of the antenna, the amplitude and phase of the antenna main link change. In order to calibrate the performance of the main link, the phase change of the internal calibration network must be accurately known. Traditional methods have poor accuracy, are difficult to implement, and have poor real-time performance. It is impossible to calibrate the phase of the internal calibration network in real time. Innovative methods must be used to improve the phase accuracy of the antenna internal calibration network and be able to perform real-time dynamic calibration. Summary of the invention

[0008] The purpose of the present invention is to realize a high-precision real-time dynamic test method for the internal calibration network of a radar antenna. The method can quickly test the phase change of the internal calibration network of the radar antenna, and the phase test accuracy of the method is better than 1°. If the working mode is integrated into the working process of the radar system and combined with the algorithm, the dynamic real-time test of the main link phase of the antenna can be realized.

[0009] After using this method, the phase change of the calibration link can be accurately tested after the antenna is disassembled for transportation and reassembled after the darkroom test, or after the antenna is unfolded; by integrating this method into the working mode of the radar system, the phase change between channels can be accurately tested instantaneously, with a test accuracy better than 1°, providing a basis for real-time beam calibration.

[0010] The invention provides a high-precision real-time dynamic test method for an internal calibration network of a radar antenna. The radar antenna array surface used in the method includes N panels, which are marked as: 1, 2, ..., N; each panel includes a state switching switch and a set of internal calibration networks, and the N panels have a total of N sets of internal calibration networks; the state switching switch is specially set to realize the calibration of the internal calibration network, and the state switching switch has two sub-ports, namely a reflection end and a passage end, the reflection end is connected to a radio frequency open circuit device, and the passage end is connected to other single machines of the antenna array surface; the radar antenna internal calibration network includes a flexible cable, a power divider, a calibration switch, an internal calibrator, a radio frequency signal excitation source and a receiver. Combined with the transmitting and receiving functions of the radar antenna, the radar antenna internal calibration network can be used to calibrate the state of the radar antenna. For a large phased array antenna, the electrical length of the flexible cable is the longest, and it is also the most important component of the internal calibration network; the calibration switch is a single-pole N-position switch, and the N moving ends of the single-pole N-position switch correspond to the N antenna panels respectively, as shown in FIG. Figure 1 shown.

[0011] In order to facilitate the disassembly, transportation and deployment of the antenna, the cable will be disassembled during the transportation of the antenna, and then the phase of the calibration network will change, and the changes of the internal calibration networks 1 to N are not completely consistent; the present invention can be used to test the phase changes of the internal calibration networks 1 to N before and after the transportation of the antenna, when the antenna is deployed and during the operation of the antenna with high precision.

[0012] The method comprises the following steps:

[0013] Step 1, the radar antenna array includes N panels, each panel has a set of internal calibration network, which is labeled as internal calibration network i, where i = 1, 2, ..., N;

[0014] Step 2: The RF signal excitation source sends the RF signal to the internal calibrator. The internal calibrator has a circulator inside, which sends the signal to the antenna. A small amount of RF signal (about -20 dB) leaks to the receiver through the internal calibrator.

[0015] Step 3, the calibration switch is a single-pole N-position switch, which sends the RF signal to panel i through the control signal;

[0016] Step 4, the RF signal passes through the calibration switch and then is sent to the panel i through the flexible cable;

[0017] Step 5: The RF signal is reflected by the state switch on the panel and returns to the calibration switch through the flexible cable, and then sent to the internal calibrator;

[0018] Step 6: The internal calibrator sends the RF signal reflected by the antenna to the receiver through the circulator;

[0019] Step 7, the receiver receives the signal A1 leaked from the excitation source through the circulator in the internal calibrator, and at the same time receives the signal A2 reflected back to the receiver through the antenna state switching switch. There is a delay between A1 and A2, and the delay time depends on the effective electrical delay of the internal calibration network;

[0020] Step 8: After the receiver receives the two signals simultaneously, it performs weighted processing on the signals to reduce the influence of the leakage signal on the reflected signal.

[0021] In the step 5, the radio frequency signal passing through the state switching switch on the panel reflects a signal specifically comprising: a signal reflected by a reflection end of the switch.

[0022] When the antenna is working normally, the status switch on the antenna panel is placed at the access end. At this time, the internal calibration network is connected to the antenna body. When the antenna is tested for the internal calibration network, the status switch is switched to the reflection end. The reflection end of the status switch in the panel is used as a reflection signal, and this port can be connected to an open circuit breaker.

[0023] Choose a circulator with good performance. The smaller the leakage signal, the less interference it will have on the reflected signal. It is usually required to be at least 20dB smaller than the direct signal.

[0024] The output port of the internal calibrator and the connections inside the antenna internal calibration network have good standing waves. It is recommended that the standing wave be better than 1.2. If the standing wave is too large, the test accuracy of the reflected signal will be affected.

[0025] The internal calibration network to be tested is the link between the internal calibrator and the state switching switch. If you want to test the internal calibration network inside the panel, the state switching switch can be moved forward to the module level or even the single-machine level.

[0026] The delay of the internal calibration network is approximately: T delay =2*L / C eff , where L is the physical length from the open end of the state switching switch in the internal calibration network to the internal calibrator, C eff is the equivalent light speed of the internal calibration network. If this section of the internal calibration network is mainly cables, then Where C is the speed of light in vacuum, ε is the effective dielectric constant, It expresses the ratio of the speed of electromagnetic waves in a cable to the speed of light in a vacuum, usually Between 0.75 and 0.85, the specific data depends on the cable model.

[0027] The delay of the internal calibration network T delay It has a greater impact on system performance. Therefore, the lower the working frequency band, the greater the delay, the smaller the impact of the leakage signal of the internal calibrator on the reflected signal, and the higher the test accuracy of the internal calibration network.

[0028] After receiving the signal, the receiver uses the amplitude weighting method to perform low sidelobe processing on the main signal during the data processing process, which can reduce the impact of various interference signals. The greater the weighting, the higher the test accuracy.

[0029] The beneficial effects of the present invention are:

[0030] The effects of the present invention mainly include:

[0031] This method can test the phase change of the internal calibration network caused by antenna disassembly and installation, antenna deployment, etc., and then combine the transmission and reception calibration to test the main path amplitude and phase change;

[0032] This method has the characteristics of strong real-time performance. By inserting this working mode into the working mode of the radar system, the phase change during the antenna operation process can be tested.

[0033] This method is highly versatile and can be applied to phased array antennas of various configurations;

[0034] This method has high test efficiency and fast test speed, and can complete the test instantly (less than 1 second);

[0035] This method has high test accuracy, and the phase accuracy is better than 1°;

[0036] This method is economical and low-cost, requiring only an open circuit in the RF link without the need for additional expensive hardware;

[0037] This method is highly operable, and after the program is solidified, the operation is simple, and no external calibration equipment or other external equipment is required;

[0038] This method is highly applicable and is suitable for phased array antennas on any platform, including satellites; this method is not only applicable to radar antennas, but also to other large antennas such as communication antennas. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Working Principle Diagram

[0040] Figure 2 Calibration switch schematic diagram

[0041] Figure 3 Proof of Principle

[0042] Figure 4 Receiver Channel 1 Link

[0043] Figure 5 Receiver Channel 2 Link

[0044] Figure 6 Energy-time characteristics of links 1 and 2

[0045] Figure 7 Changes in direct phase and reflected phase

[0046] Figure 8 Phase test error (before and after weighting) DETAILED DESCRIPTION

[0047] The technical solution provided by the present invention will be described in detail below in conjunction with specific embodiments. It should be understood that the following specific implementation methods are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0048] The invention provides a high-precision real-time dynamic test method for an internal calibration network of a radar antenna. The radar antenna array surface used in the method includes N panels, which are marked as: 1, 2, ..., N; each panel includes a state switching switch and a set of internal calibration networks, and the N panels have a total of N sets of internal calibration networks; the state switching switch is specially set to realize the calibration of the internal calibration network, and the state switching switch has two sub-ports, namely a reflection end and a passage end, the reflection end is connected to a radio frequency open circuit device, and the passage end is connected to other single machines of the antenna array surface; the radar antenna internal calibration network includes a flexible cable, a power divider, a calibration switch, an internal calibrator, a radio frequency signal excitation source and a receiver. Combined with the transmitting and receiving functions of the radar antenna, the radar antenna internal calibration network can be used to calibrate the state of the radar antenna. For a large phased array antenna, the electrical length of the flexible cable is the longest, and it is also the most important component of the internal calibration network; the calibration switch is a single-pole N-position switch, and the N moving ends of the single-pole N-position switch correspond to the N antenna panels respectively, as shown in FIG. Figure 1 shown.

[0049] In order to facilitate the disassembly, transportation and deployment of the antenna, the internal calibration network is mainly composed of passive units such as flexible cables and power dividers. The cables will be disassembled during the transportation of the antenna, and the phase of the calibration network will change, and the changes of the internal calibration networks 1 to N are not completely consistent. The present invention can be used to test the phase changes of the internal calibration networks 1 to N before and after the transportation of the antenna, when the antenna is deployed, and during the operation of the antenna with high precision.

[0050] The method comprises the following steps:

[0051] Step 1, the radar antenna array includes N panels, each panel has a set of internal calibration network, which is labeled as internal calibration network i, where i = 1, 2, ..., N;

[0052] Step 2: The RF signal excitation source sends the RF signal to the internal calibrator. The internal calibrator has a circulator inside, which sends the signal to the antenna. A small amount of RF signal (about -20 dB) leaks to the receiver through the internal calibrator.

[0053] Step 3, the calibration switch is a single-pole N-position switch, which sends the RF signal to panel i through the control signal;

[0054] Step 4, the RF signal passes through the calibration switch and then is sent to the panel i through the flexible cable;

[0055] Step 5: The RF signal is reflected by the state switch on the panel and returns to the calibration switch through the flexible cable, and then sent to the internal calibrator;

[0056] Step 6: The internal calibrator sends the RF signal reflected by the antenna to the receiver through the circulator;

[0057] Step 7, the receiver receives the signal A1 leaked from the excitation source through the circulator in the internal calibrator, and at the same time receives the signal A2 reflected back to the receiver through the antenna state switching switch. There is a delay between A1 and A2, and the delay time depends on the effective electrical delay of the internal calibration network;

[0058] Step 8: After the receiver receives the two signals simultaneously, it performs weighted processing on the signals to reduce the influence of the leakage signal on the reflected signal.

[0059] In the step 5, the radio frequency signal passing through the state switching switch on the panel reflects a signal specifically comprising: a signal reflected by a reflection end of the switch.

[0060] When the antenna is working normally, the status switch on the antenna panel is placed at the access end. At this time, the internal calibration network is connected to the antenna body. When the antenna is tested for the internal calibration network, the status switch is switched to the reflection end. The reflection end of the status switch in the panel is used as a reflection signal, and this port can be connected to an open circuit breaker.

[0061] Choose a circulator with good performance. The smaller the leakage signal, the less interference it will have on the reflected signal. It is usually required to be at least 20dB smaller than the direct signal.

[0062] The output port of the internal calibrator and the connections inside the antenna internal calibration network have good standing waves. It is recommended that the standing wave be better than 1.2. If the standing wave is too large, the test accuracy of the reflected signal will be affected.

[0063] The internal calibration network to be tested is the link between the internal calibrator and the state switching switch. If you want to test the internal calibration network inside the panel, the state switching switch can be moved forward to the module level or even the single-machine level.

[0064] The delay of the internal calibration network is approximately: T delay =2*L / C eff , where L is the physical length from the open end of the state switching switch in the internal calibration network to the internal calibrator, C eff is the equivalent light speed of the internal calibration network. If this section of the internal calibration network is mainly cables, then Where C is the speed of light in vacuum, ε is the effective dielectric constant, It expresses the ratio of the speed of electromagnetic waves in a cable to the speed of light in a vacuum, usually Between 0.75 and 0.85, the specific data depends on the cable model.

[0065] The delay of the internal calibration network T delay It has a greater impact on system performance. Therefore, the lower the working frequency band, the greater the delay, the smaller the impact of the leakage signal of the internal calibrator on the reflected signal, and the higher the test accuracy of the internal calibration network.

[0066] After receiving the signal, the receiver uses the amplitude weighting method to perform low sidelobe processing on the main signal during the data processing process, which can reduce the impact of various interference signals. The greater the weighting, the higher the test accuracy.

[0067] Figure 3 This is a schematic diagram of the principle of the internal calibration method verification. The entire radar includes an internal calibration network (including several cables, 1:2 power divider), an internal calibrator, a circulator, and a receiver. The internal calibrator outputs a radio frequency signal, which passes through the circulator and reaches the 1:2 power divider through a 16-meter-long cable. One output port of the 1:2 power divider is connected to port 2 of the receiver through a 2-meter-long cable, and the other output port is open. The electromagnetic signal reflected from the open end passes through the 16-meter-long cable, the circulator, and the 2-meter-long cable and enters port 1 of the receiver. The output signal of the internal calibrator is a linear frequency modulation signal, and the operating frequency band is the X-band.

[0068] The internal calibration network in this example is mainly composed of a 16-meter long flexible RF cable, the loss in the X-band is about 16dB, the loss of a 2-meter long cable is about 2dB, and the transmission speed of electromagnetic waves in the cable is about 0.8 times the speed of light.

[0069] The signal chain 1 of receiver channel 1 is as follows Figure 4 shown.

[0070] The RF signal received by receiver channel 2 is as follows: Figure 5 shown.

[0071] As can be seen in the figure, the main differences between Link 1 and Link 2 include the following two points:

[0072] 1. There is a difference in transmission time. It passes through the 16-meter-long RF cable twice during the transmission process. At the same time, because the transmission path of link 1 is longer, it enters the receiver earlier than link 2. The time difference between the two is: △T=△L / C eff =16 / 0.3*1 / 0.8=66.7ns.

[0073] 2. There is a difference in transmission energy. The link 1 from the RF signal to the receiving channel 1 is 16 meters longer than the link 2 to the channel 2, so the cable loss is 16dB larger; the reflection loss of link 1 in the 1:2 power divider is -7dB, while the loss of link 2 after the 1:2 power divider is -3.5dB, so the reflection loss of the power divider is 3.5dB larger than the direct loss. Therefore, the loss of link 1 is about 19-20dB greater than that of link 2, that is, the energy received by receiver channel 1 is 19-20dB less than that received by receiver channel 2.

[0074] The receiver receives two signals at the same time, and the two receiver channels simultaneously record the phase β of the reflected signal and the reflected phase α of the direct signal. The reflected signal β is normalized as follows: Figure 6 shown.

[0075] Figure 6 The middle curve is the composite signal of receiver channels 1 and 2. There are two obvious peaks in the figure. The second peak is the reflected signal β, which corresponds to time. According to the pulse repetition frequency set in the working setting, it can be calculated that 100 points correspond to 50ns. The difference between the two signals in the figure is 130 points, corresponding to 65ns, which is almost consistent with the expected time difference.

[0076] Figure 6 There are two curves in the figure. One is the test result without mathematical processing. The test result shows that the delayed interference signal energy of the second peak (corresponding to the reflected signal β) is 10dB larger than that of the first peak. The second curve is the result after weighted / windowed processing of the first peak by mathematical algorithm. It can be seen that after weighted / windowed, the delayed interference signal energy of the second peak is more than 25dB larger than that of the first peak, which greatly improves the test accuracy.

[0077] To verify the correctness and accuracy of this method, the 16-meter-long cable in the internal calibration network was placed in a hot environment. The reflection phase β and the through phase α changed over time. The test time was about 2 minutes. Figure 7 shown.

[0078] The ambient temperature is about 15°C. The cable temperature caused by heating rises rapidly by 20°C in 1 minute. The through phase changes by about 20° and the reflected phase changes by about 40°. The phase difference β-2×α changes with time in both the unweighted and weighted cases as shown in Figure 2. Figure 8 shown.

[0079] It can be seen that before weighting, the phase change accuracy is about 6° (PP). This large error is due to the low signal-to-noise ratio, which is about 10dB. After weighting, the energy of the reflected signal is 25dB greater than the noise signal, and the impact of the side lobe becomes smaller, so the phase accuracy is greatly improved to 0.7° (3σ). It can be seen that the weighted algorithm can effectively improve the test accuracy.

[0080] The above description is only the best specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0081] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A high-precision real-time dynamic test method for a radar antenna internal calibration network, characterized in that: The radar antenna array surface used in the method includes N panels, marked as: 1, 2, ..., N; each panel includes a state switching switch and a set of internal calibration network, and the N panels have a total of N sets of internal calibration networks; the state switching switch is specially set to realize the calibration of the internal calibration network, and the state switching switch has two sub-ports, namely a reflection end and a passage end, the reflection end is connected to a radio frequency open circuit, and the passage end is connected to other single machines of the antenna array surface; the radar antenna internal calibration network includes a flexible cable, a power divider, a calibration switch, an internal calibrator, a radio frequency signal excitation source and a receiver; the calibration switch is a single-pole N-position switch, and the N moving ends of the single-pole N-position switch correspond to the N antenna panels respectively; The method comprises the following steps: Step 1, the radar antenna array includes N panels, each panel has a set of internal calibration network, which is labeled as internal calibration network i, where i = 1, 2, ..., N; Step 2: The RF signal excitation source sends the RF signal to the internal calibrator. The internal calibrator has a circulator inside, which sends the signal to the antenna. A small amount of RF signal leaks to the receiver through the internal calibrator. Step 3, the calibration switch is a single-pole N-position switch, which sends the RF signal to panel i through the control signal; Step 4, the RF signal passes through the calibration switch and then is sent to the panel i through the flexible cable; Step 5: The RF signal is reflected by the state switch on the panel and returns to the calibration switch through the flexible cable, and then sent to the internal calibrator; Step 6: The internal calibrator sends the RF signal reflected by the antenna to the receiver through the circulator; Step 7, the receiver receives the signal A1 leaked from the excitation source through the circulator in the internal calibrator, and at the same time receives the signal A2 reflected back to the receiver through the antenna state switching switch. There is a delay between A1 and A2, and the delay time depends on the effective electrical delay of the internal calibration network; The delay of the internal calibration network is approximately: T delay =2*L / C eff , where L is the physical length from the open end of the state switching switch in the internal calibration network to the internal calibrator, C eff is the equivalent light speed of the internal calibration network; when this section of the internal calibration network is mainly cable, then Where C is the speed of light in vacuum, ε is the effective dielectric constant, It indicates the ratio of the speed of electromagnetic waves transmitted in the cable to the speed of light in a vacuum, and the value is between 0.7 and 0.

85. The specific data depends on the type of cable. Step 8: After the receiver receives the two signals simultaneously, it performs weighted processing on the signals to reduce the influence of the leakage signal on the reflected signal.

2. The method according to claim 1, characterized in that In the step 5, the radio frequency signal passing through the state switching switch on the panel reflects a signal specifically comprising: a signal reflected by a reflection end of the switch.

3. The method according to claim 1, characterized in that When the antenna is working normally, the status switch on the antenna panel is placed at the access end. At this time, the internal calibration network is connected to the antenna body. When the antenna is tested with the internal calibration network, the status switch is switched to the reflection end. The reflection end of the status switch in the panel is used as a reflection signal, and the port is connected to an open circuit breaker.

4. The method according to claim 1, characterized in that: The smaller the circulator leakage signal, the less interference it has on the reflected signal, which is required to be at least 20dB smaller than the direct signal.

5. The method according to claim 1, characterized in that The output port of the internal calibrator and the connections inside the antenna internal calibration network have good standing waves, and the standing wave is better than 1.

2.

6. The method according to claim 1, characterized in that The delay of the internal calibration network T delay It has a greater impact on system performance. Therefore, the lower the working frequency band, the greater the delay, the smaller the impact of the leakage signal of the internal calibrator on the reflected signal, and the higher the test accuracy of the internal calibration network.

7. The method according to claim 1, characterized in that After receiving the signal, the receiver uses the amplitude weighting method to perform low sidelobe processing on the main signal during the data processing process to reduce the impact of various interference signals. The greater the weighting, the higher the test accuracy.

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