CN109633578B - Two-channel high-precision phase calibration system and method - Google Patents

Two-channel high-precision phase calibration system and method Download PDF

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CN109633578B
CN109633578B CN201811466632.1A CN201811466632A CN109633578B CN 109633578 B CN109633578 B CN 109633578B CN 201811466632 A CN201811466632 A CN 201811466632A CN 109633578 B CN109633578 B CN 109633578B
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苏皎阳
卢护林
李银伟
阚学超
夏慧婷
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Shanghai Radio Equipment Research Institute
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Abstract

The invention relates to a dual-channel high-precision phase calibration system, which is characterized by comprising the following components: the device comprises a calibration signal source, an internal calibration component, an analog receiver and an ADC signal acquisition and signal processing system; the calibration signal source outputs two paths of calibration signals to be injected into the inner calibration assembly, and the inner calibration assembly outputs two paths of calibration signals to be transmitted to the analog receiver through a cable; the analog receiver transmits the received signals to an ADC signal acquisition and signal processing system for processing, and the total phase difference of the two paths of signals is obtained; meanwhile, the analog receiver returns part of received signals to the inner calibration component along the original path, the inner calibration component transmits the returned signals to the ADC signal acquisition and signal processing system, and the phase difference of the cable is extracted. The invention provides a double-channel high-precision phase calibration method, which is used for calibrating phase errors among multiple receiving links and eliminating the phase errors of connecting cables, and the calibration precision can reach 0.07 degrees.

Description

Two-channel high-precision phase calibration system and method
Technical Field
The invention relates to the technical field of interference radars, in particular to a dual-channel phase calibration technology.
Background
The ground elevation measurement accuracy of the interference radar system is influenced by errors of a plurality of interference parameters, and the error sources mainly comprise instrument errors, atmospheric transmission errors, orbit errors, geophysical errors, data processing errors and the like. The error sources are various in source and different in influence, and the performance of the whole height measuring system can be effectively improved by adopting corresponding measures to avoid or compensate.
Among the above factors, the influence of the error caused by the system itself is serious. Due to temperature drift, aging, electromagnetic interference and other reasons, the amplitude-frequency and phase-frequency characteristics of the system change, and therefore a height measurement error is introduced, and therefore, some technical means need to be adopted to monitor and calibrate the response characteristics of the system.
Generally, an intra-system calibration mode is adopted, in the working process of an interferometric radar, the phase characteristics in a receiving link are influenced by the interferometric phase, the phase difference between receiving channels is calibrated by monitoring the phase of the receiving link in real time, and the difference is considered to be stable within a certain time, so that the phase error of the system is calibrated, each receiving link is compensated, the interferometric phase measurement precision is improved, and the ground elevation inversion precision is improved.
In the aspects of phase calibration method and application, the on-orbit satellite-borne synthetic aperture radar ERS-1/2 and Radarsat are designed with an internal calibration system. The inner calibration loop of ERS-1/2 is to delay the transmitted signal and feed it into the receiving loop to measure the stability of the whole loop transmitted power and the stability of the receiver gain. Radarsat does not have a delay loop, but rather transmits the transmit signal to the receive loop by way of coupling. The domestic HJ-1-C satellite also adopts an internal calibration system, and three internal calibration modes including reference calibration, emission calibration and noise calibration are adopted. However, the above products are all single-channel SAR systems, not dual-channel systems, and are different from the multi-channel phase calibration method described in this patent for the case of single-channel receive links.
In the patent of phase calibration method, the patents of Qiaming, Liangxingdong, Dixibiao, Zpayjie and Hanbing of the institute of electronics of Chinese academy of sciences-an active external scaler of broadband synthetic aperture radar and its calibration method (publication number: CN101082670) are disclosed, the patent is an external scaler and its calibration method, and is aimed at improving the gain of active scaling transceiver system and obtaining larger radar cross section, and does not relate to the phase calibration of interference radar system. The invention discloses a satellite-borne SAR internal calibration signal processing platform system and an implementation method (publication number: CN101135726), which is a patent of Chengjie, Yangwei, Rongpeng, Zhouyanqing and Lichungsheng of Beijing aerospace university. However, the method is only suitable for the SAR system, and cannot acquire the phase difference value between two channels, so that the method is not suitable for an interferometric radar system. The invention discloses an external calibration method of a satellite-borne InSAR system (publication number: CN103364766A) in the patents of Wangyu, Dinghuabiao and Lingxingdong of the institute of electronics of Chinese academy of sciences, and discloses the external calibration method of the satellite-borne InSAR system. The external calibration method comprises the steps of measuring sea surface height data by a satellite altimeter, and removing time-varying influence factors to obtain average sea surface height data; obtaining sea surface height data measured by the satellite-borne InSAR system through ocean image pairs and uncalibrated interference parameters which are acquired by the satellite-borne InSAR system and distributed in preset time and space; simulating and calculating sea surface height change caused by time-varying influence factors except propagation influence under the preset time and space distribution condition; acquiring time-varying synthetic sea surface height data according to the average sea surface height and the sea surface height variation caused by time-varying influence factors except for propagation influence; and (3) taking the time-varying synthesized sea surface height data as standard data, correcting the sea surface height data measured by the satellite-borne InSAR system, and calibrating the satellite-borne InSAR system. The patent is an external calibration method for the InSAR sea surface height measurement system, which is used for correcting sea surface height data measured by a satellite-borne InSAR system and does not relate to phase calibration.
The traditional InSAR interference system has no related patent because the calibration precision of the phase is not high, and the phase calibration between channels does not consider the phase difference influence of connecting cables in a calibration component.
So far, there is no patent of the two-channel high-precision phase calibration method described in the patent.
Disclosure of Invention
The invention provides a double-channel high-precision phase calibration method, which is used for calibrating the phase difference of an interference receiving link so as to ensure the height measurement precision of the whole radar altimeter system.
In order to achieve the above object, the present invention provides a dual-channel phase calibration system, comprising: the device comprises a calibration signal source, an internal calibration component, an analog receiver and an ADC signal acquisition and signal processing system;
the calibration signal source outputs two paths of calibration signals to be injected into the inner calibration assembly, and the inner calibration assembly outputs two paths of calibration signals to be transmitted to the analog receiver through a cable;
the analog receiver transmits the received signals to an ADC signal acquisition and signal processing system for processing, and the total phase difference of the two paths of signals is obtained;
meanwhile, the analog receiver returns part of received signals to the inner calibration component along the original path, the inner calibration component transmits the returned signals to the ADC signal acquisition and signal processing system, and the phase difference of the cable is extracted.
Preferably, the analog receiver receiving port returns part of the signal sent by the inner scaling component to the inner scaling component along the original path under the influence of standing waves.
Preferably, the inner calibration assembly is connected with the analog receiver through a radio frequency connection cable.
Preferably, the inner scaling component further comprises a circulator and a down-conversion link;
the circulator is arranged at the calibration port of the inner calibration component, two paths of calibration signals are output to the analog receiver, signals returned from the analog receiver are sent to the down-conversion link of the inner calibration component, and the down-conversion link transmits the signals to the ADC signal acquisition and signal processing system.
A dual-channel high-precision phase calibration method comprises the following steps:
step 1, acquiring the total phase difference of two paths of signals;
step 2, extracting the phase difference of the cable;
step 3, eliminating the phase difference of the cable from the total phase difference;
and 4, measuring for multiple times in the steps and calculating an average value.
Preferably, in step 2, in addition to extracting the phase difference of the cable itself, the amplitude inconsistency of the two paths of signals is compensated.
Preferably, assuming that the inconsistency of the two channel signals is constant over the whole bandwidth, the complex signals of the two channels demodulated by the receiver in digital quadrature are sequentially as follows:
Figure BDA0001889971030000031
Figure BDA0001889971030000032
wherein, the formula (1) is a main channel, and the formula (2) is an auxiliary channel;
for sub-channel echo signal s02The following operation is carried out;
Figure BDA0001889971030000033
wherein the content of the first and second substances,
s01×s02 *＝(I01+jQ01)×(I02-jQ02)＝[I01I02+Q01Q02]+j[I02Q01+I01Q02](4)
so that the compensation factor is
Figure BDA0001889971030000041
And finishing amplitude-phase consistency correction through the process.
Compared with the prior art, the invention has the following advantages:
1. the calibration precision is high: the calibration precision of the phase error can reach 0.07 degree.
2. The structure is simple, and the engineering is easy: the method of the invention monitors the change condition of the phase characteristics between the receiving links in real time by combining the internal calibration component with the receiving and transmitting system of the interference radar, and is easy to engineer.
Drawings
FIG. 1 is a block diagram of the system architecture of the present invention;
FIG. 2 is a system workflow diagram of the present invention.
Detailed Description
In order to make the technical means, the original characteristics, the achieved purposes and the effects of the invention easy to understand, the invention is further explained in detail with the accompanying drawings and the specific embodiments, but the scope of the invention is not limited in any way.
As shown in fig. 1 and fig. 2, the system of the present invention comprises: the device comprises a calibration signal source, an internal calibration component, an analog receiver and an ADC signal acquisition and signal processing system;
the calibration signal source outputs two paths of calibration signals to be injected into the inner calibration component;
the inner scaling component further comprises a circulator and a down-conversion link;
the circulator is arranged at the calibration port of the inner calibration component, two paths of calibration signals are output to the analog receiver through the radio frequency connecting cable, the analog receiver transmits the received signals to the ADC signal acquisition and signal processing system for processing, the total phase difference of the two paths of signals is obtained and measured for multiple times, the average value is obtained, the fixed phase error of the interference receiving channel can be obtained, and the subsequent received signals are compensated and calibrated to reduce the interference phase error.
Meanwhile, a receiving port of the analog receiver returns part of received signals to the inner calibration component along the original path under the influence of standing waves, the signals returned from the analog receiver are sent to a down-conversion link of the inner calibration component, and the down-conversion link is transmitted to the ADC signal acquisition and signal processing system to extract the phase difference of the cable.
Because the influence of the jitter and the temperature change of the two radio frequency connecting cables is different, the phase difference caused by the radio frequency connecting cables changes, and the phase difference can be superposed in the interference phase error of the two channels, so that the interference phase is influenced, and the phase difference of the radio frequency connecting cables needs to be synchronously calibrated and eliminated.
In practical applications as an example: for two interference receiving chains, the equivalent path lengths of the receiving chains caused by the length of a radio frequency chain, temperature change and the like are respectively assumed to be R1、R2After two paths of input calibration signals injected into the two receiving chains by the inner calibration component pass through the two different paths, the phases at the output ends are different, and the receiving chain 1 is taken as a reference, so that the two paths of input calibration signals are compared with each other to obtain the calibration signalThe phase difference between the receiving chain 2 and the receiving chain 1 is delta phi1＝2π(R1-R2) The phase extraction is carried out to obtain delta phi through echo acquisition and back-end signal processing1. Because the two paths of calibration signals injected into the two receiving links by the inner calibration component are transmitted through the radio frequency connecting cable, the radio frequency cable has phase difference and must be calibrated and eliminated.
Suppose that the lengths of the radio frequency connection cables are L respectively1、L2If the cable length is taken into consideration, the equivalent path lengths of the two receiving chains are R1+L1、R2+L2Then the phase difference between the two receiving chains is delta phi1′＝2π(R1-R2)/λ+2π(L1-L2) A, where 2 π (L)1-L2) The/lambda is the phase error that needs to be eliminated, and the above process cannot directly scale L1、L2The phase difference caused by the phase difference needs to return a calibration signal output by the inner calibration component to the inner calibration component for individual calibration, so that a circulator is added in a circuit of the inner calibration component, after the calibration signal passes through a radio frequency cable, part of the signal returns to a down-conversion link of the inner calibration component due to the influence of standing waves at a simulated receiver, down-conversion, acquisition and back-end signal processing are carried out, and the radio frequency cable L can be obtained1、L2Induced phase difference of 2 pi (L)1-L2) Lambda, then eliminate 2 pi (L)1-L2) After influence of/λ, 2 π (R)1-R2) The/lambda is used as a phase calibration value between the two receive chains. During processing, the same broadband signal is input into the two receiving links, output signals of all receiving channels are collected and processed, phase difference is obtained, measurement is carried out for multiple times, an average value is obtained, a phase error value between the channels can be obtained and used as a phase compensation value, and compensation calibration is carried out on subsequent receiving signals.
In addition to the compensation of the phase error value, it is also necessary to compensate the amplitude inconsistency, and generally, calibration is performed simultaneously, taking the amplitude and phase consistency correction of the two channels as an example, assuming that the inconsistency of the two channel signals is constant over the whole bandwidth, the complex signals of the two channels demodulated by the receiver in digital quadrature are sequentially as follows:
Figure BDA0001889971030000051
Figure BDA0001889971030000052
wherein, the formula (1) is a main channel, and the formula (2) is an auxiliary channel;
for sub-channel echo signal s02The following operation is carried out;
Figure BDA0001889971030000061
wherein the content of the first and second substances,
s01×s02 *＝(I01+jQ01)×(I02-jQ02)＝[I01I02+Q01Q02]+j[I02Q01+I01Q02](4)
so that the compensation factor is
Figure BDA0001889971030000062
And finishing amplitude-phase consistency correction through the process.
While the present invention has been described in detail by way of the foregoing preferred examples, it is to be understood that the above description is not to be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (6)

1. A two-channel high-precision phase calibration system is characterized by comprising: the device comprises a calibration signal source, an internal calibration component, an analog receiver and two ADC signal acquisition and signal processing systems;
the calibration signal source outputs two paths of calibration signals to be injected into the inner calibration assembly, and the inner calibration assembly outputs two paths of calibration signals to be transmitted to the analog receiver through the radio frequency connecting cable respectively;
the analog receiver transmits the received signals to a first ADC signal acquisition and signal processing system for processing to obtain the total phase difference of the two paths of signals;
meanwhile, the analog receiver returns part of received signals to the inner calibration component along the original path, the inner calibration component transmits the returned signals to the second ADC signal acquisition and signal processing system, and the phase difference of the cable is extracted.
2. The dual channel high accuracy phase calibration system of claim 1 in which the analog receiver receive port returns a portion of the signal from the inner calibration block to the inner calibration block by standing wave effects.
3. The dual channel high accuracy phase calibration system of claim 1, wherein said inner scaling module further comprises a circulator and a down conversion link;
the circulator is arranged at the calibration port of the inner calibration component, two paths of calibration signals are output to the analog receiver, signals returned from the analog receiver are sent to the down-conversion link of the inner calibration component, and the down-conversion link transmits the signals to the ADC signal acquisition and signal processing system.
4. A two-channel high-precision phase calibration method, which utilizes the two-channel high-precision phase calibration system of any one of claims 1 to 3, and comprises the steps of:
step 1, acquiring the total phase difference of two paths of signals;
step 2, extracting the phase difference of the cable;
step 3, eliminating the phase difference of the cable from the total phase difference;
and 4, measuring for multiple times in the steps and calculating an average value.
5. The two-channel high-precision phase calibration method according to claim 4, wherein in step 2, in addition to extracting the phase difference of the cable itself, the amplitude inconsistency of the two signals is compensated.
6. The dual-channel high-precision phase calibration method according to claim 5, wherein, assuming that the inconsistency of the two-channel signals is constant over the whole bandwidth, the complex signals of the two channels demodulated by the receiver in digital quadrature are sequentially as follows:
Figure FDA0002542981270000021
Figure FDA0002542981270000022
wherein, the formula (1) is a main channel, and the formula (2) is an auxiliary channel;
for sub-channel echo signal s02The following operations are carried out;
Figure FDA0002542981270000023
wherein the content of the first and second substances,
s01×s02 *＝(I01+jQ01)×(I02-jQ02)＝[I01I02+Q01Q02]+j[I02Q01+I01Q02](4)
so that the compensation factor is
Figure FDA0002542981270000024
And finishing amplitude-phase consistency correction through the process.
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