FPGA-Based General Ultra-Wideband Calibration Direction Finding Method and System

Abstract

The present invention discloses a general ultra-wideband calibration and direction-finding system and method based on FPGA. The PDW information is processed within the FPGA. Through the phase comparison technology, the inherent phase error introduced by channel inconsistency is eliminated. Calibration is performed at fixed frequency points, and smoothing and interpolation processing are carried out. The data of multiple calibration analyses are averaged to improve the accuracy of calibration. Based on a single-bit receiver, the present invention adopts the phase comparison calibration and direction-finding technology, which has high sensitivity, an ultra-wide instantaneous bandwidth, and achieves high direction-finding accuracy with a relatively small amount of equipment.

Description

Technical Field

[0001] The present invention belongs to the field of electronic information direction finding technology, and particularly relates to a general ultra-wideband calibration direction finding method and system based on FPGA. Background Art

[0002] In recent years, with the rapid development of the fields of communication, radar and electronic countermeasure, more and more new-type radars have been applied, and the electromagnetic environment has become increasingly high-density and complex. It is urgent to develop a broadband digital receiver with ultra-wideband, high sensitivity, large dynamic range and the ability to adapt to signals arriving simultaneously.

[0003] Currently, the main methods for measuring the azimuth of incoming waves include amplitude comparison system, time difference system, spatial spectrum system, interferometer system, etc. The amplitude comparison system determines the direction based on the different amplitudes of the received signals of incoming waves from different directions by utilizing the direction characteristics of the direction finding antenna array during the propagation of the radio wave. The time difference system determines the direction of the incoming radio wave by measuring the time difference of the radio wave reaching each direction finding antenna unit of the direction finding antenna array during the propagation of the radio wave. The spatial spectrum system is still in the research and experimental stage, and requires a broadband direction finding antenna and the electrical performance consistency between each antenna array element and between multi-channel receivers. The interferometer system determines the direction of the incoming wave based on the fact that when radio waves from different directions reach the direction finding antenna array, the phases received by each direction finding antenna unit in space are different, and their phase differences are also different. The phase interferometer technology is most suitable for occasions that require high-precision measurement of the angle of arrival. When the antenna spacing is greater than 0.5 wavelengths, phase ambiguity will occur, and a combination of long and short baselines is often used. The long baseline improves the direction finding accuracy, and the short baseline eliminates the phase ambiguity. The inherent phase error introduced by the inconsistency of the system channels will affect the measurement results. Summary of the Invention

[0004] The present invention proposes a general ultra-wideband calibration direction finding system based on FPGA.

[0005] The technical solution for realizing the purpose of the present invention is: a general ultra-wideband calibration direction finding system based on FPGA, including a calibration source, a host computer, an FPGA, a receiver, and a turntable; the calibration source is connected to the host computer and the receiver, and the host computer controls the calibration source to generate a calibration signal and transmit it to the receiver; the receiver is arranged on the turntable, and the turntable is connected to the host computer. The host computer controls the azimuth of the receiver by controlling the turntable; the receiver is used to transmit the received signal and the calibration signal to the FPGA, and the FPGA is used to automatically correct the multi-channel phase information, generate a calibration table based on frequency index, find the calibrated phase difference value in the calibration table according to the signal frequency information for phase correction, and calculate the azimuth angle of the target based on the phase relationship of the calibrated multiple receiving channels.

[0006] The present invention also proposes a general ultra-wideband calibration direction-finding method based on FPGA, and the specific steps are as follows:

[0007] Scan the frequency band at fixed frequency points to obtain a calibration table indexed by frequency, and the calibration table is used to store the phase difference between channels;

[0008] Perform smoothing and interpolation processing on the calibration table, calculate the average value by correcting and analyzing the data multiple times, and obtain a calibration table storing the calibrated phase difference;

[0009] Obtain the ambiguous phases of multiple channels in real time, correct the phase difference according to the calibrated phase difference corresponding to the signal frequency, obtain the phase relationship of multiple receiving channels, and determine the target azimuth angle according to the phase relationship of multiple receiving channels.

[0010] Compared with the prior art, the present invention has the following remarkable advantages: based on a single-bit receiver, the present invention adopts a phase comparison and calibration direction-finding technology, which has high sensitivity, ultra-wide instantaneous bandwidth, low requirements for the overall device, low cost, simple design, and can achieve high direction-finding accuracy with a small amount of equipment.

[0011] The following further describes the present invention in detail with reference to the accompanying drawings. Description of the Drawings

[0012] Figure 1 is the system architecture diagram of the present invention.

[0013] Figure 2 is the schematic diagram of the side direction of the present invention.

[0014] Figure 3 is the flow chart of the present invention. Specific Embodiments

[0015] As Figure 1 shown, a general ultra-wideband calibration direction-finding system based on FPGA includes a calibration source, a host computer, an FPGA, a receiver, and a turntable; the calibration source is connected to the host computer and the receiver through network cables, and the host computer controls the calibration source to generate calibration signals and transmit them to the receiver; the receiver is arranged on the turntable, and the turntable is connected to the host computer through a network cable, and the host computer controls the azimuth of the receiver by controlling the turntable; the receiver is used to transmit the received signal and the calibration signal to the FPGA; the FPGA serves as the main control chip of the system, processes PDW information internally, performs data processing through the Microblaze soft core built in the FPGA, automatically corrects the phase information of multiple channels, generates a calibration table indexed by frequency; based on the phase relationship of multiple calibrated receiving channels, calculates the azimuth angle of the target, communicates with the host computer, receives commands from the host computer, and outputs the processing result.

[0016] As Figure 2As shown in the figure, the working principle of the present invention is as follows: Each time the device is powered on and initialized, the receiver scans the entire frequency band at a fixed frequency point, performs smoothing and interpolation processing, corrects and analyzes the data multiple times to calculate the average value, and generates the final table; when performing direction finding, it first measures the frequency, and processes the corrected phase difference in the saved table found according to the frequency and the obtained ambiguous phase, and calculates the azimuth angle of the target after ambiguity resolution.

[0017] In the present invention, the receiver is provided with 3 receiving channels, l 1 and l 2 represent the distance between channels, and λ represents the wavelength of the maximum frequency signal to be measured. Among them:

[0018]

[0019]

[0020] After Microblaze initializes modules such as the serial port, FIFO, and register control, it completes AD synchronization and processes the acquired PDW to parse information such as frequency and phase.

[0021] The formula for calculating the target angle is:

[0022]

[0023] In the above formula, is the unambiguous phase difference between the signals of channels 3 and 1, and c is the propagation speed of electromagnetic waves. To obtain the angle θ, only the phase difference

[0024] needs to be calculated. As Figure 3 shown, a general ultra-wideband calibration direction finding method based on FPGA has the following specific steps:

[0025] Turn the turntable to 0°, set the calibration source frequency fre. At this time, the phases of the three channels are theoretically the same, but the actually measured phase difference between channel 2 and channel 1 and the phase difference between channel 3 and channel 2 are both not 0. This difference is the inherent phase error introduced by channel inconsistency. Store these two differences into the table TABLE[fre], where fre is the index of this table:

[0026]

[0027] After scanning the entire frequency band at a fixed frequency point, obtain the entire calibration table indexed by frequency. Perform smoothing and interpolation processing on the calibration table, correct and analyze the data multiple times to calculate the average value, improve the accuracy of calibration, and obtain the final calibration table.

[0028] Obtain the ambiguous phases of channels 1, 2, and 3 in real time as The phases after ambiguity resolution for Channels 2 and 3 are Perform phase difference correction based on the correction table:

[0029]

[0030]

[0031]

[0032] where is the calculated ambiguous phase difference between Channel 2 and Channel 1, is the calculated ambiguous phase difference between Channel 3 and Channel 2. The value of is made to range within (-2π, 2π) by ±2π. TABLE[fre][0] is the correction phase difference between Channel 2 and Channel 1 corresponding to the frequency source, and TABLE[fre][1] is the correction phase difference between Channel 3 and Channel 2 corresponding to the frequency source. Thus, the phase difference correction is completed.

[0033] The direction finding algorithm is as follows: For Channel 2, we have:

[0034]

[0035] From Equations (5), (7), and (8), n can be deduced, where n is the ambiguity number of Channel 2.

[0036] For Channel 3, we have:

[0037]

[0038] From Equations (5), (6), (8), and (9), m can be deduced, where m is the ambiguity number of Channel 3. Thus, the azimuth angle is obtained:

[0039]

Claims

1. A general ultra-wideband calibration direction-finding method based on FPGA, characterized in that, the specific steps are as follows: Scan the frequency band with fixed frequency points to obtain a calibration table indexed by the frequency of the calibration source information, and the calibration table is used to store the phase difference between channels; Perform smoothing and interpolation processing on the calibration table, calculate the average value by correcting and analyzing the data multiple times, and obtain a calibration table storing the corrected phase difference; Obtain the ambiguous phase of multiple channels in real time, and correct the phase difference according to the corrected phase difference corresponding to the signal frequency. The specific formula is: Wherein, is the ambiguous phase of three channels obtained in real time, TABLE[fre][0] is the calibration phase difference between channel 2 and channel 1 corresponding to the calibration source information frequency, and TABLE[fre][1] is the calibration phase difference between channel 3 and channel 2 corresponding to the calibration source information frequency. are the real-time phase differences between channel 2 and channel 1, and between channel 3 and channel 2 after calibration; obtaining the phase relationships of multiple receiving channels, and determining the target azimuth angle according to the phase relationships of multiple receiving channels. The specific method is as follows: Channel 2 satisfies: Channel 3 satisfies: where n is the fuzzy number of channel 2, is the phase after defuzzification of channels 2 and 3, l 1 and l 2 represent the distances between channel 2 and channel 1, and between channel 3 and channel 2, represents the phase difference corresponding to when the distance is half the wavelength of the maximum frequency signal, where λ is the wavelength of the maximum frequency signal to be measured; Determine the ambiguous numbers n and m of channels 2 and 3 according to the formulas satisfied by channels 2 and 3 and the phase difference correction formula; According to the formula: Determine the azimuth angle θ of the target, where c is the propagation speed of electromagnetic waves and f is the frequency.

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