CN111903233B

CN111903233B - Broadband beam forming method based on specific group delay finite impulse response filter

Info

Publication number: CN111903233B
Application number: CN200810077009.7A
Authority: CN
Inventors: 解静; 李淳; 陈卫东
Original assignee: CETC 54 Research Institute
Current assignee: CETC 54 Research Institute
Priority date: 2008-10-22
Filing date: 2008-10-22
Publication date: 2014-06-11
Anticipated expiration: 2028-10-22

Abstract

The invention discloses a broadband beam forming method based on a specific group delay finite impulse response filter, and relates to a broadband beam forming technology of a specific group delay FIR filter in the field of communication reconnaissance and interference. A group of FIR filters with specific group delay are designed, and the group delay of the FIR filters is utilized to compensate the time delay between a space far-field signal and an adjacent antenna unit, so that the broadband wave beam forming within the bandwidth range of the filters is realized. The invention also has the advantages of basically consistent beam pattern in the whole design frequency band, small design calculation amount, easy engineering realization and the like. The method is particularly suitable for receiving and interfering the broadband signals in the occasions of communication countermeasure, intelligence reconnaissance and the like.

Description

Broadband beam forming method based on specific group delay finite impulse response filter

Technical Field

The invention relates to a broadband wave beam forming method based on a specific group delay Finite Impulse Response (FIR) filter in the field of communication countermeasure, which is particularly suitable for receiving and interfering broadband signals in the occasions of communication countermeasure, intelligence reconnaissance and the like.

Background

A beamformer is a spatial form of a filter that is used to receive a desired signal propagating along one direction in space while suppressing interference from other directions. Currently, there are many more mature methods for designing a narrowband beamformer. In many cases, however, the base array is required to be able to receive a wide-band signal without distortion, and thus the beam pattern of the beamformer is required to have a characteristic independent of frequency. However, the narrow-band beamforming only uses a set of fixed weight coefficients, which makes the basic array beam patterns at different frequencies different, if the wide-band signal is located outside the beam principal maximum direction, the gains obtained by different frequency components of the wide-band signal will be different, which will cause distortion of the signal waveform, and the larger the bandwidth of the signal, the more serious the distortion, and the requirement of wide-band signal processing in the communication countermeasure cannot be met.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a broadband beam forming method based on a specific group delay FIR filter, which avoids the defects in the background art. A group of FIR filters with specific group delay are designed, and the group delay of the FIR filters is utilized to compensate the time delay between a space far-field signal and an adjacent antenna unit, so that the broadband wave beam forming within the bandwidth range of the filters is realized. The invention also has the characteristic that the beam pattern is irrelevant to the frequency, so that the basic array can keep the basically consistent beam pattern in a wide frequency range, and the like.

The object of the invention is achieved in that it comprises the following steps:

setting a reference antenna unit in an array according to the antenna array and the beam pointing requirement of an interference or reconnaissance system, and determining the time delay of the rest antenna units in the array relative to the reference antenna unit;

determining the passband bandwidth of the FIR filter according to the bandwidth of the interference signal in the interference system or the bandwidth of the scout signal in the scout system, uniformly extracting M frequencies in the passband of the FIR filter, generating a sinusoidal signal with corresponding frequency as an input signal of the pseudo filter, wherein M is a natural number;

determining group delay of the FIR filter according to time delay of each antenna unit in the array relative to the reference antenna unit, and determining phase response and amplitude response of M frequency sinusoidal signals as output signals of the pseudo filter according to the passband bandwidth, the stopband rejection degree and the group delay of the FIR filter;

solving an autocorrelation matrix of the input signal of the pseudo filter and a cross-correlation column vector of the input signal of the pseudo filter and the output signal of the pseudo filter, and obtaining an inverse matrix of the autocorrelation matrix through matrix inversion operation, wherein the product of the inverse matrix and the cross-correlation column vector is a coefficient of the FIR filter with specific group delay;

selecting a window function to modify the coefficient of the FIR filter;

wideband beamforming based on a group-specific delay FIR filter is accomplished.

Compared with the background technology, the invention has the following advantages:

1) the antenna array of the interference or reconnaissance system of the present invention may take any array configuration.

2) The bandwidth of the interference signal in the interference system or the bandwidth of the scout signal in the scout system can be selected arbitrarily.

3) The FIR filter has good amplitude-frequency characteristic and strict linear phase characteristic.

4) The broadband beam forming technology of the invention has good beam pattern consistency in a wide frequency range.

5) The invention has small design calculation amount and is easy to realize engineering.

Drawings

Fig. 1 is a schematic block diagram of the wideband beamforming of the present invention. In fig. 1: 1 is an antenna array, 2 is a band-pass filter, 3 is a multiplier, 4 is an FIR filter, and 5 is an adder.

Fig. 2 is a block diagram of the adaptive implementation of the FIR filter of the present invention. In fig. 2: multiplier 6, adder 7, pseudo filter 8, adaptive FIR filter 9, and adder 10.

Fig. 3 is a two-dimensional beam pattern formed over a 50MHz bandwidth by the wideband beamforming of the present invention.

Fig. 4 is a three-dimensional beam pattern formed over a 50MHz bandwidth by the wideband beamforming of the present invention.

Fig. 5 is a diagram of the amplitude-frequency response and the phase-frequency response of an FIR filter corresponding to one antenna unit of the present invention.

Fig. 6 is a schematic diagram of FIR filter coefficients corresponding to one antenna element of the present invention.

Fig. 7 is a graph of the amplitude response and phase response of the rectangular window of the present invention.

FIG. 8 is a graph of the amplitude response and phase response of the Blackman window of the present invention.

Fig. 9 is a graph of the amplitude response and phase response of the hanning window of the present invention.

Fig. 10 is a graph of the amplitude response and phase response of the hamming window of the present invention.

FIG. 11 is a graph of the amplitude response and phase response of the Chebyshev window of the present invention.

FIG. 12 is a graph of the amplitude response and phase response of a Kaiser window of the invention.

Fig. 13 is a graph of the amplitude response and phase response of the inventive buttlet window (triangular window).

Detailed Description

Refer to fig. 1 to 13. Fig. 1 is a schematic block diagram of wideband beamforming of the present invention, which includes an antenna array 1, a band pass filter 2, a multiplier 3, an FIR filter 4, and an adder 5. In the structure, signals received by each array element of the antenna array 1 are filtered by a filter 2, amplitude weighting is carried out by a multiplier 3 to realize side lobe control, time domain filtering is carried out by an FIR filter 4 to compensate time delay between adjacent antenna units, and finally, the outputs are added by an adder 5 to obtain an output result. The amplitude weighting is mainly used to control the main-side ratio of the beam pattern, and the FIR filter 5 is used to compensate the relative delay between each path when the beam points to a specific direction. Fig. 2 is a block diagram of the adaptive implementation of the FIR filter of the present invention. It comprises multiplier 6, adder 7, pseudo filter 8, adaptive FIR filter 9 and adder 10. In this structure, the amplitude gains of M sinusoidal signals with different frequencies are first controlled by using multipliers 6, the outputs of the multipliers are added by adder 7, the output result of adder 7 is the input of adaptive FIR filter 9 and the input of pseudo filter 8, and pseudo filter 8 describes the design index meeting the beam width requirement, where the adaptive FIR filter is implemented by using LMS algorithm.

The following further describes the adaptive implementation method of the FIR filter with reference to specific embodiments, where the parameters of the embodiments are set as follows: a72-array-element uniform linear array is adopted, the spacing between the array elements is 0.5 meter, the azimuth angle theta is defined as the included angle between the incoming wave direction and the linear array normal, the channel analog intermediate frequency output is 165MHz, the sampling rate is 132MHz, a wave beam is planned to be formed on the azimuth angle of 5 degrees, a broadband signal with the bandwidth of 50MHz is received, and the signal frequency range is 225 MHz-275 MHz.

The invention comprises the following steps:

according to the antenna array and the beam pointing requirement of the interference or reconnaissance system, a reference antenna unit is set in the array, and the time delay of the rest antenna units in the array relative to the reference antenna unit is determined. In the embodiment, a reference antenna unit is set for a 72-array element uniform linear array, and the time delay tau of other antenna units in the array relative to the reference antenna unit is determined according to the parameters of 0.5 meter of array element spacing, 5-degree beam pointing and the like₁□τ₇₂。

Secondly, determining the passband bandwidth of the FIR filter according to the bandwidth of the interference signal in the interference system or the bandwidth of the scout signal in the scout system, uniformly extracting M frequencies in the passband of the FIR filter, and generating a sinusoidal signal with corresponding frequency as an input signal of the pseudo filter, wherein M is a natural number. The embodiment determines the passband bandwidth of the FIR filter according to the target signal bandwidth of 50MHz, uniformly extracts 19 frequency points of 6MHz, 9MHz, 10 MHz and 60MHz in the passband of the FIR filter, and generates a sinusoidal signal with corresponding frequency as an input signal of the pseudo filter.

Thirdly, according to the relative reference of each antenna unit in the arrayThe time delay of the antenna unit determines the group delay of the FIR filter, and the phase response and the amplitude response of the M frequency sinusoidal signals are determined by the passband bandwidth and the stopband suppression degree of the FIR filter and the group delay of the FIR filter and serve as the output signals of the pseudo filter. Embodiments rely on the time delay τ of an antenna element in an array relative to a reference antenna element₁□τ₇₂And determining the group delay of the FIR filter, determining the phase response and the amplitude response of the sinusoidal signals of the 19 frequency points by the passband bandwidth of 50MHz, the stopband rejection degree of the FIR filter and the group delay of the FIR filter, and using the phase response and the amplitude response as the output signals of the pseudo filter, wherein the phase response is obtained by multiplying the radio frequency corresponding to the 19 frequency points by the group delay of the FIR filter.

And fourthly, solving an autocorrelation matrix of the input signal of the pseudo filter and a cross-correlation column vector of the input signal of the pseudo filter and the output signal of the pseudo filter, and obtaining an inverse matrix of the autocorrelation matrix through matrix inversion operation, wherein the product of the inverse matrix and the cross-correlation column vector is a coefficient of the FIR filter with the specific group delay. The embodiment calculates an autocorrelation matrix of an input signal of a pseudo filter, a cross-correlation column vector of the input signal of the pseudo filter and an output signal of the pseudo filter, obtains an inverse matrix of the autocorrelation matrix through matrix inversion operation, and the product of the inverse matrix and the cross-correlation column vector is a coefficient h of an FIR filter with specific group delay_dAnd (n), wherein the input signal of the pseudo filter is the sum signal of the sinusoidal signals of 19 frequency points in the third step, and the output signal of the pseudo filter is the sum signal of the signals of 19 frequency points in the third step after respective phase shifting and amplitude weighting. Coefficient h of FIR filter with specific group delay_d(n) as shown in fig. 5 and 6, fig. 5 is a graph of the amplitude-frequency response and the phase-frequency response of the FIR filter corresponding to one antenna unit of the present invention; fig. 6 is a schematic diagram of FIR filter coefficients corresponding to one antenna element of the present invention.

Selecting window function to modify FIR filter coefficient. The embodiment selects the appropriate window function w (n) and modifies the FIR filter coefficients h (n) h for different signals and different processing purposes_d(n) w (n) to improve the magnitude response of the FIR filter. The window functions w (n) are shown in FIGS. 7-13, and FIG. 7 is a rectangular window of the present inventionThe window has the advantages that the main lobe is concentrated, and the window has the defects of high side lobe and negative side lobe, so that high-frequency interference and leakage are brought in during conversion, and even a negative spectrum phenomenon occurs; FIG. 8 is a graph of the amplitude response and phase response of a Blackman window of the present invention having a wider transition band but greater stop band attenuation than a rectangular window; FIG. 9 is a graph of the amplitude response and phase response of the Hanning window of the present invention, which is better than the rectangular window from the viewpoint of leakage reduction, but the Hanning window has a wider main lobe, which corresponds to a wider analysis bandwidth and a lower frequency resolution; FIG. 10 is a graph of the amplitude response and phase response of the Hamming window of the present invention, with the Hamming window weighting coefficients enabling smaller side lobes than the Hamming window; FIG. 11 is a graph of the amplitude response and phase response of the Chebyshev window of the present invention, which provides the smoothest passband for the same narrower transition band; FIG. 12 is an amplitude response and phase response plot for a Kessel window of the present invention, where the Kessel window is a window function with strong adaptability, and the main lobe width and side lobe attenuation can be selected by changing the value of the parameter; fig. 13 is a graph of the amplitude response and phase response of a bartlett window of the present invention (triangular window) having a main lobe width approximately equal to twice that of the rectangular window, but with small side lobes and no negative side lobes, as compared to the rectangular window.

And after the coefficient of the FIR filter is corrected by using the window function, the broadband beam forming based on the FIR filter with the specific group delay is completed. The broadband beam formed by the embodiment is shown in fig. 3 and 4, and fig. 3 is a two-dimensional beam pattern formed by the broadband beam forming in the bandwidth of 50MHz (225 MHz-275 MHz) according to the invention; figure 4 is a three-dimensional beam pattern formed by the broadband beamforming of the present invention over a 50MHz bandwidth (225 MHz-275 MHz). As can be seen from fig. 3 and 4, the beam patterns of different frequency components in the 50MHz bandwidth are substantially consistent by the wideband beamforming method of the present invention.

Claims

1. A method for forming a broadband beam based on a specific group delay finite impulse response filter is characterized by comprising the following steps:

selecting a window function to modify the coefficient of the FIR filter;