JP5911331B2 - Monopulse angle measuring device and monopulse angle measuring method - Google Patents

Description

  The present invention relates to a monopulse angle measuring device and a monopulse angle measuring method for estimating the direction of arrival of a radio wave arriving at a receiving antenna.

  In a conventional phased array radar, a monopulse comparator is used to form sum and difference beams, monopulse angle measurement is performed, and the arrival direction of the received target signal is estimated (see, for example, Non-Patent Document 1). On the other hand, in recent years, development of phased array radars using a DBF (Digital Beamforming) system has been increasing in order to achieve higher performance of radars.

  In such a DBF type radar, it is possible to realize monopulse angle measurement having the same angle measurement accuracy as in the past by performing the same processing as beam forming by the monopulse comparator on the digitized reception channel. In other words, the phase-shift setting for beam directing is set for the received signals of each receiving channel connected to the element antennas arranged on the antenna aperture divided into left and right (up and down) symmetrically, and then added to each other. By combining them, a sum beam is formed.

  At the same time, a “+1” or “−1” weight is given to each reception channel, and then added together to perform difference beam formation. Thereby, it is possible to obtain a sum beam and a difference beam equivalent to the case of using a monopulse comparator.

The angle measurement accuracy with respect to the receiver noise of the conventional monopulse angle measurement method based on such a monopulse comparator is theoretically given by the main beam width, the normalized monopulse slope, and the reception SNR (Signal to Noise Ratio). The standardized monopulse slope is a value uniquely determined from the sum beam pattern and the difference beam pattern. For example, when the antenna is an equidistant linear array, the standardized monopulse slope is km _Mono = 1.391.

T. Jeffrey, Phased-Array Radar Design: Application of Radar Fundamentals, SciTech Publishing, Raleigh, NC, 2009.

However, the prior art has the following problems.
The angle measurement accuracy by such a conventional monopulse angle measurement method does not coincide with the Cramer-Rao Lower Bound (hereinafter referred to as CRLB). When the monopulse angle measurement accuracy by the equally-spaced linear array matches CRLB, the normalized monopulse slope corresponds to km _CRLB = 1.607, which is 1.155 times better than the conventional monopulse angle measurement method.

  Thus, the conventional monopulse angle measurement method has a problem that the angle measurement accuracy does not match CRLB because the standardized monopulse slope is not optimized.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a monopulse angle measurement device and a monopulse angle measurement method whose monopulse angle measurement accuracy matches CRLB.

The monopulse angle measuring device according to the present invention has element antenna coordinates d arranged symmetrically with respect to the center of the antenna aperture, and M (M is an integer of 2 or more) element antennas for receiving an incoming target signal. And the M receivers that convert the target signals received by the M element antennas into digitized target signals and the digitized target signals of the M receivers, respectively, are added together. Based on the sum beam forming unit for forming the beam and the element antenna coordinates for the M element antennas, the difference beam weight is obtained as W _Δ by the equation (22) in the specification, and the digital signal by each of the M receivers is obtained. A difference beam forming unit that forms a difference beam by performing weighting with a difference beam weight on the converted target signal, and a sum beam formed by the sum beam forming unit, Enter the difference beams formed by and difference beamformer in which and a monopulse angle measurement unit obtains the monopulse angle measurement value.

In addition, the monopulse angle measuring method according to the present invention has element antenna coordinates d arranged symmetrically with respect to the center of the antenna aperture , and M (M is an integer of 2 or more) arriving target signals. Receiving step, a digital conversion step for converting the target signal received in the reception step into a digitized target signal, and a sum beam forming the sum beam by adding together the target signals digitized by the digital conversion step Based on the forming step and the element antenna coordinates for the M element antennas, the difference beam weight is obtained as W _Δ by the equation (22) in the specification, and the difference beam weight is obtained with respect to the target signal digitized by the digital conversion step. A difference beam forming step for forming a difference beam by weighting according to Sum beam is formed in the forming step, and the difference by entering the difference beams formed by the beam forming step in which and a monopulse angle measurement step obtaining a monopulse angle measurement value.

  According to the monopulse angle measuring device and the monopulse angle measuring method of the present invention, a sum beam is formed from a digitized target signal, and a difference beam weight is obtained based on given element antenna coordinates to form a difference beam. By configuring so as to obtain the monopulse angle measurement value from both beams, it is possible to achieve higher accuracy than the conventional monopulse angle measurement method, and the monopulse angle measurement device and the monopulse whose monopulse angle measurement accuracy matches CRLB An angle measuring method can be obtained.

It is a block diagram which shows the monopulse angle measuring device which concerns on Embodiment 1 of this invention. It is a block diagram which shows the monopulse angle measuring device which concerns on Embodiment 2 of this invention.

  Hereinafter, preferred embodiments of a monopulse angle measuring device according to the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing a monopulse angle measuring device according to Embodiment 1 of the present invention. In the figure, M (≧ 2) element antennas A # 1 to A # M receive an incoming target signal and are connected to M receivers R # 1 to R # M, respectively. In the receivers R # 1 to R # M, the target signals received by the antennas A # 1 to A # M are frequency-converted to the baseband to generate an analog signal, and further digitized by AD conversion Convert to

  The receivers R # 1 to R # M are commonly connected to the sum beam forming unit 1 and the difference beam forming unit 2a. The sum beam forming unit 1 forms a sum beam obtained by adding the target signals digitized by the receivers R # 1 to R # M to each other. On the other hand, the difference beam forming unit 2a obtains a difference beam weight based on the given element antenna coordinates and applies the difference beam weight to the target signals digitized by the receivers R # 1 to R # M. , Forming a difference beam.

  The sum beam forming unit 1 and the difference beam forming unit 2 a are connected to a monopulse angle measuring unit 3. The monopulse angle measuring unit 3 inputs the sum beam from the sum beam forming unit 1 and the difference beam from the difference beam forming unit 2a, and performs monopulse angle measurement.

Next, as the background theory of the monopulse angle measuring device according to the first embodiment, the CRLB of the monopulse angle measurement value is shown. In particular, in the case of an equispaced linear array, the normalized monopulse slope km _CRLB = 1.607 It corresponds to.

  A target signal arrives at M element antennas A # 1 to A # M, is digitized by receivers R # 1 to R # M, respectively, and is received signal vector x that is commonly supplied to beam forming units 1 and 2a. (T) ((t = 1,..., T) is a sample number) is expressed by the following equation (1). However, for simplicity, the antenna is a linear array antenna. In the phased array antenna, a phase shifter is arranged after the element antenna.

In the above equation (1), s (t) and n (t) indicate a target signal vector and a receiver noise vector (receiver noise average power is σ ² ), respectively. Further, a (u) is a steering vector corresponding to the arrival angle θ, and a (u) and u are given by the following equations (2) and (3).

Here, d ₁ ,..., D _M are element antenna coordinates given to the difference beam forming unit 2a, and λ is a wavelength. The superscript ^T of [•] ^T represents the transpose of [•] and is different from the sample number T.

In the above equation (1), the monopulse angle measurement accuracy σ _CRLB by u CRLB corresponding to the arrival angle θ is given by the following equation (4).

  However, ESNR is the SNR at the element antenna stage and is given by the following equation (5). H represents a complex conjugate transpose.

P _s in step (5) is a target power in each element antenna and is given by the following equation (6).

  D is a diagonal matrix having the element antenna coordinates as diagonal components, and is expressed by the following equation (7).

  Consider a case in which the element antenna coordinates are symmetric with respect to the center of the antenna aperture as in the following equation (8).

  At this time, the above equation (4) can be transformed into the following equation (9).

  Here, the SNR in the above equation (9) is a post-integration SNR given by the following equation (10).

Furthermore, σ _CRLB in the case of an equally spaced linear array can be approximated and deformed as in the following equation (11).

Here, D, BW _u , and SNR in the above equation (11) are the aperture length, beam width, and post-integration SNR of the equally spaced linear array given by the following equations (12) to (14), respectively.

The third row on the right side of the above equation (11) has the same form as the monopulse angle measurement accuracy equation (see equation (18) described later), and the normalized monopulse slope km _CRLB derived from the _CRLB is the above equation ( From the relationship between the second and third rows on the right side of 11), it is apparent that the following equation (15) is given.

On the other hand, the standardized monopulse slope km _Mono of the conventional monopulse angle measurement method in an equispaced linear array has the relationship of the following equation (16).

Therefore, km _Mono is given by the following equation (17) using the above equation (13).

As a result, the angle measurement accuracy σ _Mono of the conventional monopulse angle measurement method using the equally spaced linear array is expressed by the following equation (18).

  When the above equation (11) is compared with the above equation (18), the relational equation of the following equation (19) is derived.

  That is, the angle measurement accuracy of the conventional monopulse angle measurement method with the equal interval linear array does not reach the CRLB, and deteriorates 1.155 times compared to the CRLB.

The above is the explanation of the background theory of the first embodiment. The angle measurement accuracy by the CRLB of the monopulse angle measurement value is shown. In particular, in the case of an equispaced linear array, the normalized monopulse slope km _CRLB = 1.607. It is said that it corresponds to. Furthermore, it has been stated that the angle measurement accuracy of the conventional monopulse angle measurement method does not coincide with CRLB.

  Next, the flow of processing in the monopulse angle measuring device of the first embodiment will be described.

The sum beam forming unit 1 receives received signal vectors x (t) from M receivers R # 1 to R # M, and obtains a sum beam output y _Σ (t) by the following equation (20).

However, w _Σ in the above equation (20) is a beam weight for the sum beam, and is given by the following equation (21).

On the other hand, the difference beam forming unit 2a first obtains a difference beam weight _wΔ according to the following equation (22) using element antenna coordinates and the like.

  However, in the above equation (22), the relationships of the following equations (23) to (25) are used.

Subsequently, similarly to the sum beamformer 1 inputs the received signal vector x (t) from the M receivers R # 1 to R # M, by the following equation (26), the difference beam weight w _delta Applying (ie, weighting with the difference beam weight _wΔ ) yields the difference beam output y _Δ (t).

In the conventional monopulse angle measurement method, the element of the difference beam weight _wΔ is “+1” or “−1”.

  The monopulse angle measuring unit 3 obtains the ratio of the sum beam and the difference beam by the above equation (20) and the above equation (26) as shown in the following equation (27), and refers to the monopulse discrete pattern as a reference. Obtain the monopulse angle measurement value.

  The above is the description of the processing flow in the first embodiment.

Subsequently, the effects of the first embodiment will be confirmed below.
If the monopulse discrete pattern near u = 0 (about the beam width) of the sum beam and the difference beam is expressed by a linear function approximation of u, the following equation (28) is obtained. However, km _promoted is a normalized monopulse slope according to the first embodiment, and km _promoted / BW _u is a slope of a linear function.

  Here, for the second factor in the last row on the right side of the above equation (28), the denominator and the numerator are modified as in the following equations (29) and (30), considering the property of the above equation (8).

  At this time, the range of u is within the beam width and is sufficiently small, so the approximations of the following equations (31) and (32) hold.

  Therefore, each of the above formula (29) and the above formula (30) can be further transformed into the following formulas (33) and (34).

  When the above equation (33) and the above equation (34) are substituted into the above equation (28), the following equation (35) is obtained.

  Comparing both sides of the above equation (35), the relationship of the following equation (36) becomes clear.

Therefore, the angle measurement accuracy σ _projected of the monopulse angle measurement method is given by the following equation (37).

Now comparing the above formulas (37) Equation (9), angle measurement accuracy sigma _proposed monopulse angle measurement method of the first embodiment is, it is found that match the angle measuring precision sigma _CRLB by CRLB .

That is, in the linear array in which the element antenna coordinates satisfy the above equation (8), the sum beam weight w _Σ shown in the above equation (21) and the difference beam weight w _Δ shown in the above equation (22) are used. The effect of achieving the angle measurement accuracy σ _CRLB by CRLB by the monopulse angle measurement method was confirmed.

  As described above, the monopulse angle measuring device according to the first embodiment achieves angle measurement accuracy by CRLB with higher accuracy than the conventional monopulse angle measurement method by using the difference beam weight calculated by the element antenna coordinates. There is an effect that can be done.

Embodiment 2. FIG.
FIG. 2 is a block diagram showing a monopulse angle measuring device according to Embodiment 2 of the present invention. Compared to the first embodiment, the second embodiment is different from the first embodiment in that the sub-array dividing unit 4 is inserted immediately after the M antennas A # 1 to A # M and the difference beam forming unit 2b. The difference is that a subarray partition matrix is provided in addition to the element antenna coordinates. Here, the subarray division matrix is a matrix corresponding to the division by the subarray division unit 4.

That is, the sub-array dividing unit 4 divides the target signals from all the element antennas A # 1 to A # M into M _SA (where M> M _SA ) sub-array target signals, and these sub-array target signals are Send each receiver R _# 1~R # _{M SA.}

  After that, as in the first embodiment, the sum beam forming unit 1 generates a sum beam. The difference beam forming unit 2b obtains a difference beam weight based on the element antenna coordinates and the subarray division matrix, and applies the difference beam weight to the digitized target signal from each receiver to generate a difference beam. To do. The monopulse angle measurement unit 3 performs monopulse angle measurement based on the sum beam and the difference beam.

Next, the flow of processing in the monopulse angle measuring device according to the second embodiment will be described. In the second embodiment, the sub-array dividing unit 4 is inserted so that the number of subsequent reception channels becomes the _MSA channel. However, the sum beam forming unit 1 performs the same processing as in the first embodiment. Is called.

  On the other hand, the difference beam forming unit 2b calculates the difference beam weight by a method different from that of the first embodiment. Therefore, hereinafter, only the flow of processing in the difference beam forming unit 2b will be described.

Here, the difference beam weight obtained by the difference beam forming unit 2b is set to w _Δ ^(SA) . The received signal vector input to the difference beam forming unit 2b and obtaining the difference beam weight w _Δ ^(SA) satisfies the following equation (38). However, the T is referred to as a sub-array divided matrix satisfies ^TT H = I.

The difference beam weight w _Δ ^(SA) is given a quasi-optimal beam weight having a correlation as high as possible with the difference beam weight w _Δ obtained in the first embodiment. In other words, the solution of the linear constraint constrained least square problem with respect to r as in the following equation (39) is set as the difference beam weight w _Δ ^(SA) . The constraint condition gives a null point in the beam pointing direction.

The solution w _Δ ^(SA) of the above equation (39) can be obtained by Lagrange's undetermined multiplier method and is represented by the following equation (40).

  As described above, in the monopulse angle measuring device according to the second embodiment, by using the difference beam weight calculated from the element antenna coordinates and the sub-array division matrix, the CRLB has high accuracy compared to the conventional monopulse angle measurement method. There is an effect that the ascending angle measurement accuracy can be achieved.

  DESCRIPTION OF SYMBOLS 1 Sum beam forming part, 2a, 2b Difference beam forming part, 3 Monopulse angle measuring part, 4 Subarray division | segmentation part, A # 1-A # M Element antenna, R # 1-R # M Receiver.

Claims (3)

M (M is an integer of 2 or more) element antennas having element antenna coordinates d arranged symmetrically with respect to the antenna aperture center and receiving an incoming target signal;
M receivers that convert the target signals received by each of the M element antennas into digitized target signals;
A sum beam former for summing together the digitized target signals from each of the M receivers to form a sum beam;
Based on the element antenna coordinates for the M antenna elements, the following equation

And difference beamformer which determines the difference beam weight as W _delta, to form the difference beam by performing weighting by the difference beam weight to the digitized target signal by each of said M receivers by,
A monopulse angle measurement unit that inputs the sum beam formed by the sum beam formation unit and the difference beam formed by the difference beam formation unit to obtain a monopulse angle measurement value. Corner device. M (M is an integer of 2 or more) element antennas having element antenna coordinates d arranged symmetrically with respect to the antenna aperture center and receiving an incoming target signal;
A sub-array dividing unit that inputs a target signal output from the M element antennas and divides it into M _SA (M _SA is an integer less than M) sub-array target signals;
M _SA receivers that convert the sub-array target signals output from the sub-array dividers into digitized target signals ;
A sum beam forming section for forming a sum beam adding the target signal wherein the digitizing by each of the M _SA number of receivers to each other,
Based on the element antenna coordinates for the M element antennas and the subarray division matrix T according to the division by the subarray division unit ,

To obtain a difference beam weight as W _Δ ^(SA) , and form a difference beam by weighting the digitized target signal by each of the M _SA receivers with the difference beam weight. And
A monopulse angle measuring unit for obtaining a monopulse angle measurement value by inputting the sum beam formed by the sum beam forming unit and the difference beam formed by the difference beam forming unit;
Monopulse angle measuring device, comprising a. A reception step of receiving an incoming target signal by M (M is an integer of 2 or more) element antennas having element antenna coordinates d arranged symmetrically with respect to the antenna aperture center ;
A digital conversion step of converting the target signal received in the reception step into a digitized target signal;
A sum beam forming step of adding the target signals digitized by the digital conversion step together to form a sum beam;
Based on the element antenna coordinates for the M antenna elements, the following equation

And difference beam forming step of a difference beam weight calculated as W _delta, forming the difference difference beam by performing weighting by the beam weight to the target signal digitized by the digital conversion step by,
A monopulse angle measurement step for obtaining a monopulse angle measurement value by inputting the sum beam formed in the sum beam formation step and the difference beam formed in the difference beam formation step. Horn method.

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