阅读说明：本技术 基于时间调制阵列的mimo雷达系统及波束形成方法 (MIMO radar system based on time modulation array and beam forming method ) 是由 吴文 马越 缪晨 陈春红 汪敏 杨国 王晶琦 张若愚 齐世山 于 2021-06-23 设计创作，主要内容包括：本发明公开了一种基于时间调制阵列的MIMO雷达系统及波束形成方法,该系统包括所述发射机和接收机,发射机包括N个阵元组成的发射阵列,每个阵元对应连接第一单刀单掷射频开关,每个第一单刀单掷射频开关接入数据传输的CDMA信号发射通道；所述接收机包括M个阵元组成的接收阵列,每个阵元对应连接第二单刀单掷射频开关,所述开关接解交织器输入端,将接收的码元信息进行解交织,得到CDMA信号流,解交织器输出端和低噪放输入端连接,低噪放输出端与带通滤波器输入端连接,输出谐波信号。所述系统充分发挥MIMO系统的优势,阵元数目较少,通过射频开关可以快捷地实现控制波束形成,具有体积小、便捷性高等优势。(The invention discloses a MIMO radar system based on a time modulation array and a wave beam forming method, wherein the system comprises a transmitter and a receiver, the transmitter comprises a transmitting array consisting of N array elements, each array element is correspondingly connected with a first single-pole single-throw radio frequency switch, and each first single-pole single-throw radio frequency switch is accessed to a CDMA signal transmitting channel for data transmission; the receiver comprises a receiving array consisting of M array elements, each array element is correspondingly connected with a second single-pole single-throw radio frequency switch, the switches are connected with the input end of a de-interleaver, received code element information is de-interleaved to obtain a CDMA signal flow, the output end of the de-interleaver is connected with the input end of a low-noise amplifier, and the output end of the low-noise amplifier is connected with the input end of a band-pass filter to output harmonic signals. The system gives full play to the advantages of the MIMO system, has less array elements, can quickly realize control of beam forming through the radio frequency switch, and has the advantages of small volume, high convenience and the like.)

1. A MIMO radar system based on a time modulation array comprises a transmitter and a receiver, and is characterized in that the transmitter comprises a transmitting array consisting of N array elements and a first single-pole single-throw radio frequency switch, each array element is correspondingly connected with the first single-pole single-throw radio frequency switch, and each first single-pole single-throw radio frequency switch is connected with a CDMA signal transmitting channel for data transmission; the receiver comprises a receiving array consisting of M array elements, a second single-pole single-throw radio frequency switch, a deinterleaver, a low-noise amplifier and a band-pass filter, wherein each array element is correspondingly connected with the second single-pole single-throw radio frequency switch and used for receiving code element information, the second single-pole single-throw radio frequency switch is connected with the input end of the deinterleaver, the deinterleaver is used for deinterleaving the received code element information to obtain CDMA signal flow, the output end of the deinterleaver is connected with the input end of the low-noise amplifier used for amplifying signals, the output end of the low-noise amplifier is connected with the input end of the band-pass filter, the band-pass filter is used for band-pass filtering the signals and outputting harmonic signals.

2. The MIMO radar system of claim 1, wherein the CDMA signal transmit channels have a chip period T_sSatisfy T_s＝LT_c＝JNT_c，T_cFor the symbol period, length L of symbol is JN, J is the number of symbols that complete a transmission, L? And N is added.

3. The MIMO radar system of claim 2, wherein the transmission baseband signal c (n, t) of the nth array element in the transmit array is:

in the formula, a_iE { -1, +1} is a user code sequence, u (t-iT)_c) Is a rectangular pulse signal.

4. The MIMO radar system of claim 2, wherein the reception signals Y of the reception array are:

Y＝B^T(AS+N)

wherein A ═ a (θ)₁),L,a(θ_k)]Is a direction matrix, k is the snapshot number, S ═ beta₁,L,βk_k]^TFor the source signal, N is an additive complex Gaussian noise vector with uncorrelated termsQuantity, B is a matrix formed by harmonic vectors, and B specifically is as follows:

5. the MIMO radar system of claim 2, wherein the equivalent joint array of the transmit array and the receive array is:

wherein the content of the first and second substances,

andcomprises the following steps:

in the formula (I), the compound is shown in the specification,normalized switching times for each of the first single pole single throw radio frequency switch and the second single pole single throw radio frequency switch in the transmitter and the receiver, respectively, h represents the order of the harmonics.

6. The MIMO radar system of claim 5, wherein the spacing between the transmit and receive array elements satisfies the following equation:

|Δτ_tn(θ_k)+Δτ_rm(θ_k)-Δτ_tn′(θ_k)-Δτ_rm′(θk_k)|＝T_c

Δτ_tn(θ)＝τ_t1(θ)-τ_tn(θ),Δτ_rm(θ)＝τ_r1(θ)-τ_rm(θ)

wherein, tau_tn(theta) and tau_rm(theta) respectively, is the time delay of the nth array element in the transmitting array and the mth array element in the receiving array relative to the target, delta tau_tn(theta) and Delta tau_rm(theta) is the delay of the nth array element in the transmitting array and the mth array element in the receiving array relative to the first array element respectively, theta is the angle of the target, theta_kThe angle when the fast beat number is k, k is the fast beat number.

7. The MIMO radar system of claim 5, wherein the modulation period T of the equivalent joint array_pSatisfies the following conditions: t is_p＜T_c/MJN，F_p＞MF_s＝MJNF_c，F_pTo modulate frequency, F_sIs chip frequency, F_cIs the symbol frequency.

8. The MIMO radar system of claim 1, wherein the number of array elements of the transmit array and the receive array is 2, and the harmonic is a +1 th harmonic.

9. A beamforming method for a MIMO radar system according to any of claims 1 to 9, comprising the steps of:

setting the weight and the beam pointing angle of each array element of the transmitting array and the receiving array;

determining the switching time of each first single-pole single-throw radio frequency switch and each second single-pole single-throw radio frequency switch according to the weight and the beam pointing angle;

the equivalent joint array modulates according to the switching time to form a desired beam.

10. The method according to claim 9, wherein the determining the switching time of each of the first single-pole single-throw rf switch and the second single-pole single-throw rf switch according to the weight and the beam pointing angle specifically comprises:

the weight | w of the mn-th virtual array element of the equivalent joint array_mnThe relation between | and the switching time of each of the first single-pole single-throw radio frequency switch and the second single-pole single-throw radio frequency switch is as follows:

the beam pointing angle θ and the switching time of each of the first single-pole single-throw radio frequency switch and the second single-pole single-throw radio frequency switch are in a relation formula as follows:

wherein γ is wavenumber, d_mnThe position of the nth virtual array element;

and solving and determining the switching time through the relational expression.

Technical Field

The invention belongs to the field of radar systems and signal processing, and particularly relates to a time modulation array-based MIMO radar system and a beam forming method.

Background

A mimo (multiple input multiple output) radar is a radar system that transmits and receives echo signals through multiple antennas. Compared with a common digital array radar, the MIMO radar can detect more targets by using fewer antennas.

The Time-modulated array (TMA) uses a radio frequency switch instead of a phase shifter, changes the phase and amplitude of a beam by controlling a Time switch sequence, and can realize a low-sidelobe beam directional diagram by optimizing the Time sequence. The system structure of the time modulation array is simpler than that of the phased array, and thus is currently being studied in large quantities.

Currently, the MIMO radar based on the time modulation array is still in a theoretical research stage, and related research is mainly focused on transmit beam forming and directional pattern optimization.

Disclosure of Invention

The invention aims to provide a time modulation array-based MIMO radar system and a beam forming method, wherein the system can quickly realize beam forming control, effectively improves the flexibility of beam steering, and has the advantages of small volume and high convenience.

The technical scheme for realizing the purpose of the invention is as follows: a MIMO radar system based on a time modulation array comprises a transmitter and a receiver, wherein the transmitter comprises a transmitting array consisting of N array elements and a first single-pole single-throw radio frequency switch, each array element is correspondingly connected with the first single-pole single-throw radio frequency switch, and each first single-pole single-throw radio frequency switch is connected with a CDMA signal transmitting channel for data transmission; the receiver comprises a receiving array consisting of M array elements, a second single-pole single-throw radio frequency switch, a deinterleaver, a low-noise amplifier and a band-pass filter, wherein each array element is correspondingly connected with the second single-pole single-throw radio frequency switch and used for receiving code element information, the second single-pole single-throw radio frequency switch is connected with the input end of the deinterleaver, the deinterleaver is used for deinterleaving the received code element information to obtain CDMA signal flow, the output end of the deinterleaver is connected with the input end of the low-noise amplifier used for amplifying signals, the output end of the low-noise amplifier is connected with the input end of the band-pass filter, the band-pass filter is used for band-pass filtering the signals and outputting harmonic signals.

Further, the code chip period T of the CDMA signal transmitting channel_sSatisfy T_s＝LT_c＝JNT_c，T_cFor a symbol period, the length L of a symbol is JN, J is the number of symbols that complete a transmission, LN.

Further, the transmission baseband signal c (n, t) of the nth array element in the transmitting array is:

in the formula, a_iE { -1, +1} is a user code sequence, u (t-iT)_c) Is a rectangular pulse signal.

Further, the receiving signal Y of the receiving array is:

Y＝B^T(AS+N)

wherein A ═ a (θ)₁),L,a(θ_k)]Is a direction matrix, k is the snapshot number, S ═ beta₁,L,β_k]^TFor a source signal, N is an additive complex gaussian noise vector with uncorrelated terms, B is a matrix composed of harmonic vectors, and B specifically is:

further, the equivalent joint array of the transmitting array and the receiving array is:

wherein the content of the first and second substances, andcomprises the following steps:

in the formula (I), the compound is shown in the specification,normalized switching times for each of the first single pole single throw radio frequency switch and the second single pole single throw radio frequency switch in the transmitter and the receiver, respectively, h represents the order of the harmonics.

Further, the spacing between the array elements of the transmitting array and the receiving array satisfies the following formula:

|Δτ_tn(θ_k)+Δτ_rm(θ_k)-Δτ_tn′(θ_k)-Δτ_rm′(θ_k)|＝T_c

Δτ_tn(θ)＝τ_t1(θ)-τ_tn(θ),Δτ_rm(θ)＝τ_r1(θ)-τ_rm(θ)

wherein, tau_tn(theta) and tau_rm(theta) respectively, is the time delay of the nth array element in the transmitting array and the mth array element in the receiving array relative to the target, delta tau_tn(theta) and Delta tau_rm(theta) is the delay of the nth array element in the transmitting array and the mth array element in the receiving array relative to the first array element respectively, theta is the angle of the target, theta_kThe angle when the fast beat number is k, k is the fast beat number.

Further, the modulation period T of the equivalent joint array_pSatisfies the following conditions: t is_p＜T_c/MJN，F_p＞MF_s＝MJNF_c，F_pTo modulate frequency, F_sIs chip frequency, F_cIs the symbol frequency.

Furthermore, the number of array elements of the transmitting array and the receiving array is 2, and the harmonic is +1 harmonic.

A beam forming method based on the MIMO radar system is a combined array beam forming method and comprises the following steps:

setting the weight and the beam pointing angle of each array element of the transmitting array and the receiving array;

determining the switching time of each first single-pole single-throw radio frequency switch and each second single-pole single-throw radio frequency switch according to the weight and the beam pointing angle;

the equivalent joint array of the system is modulated according to the switching time to form the desired beam.

Further, the determining the switching time of each of the first single-pole single-throw radio frequency switch and the second single-pole single-throw radio frequency switch according to the weight and the beam pointing angle specifically includes:

the weight | w of the mn-th virtual array element of the equivalent joint array_mnThe relation between | and the switching time of each of the first single-pole single-throw radio frequency switch and the second single-pole single-throw radio frequency switch is as follows:

the beam pointing angle θ and the switching time of each of the first single-pole single-throw radio frequency switch and the second single-pole single-throw radio frequency switch are in a relation formula as follows:

wherein γ is wavenumber, d_mnThe position of the nth virtual array element;

and solving and determining the switching time through the relational expression.

Compared with the prior art, the invention has the following remarkable effects:

(1) the method is based on the time modulation array, can effectively utilize the MIMO system to carry out combined beam forming, and quickly realizes the control of beam forming;

(2) the invention adopts the code division multiplexing mode to transmit signals, which not only can ensure that the signals are transmitted at the same time, but also avoids aliasing possibly occurring in the transmission process of time modulation signals;

(3) the invention is based on the time modulation array, takes the time as the control variable of the combined array beam forming, and effectively improves the flexibility of beam steering.

Drawings

Fig. 1 is a schematic diagram of a signal detection process.

Fig. 2 is a block diagram of a system transmitter.

Fig. 3 is a block diagram of a system receiver.

Fig. 4 is a schematic diagram of a process for forming an equivalent array of the MIMO radar.

Fig. 5 is a graph of joint array beamforming simulation results.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention provides a time modulation array-based MIMO radar system. The structure of the system comprises a transmitting part and a receiving part. Meanwhile, as the time modulation array adopts the radio frequency switch for scanning and has a modulation period, if the system adopts a time division multiplexing mode to transmit signals, the receiving array cannot be ensured to receive all transmitted signals at the same moment; if the signals are transmitted by frequency division multiplexing, the signal bandwidth must be smaller than the modulation frequency, otherwise the spectrum aliasing will be caused. Therefore, the system adopts a Code Division Multiple Access (CDMA) mode to transmit signals, and the transmitting and receiving array arrangement adopts a sparse array structure based on algorithm optimization, so that better directional diagram performance is obtained under the limited array element number. By designing the array element switching time of the transmitting and receiving arrays, the phase and the amplitude of the wave beam of the combined transmitting and receiving array can be controlled, and the aim of forming the wave beam is achieved.

The present invention will be described in further detail below with reference to the accompanying drawings.

A MIMO radar system based on a time modulation array comprises a transmitter and a receiver, and comprises the transmitter and the receiver, and is characterized in that the transmitter comprises a transmitting array consisting of N array elements and a first single-pole single-throw radio frequency switch, each array element is correspondingly connected with the first single-pole single-throw radio frequency switch, and each first single-pole single-throw radio frequency switch is accessed into a CDMA signal transmitting channel for data transmission; the receiver comprises a receiving array consisting of M array elements, a second single-pole single-throw radio frequency switch, a deinterleaver, a low-noise amplifier and a band-pass filter, wherein each array element is correspondingly connected with the second single-pole single-throw radio frequency switch and used for receiving code element information, the second single-pole single-throw radio frequency switch is connected with the input end of the deinterleaver, the deinterleaver is used for deinterleaving the received code element information to obtain CDMA signal flow, the output end of the deinterleaver is connected with the input end of the low-noise amplifier used for amplifying signals, the output end of the low-noise amplifier is connected with the input end of the band-pass filter, the band-pass filter is used for band-pass filtering the signals and outputting harmonic signals.

Assuming the detected target is in the far field, the transmission baseband signal of the nth array element in the transmitting array is as follows:

in the formula, a_iE { -1, +1} is the user code sequence, u (t-iT)_c) Representing a rectangular pulse signal, the symbol having a width T. The symbol period may be denoted as T_cT/L. In data transmission, LN needs to be satisfied, J is the number of symbols completing one transmission, and the length L of the symbols is JN.

The system detects the target process referring to fig. 1, it is assumed that the time delay of a certain target in the far field relative to the nth array element in the transmitting array and the mth array element in the receiving array is tau respectively_tn(theta) and tau_rm(theta), where theta is the angle of the target, the received signal of the system can be expressed as follows

Assuming that the transmit and receive arrays each have the first array element as a reference array element, the delay time of the transmit and receive signals can be expressed as

Δτ_tn＝τ_t1-τ_tn,Δτ_rm＝τ_r1-τ_rm (3)

From the above equation, the received signal of the system can be represented as

Where σ represents the amplitude term of the signal. The spacing between array elements is assumed to be small to satisfy the following equation

|Δτ_tn(θ_k)+Δτ_rm(θ_k)-Δτ_tn′(θ_k)-Δτ_rm′(θ_k)|＝T_c (5)

Δτ_tn′(θ_k) And Δ τ_rm′(θ_k) Respectively the delay of the nth 'array element in the transmitting array and the mth' array element in the receiving array relative to the first array element.

Assuming that the modulation periods of the transmitting array and the receiving array are the same, the switching signals are respectively U_n(t) and U_m(t), which can be expressed as:

according to the Fourier series, the expressions (6) and (7) can be written as

In the formula, h represents the order of harmonic wave, ω_p＝2π/T_pRepresenting the modulation frequency of the switch, let us assume Representing the normalized switching times of the transmit and receive arrays respectively,andthe harmonic factors of the transmit and receive arrays, respectively, can be expressed as

In the formula, let τ be_ref(θ_k)＝τ_t1(θ_k)+τ_r1(θ_k) From the formulae (10) and (11), the formula (4) can be written

For the left and right sub-arrays, the complex weights can be expressed by the following two equations:

in the formula:

c(t)＝[c(1,t),L,c(N,t)]^T，[·]^Trepresenting the transpose of the matrix.

Assuming that the fast beat number is k, the received signal can be written as

Y＝B^T(AS+N) (13)

Wherein A ═ a (θ)₁),L,a(θ_k)]Is a direction matrix, S ═ beta₁,L,β_k]^TRepresenting the source signal, N representing an additive complex Gaussian noise vector with uncorrelated terms, and B representing a matrix of harmonic vectors, which can be written as

The joint transmit-receive array of the system can be represented as

In the formulaRepresenting the kronecker product. From the above formula, it can be seen that the joint transceiving array of the present system is not only related to the array arrangement, but also related to the harmonic factor generated by the time modulation.

The number of the receiving and transmitting array elements of the system is 2, and the structure diagram of the system transmitter is shown in figure 2 and comprises the following steps:

the antenna array, the affiliated antenna emission array includes two array elements, all adopt the single-pole single-throw radio frequency switch, is used for launching CDMA signal stream;

each single-pole single-throw radio frequency switch is connected to a CDMA signal transmitting channel, and the width of a symbol is T. The symbol period may be denoted as T_cT/L. In data transmission, the chip period of each channel satisfies T_s＝LT_c＝JNT_c. According to the CDMA signal transmission rule, LN must be satisfied.

Referring to fig. 3, a receiver of the system includes:

the antenna receiving array comprises two array elements, and single-pole single-throw radio frequency switches are adopted for receiving CDMA signal streams;

each single-pole single-throw radio frequency switch receives a signal stream and passes through a de-interleaver, and the de-interleaver is used for de-interleaving received code element information to obtain the signal stream;

the signal passing through the de-interleaver enters a low-noise amplifier for signal amplification;

the low-noise signal is finally filtered by a band-pass filter, and the band-pass filter is used for performing band-pass filtering on the signal so as to obtain a harmonic signal.

The received code element signal is processed by a de-interleaver, then is subjected to low-noise amplification, and finally is filtered by a band-pass filter, so that a harmonic signal is received.

In time modulation, the modulation period is guaranteed to be less than the chip period to ensure that each transmitted symbol is received by the joint receiving array. As can be seen from equation (15), the joint transceiver array can have at most MN array elements, and to ensure the integrity of the received signal, the modulation period must satisfy: t is_p＜T_c/MJN, i.e. F_p＞MF_s＝MJNF_c，F_pTo modulate frequency, F_sIs chip frequency, F_cIs the symbol frequency, otherwise a missing code condition occurs.

The forming process of the equivalent array of the MIMO radar, i.e. the joint transceiving array, is shown in fig. 4, and it can be seen that the pitch of the equivalent array and the pitch of the array elements of the transceiving array are related.

The method of beamforming for a MIMO radar system based on time modulation is described below. First, based on the formula (15), the following formula can be obtained

As can be seen from the formula (16), the MIMO equivalent array of the present system is a product of kronecker product between the harmonic matrices of the transmit-receive array and kronecker product of the transmit-receive array direction matrix. The product of the kronecker product of the direction matrix is the array manifold of the MIMO equivalent array. Therefore, for the beam forming of the time modulation MIMO system, the harmonic matrix of the transceiving array is mainly designed. The kronecker product between the harmonic matrices of the present system can be written as follows

In the formula

As can be seen from equations (17) and (18), the design of the harmonic matrix is the design of the switching time of the array elements of the transmitting and receiving arrays. The phase term and the amplitude term in the formula (18) are respectively set to required values, and then the beam forming of the MIMO equivalent array can be completed. The following is a derivation of the calculation procedure for beamforming in the present system. For example with beamforming for the +1 th harmonic, the amplitude and phase terms in (18) are first assigned separately. The amplitude term of the mn-th virtual array element is shown as the following formula

The phase term is shown below

Wherein gamma represents the wave number, d_mnIndicating the position of the mn-th virtual array element. As can be seen from equations (19) and (20), the switching time of each array element can be calculated by setting the weight w of each array element and the beam pointing angle θ.

Simulation experiment tests are performed below.

It is assumed that the amplitude term is set to be uniformly weighted, i.e.The phase of the +1 harmonic is set to 10 °, and the normalized switching time of each array element can be obtained through equations (19) and (20), as shown in table 1.

TABLE 1 array element switching time

The directional diagram obtained by computer simulation is shown in fig. 5. As can be seen from fig. 5, the +1 th harmonic orientation at this time coincides with the set target. In addition, combining the formulas (10) and (11), it can be seen that the phase of the h-th harmonic is h times of the +1 harmonic, and it can be seen from fig. 5 that the directional phase of the +2 harmonic at this time is 20 °, which is derived according to the formula.