A circular MIMO imaging system based on waveguide slot coupling

Abstract

The present invention discloses a circular MIMO imaging system based on waveguide slot coupling. The system comprises: a circular waveguide slot antenna and a MIMO array; one port of the circular waveguide slot antenna is connected to an LFM signal generator, and the other port is connected to a matching load; the MIMO array comprises M transmitting array elements and N receiving array elements; the transmitting array elements and the receiving array elements are evenly distributed on the circular waveguide slot antenna at equal intervals, the interval between the transmitting array elements is 2π / M, and the interval between the receiving array elements is 2π / N. The present invention uses only one circular waveguide slot antenna to complete the coupling of the LFM (linear frequency modulation) signal to the MIMO array, providing the MIMO array with both the transmitting signal and the local oscillator signal, saving a large number of high-cost radio frequency devices such as local oscillators.

Description

Technical Field

[0001] The invention relates to the technical field of microwave imaging, and in particular to a circular MIMO imaging system based on waveguide slot coupling. Background Art

[0002] In the design of short-range microwave imaging systems, reducing the cost of hardware, especially RF devices, and increasing the speed of signal acquisition and imaging processing are the key points of the design. The circular MIMO (multiple input multiple output) imaging system can replace the traditional single-station radar scanning process along a circular trajectory with a single snapshot to complete the acquisition of target echo signals and improve the imaging speed; and the MIMO array increases the equivalent channels for transmitting and receiving signals, thereby reducing the number of actual antennas and reducing hardware costs. Conventional circular MIMO imaging systems require more RF devices such as antenna feeds and local oscillator signal sources, and the stability of independent local oscillator signals is difficult to design. Summary of the invention

[0003] The purpose of the present invention is to provide a circular MIMO imaging system based on waveguide slot coupling, so as to effectively reduce the hardware cost of the system, maintain the stability and uniformity of the local oscillator signal, and achieve better imaging effect.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A circular MIMO imaging system based on waveguide slot coupling comprises: a circular waveguide slot antenna and a MIMO array; one port of the circular waveguide slot antenna is connected to an LFM signal generator, and the other port is connected to a matching load; the MIMO array comprises M transmitting array elements and N receiving array elements; the transmitting array elements and the receiving array elements are uniformly distributed on the circular waveguide slot antenna at equal intervals, the interval between the transmitting array elements is 2π / M, and the interval between the receiving array elements is 2π / N.

[0006] Optionally, the transmitting array element includes a first isolator, a switch and a first horn antenna connected in sequence; an input end of the first isolator is connected to the waveguide slot of the circular waveguide slot antenna.

[0007] Optionally, the receiving array element includes a second isolator, a mixer and a second horn antenna; the input end of the second isolator is connected to the waveguide slot of the circular waveguide slot antenna, the output end of the second isolator is connected to the first input end of the mixer, and the second horn antenna is connected to the second input end of the mixer.

[0008] Optionally, the output end of the mixer is sequentially connected to an intermediate frequency signal amplifier, a filter, an A / D converter and a digital signal imaging processing unit.

[0009] Optionally, the M transmitting array elements are controlled by the switch to radiate outward in sequence in a time-division manner, and echoes generated after each transmission are received by all the receiving array elements simultaneously.

[0010] Optionally, the digital signal imaging processing unit uses an ω-k algorithm of circular SAR to complete imaging of the target area.

[0011] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0012] The present invention uses only one circular waveguide slot antenna to complete the coupling of LFM (linear frequency modulation) signals to the MIMO array, providing the MIMO array with both the transmission signal and the local oscillator signal, saving a large number of high-cost radio frequency devices such as local oscillators. In addition, since the local oscillator signal used for mixing in the receiving array element is derived from the transmission signal of the same system, the stability of the local oscillator signal can be maintained, the difference frequency processing can be better completed, and finally a faster, lower-cost, and more stable imaging system can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0014] Figure 1 A schematic structural diagram of a circular MIMO imaging system based on waveguide slot coupling provided in an embodiment of the present invention;

[0015] Figure 2 A schematic diagram of a waveguide slot-coupled MIMO array provided in an embodiment of the present invention;

[0016] Figure 3 A schematic diagram of the distribution of equivalent virtual array elements of a MIMO array provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The purpose of the present invention is to provide a circular MIMO imaging system based on waveguide slot coupling, so as to effectively reduce the hardware cost of the system, maintain the stability and uniformity of the local oscillator signal, and achieve better imaging effect.

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] like Figure 1 As shown, the annular MIMO imaging system based on waveguide slot coupling provided by the present invention is arranged directly above the imaging target area 1, and an oblique downward-looking spotlight circular track SAR (synthetic aperture radar) imaging mode is used to image the imaging target area 1, and the imaging inclination angle is 0° to 90°.

[0021] The circular MIMO imaging system comprises: a circular waveguide slot antenna 4 and a MIMO array.

[0022] The MIMO array includes M transmitting array elements 2 and N receiving array elements 3. The transmitting array elements 2 and the receiving array elements 3 are evenly distributed on the circular waveguide slot antenna 4 at equal intervals, the interval between the transmitting array elements 2 is 2π / M, and the interval between the receiving array elements 3 is 2π / N.

[0023] like Figure 2 As shown, one port of the circular waveguide slot antenna 4 is connected to the LFM signal generator, and the other port is connected to the matching load; slots are evenly spaced on the inner ring surface of the circular waveguide slot antenna 4, and the coupling of the LFM signal in the waveguide with the MIMO array is completed through the slots, and the transmitting signal of the transmitting element 2 and the local oscillator signal of the receiving element 3 are provided to the MIMO array at the same time. The transmitting element 2 and the receiving element 3 couple the LFM signal through the waveguide slot connected to the circular waveguide slot antenna 4.

[0024] The transmitting array element 2 includes a first isolator, a switch, and a first horn antenna connected in sequence; the input end of the first isolator is connected to the waveguide slot of the circular waveguide slot antenna 4, and each device uses a waveguide interface. The transmitting array element 2 couples the LFM signal in the waveguide as a transmitting signal to the first horn antenna to radiate toward the imaging target area 1. Figure 2 As shown, the waveguide slot is first connected to the first isolator to prevent the transmission signal coupled to the next stage from leaking back to the waveguide cavity; then it is connected to the switch to control the transmission signal to be transmitted in sequence according to the transmission array element 2; finally, it is connected to the first horn antenna with adjustable inclination angle to transmit the signal to the target imaging area 1.

[0025] like Figure 2As shown, the receiving array element 3 includes a second isolator, a mixer and a second horn antenna; the input end of the second isolator is connected to the waveguide slot of the circular waveguide slot antenna 4, the output end of the second isolator is connected to the first input end of the mixer, and the second horn antenna is connected to the second input end of the mixer, and each device connection adopts a waveguide interface. The receiving array element 3 couples the LFM signal in the waveguide as the local oscillator signal of the receiving array element to the first input end of the mixer, and the other input end of the mixer is connected to the second horn antenna for receiving signals. The received target echo signal and the local oscillator signal are subjected to difference frequency processing through the mixer, and an intermediate frequency signal is output.

[0026] The output end of the mixer is connected to an intermediate frequency signal amplifier, a filter, an A / D converter and a digital signal imaging processing unit in sequence. The digital signal imaging processing unit uses the ω-k algorithm of the circular track SAR to complete the imaging of the target area.

[0027] The M transmitting array elements 2 are controlled by switches to radiate outward in sequence in time division, and the echo generated after each transmission is received by all receiving array elements 3 at the same time, that is, the LFM signal is transmitted M times in total, and each time the echo generated by the mth transmitting signal is received by N array elements, m=1…M, and the difference frequency, amplification, filtering, digital conversion and storage are completed in sequence at the receiving end, thereby realizing the signal collection and storage of the M-transmitting and N-receiving array.

[0028] The specific sending and receiving process is as follows:

[0029] Assume that the MIMO array has M transmitting elements 2 from T1 to TM and N receiving elements 3 from R1 to RN. First, control the switch to make the transmitting element T1 transmit the signal, and keep the other transmitting elements off. At this time, the N receiving elements from R1 to RN receive the echo signal at the same time.

[0030] Taking the receiving array element R1 as an example, R1 collects the echo signal through the receiving antenna and inputs it into the mixer. One port of the mixer inputs the received echo signal, and the other port couples the same transmission signal through the circular waveguide slot antenna and inputs it into the mixer as the local oscillator signal. The two are processed by difference frequency and the intermediate frequency signal is output at the output end. When the transmission signals at different positions of the circular waveguide slot antenna are used as local oscillator signals, a predictable phase difference will be generated, which can be compensated in subsequent processing to maintain the coherence of the system.

[0031] Similarly, N receiving array elements 3 all adopt the above configuration to complete signal reception and difference frequency processing, that is, T1 transmits the signal, and can output N intermediate frequency signals at the receiving end. The mixer of each receiving array element is then connected to the intermediate frequency signal amplifier, filter, A / D converter, etc. in sequence and sent to the digital signal processing unit for storage and processing.

[0032] After completing a complete transceiver process, continue to control the switch of the transmitting array element 2 to achieve the transmission signal to radiate to the target area in time, so that the transmitting array elements T1~TM transmit LFM signals M times in total, and repeat the collection, frequency difference, processing and other processes of the echo signal more than M times at the receiving end, and finally store M*N echo signals. That is, using M+N actual array elements to realize M*N transceiver channels can be equivalent to M*N virtual array elements with co-location of transceivers.

[0033] The position of the virtual array element 5 can be obtained by using the equivalent phase center approximation principle. This system uses a circular array, so the equivalent virtual array element 5 with co-located transmit and receive elements is defined to be located at the arc center of the actual co-located transmit and receive elements, such as Figure 3 By using the equivalent M*N virtual array elements 5 with co-location of transmitting and receiving, it is convenient to use the conventional single-station imaging algorithm to complete the final imaging process.

[0034] According to the Nyquist sampling theorem, the maximum interval of the equivalent virtual array element 5 can be obtained, which is the maximum interval of azimuth sampling in the SAR mode.

[0035] The azimuthal wavenumber spectrum support bandwidth is: Ω θ =[-2k max sinθ i ,2k max sinθ i ]

[0036] The maximum interval of the equivalent virtual array element 5, that is, the maximum interval of azimuth sampling, is:

[0037]

[0038] where k max is the maximum wave number, θ i is the radar incident angle, R0 is the radius of the target area, then the minimum number of equivalent virtual transceiver array elements 5 required is L=2π / Δθ to reconstruct the target image.

[0039] The echo data collected by each channel is corresponded to the echo signal data of M*N equivalent virtual array elements 5 with co-located transmitting and receiving, and the ω-k algorithm of circular SAR is used to complete the imaging processing.

[0040] The present invention utilizes the circular waveguide slot antenna to couple the LFM signal and uses it as the signal source of the transmitting array element and the local oscillator signal of the receiving array element at the same time. On the basis of sparse array single-shot imaging, it can further reduce local oscillator and other radio frequency devices, effectively reduce the system hardware cost, maintain the stability and uniformity of the local oscillator signal, and achieve better imaging effect.

[0041] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0042] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A circular MIMO imaging system based on waveguide slot coupling, characterized in that: include: A circular waveguide slot antenna and a MIMO array; one port of the circular waveguide slot antenna is connected to an LFM signal generator, and the other port is connected to a matching load; the MIMO array includes M transmitting array elements and N receiving array elements; the transmitting array elements and the receiving array elements are evenly distributed on the circular waveguide slot antenna at equal intervals, and the interval between the transmitting array elements is , the interval of the receiving array elements is ; The transmitting array element comprises a first isolator, a switch and a first horn antenna connected in sequence; the input end of the first isolator is connected to the waveguide slot of the circular waveguide slot antenna; The receiving array element includes a second isolator, a mixer and a second horn antenna; the input end of the second isolator is connected to the waveguide slot of the annular waveguide slot antenna, the output end of the second isolator is connected to the first input end of the mixer, and the second horn antenna is connected to the second input end of the mixer; The M transmitting array elements are controlled by the switch to radiate outward in sequence in a time-division manner, and the echo generated after each transmission is received by all the receiving array elements simultaneously.

2. The circular MIMO imaging system based on waveguide slot coupling according to claim 1, characterized in that: The output end of the mixer is connected to an intermediate frequency signal amplifier, a filter, an A / D converter and a digital signal imaging processing unit in sequence.

3. The circular MIMO imaging system based on waveguide slot coupling according to claim 2, characterized in that: The digital signal imaging processing unit utilizes the circular SAR The algorithm completes the imaging of the target area.

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