An adaptive cancellation circuit for a frequency modulated continuous wave radar

Abstract

This invention discloses an adaptive cancellation circuit for a frequency-modulated continuous wave radar, comprising the following components: a power divider, which splits the radar signal into two output signals, namely a first transmitted signal and a second signal LO; and a mixer, which receives the two output signals from the power divider, one of which serves as the local oscillator and the other as the receiver; the self-coupling signal delay at the RF input port of the mixer is the same as the delay of the second signal LO. This invention increases the LO trace delay, making the LO trace path delay equal to the antenna self-coupling path delay, thereby bringing the self-coupling intermediate frequency (IF) signal output close to zero frequency. This allows the self-coupling IF signal to be easily filtered out, significantly reducing the signal-to-noise ratio degradation caused by the impulse response.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and more specifically, to an adaptive cancellation circuit for a frequency modulated continuous wave radar. Background Technology

[0002] Frequency-modulated continuous wave (FM-CHW) radar is a continuous wave radar whose transmission frequency is modulated by a specific signal. FM-CHW radar obtains target range information by comparing the frequency of the echo signal at any given time with the frequency of the transmitted signal at that time; the range is proportional to the frequency difference between the two. The target's radial velocity and range can be obtained by processing the measured frequency difference. Compared to other ranging and velocity measuring radars, FM-CHW radar has a simpler structure.

[0003] Due to the limited product size of radar, it is difficult to achieve high isolation with antennas, resulting in self-coupling problems and hindering the improvement of the radar's signal-to-noise ratio (SNR). Currently, the following methods exist to reduce self-coupling and improve SNR: 1. Cancellation methods, such as software cancellation, intermediate frequency (IF) subtraction cancellation, and radio frequency (RF) adaptive cancellation; 2. High-isolation antennas. However, software cancellation suffers from complex algorithms that prolong computation time, and under certain conditions, the SNR may be too low to extract distance information. IF subtraction cancellation requires a loop feedback link, which is relatively complex and increases component costs. RF adaptive cancellation schemes also have relatively complex links, requiring increased component costs and more layout space. Due to size limitations, high-isolation antennas are difficult to implement and have limited isolation, resulting in persistent self-coupling signals in the IF signal.

[0004] The background description provided herein is for the purpose of generally presenting the context of this disclosure. Unless otherwise indicated herein, the material described in this section is not prior art to the claims of this application and should not be acknowledged as prior art by virtue of its inclusion in this section. Summary of the Invention

[0005] To address the aforementioned technical problems in related technologies, this invention proposes an adaptive cancellation circuit for frequency modulated continuous wave radar, comprising the following components: a power divider, which is used to divide the radar signal into two equally distributed signals for output, the two signals being a first transmitted signal and a second signal LO;

[0006] A mixer is used to receive two signals output from a power divider, one of which serves as the local oscillator of the mixer and the other as the receiver RF of the mixer.

[0007] The self-coupling signal delay at the mixer's RF input port is the same as the LO delay of the second signal.

[0008] Specifically, the delay of the second signal LO is achieved by using micro-strip lines.

[0009] Specifically, the micro-trace routing is a serpentine routing pattern.

[0010] Specifically, the microwires are cascaded inductors and capacitors.

[0011] Specifically, the cascaded inductors and capacitors can be single or multiple.

[0012] Specifically, the cascaded inductor-capacitor system consists of an inductor and a capacitor connected in series, with one end of the capacitor grounded.

[0013] Specifically, the adaptive cancellation circuit of the frequency modulated continuous wave radar also includes a signal processor, which is used to process the signal output by the filter.

[0014] Specifically, the adaptive cancellation circuit of the frequency modulated continuous wave radar further includes a filter, which receives the output of the mixer.

[0015] In a second aspect, the present invention provides a frequency modulated continuous wave radar, which includes an antenna and an adaptive cancellation circuit for a frequency modulated continuous wave radar as described above.

[0016] This invention increases the LO trace delay so that the LO trace path delay is equal to the antenna self-coupling path delay, thereby making the self-coupling intermediate frequency signal output by mixing close to zero frequency. This allows the self-coupling intermediate frequency signal to be easily filtered out by the filter, greatly reducing the signal-to-noise ratio degradation caused by the impulse response. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of an adaptive cancellation circuit for a frequency-modulated continuous wave radar provided in an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the serpentine trace provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the group delay obtained by the serpentine routing provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of series and parallel inductors and capacitors provided in an embodiment of the present invention;

[0022] Figure 5 The group delay obtained by the series-parallel inductor-capacitor model provided in this embodiment of the invention;

[0023] Figure 6 This is a schematic diagram of the S-parameters obtained from the series and parallel inductors and capacitors provided by the present invention.

[0024] In the diagram: TX: Transmit; RX: Receive; Ps: Useful echo signal; Pj: Self-coupling signal; LO: Mixer local oscillator input; RF: Mixer RF input; IF: Intermediate frequency signal; L: Microstrip line length from power divider output port 1 to mixer local oscillator input port; Pj_delay: Self-coupling signal delay from power divider output port 2 to mixer RF input port; LO_delay: Signal delay from power divider output port 1 to mixer LO input port; K: System frequency modulation coefficient. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0026] Example 1

[0027] refer to Figure 1 This embodiment discloses an adaptive cancellation circuit for a frequency-modulated continuous wave radar, which includes the following circuit components:

[0028] Signal processing circuit: The signal processing circuit is used to process radar signals and perform cancellation processing.

[0029] Power divider: A device used to divide a radar signal into two or more equally powered outputs. In this embodiment, a two-way power divider is used, which divides the radar signal into two equally powered outputs. Specifically, the two output signals are the first transmitted signal and the second signal LO. The second signal LO serves as the local oscillator of the mixer, and the first transmitted signal is transmitted through the radar antenna TX.

[0030] Mixer: Used to receive two signals output from the power divider, one of which serves as the local oscillator of the mixer, and the other as the receiving RF of the mixer. The receiving RF of the mixer refers to the signal received through the radar antenna RX and transmitted to the mixer.

[0031] The filter is used to filter the received radar signal, and then transmits the filtered signal to the signal processor for processing.

[0032] A mixer is used to multiply the received radio frequency (RF) signal with the signal generated by the local oscillator to produce an intermediate frequency (IF) signal. In this embodiment, the local oscillator signal of the mixer is one output signal from the power divider, and the signal received by the mixer is also one output signal from the power divider.

[0033] Specifically, in this embodiment, the second signal LO is used as the local oscillator input of the mixer, and the first transmitted signal is used as the received signal RF of the mixer after being received by the radar.

[0034] For details, please refer to Figure 1 Pj_delay refers to the self-coupling signal delay from the output port 2 of the power divider to the RF input port of the mixer. Specifically, it is the transmission time from the output port of the power divider through the radar transmission and reception as the receiving RF of the mixer to the RF port of the mixer.

[0035] The second signal delay LO_delay refers to the signal delay from the output port 1 of the power divider to the LO input port of the mixer.

[0036] In this embodiment, the mixer can obtain two intermediate frequency signals, with frequency points IF1 = F... LO -F Pj and IF2=F LO -F Ps IF1 is the self-coupling intermediate frequency signal that needs to be eliminated. In a frequency-modulated continuous wave radar system, the intermediate frequency is proportional to the duration of the signal delay, i.e., IF1 = K * (Pj_delay - LO_delay). To eliminate the self-coupling intermediate frequency signal, IF1 needs to be set to 0Hz, i.e., Pj_delay - LO_delay = 0.

[0037] In this embodiment, the LO_delay can be changed by controlling the length of the LO trace during board layout. Controlling L so that Pj_delay - LO_delay = 0 will make IF1 = 0Hz. That is, the intermediate frequency interference introduced by the self-coupled signal is zero frequency, and the self-coupled interference can be effectively filtered out by the IF filter without generating a large impulse response.

[0038] refer to Figure 2 The diagram illustrates a serpentine trace. In this embodiment, the signal transmission from the power divider's output port 1 to the mixer's local oscillator input port is achieved via PCB traces, which can be micro-trace traces. This embodiment uses a serpentine trace to increase the signal delay LO_delay from the power divider's output port 1 to the mixer's LO input port.

[0039] By bending the micro-strip line back and forth within a finite-sized PCB, the length of the micro-strip line between the start and end points is increased, thereby increasing the local oscillator delay LO_delay and achieving Pj_delay-LO_delay=0.

[0040] refer to Figure 3 This represents the group delay corresponding to this serpentine trace. Assuming the radar signal operates at 2 GHz, the delay of this microstrip line segment is 0.14 ns.

[0041] refer to Figure 4 This embodiment also provides a method to significantly increase trace delay by using series and parallel inductors and capacitors. Figure 4 This is a PCB trace routing method that increases delay by using series and parallel inductors and capacitors. The distance between the start and end points is... Figure 3 The serpentine routing is the same. Figure 5 for Figure 4 The group delay results corresponding to the trace show that the microstrip line has a delay of 0.54ns when operating at 2GHz. In comparison, under the same size conditions, the delay of the series-parallel inductor-capacitor method is about 3.8 times that of the serpentine trace, resulting in a significant improvement in delay.

[0042] refer to Figure 4 In this embodiment, the inductor and capacitor are connected in series, and the capacitor is grounded. The end of the inductor closer to the capacitor is the output port, and the end farther from the capacitor is the input port. The inductor and capacitor together form a basic inductor-capacitor unit.

[0043] Specifically, the input port is used to receive the output port of power divider 1, and the output port is used to connect to the local oscillator port of the mixer. The above description is based on an inductor-capacitor unit as an example.

[0044] In this embodiment, the number of cascaded inductors and capacitors can be single or multiple. This embodiment does not impose a specific limitation, and multiple inductors and capacitors can be cascaded according to specific delay requirements.

[0045] When there are multiple cascaded inductors and capacitors, the input port is used to receive the output port of the power divider No. 1 or the output port of the previous inductor and capacitor, and the output port is used to connect to the local oscillator port of the mixer or the input port of the next inductor and capacitor.

[0046] The series-parallel inductor-capacitor configuration in this embodiment not only increases trace delay but also simultaneously achieves filtering. (Reference) Figure 6 for Figure 5 The S-parameters obtained from the routing layout shown demonstrate good low-pass filtering. The solid line in the figure represents db(s(6,5)), and the dashed line represents the S-parameter curve of db(s(5,5)).

[0047] This invention increases the local oscillator signal delay of the mixer, making it equal to the delay of the self-coupled signal, thus achieving zero frequency for the self-coupled intermediate frequency (IF) signal. During PCB layout, the LO_delay can be altered by controlling the length of the LO trace. Controlling L so that Pj_delay - LO_delay = 0 makes IF1 = 0Hz. This means the IF interference introduced by the self-coupled signal is zero frequency, and the IF filter can effectively filter out the self-coupled interference without generating a large impulse response. Furthermore, by using series and parallel inductors and capacitors in the high-frequency traces, both the high-frequency trace delay and filtering effects can be achieved simultaneously.

[0048] Example 2

[0049] This embodiment provides a frequency-modulated continuous wave radar, which includes an antenna. Specifically, the antenna may include a receiving antenna and a transmitting antenna, or the receiving and transmitting antennas may share a single antenna. Furthermore, the frequency-modulated continuous wave radar also includes an adaptive cancellation circuit as mentioned in Embodiment 1.

[0050] This embodiment increases the LO trace delay so that the LO trace path delay is equal to the antenna self-coupling path delay. As a result, the self-coupling intermediate frequency signal generated by mixing is close to zero frequency, which makes the self-coupling intermediate frequency signal easy to be filtered out by the filter, greatly reducing the signal-to-noise ratio degradation caused by the impulse response.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An adaptive cancellation circuit for a frequency-modulated continuous wave radar, comprising the following components: A power divider is used to divide the radar signal into two equally distributed signals, namely a first transmitted signal and a second signal LO. A mixer is used to receive two signals output from a power divider, one of which serves as the local oscillator of the mixer, and the other as the receiving RF of the mixer; the receiving RF of the mixer refers to the signal received through the radar antenna RX and transmitted to the mixer. The self-coupling signal delay at the mixer's RF input port is the same as the delay of the second signal LO; the delay of the second signal LO is achieved through micro-strip lines; the intermediate frequency interference introduced by the self-coupling signal is zero frequency; The second signal LO is the local oscillator of the mixer.

2. The adaptive cancellation circuit for a frequency modulated continuous wave radar according to claim 1, wherein the microstrip line is a serpentine trace.

3. The adaptive cancellation circuit for a frequency modulated continuous wave radar according to claim 1, wherein the micro-strip line is a cascaded inductor-capacitor.

4. The adaptive cancellation circuit for a frequency modulated continuous wave radar according to claim 3, wherein the cascaded inductor and capacitor are single or multiple.

5. The adaptive cancellation circuit for a frequency modulated continuous wave radar according to claim 4, wherein the cascaded inductor and capacitor are an inductor and a capacitor connected in series, and one end of the capacitor is grounded.

6. An adaptive cancellation circuit for a frequency modulated continuous wave radar according to any one of claims 1-5, further comprising a filter, the filter receiving the output of the mixer.

7. The adaptive cancellation circuit for a frequency modulated continuous wave radar according to claim 6 further includes a signal processor, wherein the signal processor is used to process the signal output by the filter.

8. A frequency modulated continuous wave radar, comprising an antenna and an adaptive cancellation circuit for a frequency modulated continuous wave radar as claimed in any one of claims 1-7.

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