KR20060037777A - Apparatus for removing leakage signal of fmcw radar - Google Patents

Abstract

The present invention relates to a leakage signal removal device of a FMCW radar using a single antenna, and to match the path length of the local oscillation signal and the path of the leakage transmission signal using a rectangular waveguide in the transceiver of the FMCW radar, the intermediate frequency By constructing a high pass filter and a notch filter that remove the bit signal caused by the leaked transmission signal that forms noise in the circuit part, the FMCW radar with high sensitivity can be realized by using a single antenna.

Description

Leakage signal removal device of FMCC radar {APPARATUS FOR REMOVING LEAKAGE SIGNAL OF FMCW RADAR}

1 is a block diagram showing the configuration of a conventional FMCW radar.

2 is a waveform diagram of a frequency-modulated transmit / receive signal of a conventional FMCW radar.

Figure 3 is a waveform diagram of a leaked bit signal generated in the conventional transceiver of the FMCW radar.

Figure 4 is a block diagram showing the configuration of the FMCW radar according to the present invention.

5 is a waveform diagram of a bit signal output from each component of the FMCW radar according to the present invention.

** Description of the symbols for the main parts of the drawings **

10, 100: modulation signal generator 20, 200: transceiver unit

21, 201: voltage controlled oscillator 22, 202: directional coupler

23, 203: circulator 24, 204: transmission and reception antenna

25, 205: frequency mixer 30, 300: intermediate frequency circuit

31, 302: low noise amplifier 32, 303: bandpass filter

33, 305: intermediate frequency amplifier 40, 400: signal processing unit

41, 403a, 403b: A / D converter 42, 404: DSP section

206: Spherical waveguide 301: High pass filter

304: Notch filter 306: Power divider

401: automatic gain control device 402: log envelope detector

The present invention relates to an apparatus for canceling a leakage signal of a frequency modulated continuous wave (FMCW) radar. Particularly, in a transceiver, a path length of a local oscillation signal coincides with a path length of a leakage transmission signal. The present invention relates to an FMCW radar leakage signal elimination device capable of eliminating the influence of a leaked transmission signal by adding a high pass filter and a notch filter to the frequency circuit part.

Radar (Radar Detection And Ranging) is a sensing device that emits electromagnetic waves and receives reflected waves reflected by objects in the area to detect the existence and distance of the target.It has all-weather functions regardless of weather conditions or day and night. It has the advantage of detecting from short distances to long distance objects on the other side of the earth beyond the horizon.

The homodyne FMWC radar, which is to be dealt with in the present invention, modulates a continuous waveform signal and transmits it as a target through an antenna and receives a signal reflected from a target. At this time, since the frequency difference between the transmission signal and the reception signal delayed by the traveling distance of the electromagnetic wave and the local oscillation signal used as a reference signal for time delay measurement generates a beat signal, it is converted into a digital signal. After extracting the spectrum of the bit signal using a Fast Fourier Transform (FFT) it is possible to obtain the presence or absence of the target and distance information with the target.

Apparatuses applying this method include various fuze near field detection sensors, radio altimeters, and near field radar systems in the military field, and in the civil field, such as vehicle collision avoidance devices and aircraft collision warning systems. It is used.

Such a homodyne FMCW radar, as shown in FIG. 1, modulates the modulation signal generator 10 for generating a triangular wave transmission signal having a period T _m, and modulates the transmission signal of the modulation signal generator 10. Transmitting and receiving unit 20 for receiving a signal reflected by an object in the region formed by the radiation pattern, and generating a bit signal using the transmission signal and the received signal, and a low noise amplifier 31 ), A band pass filter 32 and an intermediate amplifier 33, the intermediate frequency circuit section 30 for amplifying a predetermined frequency band of the bit signal, and the frequency of the bit signal processed by the intermediate frequency circuit section 30 It is composed of a signal processing unit 40 for detecting the presence of the target by detecting and analyzing.

The transceiver 20 is provided by a voltage controlled oscillator 21 and a voltage controlled oscillator 21 for modulating and outputting a frequency of a transmission signal generated by the modulation signal generator 10 according to an applied voltage. A directional coupler 22 which takes a part of the frequency-modulated transmission signal and uses it as a local oscillation signal, a circulator 23 for determining the propagation direction of the radio wave so that the transmission signal is not induced to the receiving end, and the circulator 23 Transmit and receive antenna 24 to receive the transmitted signal through the outside and receive the reflected signal and a portion of the transmitted signal from the directional coupler 22 to the LO port and receives the received signal for the transmitted signal RF port It is composed of a frequency mixer 25 for receiving the IF signal to generate a bit signal of the intermediate frequency band to the IF port.

In addition, the signal processor 40 includes an analog-to-digital converter (hereinafter referred to as an 'A / D converter') 41 for converting a signal output from the intermediate frequency circuit unit 30 into a digital signal, and a fast Fourier transform. Digital signal processing unit (Fast Fourier Transform) to detect the frequency of the bit signal from the digital signal by the A / D converter 41, and compare and analyze the magnitude of the digitized bit signal to determine the target (Digital Signal) Processing: DSP, hereinafter referred to as DSP section).

The operation process of the homodyne FMCW radar configured as described above will be described with reference to the waveforms of the frequency-modulated transmit and receive signals 51 and 52 of FIG. 2 and the leaked bit signal 54 generated by the transceiver of FIG. 3. As follows.

When the modulation signal generator 10 supplies a triangular wave transmission signal having a period T _m to the voltage control port of the voltage controlled oscillator (VCO) 21, the directional coupler ( 22).

In this case, the frequency of the frequency-modulated transmission signal output by the voltage controlled oscillator 21 is represented by the following equation when the frequency gradient (Hz / sec) of the frequency-modulated transmission signal is α and the minimum frequency (Hz) is f ₀ . It is expressed as in Equation 1.

f (t) = f ₀ + αt (Hz) (0≤t≤T _m / 2)

Therefore, α is a constant that corresponds the frequency of the bit signal to the delay time, which can be expressed as follows with reference to FIG.

Where f _m (Hz) is the frequency (f _m = 1 / T _m ) of the frequency modulated transmission signal of the triangular wave modulated signal used to frequency modulate the transmission signal, and B (Hz) is frequency modulation, which is a variable range of the voltage controlled oscillator. The bandwidth, f _b (Hz) is the frequency of the bit signal output from the IF port, τ _d (sec) is the delay time (τ _d = 2R / c) of the transmission / reception signal according to the distance.

From Equation 2, the difference between the transmission signal and the reception signal including the distance information of the target can be expressed as follows.

(Hz)는 주파수 변조된 송신신호의 주파수,

(Hz)는 주파수 변조된 수신신호의 주파수, R(m)은 표적과의 거리, c(3×10⁸ m/sec)는 자유공간 내의 전파 속도를 나타낸다. here,

(Hz) is the frequency of the frequency-modulated transmit signal,

(Hz) is the frequency of the frequency-modulated received signal, R (m) is the distance from the target, and c (3 x 10 ⁸ m / sec) is the propagation speed in free space.

The power P _RX of the received signal for the same target located at distance R in the FMCW radar has a relationship of P _RX ∝1 / R ⁴ according to the radar equation. The magnitude of power received thus varies significantly with sensing distance. Therefore, the dynamic range of the FMCW radar receiver must be very wide and converted into a digital signal through the A / D converter 41 which can cover the dynamic range. The bit signal digitally converted using this A / D converter 41 is digital signal processed to determine whether a target exists in the search section and obtain distance and altitude information on the target. However, since the dynamic range of the received signal is extensive, it takes a long time for the signal processing unit 40 to process it, and thus, a high speed DSP unit 42 is used to process the signal in real time.

On the other hand, the transceiver 20 of the FMCW radar continuously emits a transmission signal, and generates a leakage bit signal corresponding to the distance traveled by the leaked transmission signal due to the finite isolation between the transmission signal and the reception signal. Since the leakage bit signal has a similar shape such that the magnitude of the leakage bit signal is much larger than that of the received signal and the singularity coincides with the modulation signal of the triangular wave form having a period T _m , the frequency spectrum of the leak bit signal 54 is transmitted. An infinite number of harmonic components corresponding to integer multiples of the signal frequency f _m (= 1 / T _m ) are formed.

That is, as shown in FIG. 3, the leakage bit signal 54 output from the IF port of the frequency mixer 25 receives harmonic components at the same point as the transmission signal 53 output from the modulation signal generator 10. A singular point 55 is formed, which is a triangular wave transmission signal input to the voltage controlled oscillator 21 repeatedly generates a sweep of the voltage controlled oscillator 21 every T _m / 2, and thus leaks. This is because the bit signal 54 is symmetrically reproduced at every integer multiple of T _m / 2 to form the singular point 55 due to the phase difference.

Due to the singularity 55, the leaky bit signal 54 forms an infinite number of harmonic components on the frequency spectrum. Therefore, if the harmonic component of the leakage bit signal 54 is larger than the bit signal formed by the received signal, it is impossible to detect the target, and thus the harmonic magnitude of the leakage bit signal 54 in the frequency band so as not to lower the sensitivity of the FMCW radar. Should be smaller than the noise floor.

The conventional method applied to the FMCW radar to solve the leak bit signal problem is to implement the transmitting antenna and the receiving antenna separately and to improve the isolation between the transmitting signal and the receiving signal as much as possible. It does not affect the signal.

However, in the prior art as described above, miniaturization of the radar has a problem that even when the transmitting antenna and the receiving antenna are separately implemented, mutual coupling occurs between the antennas and thus the desired isolation cannot be obtained.                         

In addition, in this case, there is a problem in that the structure is complicated and the implementation cost is higher than that of a radar using a single antenna.

In particular, in order to detect a target in an environment with high background reflectivity, a beam width of a transmitting / receiving antenna should be narrowly implemented. When the transmitting and receiving antennas are separated, it is difficult to implement to stare at the same point while maintaining the desired isolation between both antennas. .

Accordingly, the present invention has been made in view of the above-mentioned problems. In the FMCW radar using a single antenna, a delay distance between a local oscillation signal and a leakage transmission signal used as a reference signal for measuring a frequency difference with respect to a sensing distance in a transceiver is measured. A rectangular waveguide that matches the s, and the high pass filter and the notch filter for removing the leakage bit signal in the intermediate frequency circuit part are added to make it easy to extract the presence and distance information of the target in a large background clutter environment. An object of the present invention is to provide a leakage signal canceling device for an FMCW radar using a single antenna.

That is, the leak bit signal of the FMCW radar is about tens of millivolts, which is considerably larger than the received signal, so that the leak bit signal, which is not sufficiently removed, not only degrades the radar sensitivity but also distorts the detected signal, thereby effectively eliminating the FMCW. It is an object of the present invention to provide a radar leakage signal removing device.

The present invention for achieving the above object is a modulation signal generator for generating a transmission signal, a voltage controlled oscillator, a directional coupler, a circulator, a frequency mixer and a transceiver for generating a bit signal by transmitting and receiving antennas, In an FMCW radar composed of a low noise amplifier, a band pass filter, and an intermediate frequency amplifier, and a signal processing unit, a delay distance of the transmission signal from a voltage controlled oscillator output port to a transmission signal input port of a frequency mixer. r _LO is a sphere positioned at the connection line of the directional coupler and the frequency mixer such that the transmission signal leaked from the circulator is equal to the delay distance r _{LK (Tx)} from the voltage controlled oscillator output port to the reception signal input port of the frequency mixer. It is characterized by including a waveguide.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 is a block diagram showing the configuration of a homodyne FMCW radar using a single antenna. As shown in FIG. 4, the directional coupler 202 and the frequency mixer 205 of the local oscillation signal (LO) port of the transceiver 200 are illustrated. A spherical waveguide 206 is added to the connecting line. In the intermediate frequency circuit unit 300, a high pass filter 301 is provided at an input terminal, a notch filter 304 is disposed between the band pass filter 303 and the intermediate frequency amplifier 305, and an output terminal of the intermediate frequency amplifier 305 is provided. It further comprises a power divider 306. In the signal processing unit 400, another A / D converter is connected to an input terminal of the DSP unit 404 to which an existing A / D converter (hereinafter, referred to as a “first A / D converter”) 403a is connected. (Hereinafter referred to as a “second A / D converter”) 403b is further connected, and the signals output from the intermediate frequency circuit unit 300 are respectively fed into the automatic gain control device 401 and the log envelope detector 402. After input and processing, it is transmitted to the first A / D converter 403a and the second A / D converter 403b.

In the process of generating the transmission signal of the triangular wave in the modulation signal generator 100 and radiating through the transmission and reception antenna 204 via the voltage controlled oscillator 201, the directional coupler 202, the circulator 203, the transmission and reception antenna A portion of the transmission signal is reflected by the impedance mismatch between the 204 and the circulator 203 and is input to the RF port of the frequency mixer 205. That is, in the case of the ideal transceiver 200, the transmission signal should be input to the LO port of the frequency mixer 205, and the reception signal reflected by the transmission signal should be input to the RF port of the frequency mixer 205. The leaked leaked transmission signal is inputted from the circulator 203 to the RF port of the frequency mixer 205 together with the received signal.

Therefore, the output terminal of the directional coupler 202 to match the delay distance between the leakage transmission signal input from the circulator 203 to the RF port of the frequency mixer 205 and the transmission signal input to the LO port of the frequency mixer 205. A portion of the connection line of the LO port of the over-frequency mixer 205 is implemented with a rectangular waveguide 206.

Here, if the delay time Δτ _dLK for the additional propagation path Δr _{LK (TX)} of the leaked transmission signal is Δτ _{dLK =} Δr _{LK (TX)} / v _g , the frequency f _LKb of the leaked transmission signal is as follows.

Here, r _{LK (Tx)} is a delay distance from which the leakage transmission signal passes from the output port of the voltage controlled oscillator 201 to the RF port of the frequency mixer 205, and r _LO is the transmission signal of the voltage controlled oscillator 201. The distance passed from the output port to the LO port of the frequency mixer 205, v _g is the traveling speed of the traveling wave inside the rectangular waveguide 206.

Among these, r _{LK (Tx)} measures the delay time according to each mismatch from the input port of the transmission / reception antenna 204 to the network analyzer, and the rectangular waveguide 206 corresponding to the delay time of the leakage transmission signal having the largest value. Adjust to the length of. At this time, if r _{LK (Tx) =} r _LO in Equation 4, since the leakage bit signal output to the IF port of the frequency mixer 205 becomes a DC component, regardless of the magnitude of the leakage bit signal, the target is irrelevant. It can be easily separated from the bit signal by.

Since the transceiver 200 configured to operate as described above has multiple leakage paths, it is not possible to completely remove the leakage bit signal generated at the IF port of the frequency mixer 205 simply by adding the rectangular waveguide 206. Therefore, the high pass filter 301, the notch filter 304, and the power divider 306 are further configured in the intermediate frequency circuit unit 300.

The bit signal including the leaked bit signal inputted from the transceiver 200 to the intermediate frequency circuit unit 300 is first passed through the high pass filter 301 to filter the low frequency bit signal first, so that the low noise amplifier 302 receives the low frequency bit signal. Prevent saturation

The low noise amplifier 302 is used to improve the noise figure of the system, and the band pass filter 303 connected to the output terminal of the low noise amplifier 302 starts from the frequency f _c1 so as to extract only a bit signal corresponding to a preset sensing distance. Determine the passband up to f _c2 . The next stage of the bandpass filter 303 is the notch filter 304, and the cutoff frequency of the notch filter 304 is equal to the low cutoff frequency f _c1 of the bandpass filter 303 so that the bandpass filter ( Harmonic components of the bit signal existing near the low cutoff frequency f _c1 of 303) are removed.

Referring to the waveform diagram shown in FIG. 5A, the harmonic spectrum of the leaked bit signal is almost identical to the transmission signal of the triangular wave used as the modulation signal of the transmission signal except for the signal near DC, and thus undergoes a Fourier transform period T _m. It can be seen that the harmonic spectral power P _h (f) of the leakage bit signal having = 1 / f _m has a characteristic of rapidly decreasing as the frequency increases due to the relationship of (f / f _m ) ^-4 according to the frequency f. .

First, the bit signal passes through the high pass filter 301 to filter the low frequency bit signal as shown in FIG. 5B to prevent the low noise amplifier 302 from saturating and to output the bit output from the low noise amplifier 302. A band pass filter 302 which determines the pass band of the signal (BW _beat = f _c2- f _c1 ) is passed through to block most low frequency components as shown in FIG. 5C. However, at this time, the bit signal component in the vicinity of the low cutoff frequency f _c1 of the bandpass filter 302 has the largest power, and if the Fourier inverse transform is performed, the harmonic component not removed in the vicinity of f _c1 is T _m / 2. A spike signal 56 is generated for each integer multiple positions of to distort the output signal of the log envelope detector 402.

That is, a notch filter that most of the spike noise (56) due to the leakage-bit signal generated on the time axis is because the harmonic components that may not have removed by the high-pass filter 303 at f _c1 vicinity causing f _c1 to the cut-off frequency This is removed using 304. As a result, as shown in FIG. 5D, it can be seen that the magnitude of the spike noise 56 is greatly reduced, and only the desired bit signal 57 is output.

The intermediate frequency amplifier 305 which receives the bit signal output from the notch filter 304 has a bit signal in the dynamic range of the automatic gain control device 401 and the log envelope detector 402 connected through the power divider 306. Adjust the gain to exist.

Accordingly, the log envelope detector 402 outputs a logarithmic proportional value to the magnitude of the input bit signal and converts the digital signal into a digital signal using the second A / D converter 403b. By comparing the output size according to the search position in, it is possible to discriminate the presence or absence of the target even in a large clutter environment.

In addition, the automatic gain control device 401 generates an output of the same signal strength regardless of the magnitude of the input bit signal, and then converts it into a digital signal using the first A / D converter 403a, and the DSP unit 404. ) Detects the distance to the target by extracting the frequency of the bit signal through the fast Fourier transform.

As described in detail above, the present invention can implement a FMCW radar with excellent sensitivity as a single antenna through the transceiver and the intermediate frequency circuit unit using a leaked transmission signal removal circuit to add a rectangular waveguide for effectively removing the leakage bit signal. It works.

Claims (5)

Composed of a modulation signal generator for generating a transmission signal, a voltage controlled oscillator, a directional coupler, a circulator, a frequency mixer, and a transmission / reception antenna to generate a bit signal, and a low noise amplifier, a band pass filter, and an intermediate frequency amplifier. In the FMCW radar comprising an intermediate frequency circuit portion and a signal processing portion, The delay distance r _LO where the transmission signal passes from the voltage controlled oscillator output port to the transmission signal input port of the frequency mixer, and the transmission signal leaked from the circulator passes from the voltage controlled oscillator output port to the reception signal input port of the frequency mixer. And a spherical waveguide positioned at the connection line between the directional coupler and the frequency mixer so as to be equal to one delay distance r _{LK (Tx)} . The method of claim 1, The r _{LK (Tx)} measures impedance mismatch between the transmitting and receiving antenna and the circulator using a network analyzer at an input port of the transmitting and receiving antenna, and a delay corresponding to the delay time of the leaked transmission signal having the largest value among the measured values. Leakage signal removal device for FMCW radar, characterized in that configured to determine the distance. The method of claim 1, And the intermediate frequency circuit unit includes a high pass filter for filtering a low frequency bit signal to prevent the low noise amplifier from saturating by being positioned between the frequency mixer output port and the low noise amplifier. The method of claim 1, The intermediate frequency circuit unit includes a notch filter positioned at an output terminal of the band pass filter and having a cutoff frequency equal to a low cutoff frequency of the bandpass filter to remove harmonic components of the bit signal near the cutoff frequency. Leakage signal removal device of FMCW radar. The method of claim 1, The signal processing unit, an automatic gain control device for receiving the output signal of the intermediate frequency circuit unit to generate an output of the same signal strength; A log envelope detector configured to receive an output signal of the intermediate frequency circuit unit and generate an output that is logarithically proportional to its magnitude; An analog-to-digital converter for converting the output of the automatic gain control device and the log envelope detector into a digital signal; Digital signal processing unit for processing the output of each analog-to-digital converter signal by the Fast Fourier Transform (Fast Fourier Transform) method to read the presence or absence of the target value and the distance value of the target to remove the leakage signal of the FMCW radar Device.

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