JP2010236927A - Multiple-frequency doppler system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain miniaturization and cost reduction of a high-frequency circuit module of a multiple-frequency Doppler system. <P>SOLUTION: The high-frequency circuit module of the multiple-frequency Doppler system includes a frequency conversion part which consists of a diode 21, having a non-linear characteristic and a filter 23 and an open stub 22, connected respectively to an output end of the diode 21 and is provided in a front end part of an antenna 17 used for transmission and reception in common, and the output side of the filter 23 is made an output terminal for a Doppler signal d. According to such a constitution, the miniaturization is attained by using a simple circuit constitution which does not have a distributor provided for a conventional circuit module outputting the Doppler signal and does not need other high-frequency circuit components, such as, an amplifier provided for preventing lowering of a power level. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multi-frequency Doppler device that detects the distance of a moving object by using a Doppler radar system using two or more multi-frequency microwaves or millimeter waves, and a multi-frequency having a circuit module adapted to a transmission / reception antenna integrated type. The present invention relates to a Doppler device.

Conventionally, a method for measuring the distance of an object using microwaves and millimeter waves and a method for detecting the presence / absence of an object (hereinafter referred to as a “distance measurement method” includes a “detection method for presence / absence”). ) Is known and has the properties that microwaves and millimeter waves are more transmissive than light that is the same electromagnetic wave and cannot be seen by humans, so it is put to practical use mainly in fields where this property can be used. Is planned.
The distance measurement method is a method of irradiating an object with microwaves and millimeter waves and detecting a reflected wave from the object. For example, (1) FM-CW (Frequency Modulation-continuous wave) method, (2) Two-frequency Doppler method and (3) standing wave method are known. The present invention relates to the multi-frequency (two-frequency) Doppler method.
In the conventional two-frequency Doppler system, a signal having two frequencies transmitted from a transmitting antenna is irradiated to a moving detection target, and after receiving a Doppler-shifted reflected wave, the signal is converted into a Doppler frequency by a mixer. The distance to the detection target can be calculated from the phase difference between the two frequency-converted Doppler signals.

By the way, the conventional two-frequency Doppler device includes a circuit module for performing an operation in accordance with the above-described principle. However, since two frequencies are used, the number of components mounted on the circuit module is considerably increased.
FIG. 4 is a diagram showing a configuration of a circuit module conventionally proposed in the two-frequency Doppler system. In the figure, configuration examples of two types (A) and (B) are shown. The configuration example (A) is a type in which the transmission / reception antennas 18 and 19 are separated, and the configuration example (B) is a type in which the transmission / reception antenna 17 is integrated. As shown in FIG. 4, the configuration example (B) has the advantage that only one antenna is required, but both the configuration examples (A) and (B) have two high-frequency circuit sections corresponding to two frequencies. In each system, mixers 37 and 38 and distributors 31 to 34 and 39 are required on the oscillator side and the antenna side.

Further, in the transmission system, a combination loss of 3 db or more occurs at the time of combining transmission signals by a combiner immediately before the antenna (shown as distributors 33 and 39 in FIG. 4), which affects transmission power reduction. In the receiving system, similarly to the transmitting side, a distribution loss of 3 db or more occurs when the received signal is distributed in the distributors 34 and 39 immediately after the receiving antenna, which affects the noise figure of the receiving system. If amplifiers and filters 40 to 42 are provided in order to reduce the influence of these losses, the circuit scale becomes large.
In addition, as shown in the configuration example (B), the circulators 35 and 36 are often used in the transmission / reception antenna integrated type. Make it difficult.

As described above, both types of modules shown in FIGS. 4A and 4B as the conventional example of the two-frequency Doppler circuit module have problems in size and cost, and the condition as a module applicable to a wide range of applications. It is not equipped with.
The present invention has been made in order to solve the above problems in the conventional two-frequency Doppler type high-frequency circuit module, and its object is to reduce the size and cost of the circuit module. .

  The present invention has a high-frequency circuit for simultaneously transmitting a large number of continuous waves of different set frequencies for transmission and reception, and for extracting a Doppler signal corresponding to the frequency from a reception signal of a reflected wave that returns after transmission. In the multi-frequency Doppler device, the high-frequency circuit has a frequency conversion unit that mixes a reception signal and a transmission signal at an end directly connected to an antenna.

  According to the present invention, the front end portion of the multi-frequency Doppler type high-frequency circuit module (the end portion of the high-frequency circuit portion connected to the antenna) is made into a single system, so that the circuit module is reduced in size and consumption. Power consumption and cost reduction can be achieved, and the application field can be expanded to various applications that require distance measurement of objects using microwaves and millimeter waves and detection of presence / absence of objects. it can.

It is a figure which shows the circuit structure of the 2 frequency Doppler module concerning embodiment of the multifrequency Doppler apparatus of this invention. It is a table | surface which shows the relationship of the variable which concerns on operation | movement of the 2 frequency Doppler module of this embodiment. It is a figure which shows the circuit structure concerning other embodiment of the multifrequency Doppler apparatus of this invention. It is a figure which shows the prior art example of the circuit module employ | adopted as a 2 frequency Doppler apparatus.

Hereinafter, an embodiment of a multi-frequency Doppler device according to the present invention will be described.
In the embodiment described below, an example in which the multi-frequency Doppler device according to the present invention is applied to a two-frequency Doppler is shown. Since the principle of distance measurement by the two-frequency Doppler method and the basic process of calculating the distance from the Doppler signal are common to the prior art, in this embodiment, the two frequencies constituting the characteristic part of the present invention are used. A Doppler module, that is, a high-frequency circuit module for transmitting a continuous wave of two frequencies from an antenna shared for transmission and reception, and extracting a Doppler signal corresponding to the two frequencies from a reception signal of a reflected wave returned after transmission (hereinafter referred to as a “high frequency circuit module”). It will be described mainly with reference to “circuit module”.

In the two-frequency Doppler module, when the microwave and millimeter wave frequencies used are increased, high gain and high P ₁ db (output power at ₁ db gain compression) can be obtained at low cost, and signals can be transmitted with low loss. It becomes difficult to synthesize and distribute. For this reason, in the above [Background Art] section, as in the conventional circuit module described with reference to FIG. 4, the transmission signals Tx, LO ( It has become necessary to provide a distributor that distributes the signal (Local Oscillator), which increases the size of the circuit, leading to a reduction in power and cost of the signal.
Therefore, in this embodiment, a circuit module that outputs a Doppler signal by adopting a single diode mixer in the front end portion (the end portion of the circuit connected to the antenna) and utilizing the transparency of microwaves and millimeter waves. Therefore, the received signal distributor and the transmission signal Tx and LO signal distributors required in the prior art are eliminated, the power level lowering than the isolation resistance is given priority, and the power level reduced by the conventionally adopted distributor is reduced. Other circuit elements such as an amplifier provided for maintenance are eliminated, and a simple circuit configuration is obtained.

FIG. 1 is a diagram illustrating a circuit configuration of a two-frequency Doppler module according to the present embodiment.
In the high-frequency circuit module shown in FIG. 1, the antenna 17 is an antenna shared for transmission and reception that transmits the transmission signal Tx and receives the reception signal Rx.
The circuit on the transmission side transmits a continuous wave of two frequencies includes an oscillator 11 the oscillation frequency f _1, an oscillator 12 the oscillation frequency f _2, the synthesizer respectively oscillator 11 and the oscillator 12 is combining signals generated 14 And an amplifier 15 for amplifying the signal synthesized by the synthesizer 14.
Further, the circuit on the receiving side has a single diode mixer at the front end. The single diode mixer includes a diode 21 having nonlinear characteristics, a filter 23 and an open stub 22 connected to the output terminal of the diode 21.
Here, the terminal of the signal output d including the Doppler signal is the output side of the filter 23.

The filter 23 of the frequency conversion unit is a filter that passes the Doppler signal frequency band. An open stub 22 of the frequency conversion unit is a circuit in which the output terminal of the diode 21 becomes a short point in the vicinity of the set frequency of the oscillators 11 and 12. In the present embodiment, the length of the stub in the open stub 22 is λg / 4 (λg: wavelength on the line of the high-frequency signal) when the oscillation frequencies of the two-frequency oscillators 11 and 12 are set to f ₁ and f ₂ , respectively. By setting the length to, a short point at the set frequency of the oscillator can be created at the output end of the diode 21. (Short at the set frequency of the oscillator and Open at the Doppler frequency.)
As described above, the single diode mixer is employed in the circuit on the receiving side of the present embodiment because the output signals from the oscillators 11 and 12 are used in two roles of the LO signal and the transmission signal Tx, and therefore are as low as possible. In order to reduce costs, we selected a mixer that does not have a demultiplexer.
In the embodiment of FIG. 1, an example is shown in which the filter 23 is added to the components of the frequency conversion unit. However, depending on the function of the signal processing means at the subsequent stage, the filter 23 may be omitted. .

Further, the synthesizer 14 of the circuit on the transmission side cannot realize a thin film resistor depending on the material of the printed circuit board. Therefore, when a lumped component is used instead, power is generated in the isolation resistor and the 50Ω termination portion constituting this component. As a transmission loss.
In order to suppress this transmission loss, one solution is to employ a T-branch and an impedance transformer in the synthesizer 14. If a desired output power can be obtained from the effect of this solution and the performance of the oscillator, the amplifier 15 provided in the circuit on the transmission side becomes unnecessary.

Next, the operating conditions of the two-frequency Doppler module (FIG. 1) will be described. FIG. 2 is a table of three types (A) to (C) that summarizes the relationship of variables relating to the operation of the two-frequency Doppler module of this embodiment, and will be referred to in the following description. The numerical values in each table are obtained when the carrier frequency is 24.15 GHz and the direction in which the detection target moves matches the direction in which the radio wave travels.
A predetermined oscillation frequency is set in the two-frequency oscillators 11 and 12.
When the oscillation frequency set in the oscillator 11 is f ₁ (corresponding angular frequency ω ₁ ), the phase constant β ₁ is expressed as (2πf ₁ ) / c (c: speed of light).

Similarly, when the oscillation frequency set in the oscillator 12 is f ₂ (corresponding angular frequency ω ₂ ), the phase constant β ₂ is (2πf ₂ ) / c.
As shown in the table (A) of FIG. 2, the relationship between the oscillation frequencies f ₁ and f ₂ respectively set in the two-frequency oscillators 11 and 12 is as the maximum detection distance (m) to the detection target increases. The frequency difference (MHz) between the oscillation frequencies f ₁ and f ₂ becomes small (at the carrier frequency: 24.15 GHz, the frequency difference is 5 MHz with respect to the maximum detection distance of 15 m). Therefore, if a long detection distance is to be obtained, the frequency difference (f ₁ −f ₂ ) becomes small, so that the frequency stability (ppm) of the oscillators 11 and 12 becomes low and it becomes difficult to maintain detection accuracy.

In order to transmit two continuous waves, the output power of the signal transmitted from the oscillator 11 is V ₁ = A cos (ω ₁ t), and the output power of the signal transmitted from the oscillator 12 is V ₂ = B cos (ω ₂ t), the reflected waves subjected to the Doppler shift from the detection object moving at the speed ± v existing at the distance l ₀ from the two-frequency Doppler module are V ₃ = C cos (ω ₁ t + 2β ₁ L), V ₄ = Dcos (ω ₂ t + 2β ₂ L). Here, L represents the distance to the moving detection object.
The distance L to the detection object is L = l ₀ ± vt (t: time) because the detection object moves, but assuming that the time t is a very short time, L≈l ₀ Can be approximated.
As shown in the table (B) of FIG. 2, the time (ns) for the radio wave to reciprocate between the detection objects becomes longer as the detection distance (m) is longer. The approximate value is closer to the true value when the moving speed v of the object is slower.

The received signals Rx and LO signals are frequency-converted by passing through the diode 21 (mixer), and the main signals appearing at the converted mixer output terminals are signals represented by the following equations (1) to (6).
A cos (ω ₁ t) · B cos (ω ₂ t) Equation (1)
Ccos (ω ₁ t + 2β ₁ l ₀ ) · Dcos (ω ₂ t + 2β ₂ l ₀ ) Equation (2)
A cos (ω ₁ t) · C cos (ω ₁ t + 2β ₁ l ₀ ) Equation (3)
A cos (ω ₁ t) · D cos (ω ₂ t + 2β ₂ l ₀ ) Equation (4)
Bcos (ω ₂ t) · C cos (ω ₁ t + 2β ₁ l ₀ ) Equation (5)
Bcos (ω ₂ t) · Dcos (ω ₂ t + 2β ₂ l ₀ ) Equation (6)

The main signals shown in the above equations (1) to (6) appearing at the output terminal of the diode 21 (mixer) include the Doppler frequency component and the oscillation frequencies f ₁ set for the two-frequency oscillators 11 and 12, respectively. And the frequency difference of f ₂ | f ₁ −f ₂ | = Δf. However, the frequency of the Doppler signal to be detected is very low compared to the frequency difference Δf between the oscillation frequencies f ₁ and f ₂ . In addition, this point is a detection target that moves at a low speed of 20 km / h or less, whereas Δf is 5 to 75 MHz when the Doppler frequency shown in Table (C) in FIG. 2 is compared with the frequency difference in Table (A). If present, it is clear from the fact that the Doppler frequency does not exceed 1 KHz.
Therefore, by using the filter 23 added to the output terminal of the diode 21 as an LPF (low-pass filter), a signal having a relatively high frequency such as equations (1), (2), (4), and (5) having a Δf component can be obtained. Can be removed.

The signal output d including the Doppler signal passing through the LPF (filter 23) is processed to obtain distance information by the processing method described below.
When Expression (3) representing the signal related to the oscillation frequency f _{1 including} the information of the distance l ₀ to the detection target is developed,
A cos (ω ₁ t) · C cos (ω ₁ t + 2β ₁ l ₀ ) = (AC / 2) {cos (2ω ₁ t + 2β ₁ l ₀ ) + cos (2β ₁ l ₀ )} Equation (7)
Thus, the phase φ ₁ of the Doppler frequency component signal on the right side of the expanded equation (7) is
φ ₁ = 2β ₁ l ₀ = (4πf ₁ l ₀ ) / c Equation (8)
It is expressed. The phase constant β ₁ is (2πf ₁ ) / c.
Similarly, when the signal of the equation (6) representing the signal related to the oscillation frequency f ₂ is expanded, the phase φ ₂ of the Doppler frequency component signal is
φ ₂ = 2β ₂ l ₀ = (4πf ₂ l ₀ ) / c Equation (9)
It is expressed. The phase constant β ₂ is (2πf ₂ ) / c.

From the output terminal of the filter 23, an output signal d including a Doppler frequency component in which two IF (intermediate frequency) signals having different phases but the same Doppler frequency and the same amplitude are superimposed is output. Digital signal processing is performed under the conditions of the same frequency and the same amplitude, two IF signals before superposition are determined, and a phase difference Δφ between the obtained signals is calculated.
This Δφ corresponds to the phase difference between the phases φ ₁ and φ ₂ described above of the Doppler frequency component signals corresponding to the oscillation frequencies f ₁ and f ₂ , respectively. That is,
Δφ = | φ ₁ −φ ₂ | = | (4πl ₀ ) / c || f ₁ −f ₂ | Equation (10)
It is expressed.
Therefore, the distance l ₀ is based on the phase difference Δφ obtained by the signal processing for the signal output d of the frequency converter.
l ₀ = {c / (4π | f ₁ −f ₂ |)} · Δφ Equation (11)
Can be calculated.

Next, an embodiment according to a two-frequency Doppler module in which the above-described frequency conversion unit is provided for each of the set oscillation frequencies f ₁ and f ₂ will be described.
The two-frequency Doppler module described above with reference to FIG. 1 employs a configuration in which a single frequency conversion unit is shared by two frequencies of the oscillation frequencies f ₁ and f ₂ . For this reason, in the process for the signal output d of the frequency conversion unit, it is necessary to calculate the signal corresponding to the oscillation frequencies f ₁ and f ₂ from the superimposed signal, and the processing capability of the device using the detection signal such as the distance Depending on the case, it may become an obstacle to use.
Therefore, in this embodiment, a frequency converter is provided for each of the oscillation frequencies f ₁ and f ₂ so that signals corresponding to the oscillation frequencies f ₁ and f ₂ can be separated and output by the circuit of the two-frequency Doppler module. Change to configuration.

FIG. 3 is a diagram showing a circuit configuration of the two-frequency Doppler module of the present embodiment.
In the high-frequency circuit module of the two-frequency Doppler device shown in FIG. 3, the antenna 17 is an antenna shared for transmission and reception that transmits the transmission signal Tx and receives the reception signal Rx.
In addition, the circuit on the receiving side is not different from the circuit configuration of FIG. 1 described above in that it has a frequency conversion unit in the front end unit, but in this embodiment, the oscillation frequencies f _{1 of the} two-frequency oscillators 11 and 12 are each. providing a frequency conversion unit corresponding to each f ₂ and.
The frequency converter provided for each of the oscillation frequencies f ₁ and f ₂ includes diodes 21 ₁ and 21 ₂ having nonlinear characteristics, and filters 23 ₁ and 23 ₂ connected to output terminals of the diodes 21 ₁ and 21 ₂ , respectively. It consists of open stubs 22 ₁ and 22 ₂ .
Here, the terminal of the signal output d including the Doppler signal is the output side of the filters 23 ₁ and 23 ₂ .

Further, in this embodiment, the circuit on the transmission side that transmits a continuous wave of two frequencies separates and outputs the signals corresponding to the oscillation frequencies f ₁ and f ₂ on the reception side, so that a single frequency conversion unit is provided. The configuration is such that the synthesizer and amplifier employed in the circuit configuration of FIG.
With the circuit configuration shown in FIG. 3, compared with the conventional circuit configuration illustrated in FIG. 4B, the transmission signal Tx can be transmitted without using many microwave and millimeter wave components such as a circulator and a lossy distributor. The transmission loss of the received signal Rx can be minimized and the high frequency circuit module can be reduced in size.

The effects obtained by the two-frequency Doppler module having the frequency conversion unit of this embodiment are as follows. ~ 11. Shown in
1. The high frequency module including the housing can be reduced in size.
2. Since expensive microwave and millimeter wave components such as circulators and distributors required by the conventional circuit (see FIG. 4) are not used, the cost can be reduced.
3. There is no need to consider a structure that avoids the intersection of the high-frequency transmission lines (the conventional transmission / reception antenna separation type shown in FIG. 4A is an example of avoiding the intersection of the high-frequency transmission lines).
4). In the concept of giving priority to transmission loss reduction over isolation resistance, it is not necessary to provide a distributor between the front end and the antenna, so transmission loss can be minimized and an amplifier to increase transmission power can be installed. Make it unnecessary.
5). 4. above. By eliminating the distributor described in (2), it is possible to suppress degradation of the noise figure due to transmission loss caused by the distributor during reception.

6). Since it is not necessary to use a plurality of amplifiers, power consumption can be suppressed, the housing thermal design is facilitated, and the failure rate can be reduced.
7). Since a circulator is not required, complicated mounting work can be saved.
The case design is facilitated by downsizing the 8.2 frequency Doppler module.
9. Since it is a transmission / reception integrated structure, there is no need to consider transmission leakage power from the receiving antenna.
10. In conventional heavy-duty modules such as circulators and distributors that use a lot of microwave and millimeter wave components, the printed circuit board area is large and the transmission line loss is large. However, the downsizing of the module reduces the board area. Thus, the loss of the transmission line can be minimized.
11. When a relatively short distance is used as a detection range (see FIGS. 2A and 2B), performance equivalent to or better than a distance detector of the reflected power detection type can be obtained.

11 ... oscillator (oscillation frequency _f 1), 12 ... oscillator (oscillation frequency _f 2), 14 ... synthesizer, 15 ... amplifier, 17 ... antenna, 21, 21 _1, 21 ₂ ... Diode, 22, 22 ₁ , 22 ₂ ... Open stub, 23, 23 ₁ , 23 ₂ ... Filter.

Claims (4)

A multi-frequency Doppler having a high-frequency circuit for simultaneously transmitting a large number of continuous waves of different setting frequencies from an antenna shared for transmission and reception and extracting a Doppler signal corresponding to the frequency from a reception signal of a reflected wave returning after transmission A device,
The multi-frequency Doppler device, wherein the high-frequency circuit has a single frequency conversion unit that mixes a reception signal and a transmission signal at an end directly connected to an antenna. The multi-frequency Doppler device according to claim 1,
The frequency converter comprises a diode and an open stub connected to the output terminal of the diode. The multi-frequency Doppler device according to claim 1 or 2,
The frequency converter comprises a diode and a filter connected to an output terminal of the diode. The multi-frequency Doppler device according to any one of claims 1 to 3,
The multi-frequency Doppler device, wherein the frequency converter is provided for each set frequency.

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