JPS63169584A - Device for identifying mobile body - Google Patents

Abstract

PURPOSE:To obtain a constant demodulation level by providing a high frequency detecting circuit between a circulator and an impedance matching circuit. CONSTITUTION:The high frequency detecting circuit which extracts the reflected wave of a high frequency signal, i.e. directional coupler 11 is provided between the circulator 3 and impedance matching circuit 10. Therefore, the state of matching with the circulator 3 while an antenna 4 is connected to the high frequency signal can be optimized by the circuit 10 while the output of the coupler 11 is monitored. Consequently, the reflected wave at the antenna varies either the phase nor amplitude of a local oscillation signal, so the constant demodulation level can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a moving object identification device having a high frequency transmitting/receiving circuit.

Conventional technology Recently, a device using high frequency waves has been reported as an identification device for vehicles and other moving objects, and it has the advantage of being able to achieve a longer identification distance than devices that use electric inductive coupling and light, and being resistant to environmental conditions and dirt. It is attracting attention as having the following advantages.

Hereinafter, a conventional mobile object identification device will be explained with reference to FIG.

In FIG. 3, 1 is a high-frequency signal generation source, 2 is a direct coupler that extracts a part of the high-frequency signal from the high-frequency signal generation source 1 as a local signal, 3 is a circulator that separates the transmitted signal and the received signal, and 4 is an antenna for transmitting and receiving high-frequency signals, 5 is a 90° power divider that distributes local signals with a 90° phase difference, 6 is an in-phase power divider that distributes received signals in the same phase, 7 .8 is a mixer that inputs the local oscillator signal and received signal from each divider 5.6, and 9 is a demodulator consisting of a 90° power divider 5, an in-phase power divider 6, and a mixer 7.8. It is.

The operation of the above configuration will be explained below.

First, a high-frequency signal generated by a high-frequency signal generation source 1 is amplified to a desired level using an amplifier (not shown) as necessary, and a part of the signal is extracted as a local signal using a directional coupler 2, and then the signal is output via a circulator 3. and transmits it from the antenna 4 as an interrogation signal. The interrogation signal is reflected by a transponder (not shown) as a modulated signal, and is again incident on the antenna and received as a response signal. The modulated received signal is obtained from a terminal one position adjacent in the remaining rotational direction of the circulator 3, and subjected to homodyne detection together with the local oscillation signal. However, for example, when the distance between the interrogator and the transponder changes, the amplitude of the demodulated signal changes in accordance with the change in the phase of the received signal relative to the local signal, and the amplitude becomes O at a certain phase. That is, there is a phenomenon in which the demodulated signal disappears. Therefore, here, the demodulator 9 is constructed from the in-phase power divider 6, the 90° power divider 5, and the mixer 7.8.
If the received signal distributed by the in-phase power divider 6 and the local oscillation signal distributed by the 90° power divider 5 are used as input to the mixer 7.8, and the squared sum value of each output is calculated, the received signal It is made to be a constant value regardless of the phase of .

The output of the mixer 7.8 then reaches the signal processing circuit,
Since it is not directly related, the explanation will be omitted here.

Problems to be Solved by the Invention However, in the above configuration, due to the mismatch between the circulator 3 and the antenna 4, the high-frequency signals that are reflected from the antenna 4 without being transmitted are not transmitted through the circulator 3 and are subjected to in-phase power distribution. mixer 7.8 (usually a balanced mixer is used in this conventional configuration)
Then, a linear combination occurs with the local oscillator signal distributed by the 90° power divider 5. As shown in Fig. 4, the local oscillation signal obtained by dividing the reflected signal by fR1 is ft, +, ft, 2
As a result of the linear combination, the phase and amplitude relationships change as fLI and fL, respectively, and using two local oscillation signals with a 90° phase difference, a constant demodulated output is always obtained regardless of the phase of the received signal. Unable to achieve initial objectives.

The present invention solves the above-mentioned conventional problems, and has two
The purpose is to maintain desired phase and amplitude relationships between two local oscillators and obtain a constant demodulation level.

Means for Solving the Problems The present invention provides an impedance matching circuit between a circulator and an antenna, and a line connected between the circulator and the impedance matching circuit or to a circulator terminal for extracting reflected signals from the antenna. The above object is achieved by providing a high frequency detection circuit for monitoring the reflected signal.

According to the above configuration, the present invention reduces the level of the reflected signal by adjusting the impedance matching circuit while monitoring the amount of reflection of the high frequency signal due to mismatching when the antenna is connected to the high frequency circuit using the high frequency detection circuit. In this way, the influence on the phase and amplitude of the local oscillator signal is minimized and a constant demodulation level is obtained.

EXAMPLE A first example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a high frequency circuit of an interrogator of a moving object identification device in a first embodiment of the present invention.

In FIG. 1, parts having the same functions as those in FIG. 3 are given the same numbers. 1 is a high-frequency signal generation source, 2 is a directional coupler that extracts a part of the high-frequency signal from the high-frequency signal generation source 1 as a local signal, 3 is a circulator for separating the transmission signal and the reception signal, and 4 is a circulator for separating the high-frequency signal from the high-frequency signal generation source 1. An antenna for transmitting and receiving, 5 a 90° power divider that distributes the signal from the directional coupler 2 with a 90° phase difference, and 6 an in-phase power divider that distributes the received signal in the same phase. vessel,
7.8 is a mixer that inputs the local oscillator signal distributed by the divider in 5.6 and the received signal, and is composed of a 90° power divider 5, an in-phase power divider 6, and a mixer 7.8. The demodulator has the same structure as that shown in FIG. 3. In Figure 1,
The difference from the configuration in FIG. 3 is that the impedance matching circuit 10
In addition, a high frequency detection circuit for extracting a part of the reflected wave of the high frequency signal from the antenna 4, that is, a directional coupler 11 is provided.

The operation of the above configuration will be explained below.

First, a high-frequency signal generated by a high-frequency signal generation source 1 is amplified to a desired level using an amplifier (not shown) as necessary, a part of it is extracted as a local signal by a directional coupler 2, and then the signal is transmitted via a circulator 3. , the interrogation signal is transmitted from the antenna 4 as an interrogation signal, but is reflected from the antenna 4 due to mismatch between the circulator 3 and the antenna 4. The interrogation signal is extracted from the directional coupler 11 and its level is monitored, and the level is determined to be the minimum. Impedance matching circuit 1 so that
Optimize 0.

On the other hand, the interrogation signal is reflected as a modulated signal by a transponder (not shown) and is again incident on and received by the antenna 4 (antenna) as a response signal.

The received signal reaches the in-phase power divider 6 via the circulator 3 and is distributed in the same phase, and then is sent to the mixer together with the local oscillator signal distributed by the 90° power divider 5 with a 90' phase difference. 7 or 8, homodyne detection is performed, and a demodulated signal is obtained. The demodulated signal becomes a constant value regardless of the phase of the received signal, for example, by calculating the squared sum value. The subsequent signal processing circuit is not directly related here, but the impedance matching circuit 10 monitors the output of the directional coupler 11 to check the coupling state with the circulator 3 with the antenna 4 connected to the high frequency circuit. As a result, the reflected wave from the antenna 4 does not change the phase and amplitude of the local signal, and as a result, a constant demodulated output level can be maintained regardless of the phase of the local signal and the received wave. Obtainable.

In addition, in the above explanation, the detection circuit (here, the directional coupling circuit 11) of the high frequency signal reflected from the antenna 4 due to mismatching is connected to the circulator 3 and the impedance matching circuit 1.
0, the high frequency detection circuit 11 may be provided between the circulator 3 and the in-phase coupler 6, as shown in FIG.

Effects of the Invention As described above, the present invention optimizes the matching state in a connected state between an antenna and a high-frequency circuit using an impedance matching circuit while monitoring the level of the reflected wave by a high-frequency detection circuit. By doing so, it is possible to eliminate the influence on the phase and amplitude relationship between two local oscillator signals having a phase difference of 90°, and to obtain a stable demodulated output, which is highly effective.

Fig. 2 is a block diagram of the main part of the identification device, Fig. 2 is a block diagram of the main part of the conventional displacement identification device, Fig. 4 is the phase and amplitude of the conventional local signal. FIG. 3 is a vector diagram showing how the signal changes depending on the reflected signal from the antenna.

1... High frequency signal generation source, 2... Directional coupler, 3
・、・Circulator, 4...Antenna, 5...90
°Power divider, 6... In-phase power divider, 7.8...
- Mixer, 9... Demodulator, 10... Impedance matching circuit, 11... High frequency detection circuit.

Name of agent: Patent attorney Toshio Nakao and one other person Figure 2 Figure 3

Claims (3)

[Claims] (1) An impedance matching circuit is provided between one terminal of the circulator and the antenna, and at least one of the lines is connected between the terminal of the circulator and the impedance matching circuit, or to the terminal next to the terminal in the rotating direction of the circulator. A moving object identification device characterized in that one of the devices is provided with a high frequency detection circuit. (2) The moving object identification device according to claim 1, wherein the high frequency detection circuit is a directional coupler. (3) The moving object identification device according to claim 1, wherein the high frequency detection circuit is a directional coupler in which a high frequency signal propagating from an antenna or an impedance matching circuit toward the circulator is amplified.