JPS638578A - Responder and identification of moving body - Google Patents

Abstract

PURPOSE:To increase the service time of a portable responder with the realization of an amplitude modulator extremely low in the power consumption, by mounting a variable capacity diode on an oscillator connected to an antenna to vary oscillation frequency with voltage of a modulation signal. CONSTITUTION:An antenna 12 is connected to an oscillator 14 directly or through a connection path while a varactor diode 15 is mounted on the oscillator 14 to vary the oscillation frequency with voltage of a modulation signal and a nonmodulation wave to be inputted from the antenna 12 is subjected to an amplitude modulation to be reradiated. With such an arrangement, the capacitance across terminals of the varactor diode 15 varies with the voltage levels VH and VL at a modulation input terminal 19 but little current flows because of a reverse bias. In addition, the oscillation frequency varies with changes in the capacitance thereby allowing the impedance of the oscillator viewed from the antenna 12 to change to the position A for the voltage level VL and the position B for the voltage level VH as shown by the Smith's chart.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a low power consumption transponder for mobile object identification.

Conventional technology A mobile object identification device is a device that emits electromagnetic waves (usually in the microwave band) from a fixed interrogator toward a moving object, and uses a passive transponder installed on the moving object to emit electromagnetic waves (usually in the microwave band). modulates the incident wave, sends the reflected wave back to the interrogator, detects the modulated reflected wave, and reads the information sent from the mobile object.

Characteristics required of the transponder include a high degree of modulation, a small and simple circuit, and low power consumption.

FIG. 4 shows the basic configuration of a conventionally known transponder.

In FIG. 4, 41 is an antenna that receives an incident wave ei from the interrogator and emits a reflected wave (modulated wave) er. 4
2 and 43 are transmission lines of IJ tube lines, 44 is a switching or PIN diode, and 45 is a terminating resistor. 46 and 47 are inductors, and 48 is a capacitor, and these 46, 47, and 48 form a low-pass filter. Further, 49 is a modulation input terminal.

Now, a rectangular wave modulation input of vH and vL levels is applied from the modulation input terminal 49, and the voltage level Vll is set so that the diode 44 conducts at voltage level vH and becomes low impedance, and turns off at voltage level vL and becomes high impedance. v
Set the level of , . At this time, when the voltage level is VH, almost all the energy of the input wave e1 is absorbed by the terminating resistor 45, and no reflected wave is generated. Further, in the case of voltage level vL, almost all of the input wave e1 is reflected by the diode 44, and the reflected wave is radiated from the antenna 41.

Therefore, the level of the reflected wave e' is the voltage level VH.

It can be seen that the wave is amplitude modulated according to VL.

Problems to be Solved by the Invention However, as mentioned above, one of the characteristics required of the transponder is low power consumption, and the configuration shown in FIG. 4 uses a switching diode or Since a PIN diode is used, it is necessary to increase the bias current of the diode 44 in order to reduce the ON resistance.

Especially when the transponder is powered by a battery, the ON current of this diode 44 almost determines the power consumption of the transponder, so reducing the power consumption of the modulation circuit is an urgent requirement for portable transponders. This is a problem to be solved.

In view of the drawbacks of the prior art described above, the present invention provides a mobile body identification transponder with low power consumption.

Means for Solving the Problems The present invention couples the antenna and the resonator directly or through a connection, and also equips the resonator with a variable capacitance diode to change the resonant frequency according to the voltage of the modulation signal. It applies amplitude modulation to the unmodulated wave input from the antenna and causes it to be re-radiated.

Function: With the above configuration, the present invention does not utilize a change in resistance value due to a change in forward current of a diode as in the past, but uses a diode barrier capacitance due to a voltage change during reverse bias of a variable capacitance diode (varactor diode). This is an attempt to reduce power consumption by utilizing changes in .

Embodiment FIG. 1 shows a plan view of the main part of a transponder for identifying a mobile object in a first embodiment of the present invention.

In FIG. 1, 11 is a dielectric substrate that constitutes the RF' section of the transponder, 12 is a slot antenna, 13 is a strip line, 14 is a strip line resonator, 15 is a modulating varactor diode, and 16 is an LPF. (low-pass filter), 19 is a modulation input terminal, and 20 is a ground conductor.

Still, 21 is the slot antenna 12 and Su.

This is a through hole for connecting the trip line 13.

In this embodiment, the antenna is the slot antenna 12, but the antenna may be realized by other methods.Although the resonator 14 and the antenna 12 are still coupled via the strip line 13, there is no problem even if they are coupled directly. do not have.

In addition, the strip line 13 and the resonator 14 are coupled at the parallel portion, and by changing the gap between the two lines,
You can cook up the size of the bond.

According to the above configuration, the inter-terminal capacitance of the varactor diode 15 changes with the voltage level vHvL of the modulation input terminal 19, but since it is biased in the reverse direction, almost no current flows. Also, since the resonant frequency changes as the capacitance changes, the impedance of the resonator exposed from the antenna 12 is determined by the voltage level
When the voltage level is L, it can be changed to the position A, and when the voltage level is VH, it can be changed to the position B. That is, at VL, almost all the incident wave from the antenna 12 is not absorbed by the resonator 14 and is re-radiated from the antenna 12, but at vH, almost all the incident energy can be absorbed by the resonator 14. It can be understood that the reflected wave from the transponder becomes an amplitude modulated wave.

By combining the varactor diode 15 and the resonator 14 in this way, an amplitude modulator with extremely low power consumption can be realized, and the usage time of the portable transponder can be greatly extended.

FIG. 3 shows another embodiment of the invention. Third
Figure (a) uses a ring resonator 14 as a resonator, and the LPF 16 is made into a lumped constant. In addition, in the figure, 31 is an RF choke, and the resonator 14 and the strip line 13 are coupled in parallel.

On the other hand, in FIG. 3(b), both the resonator 14 and the LPF 16 are lumped constants, which is suitable for miniaturization. In addition, in the figure, 32 indicates the resonator 14 and the strip line 1.
The coupling capacity is 3.

Effects of the Invention As described above, the present invention applies a reverse bias to a diode and performs two-way modulation, and because it achieves low power consumption, it provides an extremely effective means for making the transponder portable. So, there is something called dog that has industrial value.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a transponder for mobile object identification in the first embodiment of the present invention, FIG. 2 is a Smith chart showing the characteristics of the configuration of FIG. 1, and FIGS. FIG. 4 is a plan view of a moving object identification transponder according to another embodiment of the present invention, and FIG. 4 is a plan view of a conventional moving object identification transponder. 11... Dielectric substrate, 13... Strip line ,1
4...Resonator, 15...Varactor diode, 1
6...L P F (low pass filter), 19...
Modulation input terminal. Name of agent: Patent attorney Satoshi Nakao and one other person Figure 1

Claims (1)

[Claims] The antenna and the resonator are coupled directly or through a connection, and the resonator is equipped with a variable capacitance diode to change the resonant frequency depending on the voltage of the modulation signal, thereby applying amplitude modulation to the unmodulated wave input from the antenna. A transponder for mobile object identification that emits light and re-radiates.