JP2628892B2 - Microwave modulator and moving object identification system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave modulator and a mobile object identification system in a response device of a mobile object identification system that transmits and receives data at a relatively short distance by using microwaves. .

2. Description of the Related Art In recent years, a moving object identification system in a microwave band has been widely used for management of parts in a factory or for gate control and entry / exit supervision by allowing a person to have a transponder. The response device of the mobile identification system is particularly lightweight,
It is required to be small and inexpensive.

Conventionally, as a microwave mobile object identification system, there is a system provided with an inquiry device 7 and a response device 8 as shown in FIG. In this interrogation device 7, the frequency f generated by the oscillator 701
The non-modulated wave of ₀ is split into two by a splitter 702, and one of the split is radiated as an interrogation signal from a transmission / reception antenna 704 via a circulator 703 to the above-mentioned response device, and the other is a local oscillation source for homodyne detection. As mixer 70
Sent to 5. In the above-mentioned response device 8, the built-in data is digitally frequency-modulated (FS
K) or amplitude modulation (ASK) or the like, and the interrogation signal received by the transmission / reception antenna 801 by the modulated signal is modulated by the modulator 802 including a diode or the like, and is interrogated as a response signal by the transmission / reception antenna 801. It is re-emitted to the device 7. The response signal re-radiated to the interrogator 7 is received by the transmitting / receiving antenna 704 and reaches the mixer 705 through the circulator 703. The mixer 705 demodulates the data by a signal processing unit 706 that performs homodyne detection on the oscillator 701 as a local oscillation source. When the interrogation device 7 is a homodyne system, the answering device 8 is usually used.
The AM or the PM method can be considered as the modulation method of. Hereinafter, the relationship between the homodyne detection output of the interrogator 7 and the modulation method of the responder 8 will be described in detail. In FIG. Is input to the response device 8, that is, an interrogation signal (unmodulated wave)
Then, the operation according to the modulation signal is performed by the modulator 802,
Response signal from transmit / receive antenna Re-emitted. Such a modulator 802 is called a reflection type, and in this principle a response signal Are both input signals Not exceed the size of The modulation signal is a pulse signal that is amplitude-modulated (ASK) or frequency-modulated (FSK) with built-in data, and is a response signal. Are reflected waves at high potential (for example, 3 V) and low potential (for example, 0 V) of the modulation signal. This response signal Is received by the transmitting / receiving antenna 704 of the interrogating device 7,
The signals entering the mixer 705 through the circulator 703 are respectively And Also, the local oscillation signal in the interrogator 7 is Then Is as shown in FIG. However, The size of each Proportional to the size of The angle made When Is equal to the angle between Also, the local oscillation signal Varies depending on the distance between the interrogating device 7 and the answering device 8, but here, the description will be made assuming that the distance is constant.

V _l = V _l sin (ωt + θ ₂ ) (1) Here, ω = 2πf, where f is the interrogation signal (unmodulated wave)
Frequency.

The homodyne detection output performed in the interrogator 7 is a local oscillation signal. And signal Is the inner product of Therefore, The homodyne detection output corresponding to In Equations (4) and (5), the second term is removed by a high-frequency cutoff filter or the like, so that the homodyne detection voltage
Assuming that peak-to-peak is Vdet, from equations (4) and (5) and FIG. Here, V _ON cos θ _ON −V _OFF cos θ _OFF = K cos α (7) V _ON sin θ _ON −V _OFF sin θ _OFF = K sin α (8) Becomes Where K and α are Than, On the other hand, (Kcosα) ² + (Ksinα) ² = K ² Becomes

In order to increase the output Vdet of such homodyne detection, the magnitude (V _l ) of the local oscillation signal is obtained from equations (9) and (11).
Is constant, V _ON and V _OFF are maximized, and θ _ON −θ
_OFF = π It turns out that it is sufficient to make them face in opposite directions.
Here, the angle α in Expression (9) is represented by Expression (10), Is determined uniquely.

Therefore, the reflected wave transmitted from the response device 8 And the reflected wave Are set in opposite directions (phase difference = π), Vdet can be increased. That is, this means that the interrogation signal (non-modulated wave) is substantially 0-π phase modulated (PSK) by the modulated signal from the signal processing unit 803.

However, in the moving object identification system shown in FIG. 7, when the distance between the interrogating device 7 and the responding device 8 changes, a signal input to the mixer 705 of the interrogating device 7 changes. The amplitudes V _ON and V _OFF and the phases θ _ON and θ _OFF also change, When (n = 0, 1, 2,...), The homodyne detection output becomes Vdet = 0 from equation (9). That is, the demodulation output disappears, and there is a big problem that the system does not operate at this distance.

In addition, it has been impossible to achieve both low power consumption of the response device and increase in the phase difference (π) of the reflected wave from the response device.

Means for Solving the Problems In order to solve the above problems, the present invention uses a homodyne detection method of two systems as an interrogator.

Furthermore, an impedance conversion circuit composed of a microwave modulator of the transmission line and the length L ₂ of the length L ₁ open-end parallel lines of response units to this, a diode that changes in barrier capacity depending on the applied voltage, the A bias supply circuit for applying a modulation signal to the diode is provided. One end of the transmission line (length L ₁ ) has a transmitting / receiving antenna and the open-ended parallel line (length L ₂ ) at the other end, and The diode and the bias supply circuit are connected, and the impedance conversion circuit is adjusted so that the phase difference between the reflection coefficient when the voltage applied to the diode is high and the reflection coefficient when the voltage applied is low is approximately π or in the vicinity thereof. I am trying to be.

The interrogation signal, which is an unmodulated wave input from the transmission / reception antenna of the transponder, is modulated by a diode with a signal that is frequency-modulated or amplitude-modulated by the built-in data in the signal processing unit. The response signal is such that the phase difference between the reflection coefficient at the time of the high potential and the reflection coefficient at the time of the low potential is approximately π or in the vicinity thereof, and is re-emitted from the transmitting / receiving antenna toward the interrogator. Therefore, a good 0-π phase modulator is constructed.

Further, the voltage applied to the diode from the bias supply circuit does not make the diode conductive.

Embodiment FIG. 1 is a block diagram of an embodiment of a transponder provided with a modulator according to the present invention and an interrogator transmitting an interrogation signal to the transponder and receiving a response signal from the transponder. First, the interrogation device will be described.

In the figure, reference numeral 1 denotes an interrogator, which is configured to perform two-system homodyne detection. Oscillator 101 that generates a signal of frequency f ₀ is connected to circulator 103 and distributor 106 via distributor 102, and circulator 103 is connected to transmitting / receiving antenna 104 and distributor 105. One output of each of the distributors 105 and 106 is guided to a mixer 107, and the other output is guided to a mixer 108, and the homodyne detection output is detected by the two mixers.
X and Y are demodulated by the signal processing unit 109 and extracted as a received signal. Therefore, in the interrogation device 1, the unmodulated wave of the frequency f0 generated by the oscillator 101 is divided into two by the distributor 102, and one of the distributed _ones will be described later as an interrogation signal from the transmitting / receiving antenna 104 via the circulator 103. It is radiated to the response device 2. The other signal split by splitter 102 enters splitter 106 and has two signals having equal amplitude and a phase difference of 90 °.
And distributed to the mixers 107 and 108. The response signal from the response device 2 is a transmission / reception antenna
After being received by the signal 104 and passing through the circulator 103, the signal is divided by the divider 105 into two signals having the same amplitude and the same phase, and reaches the mixers 107 and 108, respectively. Then, the mixers 107 and 1
In 08, homodyne detection is performed, and two outputs, X and Y, are obtained. These two outputs are equal-amplitude signals having a phase difference of 90 ° from each other, and can be expressed as follows by using equation (9).

Here, α and K are expressed by equations (10) and (11), respectively.
Since θ _l −α and K in equations (12) and (13) change according to the distance d between the interrogating device 1 and the answering device 2, the distance d
FIG. 2 schematically shows the relationship between the two homodyne detection outputs X and Y. As can be seen from the figure, X and Y each produce a zero point for every quarter wavelength, but do not become zero at the same time. That is, when X = 0, Y is the maximum positive or negative value, and information is always stored in either X or Y. Therefore, two systems of homodyne detection output
After separately demodulating X and Y in the signal processing unit 109, respectively,
Taking advantage of the fact that one of the outputs does not become zero,
Data is demodulated correctly. As described above, if two systems of homodyne detection having phases shifted from each other by 90 ° are performed, the system can always be operated regardless of the distance between the interrogator 1 and the responder 2.

Next, the modulator of the present invention used in the response device will be described in detail.

The first figure 2 a response unit, the response unit 2 and the transmission line 202 and an open end parallel lines 203 of a length L ₂ of the length L ₁ connected to the transmission and reception antenna 201 and the antenna, the transmission It comprises a diode 204 whose barrier capacitance changes according to an applied voltage connected to the line 202, a bias supply circuit 205 for applying a modulation signal to the diode 204, and a signal processing unit 206 connected to the bias supply circuit 205. . The modulator 20 of the present invention includes the transmission line 202,
The transmission line 202 and the open-ended parallel line 203 form an impedance conversion circuit of the microwave modulator 20. In order to realize a 0-π phase modulator, it is necessary to know the impedance when the voltage applied to the modulation diode 204 is a high voltage (for example, 3 V, but reverse bias) and when the voltage is low (for example, 0 V). is there. Figure 3 shows a Schottky barrier diode (1ss9) often used in the microwave band.
9) Measures the applied voltage dependence of the impedance (reflection coefficient) at 2.45 GHz.

It can be seen from the figure that the barrier capacitance decreases as the reverse bias increases. However, the resistance is hardly changed. Table 1 shows the admittance and the reflection coefficient of the diode (1ss99) at the applied voltage of 0 V and 3 V for the normal value.

In addition, the phase difference between the reflection coefficients when the bias is 0 V and when the reverse bias is 3 V is 42.2 ° from the figure. Therefore, if a modulation signal (0v and 3v) is applied as it is, a good 0-π phase modulator cannot be obtained. To make this a good 0-π phase modulator, adjust the impedance conversion circuit consisting of the transmission line 202 and the open-ended parallel line 203 to adjust the reflection coefficient when the applied voltage is high. And reflection coefficient at low voltage May be made substantially π.

in this way Various combinations of the lengths L ₁ and L ₂ of the transmission line 202 and the open-ended parallel line 203 that make the phase difference of approximately π are conceivable. Table 2 shows an example.

In addition, in the case of each impedance conversion circuit, the reflection coefficient Is shown on the Smith chart in FIG.

From the figure, the reflection coefficient for these combinations of L ₁ and L ₂ lengths It can be seen that the phase difference is substantially π. When using this diode (1ss99) The reflection coefficient of the upper limit of the length of L ₁ to the phase difference is approximately π when the modulation signal is a high potential (3 v) of The admittance conductance g represented by is g1.
In this case, L ₁ = 0.145λg. As a result, when the diode 1ss99 is used, L ₁ and L ₂ are respectively L ₁ = 0.062λg0.145λg (14) L ₂ = 0.300λg to 0.360λg (15) (λg: wavelength in the dielectric substrate) If you choose from the range of Can be made approximately π, and Can be increased. As a result, it becomes possible to increase the homodyne detection output Vdet in the interrogator. In this modulator, since no forward current flows through the diode, the consumption of the internal battery of the response device can be significantly reduced.

Next, FIG. 5 shows the applied voltage dependence of the impedance of another diode (1sv183) widely used in the microwave band. The phase difference between the reflection coefficient of this diode (1sv183) at the time of high potential (3v of reverse bias) and the time of low potential (0v) is about 20 ° from the figure. Therefore, the modulation signal (0v
/ 3v) does not result in a good 0-π phase modulator. Therefore, the length L ₁ of the transmission line 202 and the open-ended parallel line 203
Assuming that the length L ₂ is, for example, L ₁ = 0.37λg and L ₂ = 0.305λg, as shown in FIG. Is 195 °, and a phase modulator of almost 0-π can be realized.

Effects of the Invention According to the present invention, therefore, it is only necessary to appropriately adjust the impedance conversion circuit for a diode whose barrier capacitance changes in accordance with the applied voltage, and it is possible to obtain an approximately 0-
A phase modulator of π can be configured, and the homodyne detection output of the interrogator can be increased. Also, if the interrogator performs homodyne detection of two systems with phases different from each other by 90 °, good communication will always be performed regardless of the distance even if the distance between the interrogator and the responder changes. Becomes possible.

Further, in the microwave modulator of the present invention, since no forward current flows through the diode, the consumption of the built-in power supply of the response device is extremely reduced, the life of the built-in power supply is significantly extended, and the built-in power supply is downsized. Is realized, and a light-weight, small-sized, and inexpensive response device can be realized. Therefore, a mobile object identification system that is inexpensive, has a wide field of application, and has very good characteristics is constructed.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a moving object identification system using the present invention, FIG. 2 is an explanatory diagram of a homodyne detection output of two systems, and FIG. 3 is a graph showing an applied voltage dependency of an impedance of a diode (1ss99). FIG. 4, FIG. 4 is a characteristic diagram of an embodiment of the modulator of the present invention, FIG. 5 is a diagram showing the applied voltage dependency of the impedance of the diode (1sv183), and FIG. 1sv183) Characteristic diagram when using 7th
FIG. 1 is a configuration diagram of a conventional example of an interrogation device and a response device, and FIG. 8 is an explanatory diagram of homodyne detection output. 1 ... Interrogator, 2 ... Responder, 20 ... Modulator, 201 ...
Transmission / reception antenna, 202: transmission line, 203: open-ended parallel line, 204: diode, 205: bias supply circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-123381 (JP, A) JP-A-63-75584 (JP, A) JP-A-63-121773 (JP, A) JP-A-1- 199185 (JP, A) Actually open 1986-195623 (JP, U)

Claims (2)

(57) [Claims] 1. A interrogation signal to a microwave modulator responsive device for re-emitted as a response signal by modulating the receiving internal organs data by the antenna, open-end of the transmission line and the length L ₂ of the length L ₁ An impedance conversion circuit composed of a parallel line, a diode whose barrier capacitance changes in accordance with an applied voltage, and a bias supply circuit for applying a modulation signal to the diode are provided, and one end of the transmission line connected to the antenna. Is connected to the open-ended parallel line, the other end is connected to the diode and the bias supply circuit, and the voltage applied to the other end is a voltage within a range for reverse-biasing the diode, and the length of the line is is this applied voltage of L ₁ and L ₂ the diode is a phase difference of the reflection coefficient when the reflection coefficient and a low voltage when the high voltage is chosen such schematic π or becomes near Microwave modulator, characterized in. 2. The interrogator emits an interrogation signal, modulates the interrogation signal received by the antenna by a microwave modulator of the responder, and re-radiates the interrogator as a response signal.
In the mobile identification system the inquiry device performs homodyne detection of the phases of the reply signal is [pi / 2 different two systems, the microwave modulator, the transmission line and the length L ₂ of the length L ₁ tip opening An impedance conversion circuit comprising a parallel line;
A diode whose barrier capacitance changes according to an applied voltage, and a bias supply circuit for applying a modulation signal to the diode; the open-ended parallel line at one end of the transmission line connected to the antenna; the end connected to the diode and the bias supply circuit, that the voltage applied to the other end is a voltage in the range of reverse bias the diode, and the line length L ₁ and L ₂ is the diode A moving object identification system characterized in that a phase difference between a reflection coefficient when a voltage applied to the substrate is high and a reflection coefficient when the voltage is low is approximately π or in the vicinity thereof.