JPH04250725A - Diversity transmitter - Google Patents

Abstract

PURPOSE:To prevent coupling with plural antennas even when they are approached to each other in a small sized transmitter having the plural antennas, to avoid fluctuation in the antenna impedance caused thereby and to prevent the reduction in the antenna gain and the reduction in the radiation power from the antennas. CONSTITUTION:The transmitter is provided with switching circuits 4H, 4V allowing an antenna switching circuit 2 to select and antenna connected to a transmission circuit 3 among plural antennas 1H, 1V in the control of a control circuit 5 bringing only the selected antenna to be in resonance state with respect to a carrier signal and the other antenna to be in non-resonance state with respect to the carrier signal. Thus, even when the antennas 1H, 1V are arranged closely for the miniaturization of the transmitter, the antenna impedance is not fluctuated and the antenna gain is not reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity transmitter having multiple antennas.

0002

2. Description of the Related Art FIG. 2 is a block diagram of a conventional diversity transmitter. In the figure, 1H and 1V are loop antennas, 2
3 is an antenna switching circuit, 3 is a transmitting circuit, and 5 is a control circuit. Each loop antenna 1H, 1V resonates with the carrier frequency output from the transmitting circuit 3. The antenna switching circuit 2 selectively connects one of the antennas to the transmitting circuit 3 in a time-sharing manner under the control of the control circuit 5.

However, in this conventional example, all the antennas resonate with the carrier frequency output from the transmitting circuit 3, so when multiple loop antennas are brought close to each other for miniaturization, magnetic field coupling occurs, which causes Another problem is that the antenna impedance fluctuates, the antenna gain decreases, and the radiated power from the antenna also decreases.

0004

[Problems to be Solved by the Invention] The present invention has been made in view of the above points, and its purpose is to provide a compact transmitter equipped with a plurality of antennas. It is an object of the present invention to provide a diversity transmitter in which there is no change in antenna impedance even when the antenna approaches, and a reduction in antenna gain and radiation power from the antenna can be prevented.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the diversity transmitter of the present invention, as shown in FIG. , a transmitter comprising an antenna switching circuit 2 for selecting an antenna to be connected to the transmitting circuit 3 from among the plurality of antennas 1H and 1V, and a control circuit 5 for controlling the switching operation by the antenna switching circuit 2. A switch circuit 4H that sets an antenna connected to the transmission circuit 3 via the circuit 2 into a resonant state with respect to the carrier wave signal, and sets other antennas into a non-resonant state with respect to the carrier wave signal.
, 4V.

[0006]

[Operation] The operation of the present invention will be explained with reference to FIG. In this transmitter, when the antenna 1H is connected to the transmitting circuit 3 via the antenna switching circuit 2 under the control of the control circuit 5, the transmitting antenna 1H is set to a resonant state by the switching circuits 4H and 4V, and the other antenna 1H is connected to the transmitting circuit 3 via the antenna switching circuit 2. is in a non-resonant state. Also, when the antenna 1V is connected to the transmitter circuit 3,
The switch circuits 4H and 4V bring the transmitting antenna 1V into a resonant state and put the other antenna 1H into a non-resonant state. Therefore, even if the antennas 1H and 1V are placed close to each other, the antenna gain will not decrease due to magnetic coupling.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a schematic configuration of a diversity transmitter 6 according to the present invention. This transmitter 6 includes a pair of antennas 1H and 1V, an antenna switching circuit 2 that selects which antenna to transmit from, a transmitter circuit 3 that generates a transmission output, and a switch that turns ON/OFF the antenna operation. It includes circuits 4H and 4V, and a control circuit 5 that controls the antenna switching circuit 2 and the switch circuits 4H and 4V.

[0008] Here, the loop antennas 1H and 1V are formed in a loop shape with one open end, and one point of the open end is used as a grounding point, and the other point is used as a feeding point. Further, a tuning capacitor is connected in parallel to the open end of each loop antenna 1H, 1V, and a switch circuit 4H, 4V is connected in parallel to this tuning capacitor. When one loop antenna is placed in a resonant state, the switch circuit of that loop antenna is controlled to be OFF, and the switch circuit of the other loop antenna is controlled to be ON. This results in
The other loop antenna becomes non-resonant. Transmission circuit 3
The signal outputted by is transmitted by the antenna switching circuit 2 using either a 1H or 1V antenna. For example, if the antenna switching circuit 2 connects the transmitting circuit 3 to the loop antenna 1H by the control circuit 5, at the same time, the switching circuit 4H connects the transmitting circuit 3 to the loop antenna 1H.
is turned off so that it is in a resonant state where it can transmit, and the switch circuit 4V is turned on so that the loop antenna 1V is in a non-resonant state.

FIG. 3 shows the circuit configuration of a specific embodiment of the diversity transmitter of the present invention. Each of the antennas 1H and 1V is a loop antenna, and as shown in the figure, tuning capacitors C1 and C4 are connected between the open ends of the loop antennas 1H and 1V, which are open at one end. Bypass capacitors C2 and C3 whose capacitance values are set to have sufficiently low impedance to
A series circuit with is connected. In addition, diodes D1 and D4 are connected in parallel with the tuning capacitors C1 and C4.
are connected to each other, and these are connected to the switch circuit 4H.
, is used as 4V. Each diode D1, D4
may be configured with a PIN diode, for example.

FIG. 4 is an equivalent circuit diagram of the loop antenna 1H. Loop antenna 1H and both capacitors C1 and C2
A power feeding point a and a grounding point b are provided at two points of a loop circuit consisting of. Here, feeding point a and grounding point b are provided with capacitor C2 in between, and grounding point b is provided between both capacitors C1.
, C2. A capacitor Cs is connected to the feeding point a.
The output signal from the signal source Vs of the transmitting circuit 3 is inputted through the signal source Vs of the transmitting circuit 3. A diode D1 is connected in parallel to the capacitor C1 with its cathode connected to the ground point b, and a switch signal line L for applying a bias current is connected to the anode of the diode D1 via a bias resistor R4 and a loop antenna 1H. connected. Therefore, the capacitor C2 has a function of cutting DC between the switch signal line L through which the bias current flows to the diode D1 and the ground point b. Bias resistor R4 is diode D1
The impedance is set so high that the high frequency signal leaking through the switch signal line L can be ignored.

[0011] The antennas 1H and 1V configured in this way
Now, when the switch signal input terminal S is open or at zero potential, no bias current flows through the diode D1, so the impedance of the diode D1 exhibits capacitance of about several pF with little loss. Therefore, it can be considered that a capacitor with the equivalent capacitance of the diode D1 is connected in parallel to the tuning capacitor C1, and if the combined capacitance at this time is considered as C0, the equivalent circuit for a high-frequency signal is shown in Figure 5. It becomes as follows, and the composite capacitance C0
If it is set so that it can be tuned to the value of , it will operate as a small loop antenna. The above is an operation when the antenna 1H is in a resonant state and the switch circuit 4H made of the diode D1 is in an OFF state.

On the other hand, when a predetermined voltage is applied to the switch signal input terminal S, a bias current flows through the diode D1, and the impedance of the diode D1 becomes equivalent to a small resistance and a small inductive reactance. therefore,
Since the combined capacitance C0 deviates from the capacitance value that allows tuning, and a resistor of a small value is connected in parallel to the capacitor C1, the loss of the loop circuit increases and the operation as an antenna almost stops. The above is antenna 1
The operation is performed when H is in a non-resonant state and the switch circuit 4H made up of the diode D1 is in the ON state.

Similarly, for the other antenna 1V, the switch circuit 4V can be turned on and off by turning on and off the bias current flowing through the diode D4 via the bias resistor R5. Note that the bias resistor R5 is applied with a voltage obtained by inverting the voltage at the switch signal input terminal S by the inverter gate G, so when the switch circuit 4H is ON, the switch circuit 4V is OFF.
F, and when the switch circuit 4H is OFF, the switch circuit 4V is ON.

Next, the configuration of the antenna switching circuit 2 is shown in FIG. 6, and its relationship with the operations of the switching circuits 4H and 4V will be explained. Now, the control signals from the control circuit 5 are at two points P1 and P2.
, High level (3.5V), L
If it is OW level (0V), antenna switching circuit 2-3
The levels at points P3, P4, and P5 are such that P3 is Hi.
gh, P4, and P5 become Low. Therefore, diode D2 is forward biased, diode D3 is reverse biased, and diode D2 is turned on. Resistance R1,
When R2 and R3 are set to very large values compared to the antenna input impedance, the transmission output does not flow to the control circuit 5, but flows to the antenna 1H through the diode D2, and is transmitted. At this time, since the antenna 1H is in a resonant state and the antenna 1V is in a non-resonant state, the antennas 1H, 1
No magnetic coupling occurs between Vs. Conversely, when P1 is low level and P2 is high level, diode D
3 is turned ON, and the transmission output flows to the antenna 1V. At this time, since the antenna 1H is in a non-resonant state and the antenna 1V is in a resonant state, no magnetic coupling occurs between the antennas 1H and 1V. In addition, capacitors C5, C6, C7
is a coupling capacitor that cuts the bias DC signal component and passes only the high frequency signal component.

[0015]

[Effects of the Invention] In the diversity transmitter of the present invention, among the plurality of antennas, only the antenna connected to the transmission circuit by the antenna switching circuit is in a resonant state with respect to the carrier frequency, and the other antennas are in a non-resonant state. Therefore, even if the antennas are placed close to each other to reduce the size of the transmitter, magnetic field coupling does not occur, the antenna impedance does not change, so the antenna gain does not decrease, and the radiated power from the antenna does not decrease. can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the present invention.

FIG. 2 is a block diagram of a conventional example.

FIG. 3 is a circuit diagram of an embodiment of the present invention.

FIG. 4 is a circuit diagram of a switch circuit used in one embodiment of the present invention.

FIG. 5 is an equivalent circuit diagram of a loop antenna used in an embodiment of the present invention.

FIG. 6 is a circuit diagram of an antenna switching circuit used in an embodiment of the present invention.

[Explanation of symbols]

1H Loop antenna 1V loop antenna 2 Antenna switching circuit 3 Transmission circuit 4H Switch circuit 4V switch circuit 5 Control circuit 6 Transmitter

Claims (1)

[Claims] 1. A plurality of antennas, a transmission circuit that outputs a carrier signal, and an antenna switching circuit that selects an antenna to be connected to the transmission circuit from among the plurality of antennas.
In a transmitter that includes a control circuit that controls switching operations by an antenna switching circuit, the antenna connected to the transmitting circuit via the antenna switching circuit is set in a resonant state with respect to a carrier signal, and the other antenna is set to a resonance state with respect to the carrier signal. A diversity transmitter characterized by being provided with a switch circuit that brings the device into a non-resonant state.