JPH0522202A - Space diversity circuit - Google Patents

Abstract

PURPOSE:To realize the small sized and economical space diversity circuit by forming the circuit with only two amplifiers having AGC and simplifying the circuit. CONSTITUTION:The space diversity circuit of a system in which both reception signals of a microwave main reception system and a microwave diversity reception system are synthesized in phase at an IF band is provided with a 1st AGC amplifier 2A compensating an input level fluctuation of the main reception system, a 2nd AGC amplifier 2B compensating input level fluctuation of the diversity reception system, variable attenuators 3A, 3B connecting respectively to the outputs of the 1st and 2nd AGC amplifiers, and a control circuit 1 varying the attenuation of each variable attenuator based on the gain control voltage of the 1st and 2nd AGC amplifiers, and the control circuit controls the attenuation of the variable attenuator of a relevant reception system so as to be increased corresponding to the gain control voltage of the reception system whose reception input level is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IF band in-phase combining type space diversity circuit used in a microwave radio transmitter / receiver.

[0002]

2. Description of the Related Art In a conventional IF band in-phase combining type space diversity circuit used in a microwave radio transmitter / receiver or the like, a receiving system connected to a main antenna 4A is converted to an IF frequency as shown in FIG. Converter 5A, receiving local oscillator 7, hybrid 9A for two branches of IF signal, AG
It is composed of an amplifier 2A with C. On the other hand, the receiving system connected to the diversity antenna 4B includes the converter 5B, the hybrid 9B, and the amplifier 2B with AGC. Further, a phase detector 8 for detecting a phase difference between the outputs of the amplifiers 2A and 2B with AGC for the IF band in-phase synthesis, a phase shifter 6 for changing the phase of the local oscillation signal based on the phase difference signal, It is composed of a hybrid 10 for synthesis for performing IF synthesis and amplification, and an amplifier 2C with AGC. The operation of the conventional space diversity circuit of the IF in-phase combining method is performed in order to compensate the fluctuation of the reception input level due to the fading of the main and space diversity reception waves.
The amplifiers 2A and 2B are provided, and the phase detector 8 compares the phases of the input signals from both antennas at the outputs. Based on the result of the phase comparison, the phase of the signal from the receiving station of the space diversity receiver is controlled by the phase shifter 6 to perform in-phase combining in the IF band. In order to perform in-phase synthesis, it is necessary to perform synthesis by the hybrid 10 before gain control by the amplifier 2C with AGC. If they are combined after gain control, the gain on the low input level side increases and this AG
The thermal noise included in the output signal of the amplifier with C also increases. Since this is combined, it becomes a factor of deteriorating the signal-to-noise ratio of the combined output. Therefore, the combined output is amplified before gain control as shown in FIG. The extracted IF signal was taken out.

[0003]

The above-mentioned conventional space diversity circuit requires three amplifiers with AGC, so that it has a large size and the structure as a diversity device is expensive.

[0004]

The space diversity circuit of the present invention is a space diversity circuit of the type in which both reception signals of a microwave main reception system and a diversity reception system are in-phase combined in the IF band. A first amplifier with AGC for compensating for fluctuations, a second amplifier with AGC for compensating for input level fluctuations in a diversity receiving system, and variable attenuators connected to the outputs of the first and second amplifiers with AGC, respectively. A control circuit for changing each of the variable attenuators based on the gain control voltages of the first and second amplifiers with AGC, corresponding to the gain control voltage of the receiving system in which the receiving input level is lowered. Then, control is performed so as to increase the attenuation amount of the variable attenuator of the receiving system.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention. 1, the same reference numerals as those in the conventional example of FIG. 2 have the same functions and configurations. That is, in this embodiment, the AGCs of the amplifiers 2A and 2B with AGC of the main receiving system and the diversity receiving system are respectively.
A variable attenuator 3A, which receives a voltage and is attached to the output sections of the main receiving system and the diversity receiving system, which will be described later,
The control circuit 1 which controls 3B is provided.

Next, the operation of this embodiment will be described. The input level difference between the main reception wave and the diversity reception wave is the same for both AGCs.
It is detected by inputting the voltages 1A and 1B to the control circuit 1. Therefore, the control circuit 1 controls the variable attenuators 3A and 3B so as to increase the attenuation amount on the low input level side. When one of the reception input levels decreases, the gain of the AGC amplifier in the reception system increases, and the IF output level operates so as to be a constant level, but the thermal noise output level also increases. However, as described above, the attenuation amount of the variable attenuator 3A or 3B is increased in accordance with the AGC voltage, and the IF level on the side where the reception input is high is mainly output. Therefore, the thermal noise level input to the in-phase combiner can be attenuated, and the deterioration of the thermal noise as a whole can be prevented.

[0007]

As described above, according to the present invention, I
Since the F-band in-phase combining type space diversity circuit can be configured by only two amplifiers with AGC, the circuit can be simplified. Therefore, there is an effect that a compact and economical space diversity circuit can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a space diversity circuit of the present invention.

FIG. 2 is a circuit diagram of a conventional space diversity circuit.

[Explanation of symbols]

 1 Control Circuit (CONT) 1A, 1B AGC Voltage 2A, 2B Amplifier with AGC 3A, 3B Variable Attenuator 4A Main Antenna 4B Diversity Antenna 5A, 5B Converter 6 Phase Shifter (EPS) 7 Receiver Local Oscillator 8 Phase Detector 9A , 9B, 10 Hybrid 11 output terminals

Claims (1)

Claim: What is claimed is: 1. A space diversity circuit of a method of in-phase combining both reception signals of a microwave main reception system and a diversity reception system in an IF band, the input level fluctuation of the main reception system being compensated. No. 1 amplifier with AGC, a second amplifier with AGC for compensating for input level fluctuation of the diversity reception system, variable attenuators respectively connected to the outputs of the first and second amplifiers with AGC, and their respective variable And a control circuit that changes the attenuator based on the gain control voltages of the first and second amplifiers with AGC, respectively, and the reception system corresponding to the gain control voltage of the reception system whose reception input level is lowered. A space diversity circuit characterized by controlling so as to increase the attenuation of the variable attenuator.