JP2000315960A - Microwave receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave receiver that prevents saturation of a high frequency amplifier due to up-fading and avoids reduction in an input level to the amplifier on the occurrence of attenuating fading. SOLUTION: In the microwave receiver that uses a high frequency amplifier 6 to amplify a microwave signal received by an antenna 1 and provides an output of the amplified signal, a level detector 7 detects a reception input level, a voltage comparator 8 discriminates this reception input level to control a changeover switch 2 so as to give the microwave signal passing through a fixed attenuator 3 to the high frequency amplifier 6 in order to prevent the saturation of the high frequency amplifier 6 due to an up-fading in a steady- state, but to give the amplifier the microwave signal on a bypass line 4 not passing through the fixed attenuator 3 in the case that the reception input level reaches a reference level Vth1 or below resulting from the occurrence of an attenuating fading.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus in a microwave radio communication system, and more particularly to a microwave receiving apparatus capable of performing stable reception with respect to a change in a reception input level.

[0002]

2. Description of the Related Art Generally, in a microwave communication system, a reflected wave reflected on the ground surface, a forest, a building, a sea surface, or the like interferes with a direct wave directly arriving from a transmitting side to a receiving side. The reception input level fluctuates. Fading includes up-fading, where the received input level is higher than the standard level,
There is attenuating fading where the received input level is lower than the standard level.

When the up-fading occurs, the reception input level becomes excessive, and the high-frequency amplifier in the receiving device may be saturated. In such a case, large distortion occurs. In order to avoid this problem, in the conventional microwave receiver, a fixed attenuator is inserted in front of the high-frequency amplifier to attenuate the received microwave signal, and the input level of the high-frequency amplifier is reduced, so that even in the case of up-fading. The high frequency amplifier was not saturated.

FIG. 5 is a diagram showing an operation example of a conventional microwave receiving apparatus. In a configuration that does not use a fixed attenuator, if the reception input level exceeds a saturation level that is a certain value or more than the standard reception level due to up-fading, the high-frequency amplifier becomes saturated, and the microwave signal cannot be amplified without distortion. . If a fixed attenuator is inserted before the high-frequency amplifier, saturation of the high-frequency amplifier during such up-fading can be avoided.

However, in the method of always inserting the fixed attenuator, the input level of the high-frequency amplifier is further reduced by the fixed attenuator when attenuating fading occurs as shown on the right side of FIG. S / N
And the error rate increases.
In particular, this problem becomes serious when the input level of the high-frequency amplifier becomes lower than the amplification lower limit level.

[0006]

As described above, in order to prevent the high-frequency amplifier from being saturated due to up-fading, a conventional microwave receiving apparatus in which a fixed attenuator is inserted in front of the high-frequency amplifier is used. At the time of occurrence, there is a problem that the input level of the high-frequency amplifier is remarkably reduced, which causes a reduction in S / N and an increase in error rate.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a microwave receiver capable of preventing saturation of a high-frequency amplifier due to up-fading and preventing a decrease in the input level of the amplifier when attenuating fading occurs.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention basically has a feature that a fixed attenuator is selectively inserted in front of a high-frequency amplifier according to a reception input level.

More specifically, a microwave receiving apparatus according to the present invention comprises a receiving means for receiving a microwave signal, a high-frequency amplifier for amplifying the microwave signal received by the receiving means, and a receiving means for receiving the microwave signal. Fixed attenuator for attenuating the obtained microwave signal, level detecting means for detecting the reception input level of the microwave signal by the receiving means, and the microwave signal passing through the fixed attenuator according to the detection result of the level detecting means And switching means for selectively switching any one of the microwave signals not passing through the fixed attenuator and inputting the signal to the high-frequency amplifier.

According to one aspect, the switching means inputs the microwave signal that has passed through the fixed attenuator to the high-frequency amplifier in a steady state, and the reception input level detected by the level detection means falls below the first reference level. In such a case, a microwave signal that does not pass through the fixed attenuator is input to the high-frequency amplifier. Here, the first reference level is set to a level lower than a standard reception level (standard reception level) by a predetermined value, for example.

In this way, in the steady state, the microwave signal attenuated by the fixed attenuator is input to the high-frequency amplifier, so that saturation of the high-frequency amplifier due to up-fading is prevented. Since a microwave signal that is not attenuated by the attenuator is input to the high-frequency amplifier, problems such as a decrease in S / N and an increase in error rate due to an unnecessarily low input level of the high-frequency amplifier are avoided.

According to another aspect, the switching means inputs a microwave signal which does not pass through the fixed attenuator in the steady state to the high frequency amplifier, and the reception input level detected by the level detection means becomes higher than the second reference level. Then, the microwave signal passed through the fixed attenuator is input to the high frequency amplifier. Here, the second reference level is set to a level higher than a standard reception level (standard reception level) by a predetermined value, for example.

With this configuration, a microwave signal that is not attenuated by the fixed attenuator in the steady state is input to the high-frequency amplifier, so that a decrease in S / N and an increase in an error rate due to attenuating fading are avoided, and up-fading is performed. Occurs, the microwave signal attenuated by the fixed attenuator is input to the high frequency amplifier 6, thereby preventing the high frequency amplifier from being saturated.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a configuration of a microwave receiving apparatus according to a first embodiment of the present invention.

In FIG. 1, a microwave signal received by an antenna 1 is transmitted to either a fixed attenuator 3 or a bypass line 4 by a changeover switch 2. Either the microwave signal passing through the fixed attenuator 3 or the microwave signal passing through the bypass line 4 is input to the high frequency amplifier 6 via the hybrid circuit 5 and amplified. The microwave signal amplified by the high-frequency amplifier 6 is sent to a subsequent circuit (not shown).

The level detector 7 extracts a part of the microwave signal in the amplification process from the high-frequency amplifier 6 in this example,
This is a circuit for detecting this and detecting the reception input level of the microwave signal, and generates a DC level detection voltage corresponding to the reception input level. The output voltage of the level detector 7 is input to an inverting input terminal of a voltage comparator 8, and the voltage comparator 8 determines a reception input level.

That is, a first reference level Vth1 lower than the standard reception level by a predetermined value is given to the non-inverting input terminal of the voltage comparator 8, and the reception level detected by the level detector 7 is changed to the first level. When the voltage falls below the reference level Vth1, the output of the voltage comparator 8 is inverted from a low level to a high level.

The changeover switch 2 is controlled by the output of the voltage comparator 8 so that the reception input level becomes the first reference level V
In a steady state higher than th1 (a state in which the output of the voltage comparator 8 is at a low level), although connected to the fixed attenuator 3 side,
When the reception input level becomes equal to or lower than the first reference level Vth1, that is, when the output of the voltage comparator 8 becomes high level, it is connected to the bypass line 4.

Next, the operation of the microwave receiving apparatus according to the present embodiment will be described with reference to FIG. FIG. 2 shows a change in the insertion state of the fixed attenuator 3 with respect to a change in the reception input level.

In this embodiment, in a steady state, the changeover switch 2 is connected to the fixed attenuator 3 side, and the microwave signal attenuated by the fixed attenuator 3 is input to the high frequency amplifier 6 via the hybrid circuit 5. Have been. Therefore, even when, for example, the reception input level becomes excessive due to up-fading, the input level of the high-frequency amplifier 6 does not exceed the saturation level, and the received microwave signal causes distortion in the high-frequency amplifier 6. Amplified stably without accompanying

On the other hand, when the reception input level decreases due to, for example, attenuating fading, and the reception input level detected by the level detector 7 becomes equal to or lower than the first reference level Vth1 lower than the standard reception level by a predetermined value, the voltage becomes lower. The output of the comparator 8 is inverted. As a result, the changeover switch 2 is connected to the bypass line 4 side, and a microwave signal which is not attenuated by the fixed attenuator 3 is input to the high frequency amplifier 6 via the hybrid circuit 5.

The first reference level Vth1 is set to a level lower than the standard reception level by a predetermined value as described above. However, as shown in FIG. Level). Accordingly, when the reception input level becomes equal to or lower than the first reference level Vth1 and the fixed attenuator 3 is removed from the signal path, the level of the microwave signal input to the high-frequency amplifier 6 as shown by a broken line in FIG. Does not fall below the lower amplification level.

As described above, in the present embodiment, the microwave signal attenuated by the fixed attenuator 3 is input to the high frequency amplifier 6 in a steady state, so that saturation of the high frequency amplifier 6 due to up-fading can be prevented. Further, when attenuating fading occurs, a microwave signal that is not attenuated by the fixed attenuator 3 is input to the high-frequency amplifier 6, so that the input level of the high-frequency amplifier 6 is unnecessarily reduced, resulting in an S / N ratio. Problems such as a decrease in the error rate and an increase in the error rate can be avoided.

In this embodiment, the voltage comparator 8
It is desirable to have a hysteresis characteristic. That is, when the received input level detected by the level detector 7 falls below the first reference level Vth1, the output of the voltage comparator 8 is inverted from a low level to a high level. Prevents the reception level from reverting from the high level to the low level again until it returns to the level (Vth1 + ΔV1) higher than the reference level Vth1 by a certain minute level ΔV1.

When the voltage comparator 8 has the hysteresis characteristic as described above, the reception input level becomes equal to the first reference level V.
Changeover switch 2 due to fluctuation before and after th1
Can be prevented, and a stable reception operation can be performed even with a minute change in the reception input level.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
It is a block diagram showing the composition of the microwave receiver concerning an embodiment.

In FIG. 3, the same parts as those in FIG. 1 are denoted by the same reference numerals. In this embodiment, the output voltage of the level detector 7 is input to the non-inverting input terminal of the voltage comparator 9,
The difference from the first embodiment is that the second reference level Vth2, which is higher than the standard reception level by a predetermined value, is given to the inverting input terminal of the voltage comparator 9. Therefore, the output of the voltage comparator 9 is inverted from a low level to a high level when the reception level detected by the level detector 7 becomes higher than the second reference level Vth2.

The changeover switch 2 is controlled by the output of the voltage comparator 9 so that the reception input level becomes the second reference level V
In a steady state lower than th2 (a state where the output of the voltage comparator 9 is at a low level), although connected to the fixed attenuator 3 side,
When the reception input level becomes equal to or higher than the second reference level Vth2, that is, when the output of the voltage comparator 9 becomes high level, it is connected to the bypass line 4.

Next, the operation of the microwave receiving apparatus according to the present embodiment will be described with reference to FIG. FIG. 4 shows a change in the insertion state of the fixed attenuator 3 with respect to a change in the reception input level.

In this embodiment, in a steady state, the changeover switch 2 is connected to the bypass line 4 side, and a microwave signal which is not attenuated by the fixed attenuator 3 is input to the high frequency amplifier 6 via the hybrid circuit 5. I have. Therefore, for example, even when attenuated fading occurs and the reception input level decreases, the input of the high-frequency amplifier 6 does not drop to the amplification lower limit level, and the S / N decreases and the error rate increases. Is avoided.

On the other hand, when the reception input level increases due to, for example, up-fading and the reception input level detected by the level detector 7 becomes equal to or higher than the first reference level Vth2 which is higher than the standard reception level by a predetermined value, the voltage comparison is performed. Since the output of the device 9 is inverted, the changeover switch 2 is connected to the fixed attenuator 3 side, and the microwave signal attenuated by the fixed attenuator 3 is input to the high frequency amplifier 6 via the hybrid circuit 5.

The second reference level Vth2 is set to a level higher than the standard reception level by a predetermined value as described above, but is set to a level lower than the saturation level of the high-frequency amplifier 6 as shown in FIG. . Therefore, the microwave signal input to the high-frequency amplifier 6 does not reach the saturation level.

As described above, in the present embodiment, the microwave signal that is not attenuated by the fixed attenuator 3 in the steady state is input to the high-frequency amplifier 6, so that S
/ N and an increase in error rate can be avoided. When up-fading occurs, the microwave signal attenuated by the fixed attenuator 3 is input to the high-frequency amplifier 6, so that saturation of the high-frequency amplifier 6 can be prevented.

In this embodiment, the voltage comparator 9
It is desirable to have a hysteresis characteristic. That is, when the reception input level detected by the level detector 7 becomes equal to or higher than the second reference level Vt2, the output of the voltage comparator 9 is inverted from a high level to a low level. Is the level (V) at which the reception input level is lower than the reference level Vth2 by a small level ΔV2.
Until returning to (th1−ΔV2), the level is not inverted from the low level to the high level again.

When the voltage comparator 9 has the hysteresis characteristic as described above, the reception input level becomes equal to the second reference level V.
Chattering of the changeover switch 2 due to the fluctuation before and after t2 can be prevented, and a stable reception operation can be performed even with a minute fluctuation of the reception input level.

[0036]

As described above, according to the present invention, for example, in a steady state, when a microwave signal that has passed through a fixed attenuator is input to a high-frequency amplifier and the reception input level falls below the first reference level, Inputs a microwave signal that does not pass through the fixed attenuator to the high-frequency amplifier, or inputs a microwave signal that does not pass through the fixed attenuator to the high-frequency amplifier in a steady state, and the reception input level exceeds the second reference level. When this happens, the microwave signal that has passed through the fixed attenuator is input to the high-frequency amplifier to prevent the high-frequency amplifier from saturating due to up-fading and to prevent the input level of the high-frequency amplifier from decreasing when attenuating fading occurs. Thus, a stable reception operation can be performed with respect to a change in the reception input level due to fading.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a microwave receiving device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a change in an insertion state of a fixed attenuator with respect to a change in a reception input level for explaining an operation of the embodiment.

FIG. 3 is a block diagram showing a configuration of a microwave receiving apparatus according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a change in an insertion state of a fixed attenuator with respect to a change in a reception input level for explaining an operation of the embodiment.

FIG. 5 is a diagram for explaining a problem of a conventional microwave receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 2 ... Changeover switch 3 ... Fixed attenuator 4 ... Bypass line 5 ... Hybrid circuit 6 ... High frequency amplifier 7 ... Level detector 8, 9 ... Voltage comparator

Continuation of the front page (72) Inventor Hiroshi Murakami 3-term Asahigaoka, Hino-shi, Tokyo 1-term F-term in Toshiba Hino Factory (reference) 5J100 JA01 LA09 LA10 QA02 SA02 5K061 AA10 BB12 CC06 CC08 CC47 CD05 5K062 AA09 AB03 AB04 AB06 AD04 AD07 BA02 BA06 BE03

Claims (4)

[Claims] 1. A microwave receiving apparatus for receiving a microwave signal and amplifying the signal by a high-frequency amplifier, wherein a fixed attenuator is selectively inserted in front of the high-frequency amplifier according to a reception input level of the microwave signal. A microwave receiver characterized by the above-mentioned. 2. A receiving means for receiving a microwave signal, a high-frequency amplifier for amplifying the microwave signal received by the receiving means, a fixed attenuator for attenuating the microwave signal received by the receiving means, Level detecting means for detecting a reception input level of a microwave signal by the receiving means; a microwave signal passing through the fixed attenuator and a microwave signal not passing through the fixed attenuator according to a detection result of the level detecting means Switching means for selectively switching any one of the above and inputting to the high-frequency amplifier. 3. The switching means inputs a microwave signal which has passed through the fixed attenuator to the high frequency amplifier in a steady state, and a reception input level detected by the level detection means falls below a first reference level. 3. The microwave receiving apparatus according to claim 2, wherein a microwave signal that does not pass through the fixed attenuator is input to the high-frequency amplifier when it becomes. 4. The switching means inputs a microwave signal which does not pass through the fixed attenuator in a steady state to the high-frequency amplifier, and a reception input level detected by the level detection means is higher than a second reference level. 3. The microwave receiving apparatus according to claim 2, wherein the microwave signal that has passed through the fixed attenuator is input to the high-frequency amplifier.