JPS6015186Y2 - Reflected wave detection circuit in radio equipment - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a reflected wave detection circuit for accurately determining the load condition of an antenna system in a radio transmitter.

As shown in FIG. 1, a conventional reflected wave detection circuit for a radio transmitter includes a stripline type directional coupler 3 (which extracts reflected waves) provided between a transmission power amplifier 1 and an antenna 2.
(including strip lines Ll, L2 and resistor R□),
It consists of a reflected wave detector 4 (including a diode X and a capacitor C) which obtains a voltage proportional to the extracted reflected wave, and obtains a voltage proportional to the mismatch state of the antenna 2.

However, there is a need to downsize directional couplers used in mobile radio equipment, etc. due to their usage characteristics, but as the frequency decreases, the coupling length of a stripline directional coupler becomes λ/4 of the wavelength λ. Therefore, even if the reflection coefficient at the break point of the antenna 2 is constant, there is a drawback that standing waves generated between the break point of the antenna 2 and the transmitting power amplifier 1 are detected, and the antenna 2 is damaged. Since the standing wave generated at the directional coupler 3 changes between the maximum voltage and the minimum voltage depending on the position of the point, the reflected wave detection voltage is not constant.

It had the drawback of lacking accuracy. Also, as other circuits,
There is also a lumped constant type coupler, but in addition to the above-mentioned drawbacks, it has new drawbacks such as complicated implementation.

The purpose of the present invention is to eliminate the above-mentioned drawbacks by providing a phase shifter using a lumped constant between two directional couplers to create a reflected wave detection circuit that accurately detects reflected waves regardless of changes in load conditions. It is about providing.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the present invention.

10° and 11 are directional couplers that connect strip lines Ll and L2, resistor R1, and strip lines L3 and L, respectively.
4 and resistor R2.

12 is a lumped constant phase shifter (including capacitors CI, C2 and inductance L5).

Reference numerals 13 and 14 indicate reflected wave detectors (consisting of capacitors C3 and C4 and diodes X1 and X2).

Furthermore, R□. R2 is a terminating resistor, C3 and C4 are smoothing capacitors, and Xl and X2 are detection diodes.

By setting the two directional coupling circuits 10.11 apart from the phase shifter 12 by 4/4 (input: wavelength) and adding the outputs of the two reflected wave detectors 13.14, damage to the antenna 2 can be detected. Even if the phase of a constant number that occurs between the point and the transmission power amplifier 1 changes, the output of the adder circuit 15 is kept almost constant.

For example, when the directional coupler 10 detects the maximum voltage of the constant number, the directional coupler 11 detects the minimum voltage because it is separated by λ/4.

The sum of the outputs of each reflected wave detector will be the maximum value even if the position of the wave loss point of the antenna with wave loss shifts under the same conditions and each directional coupler no longer detects the maximum voltage or minimum voltage. The level of the output of the reflected wave detector that was detecting the voltage decreases, and the level of the output of the reflected wave detector that detects the minimum voltage increases, so the added value becomes almost equal to the previous added value, which is different from the conventional This method detects the wave loss state of the antenna more stably than the above method.

In addition, input/4 is possible at the commonly used VHF band and UIF band frequencies.
Separating the directional couplers 10.11 by a distance of 10.1 requires a large space, which is inconvenient when considering miniaturization of the device.

The present invention provides a phase shifter 12 consisting of a capacitor CI, C2 coil L5 between two directional couplers 10 and 11, and C
Directional coupler 10 by adjusting I, C2, L5
．． By adjusting the electrical distance of 11 to, for example, an odd multiple of input/4, a large space is not required and the device can be miniaturized.

Even if the voltage standing wave ratio and phase of the load change due to the above,
A voltage proportional to the voltage standing wave ratio can be obtained, and when used in a transmitter protection circuit, it becomes a reflection detection circuit that can respond to load fluctuations with high accuracy.

Although the number of elements in this invention has increased compared to conventional reflected wave detection circuits, the cost does not increase significantly because it can be mounted on a printed circuit board.Moreover, it detects reflected waves with high precision, so This method has the advantage of reducing the time required to replace the final stage transistor, since damage to expensive transistors can be eliminated, and is highly practical.

[Brief explanation of drawings]

FIG. 1 shows a conventional reflected wave detection circuit, and FIG. 2 shows a reflected wave detection circuit according to the present invention. In the figure, 1 is a transmission power amplifier, 2 is an antenna, 3, 1
0.11 is a directional coupler, 4,13°14 is a reflected wave detector, 12 is a phase shifter, and 15 is an adder circuit.

Claims (2)

[Scope of utility model registration request] (1) Two directional couplers provided between the wireless transmission power amplifier and the antenna, a phase shifter provided between the two directional couplers, and the two directional couplers. A reflected wave detection circuit in a radio device, characterized in that it includes an addition circuit that adds a voltage proportional to the reflected wave extracted from the reflected wave and outputs the result. (2) A reflected wave detection circuit in a radio device according to claim 1, characterized in that a lumped constant is used as the phase shifter.