Directional coupling method for radio frequency transmission system and coupler

Abstract

The invention relates to a directional coupling method for a radio frequency transmission system and a coupler. The coupling method comprises the following steps that: a main transmission line samples a total voltage at two ends of a spacing distance with an electric length theta along the signal transmission direction in the same mode respectively, wherein theta is more than 0 degree and less than or equal to 90 degrees; and the sampled voltage is delayed by a phase delay transmission circuit and then superposed to acquire a corresponding voltage, so that an incident voltage and a reflected voltage mixed in the total voltage of the main transmission line are separated by different phases to realize a directional coupling function and obtain the directional coupler of the corresponding structure, wherein the phase delay transmission circuit is bridged over two sampling points and has an electric length theta+180 degrees. Since the working principles of the coupling method and the coupler are not based on the even and odd mode theory of parallel coupled lines, the problem of directional deterioration caused by a micro-strip hybrid medium can be solved; and the implement method is very flexible; the lumped parameter element equivalent transmission line can also be used for the low radio frequency application; and meanwhile, the space of the voltage sampling points can be far less than 1 / 4 wavelength so as to miniaturize the circuit.

Description

technical field [0001] The invention relates to a method for directional coupling in radio frequency transmission and a corresponding coupler. Background technique [0002] The directional coupler is an important device in microwave transmission, and the low-coupling directional coupler is often used in power detection and standing wave protection applications. For radio frequency components implemented by microstrip planar circuits, the most convenient and cheap way to implement directional couplers is to use 1 / 4 wavelength microstrip parallel coupled lines. [0003] According to coupled transmission line theory, parallel coupled lines support two TEM wave modes: even mode and odd mode. The field structure of even mode and odd mode is different. For the inhomogeneous microstrip mixed medium, this means that the propagation speed of the two modes is not equal, which leads to poor directivity of the directional coupler realized by the microstrip parallel coupling line, espec...

AI Technical Summary

Problems solved by technology

The field structure of even mode and odd mode is different. For the inhomogeneous microstrip mixed medium, this means that the propagation speed of the two modes is not equal, which leads to poor directivity of the directional coupler realized by the microstrip parallel coupling line, especially for the case of low coupling

[0004] For low radio frequency applications, because the wavelength of the signal is very long, it is not practical to use a 1 / 4 wavelength microstrip parallel coupling line because the size of the coupling area is too large, so currently only a microstrip parallel coupling that is much shorter than 1 / 4 wavelength can be used Wire

On the one hand, it will lead to an increase in the fluctuation of the in-band coupling degree as the frequency changes. At the same time, the distance between the coupling port and the isolation port will reduce the directivity, resulting in the deterioration of the directivity of the microstrip parallel coupled line.

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