UHF and SHF Micro-strip Directional Couplers

Abstract

The paper gives a review to analyse the outcomes achieved in the field of micro-strip directional couplers within 2010 – 2017. Considers design features of over twenty original or modified quadrature micro-strip directional couplers within ultrahigh (UHF) and super-high frequency (SHF) bands. The focus is on the ways to reduce overall dimensions of traditional loopback, printed and coupled couplers, enhance their use in several frequency bands, suppress higher order harmonics up to the sixth, provide broad-banding operation frequency to several octaves, change a type of the laterally-coupled coupler directionality from the counter-directional to the co-directional and trans-directional ones. The results obtained are achieved due to the following: the change of the quarter-wave line segments for their equivalent micro-strip “П”- and “T”- like structures and their combinations, the quasi-fractal topological implementation of devices, the use of composite transmission lines with the properties of meta-materials, the use of defects of various shapes in the ground plane, the samples in the signal layer of metallization, the low-pass filters in combination version of high-resistance and low-resistance lines, the use of special-form coupling apertures in a multilayer response which allows to compensate for the differences in phase lengths of the segments of connected lines for the even- and odd-order modes, thereby enabling significant improvement of coupler characteristics. The paper briefly describes coupler topologies, equivalent circuits and device layouts. Shows amplitude-frequency and phase-frequency characteristics simulated in computer-aided design systems. Also presents measuring results of the fabricated mock-ups of micro-strip directional couplers. The results obtained may be of interest to the creators of SHF devices and those involved in further investigation to seek and improve couplers of known designs.