A Comprehensive Review on Microstrip Couplers: Structure, Design Method, and Performance

-In this paper, several types of microstrip couplers are investigated in terms of structure, performance, and design methods. These planar 4-ports passive devices transmit a signal through two different channels. Designers' competition has always been in miniaturizing and improving performance of couplers. Proposing a novel structure is an advantage of some previously reported couplers. A high-performance coupler should have high isolation and low losses at both channels. The common port return loss in the pass band should have a low value. Among the couplers, those with balanced amplitude and phase are more popular. The popular mathematical analysis methods are even/odd mode analysis, extracting the information from the ABCD matrix and analyzing the equivalent LC circuit of a simple resonator. According to the phase shift value, couplers are classified as 90 degrees and correct multiples of 90 degrees, where a microstrip 0 degrees coupler can be used as a power divider. Some couplers have filtering and harmonic elimination features that are superior to other couplers. However, few designers paid attention to suppressing the harmonics. If the operating frequency is set in according to the type of application, the coupler becomes particularly valuable.

Automated summary

In this paper, various types of microstrip couplers are studied, focusing on their structure, performance, and design methods. These planar 4-ports passive devices transmit signals through different channels, and their miniaturization and performance improvement have always been the competition among designers. Some previously reported couplers have the advantage of proposing a novel structure. A high-performance coupler should possess high isolation and low losses in both channels, as well as a low common port return loss in the pass band. Couplers with balanced amplitude and phase are more popular, and mathematical analysis methods include even/odd mode analysis, information extraction from the ABCD matrix, and analysis of the equivalent LC circuit of a simple resonator. Couplers are classified based on the phase shift value, with some having filtering and harmonic elimination features that surpass others. Setting the operating frequency according to the application type makes the coupler particularly valuable.