Compact Uniform Folded Section Rat-Race Couplers with Harmonic Suppression

In this paper, two 50Ω terminated rat-race hybrid couplers based on uniform folded structures are proposed for equal division of power. The proposed designs are of simple in geometry and have an area of only one-fourth of the conventional coupler. The first technique is two-fold double section topology operating at 1.77 GHz designed with the conventional impedance ratio of √2 between port and transmission line which exhibits good in-band characteristics and requires a minimum track width of 0.8 mm. The second technique is stub-loaded double section topology where the novelty lies in deploying impedance matched stubs which avoids high impedance lines by maintaining an impedance ratio less than 2 between port and transmission line. In addition to good passband characteristics, it also suppresses higher harmonics up to 6.3f0and requires a minimum track width of 0.41 mm which makes it easy for realization. The bottom line of both designs is to achieve extreme structural simplicity without using high impedance transmission lines of more than 100Ω, narrow tracks less than 0.4 mm, lumped elements, and via holes. The prototype of the proposed coupler is fabricated and the simulated results are validated using measurements.