Design of a compact Rat-race coupler with harmonics suppression using lumped component elements for wide coverage applications

In the coupler design, there are some important parameters, including size reduction, harmonic suppression and insertion loss, which affect the quality of the final product. Thus improving each of these parameters contributes to a more efficient design. In this paper a novel Rat-race coupler with size reduction and harmonics suppression is designed. In the proposed coupler structure, parallel capacitor and indicator are used. The proposed device correctly works at 800 MHz and occupied small size of 46.3mm×23.15mm (0.17λ ×0.08λ), which shows more than 63% size reduction compared to the conventional coupler. The proposed coupler not only reduce the circuit size but also suppresses 2nd, 3rd and 4th harmonics with 21dB, 38 dB and 20 dB attenuation levels, respectively. The proposed coupler provides wide rejection band from 1.6 GHz to 3.3 GHz with more than 20 dB attenuation level. The insertion loss parameter is less than 0.1 dB and more than 40 dB return loss and isolation are obtained at operating frequency, which show superior performance of the proposed Rat-race coupler.