Low Insertion Loss Compact Quadrature Coupler for Conformal Space Applications

This paper presents a compact quadrature coupler with low insertion loss for conformal space applications. Compactness is achieved by introducing a simple double U-bend in the microstrip transmission lines and using a thin substrate with a higher dielectric constant. This method reduces the size of the coupler by 33% without increasing the complexity of the structure. The coupler is designed at 1.5 GHz operating frequency. The dimensions of the coupler are optimized by a design of experiments technique (DoE) for the required frequency of operation. Simulation results are presented to analyze the |S|- Parameters of the proposed coupler and compared with that of the conventional one. The 10 dB return loss and 10 dB isolation operational bandwidth of proposed coupler is 29.8% and 59.3%, respectively. The proposed coupler insertion loss at both port 2 and port 3 is 3.1 dB. Proper selection of the substrate reduces the spurious back radiation, which in turn reduces the insertion loss.