Abstract
Numerical analysis and design of millimeter-wave (mmWave) slot-coupled microstrip 90 degrees hybrid couplers employing circular ring patches, which is operating between 18 and 40 GHz frequency range for K-Band and Ka-Band radar applications, is presented in this paper. The proposed design uses multilayer printed circuit board (PCB) technology that allows having a compact and broad bandwidth coupler. The proposed couplers use broadside coupling between microstrip patches at the top and the bottom layers via an elliptical-shaped slot in the common ground plane (mid-layer). The design uses circular ring shaped broadside coupled patches and an elliptical-shaped slot created in a common ground plane between two identical dielectric substrates. The 3 dB coupler prototype has been fabricated on two 0.127 mm thick Rogers Duroid RT5880 substrates. The circuit occupies the dimensions of less than 5 mm 9 5 mm without the extension that is required to insert the connectors. Extensive parametric studies are performed to address the effect of varying the coupler parameters on the coupling values, return losses, isolations, transmission magnitudes and phases through the operational frequency bandwidth. A 3 dB/90 degrees hybrid coupler prototype is fabricated and then tested experimentally using Agilent E8364B PNA Network Analyzer. The simulation and experimental results show a good performance in terms of bandwidth, which covers the entire desired frequency range. In addition, detailed design for different coupling values of the proposed coupler is presented in this paper. The proposed coupler can achieve different coupling values range from 3 up to 9 dB that can be used for switched beam antenna array systems.