Novel Methodology for Compact Ring Hybrids
A design method for miniaturization of microstrip rat-race couplers with good frequency bandwidth employing coupled line sections is reported in this paper. The footprint of the proposed design occupies 14.9% of the area of the conventional similar design. Moreover, the circuit is planar, without any high impedance section (fine line), multilayer substrates, plated thru holes, bonding wires, reactive components or artificial transmission lines. These lead to low insertion loss, high power handling and easy and low cost fabrication of the circuit. For experimental verification, one rat-race coupler is designed and fabricated with center frequency of 1 GHz. Simulation and measurement results verify that the frequency responses of the conventional coupler are remained unchanged during the miniaturization. Across the frequency bandwidth, the maximum amplitude imbalance is 0.5 dB, the phase variation is 5o, the isolation and return loss are better than 20 dB.
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