Ultra-Wideband Filtering 180° Hybrid Coupler With Super Wide Upper Stopband Using Swap Phase Inverter and Electromagnetic Bandgap Structures on Double-Sided Parallel-Strip Line

In this paper, a multifunctional 180° hybrid coupler is proposed, with an ultra-wideband filtering response and a super wide upper stopband. The component, realized with double-sided parallel-strip line (DSPSL), is built up on the basis of a hybrid ring incorporated with a swap phase inverter and then extended with commensurate-line networks at its four ports. The quasi-lowpass electromagnetic bandgap (EBG) structures are embedded into the circuit. The collaboratively designed component occupies the area of 0.92 × 0.76 λg
²
, where λg is the guided wavelength at the central frequency. The developed prototype provides a 110% wide passband from 0.7 to 2.4 GHz with the return loss better than 11 dB for both the in- and out-of-phase output cases. The measured additional in-band insertion loss is 1.3 to 4.7 dB over the 3-dB power division, mainly due to the losses of the DSPSL swap and EBG structures. The output phase imbalance is within the range of ±4°. The rejection of over 20 dB is achieved up to 30 GHz.