Bandwidth Improvement of a Compact Quadrature Hybrid Coupler With Harmonic Rejection Using Lumped Elements

Abstract

Abstract-A compact quadrature hybrid coupler with harmonic suppression using lumped-element band-stop resonator is proposed for bandwidth improvement. Conventionally, harmonic rejection is realized by three band-stop resonators in lumped hybrids. The using of three band-stop resonators realizes better harmonic suppression while exhibiting narrower frequency response. So as to improve operation bandwidth behavior, the number of band-stop resonator applied in the proposed topology is minimized to one. Trading off with acceptable reduction in harmonic rejection, the proposed hybrid enlarges working bandwidth with fewer numbers of lumped devices. Detailed design and theoretical analysis are presented and the expressions of lumped elements with dependence of rejected frequency are obtained. To validate the analysis, three 2.45 GHz couplers are fabricated on an FR-4 printed circuit board. The experimental results exhibit 27.3%, 26.9% and 23.3% operation bandwidth with better than 16 dB, 17 dB, and 21 dB harmonic suppressions at 4.9 GHz, 6.1 GHz, and 7.35 GHz, respectively. Less than 0.8 dB amplitude imbalance and 2 • phase error are achieved for all the three couplers, which are matched well with theoretical analysis.