ROMJIST Volume 28, No. 4, 2025, pp. 353-364, DOI: 10.59277/ROMJIST.2025.4.04
Iulia Andreea MOCANU, Norocel Dragos CODREANU, Mihaela PANTAZICA Miniaturized High Frequency Ratio Quadrature Coupler for Dual Band Wireless Systems
ABSTRACT: Dual band high frequency ratio quadrature couplers are needed in wireless systems to work with similar performances in low and high frequency bands, keeping the dimensions reduced and being easy to manufacture and integrate in planar structures. To address these challenges, in this paper, a miniaturized dual-band branch-line coupler with large frequency ratio and coupling losses around 3.5 dB for both bandwidths is proposed, implemented, and measured. Miniaturized impedance inverter transmission lines were used to replace the classical transmission lines (TLs) of the branch-line coupler. Two arbitrary frequencies, 0.7 GHz and 5.6 GHz, with a ratio of 8.28 were chosen to implement and measure the coupler’s performances. The simulation results of the dual band coupler show good agreement with the measurements. The return loss and isolation loss are greater than 30 dB, while the insertion and coupling losses are around 3.5 dB for both bandwidths. The phase difference is 90o and a relative bandwidth of more than 20% for both frequencies is obtained considering a phase imbalance of ±5o. The bandwidth for the coupling attenuation is around 50% for both frequency ranges when imposing a magnitude imbalance of ±1.5 dB. The dimensions of the proposed coupler are around 0.45λg0.23λg at the central frequency of 3.25 GHz, showing that excellent performances can be attained with miniaturized dual band transmission line.KEYWORDS: Dual-band microwave passive component; high band ratio; measurement of S-parameters; miniaturized branch-line coupler; wireless applicationsRead full text (pdf)