A lumped quadrature coupler based on a ferromagnetic core is proposed for high-frequency (HF) application. The four terminals of the transformer are connected to the four ports, whereas two inductors and two capacitors are connected between two adjacent ports. The bandwidth is only limited by magnitude imbalance. A 13.56 MHz prototype is designed and tested. A 69% bandwidth is achieved with ±3 dB magnitude imbalance. Within the frequency band, the measured return loss is greater than 31.57 dB, port-to-port isolation is greater than 33.21 dB and the phase imbalance is <2°.
Load-variation insensitivity for impedance matching between power amplifiers (PAs) and transmitted antennas contributes to challenge the design of millimeter-wave wireless systems. In this paper, a W-band two-way balanced power amplifier (PA) based on a compact quadrature coupler with broadside coupled strip-line (BCSL) as the core section has been presented to enhance the load-variation insensitivity and stability. By utilizing the proposed coupler topology, the proposed coupler obtains broadband performances with low amplitude and phase imbalance. The designed W-band PA achieves higher power-added efficiency (PAE) and saturated output power Psat over wide frequency bandwidth. The proposed W-band balanced PA is implemented in a 0.13-μm SiGe BiCMOS process and achieves a measured Psat of 16.3 dBm and a peak PAE of 14.1% at 100 GHz under 1.6-V power supply. The measured Psat with 1-dB bandwidth is from 91 to 102 GHz. The measured results present the feasibility of the compact quadrature coupler. The total chip area (with pads) is 0.64 mm 2 , where the size of the proposed quadrature coupler is only 0.04 mm 2 . Index Terms-SiGe, W-band, quadrature coupler, broadside coupled strip-line (BCSL), balanced power amplifier.
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