A reduced-size and tunable branch-line 3dB hybrid

This paper proposes a reduced-size and tunable 3dB branch-line hybrid. The proposed hybrid consists of short transmission lines with equal characteristic impedance and shunt lumped tuning capacitors. The authors fabricated the proposed hybrid on PTFE substrates at 2GHz. In the measurements, while tuning capacitance changes from 1.3pF to 2.7pF, center frequency shifted 1.8GHz to 2.4GHz, with -19.5dB return loss, ±0.3dB outputs amplitude difference, and 90±3° phase difference. These measurement results agree with analytical calculation accurately. In general, these hybrids are particularly useful for power dividers or power combiners in microwave circuit as balanced mixers, image-rejection mixers, and balanced amplifiers.