Miniature on-chip bandpass power divider with equalripple response and wide upper stopband

In this study, a miniature bandpass power divider based on capacitive-loaded multicoupled line is proposed, which features equal-ripple insertion loss, return loss and isolation responses. Owing to the employment of capacitive-loaded transmission line resonators, it can achieve very compact size and wide upper stopband. The proposed bandpass power divider can be designed according to the conventional filter synthesis techniques, and is suitable for on-chip implementation. Specifically, a bandpass power divider with a centre frequency f0 of 5.5 GHz, 18.2% fractional bandwidth, and third-order equal-ripple response is designed and implemented using the commercial GaAs pseudomorphic high electron mobility transistor (pHEMT) process. The circuit size without pads is 0.87 mm × 0.95 mm, and the electrical size is only 0.057 λ^g × 0.062 λ^g at f₀. The in-band insertion loss is less than 6 dB with a minimum insertion loss of 5.12 dB. The in-band return loss is better than 10 dB, and the isolation is better than 15 dB. In addition, a wide 30-dB upper stopband up to 57 GHz is achieved.