Miniaturized IPD-based bandpass filter chip with edge self-coupled SRR and mixed coupling structure for 5G new radio

A miniaturised millimetre-wave bandpass filter chip based on the integrated passive device (IPD) process for 5 G new radio is proposed in this paper. Two techniques are utilised to minimise the circuit footprint. Firstly, the innovative edge self-coupled split ring resonator (ES-SRR) is proposed, which incorporates a self-coupled effect by narrowing the gap between the vertical microstrip line and the two split stubs. The theoretical model of the ES-SRR is examined to identify its resonating characteristics. Secondly, the magnetic dominant mixed-coupling structure is implemented in the planar filter by meticulously adjusting the resonator line widths. This configuration generates two transmission zeros at each side of the passband. To demonstrate their effectiveness, a sixth-order bandpass filter, operating within the frequency range of 24.25–29.5 GHz, is simulated and fabricated using 100-µm-thick GaAs IPD technology. Experimental results reveal an insertion loss of 2.95 dB and a minimum return loss of 17 dB, achieving a fractional bandwidth of 21%. Notably, the filter exhibits two transmission zeros at 21 GHz and 33 GHz with rejection levels of 55 dB and 60 dB, respectively.