Silicon RFIC UWB bandpass filter using bulk-micromachined trench couplers

A low loss silicon RFIC UWB bandpass filter is reported. The filter exploits a novel metalized coupled trench structure, fabricated by advanced silicon bulk micromachining. The couplers can achieve more than -2 dB coupling, with good even-odd mode phase velocity balance, while having practical dimensions. The CPW filter is designed using well-known interdigital filter design equations. The measured fractional bandwidth is 115%, with only 1 dB mid-band insertion loss at 6.4 GHz and better than -11 dB return loss across the whole passband. The measured differential-phase group delay is less than 200 ps from 2.6 to 10.1 GHz. Being a monolithic filter, it has a compact area of only 3.5 × 5.5 mm2.