TABLE I. Sputtering conditions for BST deposition. Target Ba 0.5 Sr 0.5 TiO 3 Target diameter 3 in. Source to substrate distance 4 in. RF power 90 W Sputtering gas Ar/O 2 ͑sccm͒ Substrate temperature 450-650°C Gas pressure 50 mT Deposition rate 0.4 nm/min

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A monolithic Ka-band phase shifter circuit that employs voltage tunable BaSrTiO 3 (BST) parallel plate capacitors is presented here. The circuit is capable of continuous 0-157 phase shift at 30 GHz with an insertion loss of only 5.8 dB and return loss better than 12 dB. In addition to promising loss performance (27.1 /dB) at 30 GHz, the circuit reported here has several advantages over previously reported BST phase shifters such as moderate control voltages (20 V), room temperature operation, and compatibility with monolithic fabrication techniques.

This letter presents a one-bit low-loss-band phase shifter circuit that employs microelectromechanical systems (MEMS) capacitors. The measured results demonstrate a delay line with a 180 phase shift/1.17 dB loss phase shift at 25 GHz, 270 phase shift/1.69 dB loss at 35 GHz, and a return loss better than 11 dB over a 0-35-GHz band. The state-of-the-art insertion loss performance, 154 /dB at 25 GHz and 160 /dB at 35 GHz, demonstrates the potential for the implementation of a very low-loss multibit digital MEMS phase shifter.