This paper presents continuously variable 20- and 30-GHz ferroelectric 360 deg phase shifters. A lumped-element all-pass network topology is used for the phase-shifter designs. The phase shifters are fabricated using barium-strontium-titanate (BST) capacitors as the tuning element. The BST thin films are epitaxially grown on sapphire substrates using the combustion chemical vapor deposition process, exhibiting low loss and high tunability. The 20-GHz phase shifter has a dimension of 0.95 X 1.32 X 0.5 mm~(3); its maximum phase shift occurs at 21.7 GHz, where the insertion loss varies from 6.1 to 3.9 dB and the return loss is from 15.2 to 4.7 dB. Measured figure-of-merit is 54 deg/dB using the highest insertion loss. The dimension of the 30-GHz phase shifter is 1 X 1.2 X 0.5 mm~(3). Measured insertion loss and return loss vary from 7.0 to 4.3 dB and from 29 to 4.8 dB, respectively, at a center frequency of 32 GHz. The figure-of-merit is 51 deg/dB. The dc bias required to tune the low-voltage phase shifters is 0-30 V. Typical third-order input intercept power (IIP_(3)) of the phase shifters is greater than 30 dBm.
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