Low-loss Ku-Band analog DMTL phase shifter with full phase shift

Traditionally tunable or switchable phase shifter circuits have been realized in microwave and millimetre wave systems with varactor diodes and transistors. Microelectromechanical systems (MEMS) got a lot of attention as the group of prof. Rebeiz started to study the idea of distributed-MEMS-transmission-lines (DMTL) [1]. Their group reported the first analog DMTL based phase shifter [2]. Above 20 GHz radio frequency (RF) MEMS seems to be the most attractive solution in critical applications, where phase shifters are between antenna elements and low noise amplifiers in receivers. At VTT we designed an analog phase shifter for Ku-band operation with full phase shift at 17 GHz. The DMTL type phase shifter was fabricated on quartz wafer using VTT's own CMOS compatible RF MEMS process which is similar to switched capacitor process reported in [3]. The designed device used mechanical MEMS varactors evenly distributed along a high impedance coplanar wave guide. The total device length is 19.4 mm. Experimental results showed that the phase shifter had a maximum insertion loss of 2.3 dB at 17.5 GHz with a 360° phase shift. These values correspond to a figure of merit of approximately 160°/dB which is to our knowledge the best value reported for an analog phase shifter that is capable of a full 360° phase shift. With analog phase shifters these figures have been met only above 40 GHz [4] but without a full 360° phase shift. MEMS varactors with a suitable bridge layout reached a 100% tuning range for the capacitance. Input matching of the phase shifter was better than -14 dB in all cases. 1. N. S. Barker and G. M. Rebeiz, "Distributed MEMS true-time delay phase shifters and wideband switches," IEEE Transactions on Microwave Theory and Techniques, vol. 46, no. 11, pp. 1881-1890, November 1998. 2. N. S. Barker and G. M. Rebeiz, "Distributed MEMS true-time delay phase shifters and wideband switches," IEEE Transactions on Microwave Theory and Techniques, vol. 46, no. 11, pp. 1881-1890, November 1998. 3. T. Vähä-Heikkilä, M. Ylönen, "G-Band Distributed Microelectromechanical Components Based on CMOS Compatible Fabrication", IEEE Transactions on Microwave Theory and Techniques, Vol. 56, No. 3, pp. 720 - 728, March 2008 4. Greg McFeetors and Michal Okoniewski, "Distributed MEMS Analog Phase Shifter With Enhanced Tuning", IEEE Microwave and Wireless Components Letters, Vol. 16, No. 1, January 2006, pp. 34 - 36