Document Type : Research Paper
Authors
Abstract
Modern microwave and millimeter wave phased array antennas are attractive because of their ability to steer wave beams in space without physically moving the antenna element. A typical phased array antenna may have several thousand elements fed by a phase shifter for every antenna, which can steer the resulting array beam to different directions. Their low loss, low cost and lightweight phase shifters are important for the design of phased array antennas. The ferrite phase shifters have low insertion loss and can handle significantly higher powers, but they are complex in nature and have a high fabrication cost. While semiconductor phase shifters using PIN diodes or FET’s are less expensive and smaller in size than ferrites, their application is limited because of high insertion losses. Recently, others types of phase shifters using MEMS technology have been investigated to overcome the above limitations.
This paper presents analysis and design of distributed MEMS phase shifters for Ka-band communication systems. The phase shift can be obtained by changing MEMS bridge capacitors located periodically over the transmission line. Simulation results of phase shifters with various structural parameters are analyzed to develop the optimized designs. It is observed that the distributed microelectromechanical transmission-line (DMTL) phase shifter can be accurately modeled using a combination of full-wave electromagnetic and microwave circuit analysis. The full-wave electromagnetic simulation of the unit cell is done by finite element using Ansoft High Frequency Structure Simulator (HFSS). After the full wave analysis is performed, S-parameters are extracted in the frequency range going from 26 to 40 GHz for different widths and heights of the MEMS bridge. S-parameter presentation of phase shifters is very important in computer aided design (CAD). Finally, the S-parameters are combined to obtain the overall phase shifter performance over Ka-band. This phase shifter offers the potential for building a low loss device for a variety of phased arrays and radar. The average insertion loss and return loss and the phase errors of our phase shifter are compared with the reported MEMS phase shifters at various references.
The overall performance of n-bit phase shifter is obtained, using S-parameters and microwave circuit theory. Using phase shifts versus numbers of cells, it is shown that the n-bit phase shifter can be obtained with a suitable combination of one-bit phase shifters with 11.25, 22.5, 45, 90 and 180 degrees. Insertion losses, return losses, and phase shifts ware obtained in 32-states at the frequency range 26-40 GHz. Average insertion loss –1.68 dB, return loss –11.94 dB, and phase errors of 2.33 was obtained in 33 GHz for 4-bit phase shifter. The results are in good agreement in comparison with the reported MEMS phase shifters.
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