Widely tunable, high-Q, evanescent-mode cavity filters: Fabrication, control, and reconfigurability

The recent trend in wireless and radio frequency (RF) components and systems has been towards tighter integration and increased functionality without sacrificing quality. Important components for the front-end of such systems includes: antennas, low-noise amplifiers (LNAs), and filters. High quality factor (Q) band pass filters allow for very narrow bandwidths which can be used for band pre-selection and even direct channel selection without having outrageous losses that will degrade vital system performance metrics such as: noise figure, dynamic range, quality of service, and data rate. This work addresses the tighter integration issue by creating high-Q filters out of three-dimensional polymer evanescent-mode cavities. These filters are then integrated with a CMOS RFIC receiver embedded in a functional silicon carrier wafer to demonstrate a full front-end receiver, showing the potential of heterogeneous integration of three different technologies. The polymer evanescent-mode filter work led to the development of tunable band pass filters which is the second part of the work presented here. The high frequency sensitivity of the evanescent-mode cavity structure allows for very wide frequency tuning with a small dimensional change that can be realized using commercially available piezoelectric actuators. The initial targeted filter performance is: tuning from 3 to 6 GHz with an insertion loss less than 4 dB while keeping the bandwidth less than 25 MHz. A novel integration of the evanescent-mode cavity filter into a double sided printed circuit board is introduced and the electrical specifications made more stringent: tuning from 0.8 to 6 GHz with loss ranging from 2.5 to 3.5 dB with a fixed absolute bandwidth of 25 MHz. The integrated cavity filter approach is used to realize tunable multiplexers that show promise for multi-band communications. Arrays of reconfigurable evanescent-mode cavities are also used to form unprecedented filter functions with a path towards an arbitrary shape, reconfigurable filtering block. This concept is demonstrated by a reconfigurable order filter that can be electronically modified to have 2nd or 4th order filter characteristics. An important aspect of this work is to create a feedback mechanism to control the center frequency of the filters. This is critical component to make this technology ready for commercial use due to the high frequency sensitivity of the filters as well as the non-linear and non-repeatable behavior of the actuators