Theory, Design, and Fabrication of Frequency Agile Filtennas

Abstract

With the development of modern wireless systems, the spectral environment has become increasingly crowded. This has spawned a strong interest in frequency, bandwidth, and pattern reconfigurable RF front ends, which can adaptively tune their response to reduce interference. A filtenna (filter' and antenna') is a device that combines an antenna and at least one other resonator together to achieve the same or better performance as an antenna and filter cascade in a smaller and lighter package. Most frequency reconfigurable filtennas tune by using microelectromechanical systems, pin diodes, or varactors. These tuning techniques are ill-suited for high power applications due to breakdown, non-linear effects, and/or high loss. These problems can be solved by the use of mechanical tuning. In this thesis, a piezoelectric actuator tuned, 2\textsuperscript{nd} order filtenna is presented. The design is based upon changing the capacitive loading of an antenna and an evanescent-mode cavity resonator, thereby altering the resonant frequency. Loading agility is achieved through physical displacement of a metal disk. A time domain based tuning method is applied to tune the filtenna, allowing highly accurate tuning with only access to {$S_{11}$}. The filtenna is simulated to have a 2\textsuperscript{nd} order response and tune across S-band (2-4 GHz, 2:1 ratio). Simulations also show a greater than 65% radiation efficiency and greater than 3~dBi broadside gain throughout the entire tuning range. This filtenna demonstrates the feasibility of a widely tunable, highly linear, and compact front end for modern RF systems, as well as a design methodology to allow for future development of frequency agile filtennas.