External quality factor of antennas and their use in filtenna design

Abstract

Filtering antennas, or filtennas, have become a growing topic of interest in the pursuit of the minimization of the RF front end. Combining the filter and antenna, which are integral to RF front ends, allow for a decrease in the size, weight, and power consumption. In addition, a fully integrated filtenna can improve the overall performance of the RF system due to decreases in losses without sacrificing filtering capabilities. This improvement in performance is demonstrated through a noise analysis comparing a traditional RF front end utilizing a wideband antenna and an RF front end utilizing a tunable filtenna. The design of filtennas has been mostly outlined already in the existing literature and is achieved through similar methods to filter design. However, the existing filtenna literature has very little discussion on the external quality factor of the antenna, a parameter that is important to obtaining the correct desired bandwidth and correct desired response of the structure. The discussion of this topic is expanded upon in this work, and in doing so another method for finding this parameter is presented. Other methods for finding the external quality factor of antennas can also be applied from the antenna literature once the relationship between the external quality factor in filter design and the external quality factor of an antenna is understood as is presented in this work. An example second-order tunable filtenna covering all of S-band is simulated and fabricated to validate the ideas presented.