Highly Miniaturized VHF Helical Filters with Fully Reconfigurable Capabilities

Abstract

The demand for frequency reconfigurable bandpass and bandstop filters within the VHF-UHF frequencies continues to rise due to the increasingly crowded radio frequency (RF) spectrum. As a result, higher levels of isolation and an increase in selectivity are essential for the next-generation of intelligent microwave communication systems. Additionally, compact structures that maintain performance and are integratable with other RF components are very desirable. One way to cope with this reality is to investigate reconfigurable capabilities while reducing the physical size of well-known high-performance structures in the VHF-UHF realm. This thesis presents a second-order bandpass filter to demonstrate a method of miniaturizing a helical resonator filter utilizing varactor diodes as the capacitive loading element. This technique not only miniaturizes the helical structure but also allows for a voltage-controlled resonant frequency tuning mechanism. To achieve agility in the external coupling as well as the inter-resonator coupling, a new method of coupling into the helical structures is used to incorporate the use of varactor diodes as a tuning element. As a result, a fully reconfigurable miniaturized helical bandpass filter is simulated, fabricated, and measured, offering promising results for dynamic frequency access in future wireless systems.