Center Frequency and Bandwidth Tunable Filter with Varactors

This paper presented a deformed microstrip combline UHF (Ultra High Frequency) bandpass filter structure with continuous tunability for both center frequency and bandwidth. By using bandwidth control subnetwork, couplings between resonators can be controlled, so as to achieve the tunability of the bandwidth. The electrical length of the deformed filter resonator approximately equals to lambda g/8, it not only decreases the size of the filter, but also has the second passband centered at somewhat over four times from the first passband. This filter has a 66% tuning range from 400 MHz to 800 MHz, and it can operate in the IMT-Advanced system (450-470 MHz), the Amateur Radio system (430-440 MHz), and part of the Digital Video Broadcasting (DVB-T) system (470-800 MHz).