Research on dual-band fully tunable filter based on T-shaped dual-mode resonator

Combining two T-shaped resonators operating in different frequency bands, designing a dual-mode dual-band fully tunable filter indirectly couples parallel coupling lines into a feed structure, which makes the bandwidth independently tuning and central frequency and ensures the stability of the other passband in the process of tuning one passband. The spindle frequencies of the two passbands are 1.2 GHz and 1.7 GHz, and meanwhile, the bandwidth is 120 MHz and 100 MHz, respectively. The relative tuning range of the two bands is greater than 15%. The specific bandwidth tuning range is 60–180 MHz and 60–140 MHz. During the tuning process, the insertion loss is lower than 3 dB, and the return loss is clearly better than 10 dB.