Dual-mode-resonator-based pseudo-elliptic filters with tunable response

This paper presents the design of filters having frequency-tunable response based on microstrip dual-mode patch resonators. Discrete tunability is achieved through a modified version of a standard patch resonator which allows one to switch between different centre-frequency states. Besides, the selectivity of the filter is enhanced by transmission zeroes (TZs), two at each side of the pass-band. The method has been proven by the design and measurement of a dual-mode cavity activated by PIN diodes. The single resonator is then employed to build a filter whose electrical measurement resulted in a very good agreement with the simulations and showed a maximum IL=1.4 dB (Q-factor of 160).

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