Single switch reconfigurable bandpass filter with variable bandwidth using a dual-mode triangular patch resonator

A reconfigurable bandpass filter is demonstrated using a dual-mode microstrip triangular patch resonator. The proposed circuit uses a single switch to control its fractional bandwidth while keeping a fixed center frequency of 10 GHz. The switching mechanism is accomplished by a p-i-n diode that connects and isolates a tuning stub from the rest of the circuit. The on and off state of the diode effectively controls the resonance frequencies of the two poles, produced by the dual-mode behavior of the resonator. The filter achieves a measured 1.9:1 tunable passband ratio. The circuit presented here represents the first single switch bandwidth reconfigurable filter that requires no size compensation to maintain a fixed center frequency.