An Ultra-wideband Bandpass Filter using a novel "Concentric Rings DGS"

An UWB-BPF is proposed using a new type of concentric ring defected ground structure (DGS), aiming at transmitting the signals in the whole UWB passband of 3.1GHz to 10.6GHz. In the Design DGS is used to realize high impedance microstrip lines, which make the edge of passband frequency range convenient. DGS structure looks as two concentric rings placed between two parallel plates. The passband edges can be tuned to desirable frequency by varying dimension of these plates and radius of the two concentric rings. In the design, interdigital coupled lines are used to feed open stub loaded resonator. The spacing between the coupled lines is adjusted so as to raise frequency dispersive coupling degree with the coupling peak at 6.85GHz and still providing the required tight coupling in UWB-BPF feed structure. After optimization of the filter design, a good UWB-BPF behavior with three transmission poles at 4.2GHz, 6.9GHz and 9.4GHz is theoretically realized and found in excellent agreement with simulated results. Within the whole UWB passband, the return loss is found higher than 12 dB and group delay variation is less than .38 ns