Mirzaee, Milad, Virdee, Bal Singh and Noghanian, Sima (2014) Compact ultra-wideband bandpass filter with variable notch characteristics based on transversal signal-interaction concepts. International Journal of RF and Microwave Computer-Aided Engineering, 24 (5). pp. 549-559. ISSN 1096-4290
A novel technique is presented to design highly compact microstrip ultra-wideband (UWB) bandpass filters that exhibit high selectivity quasi-elliptical response. The design is based on transversal signal-interaction concepts that enable the inclusion of single or dual notch-bands within the filter's passband to eliminate interference from other services that coexist within the UWB spectrum. The filter configuration comprises of two transmission paths which include folded T-shaped stepped impedance resonators (SIRs) that are capacitively coupled with the input/output lines to enable signal transmission. It is shown that by combining the filters of different passband centre frequencies an UWB filter can be realised with either a single- or dual-notch function. The theoretical performance of the filter is corroborated via measurements to confirm that the proposed filter exhibits UWB passband of 123% for a 3 dB fractional bandwidth, a flat group-delay with maximum variation of less than 0.3 ns, passband insertion loss less than 0.94 dB, high selectivity, a sharp rejection notch-band with attenuation of −23 dB, and a good overall out-of-band performance. Furthermore, the filter occupies a significantly small area of 94 mm2 compared with its classical counterparts.
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