A Compact UWB Bandpass Filter with High Selectivity and Dual Notched-Band

A novel compact-sized ultra-wideband (uwb) bandpass filter (bpf) is proposed in this paper. the proposed bpf is highly selective and is able to eliminate wlan signals from 5.15-5.35 ghz, and downlink of x-band satellite communication signals from 7.25-7.75 ghz. generally, a multiple-mode resonator (mmr), comprised of a u-shaped line, with two high impedance stubs connected to it, and one stepped impedance resonator placed in the center of the u-shaped line is used to generate five resonate modes in the desired band (range of 3.1-10.6 ghz). two transmission zeroes (tzs) are also placed to improve the bandage steepness. one of these tzs is with a lower cutoff frequency and the other tz is with a higher cutoff frequency. a c-shaped open-circuited stub without adding any circuit size is parasitically coupled to the inner part of the u-shaped stub and can provide a narrow notched band at any desired frequency with appropriate bandwidth through the dimension of the parasitic element and its distance to the mmr. this c-shaped stub is used to reject wlan signals. furthermore, uwb passband is fully covered using asymmetric feed lines with defected interdigital coupled-lines. at the same time, another notched-band is implemented to reject x-band signals. slots in the ground plane and input/output ports are etched to increase coupling and improve the in-band performance. the proposed bpf in the study covers uwb span completely and eliminate two bands of unwanted wlan and x-band signals, with good linearity in the passband. a prototype filter was fabricated and its performance was measured to validate the simulation results.