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This letter presents a novel microstrip tri-band filter in which a shunt-stub bandpass filter and a dual-band bandstop filter are integrated into a single structure of short length. The two stopbands of the bandstop filter are allocated within the wideband passband of the bandpass filter, resulting in a filter having three passbands. Good return loss is obtained using an optimization routine. This technique has high flexibility on setting the bandwidths and center frequencies of passbands. A prototype filter is designed and fabricated. Good agreements between simulation and measurement in respect of low insertion loss and high isolation are demonstrated.

This paper presents an ultra-wideband bandpass filter (UWB BPF) using quarter-wavelength inverter-lines at both sides of a three-pole interdigital filter. The relations between the impedances of the inverter-line with the load and those of the interdigital filter connected to the inverter-line were studied. From these, the design procedures for the impedance matching at the UWB passband edges were shown. Then the designed BPF from the above results showed that the bandwidth was 24% wider than that of the sole interdigital filter by additional two conjugate matching poles. The fabricated BPF achieved the performances of the required passband by the five matching poles.

A UHF-band RF tunable filter is developed for TV white space CMOS transmitter applications. It is based on the combined Sallen-Key and LC notch structure. The inherent transmission zero of the Sallen-Key core is carefully chosen to suppress the 7th-harmonic component of the transmitter output, and the LC notch filter is set to suppress the 9th-harmonic component. The filter is built in 0.18-µm CMOS process and consumes 6.2-mA from a 1.8-V supply. The filter's cutoff frequency is tuned from 100-MHz to 500-MHz in five steps. It is successfully adopted in a TV white space CMOS transmitter integrated circuit.

A new method of designing FIR notch filters with arbitrary notch frequency is proposed, where a modified sampling kernel is introduced and utilized along with a complementary filter concept. In particular, the proposed sharp notch FIR filter design provides a closed-form solution for filter coefficients, leading to further utilization for designing reconfigurable FIR notch filters.