Wideband microstrip band-pass filter for L-band low-noise receiver

This paper presents a novel wideband microstrip band-pass filter for L-band low noise receiver of radio telescope. By introducing a stepped-impedance one-wavelength ring resonator (SORR) into a stepped-impedance half-wavelength resonator (SHR), excellent in-band performance is realized. In order to suppress the harmonic responses of the filter for a wide stop-band, two band-stop sections with asymmetrical π-type structure are designed. A prototype filter having 49.3% of 1-dB and 57.9% of 3-dB fractional bandwidth is fabricated with advantages of compact size, high selectivity and high out-of-band rejection. In the pass-band, return loss is less than -18.8dB and the minimal insertion loss is 0.6 dB.