Packaged Ultra-Wide-Band Bandpass Filter Based on Inverted-T Multiple-Mode Resonators and Inverted-F Impedance Transformers [TC Contests]

The packaged UWB bandpass filter based on the inverted-T multiple-mode resonator and inverted-F impedance transformer was designed, fabricated and measured. The inverted-T multiple-mode resonator was designed to have three resonance modes locating inside the passband (3.1-10.6 GHz), ensuring the flat passband insertion loss. The stepped-impedance open stubs in both inverted-T multiple-mode resonator and inverted-F impedance transformer bring numerous desired transmission zeros, helping enhance the stopband attenuation. The transmission-zero frequency is controllable by the step impedance ratio and step length ratio. The capacitive packaging effect from the Stratedge FP118118-1 is absorbed into the inverted-F impedance transformer design. The parasitic cavity modes excited in the enclosed package are suppressed by the microwave absorber attached on the lid. The integration of inverted-T multiple-mode resonator and inverted-F impedance transformer achieves a compact low-loss UWB filter with significant stopband attenuation. The packaging cases with no lid, 3.3 mm height lid, and 6.6 mm height lid were measured. The filter with 6.6 mm height lid achieves the best measured performance, which are a 4.3 dB insertion loss, 9 dB return loss over the passband of 3.1-10.6 GHz and greater than 37 dB stopband attenuation in the lower (0-2 GHz) and upper (12.515 GHz) stopbands.