Super compact UWB bandpass filter using unit-cell CRLH-TL based on via-pin capacitor

This paper presents a super compact ultra-wideband (UWB) bandpass filter using unit-cell composited right/left-handed transmission line (CRLH-TL) based on via-pin capacitor for size reduction. The proposed filter can extremely reduce size by adopting arch-shaped Teflon coated pin which is inserted into shorting via as vertical cylinder type capacitor. The proposed filter has a compact size of 7.2 × 3.315 mm², which amounts to 0.3 λ_g by 0.14 λ_g. Simulated and measured results are found in good agreement with each other, showing a UWB passband from 2.9 GHz to 10.2 GHz, 10.5 dB return loss bandwidth of about 7 GHz, minimum insertion loss of 0.7 dB at 7.4 GHz. Finally, tolerance test is executed by measuring 15 manufactured samples for verifying Teflon coating stability.