Title :
An Ultracompact Superconducting Bandpass Filter at 40 MHz Using Spiral Resonators and a New Feedline Structure
Author :
Ying Zhang ; Xubo Guo ; Bisong Cao ; Bin Wei ; Xiaoping Zhang ; Xiaoke Song ; Guannan Suo ; Guoyong Zhang
Author_Institution :
Dept. of Phys., Tsinghua Univ., Beijing, China
fDate :
4/1/2012 12:00:00 AM
Abstract :
This paper presents a superconducting filter with a bandwidth of 0.5 MHz at 40 MHz on a LaAlO3 substrate. It has a compact size of 40 mm × 19 mm, which amounts to only 0.02 λg0 × 0.01 λg0, where λg0 is the guided wavelength of the 50-Ω line on the substrate at the midband frequency. The effect of the resonator structure on the unwound length and, hence, the size of the resonator is analyzed. A spiral resonator with positive mutual inductances between adjacent microstrip turns can greatly reduce the resonator´s unwound length and is used to miniaturize the filter size. A feedline structure spiraled inside the spiral resonator is proposed to realize a strong external coupling. Furthermore, a cross-coupling line is added to the six-pole filter to improve the band-edge steepness. The filter is successfully designed and fabricated. The measured results demonstrate a 0.3-dB insertion loss, a -19.2 dB return loss, an 80-dB out-of-band rejection, and steep band edges, which are in good agreement with electromagnetic simulations.
Keywords :
VHF filters; band-pass filters; high-temperature superconductors; microstrip filters; passive filters; superconducting filters; superconducting thin films; LaAlO3; band-edge steepness; bandwidth 0.5 MHz; cross-coupling; electromagnetic simulations; external coupling; feedline structure; frequency 40 MHz; high-temperature superconducting thin films; insertion loss; microstrip; out-of-band rejection; return loss; six-pole filter; spiral resonators; steep band edges; ultracompact superconducting bandpass filter; unwound length; Couplings; Educational institutions; High temperature superconductors; Physics; Resonant frequency; Spirals; Superconducting microwave devices; Bandpass filter; high-temperature superconducting (HTS); microstrip; spiral resonator;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
DOI :
10.1109/TASC.2012.2187648