Narrow-band High-temperature Superconducting Research Articles

Varactor-Tuned Narrow-Band High Temperature Superconducting Notch Filter

A tunable narrow band high temperature superconducting (HTS) notch filter is presented. HTS folded square open loop resonator loaded with hyper-abrupt GaAs varactor is used to reach high tunability and avoid the via-hole grounding. Measured results show that the notch frequency can be tuned from 286 to 485 MHz (tuning range of 51.6%), and the attenuation from 26 to 70 dB when the bias voltage of the varactors is from 1 to 20 V. The -3 dB bandwidth is between 6.9 and 7.9 MHz, and the out-of-band insertion loss is less than 0.2 dB. Furthermore, the reliability of manufacture techniques of the filter is proved by mechanical vibration and shock tests.

A narrow-band high-temperature superconducting filter with wide upper stopband

This article presents a novel interdigital capacitor resonator (ICR), which has a high spurious frequency and compact size. A six-pole high-temperature superconducting (HTS) bandpass filter (BPF) has been designed and fabricated with this ICR on a double-sided MgO-based YBCO thin film. Measurement at cryogenic temperature shows a fractional bandwidth of 0.4%, and an ultra high spurious passband at about 4.1 f0. Moreover, the measurement shows a good agreement with simulation in wideband response. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:443–447, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27324

A high-performance narrowband high temperature superconducting filter

Recent development of a high-performance narrowband high-temperature superconducting (HTS) filter is presented. A 10-pole quasi-elliptic function response filter with two pairs of transmission zeros (for high selectivity), which has a center frequency of 2.185 GHz and a 3 dB bandwidth of 10 MHz (a fractional bandwidth of 0.45%), is introduced. The filter was fabricated on a 40 mm×16 mm×0.5 mm MgO wafer with double-sided YBCO films. The measured results show that the filter has 0.15 dB insertion loss at the center of the passband and a return loss better than −22.5 dB at a temperature of 67 K. Band edge steepness reaches over 28.3 dB/MHz at both the low and high frequency edges. The out-of-band rejection is over 78 dB at 8 MHz away from the center frequency and close to 100 dB in a wideband range.

Center Frequency Tuning for a Narrowband Superconducting Filter in the Time Domain

This paper presents a mechanical tuning method for tuning the center frequency of a narrowband high-temperature superconducting filter. The filter is designed with 0.5-MHz bandwidth at 166.9 MHz and is fabricated. Tuning is carried out based on the time-domain response of filter return loss. The filter can be precisely tuned to a desired center frequency while maintaining a high-frequency performance. The center frequency is tuned from 167.2 to 166.5 MHz. The tuning range is 0.7 MHz and is sufficient to compensate the frequency offset caused by 0.72% variation in the substrate effective dielectric constant or 4% that of the substrate thickness.

8-GHz Narrowband High-Temperature Superconducting Filter With High Selectivity and Flat Group Delay

This paper reports a development of a narrowband high-temperature superconducting filter with both high selectivity and flat group delay. The filter has a center frequency of 8.625 GHz and a 3-dB bandwidth of 42 MHz (a fractional bandwidth of 0.49%). In order to achieve both high band-edge steepness and excellent group-delay flatness, we introduce a 14-resonator quasi-elliptic function response with three pairs of transmission zeros (one pair for high selectivity and two pairs for flat group delay) in the cascaded quadruplet coupling structure. We also develop a novel low radiation resonator (double-folded resonator) to reduce the parasitic coupling and meet other requirements for the 8-GHz filter. The filter was fabricated on a 2-in-diameter 0.5-mm-thick MgO wafer with double-sided YBCO films. The measured results show a midband insertion loss of 1.6 dB and a return loss better than 15.5 dB. Band-edge steepness reaches over 11.7 dB/MHz at both the high- and low-frequency edges. The 60-dB rectangle ratio is less than 1.25. The out-of-band rejection is over 70 dB at 5.98 MHz from the 3-dB band edge. The variation of group delay is less than 23 ns over 33 MHz (78.5% of 3-dB bandwidth), and less than 30 ns over 34.5 MHz (82% of 3-dB bandwidth).

Narrowband high temperature superconducting filter for mobile communication systems

The paper reports a recent development of a narrowband high temperature superconducting (HTS) bandpass filter for future mobile communication systems. The filter is designed to have a 5 MHz passband in the UMTS base station's receive band. The filter exhibits an 8-pole quasi-elliptic function response implemented with a cascaded quadruplet coupling structure. The filter was fabricated on a 0.43 mm-thick sapphire wafer with double-sided YBCO films. The measured filter showed a midband insertion loss of 0.5 dB at 1973 MHz and a return loss better than � 15 dB over the passband. It also exhibited an excellent rejection over the entire UMTS base station transmission band.