Aisheng He

A 12-Pole Narrowband Highly Selective High-Temperature Superconducting Filter for the Application in the Third-Generation Wireless Communications

An ultra-selective high-temperature superconducting bandpass filter was designed and fabricated to satisfy the demands of the third-generation wireless communications. This filter was designed to have 12-pole quasi-elliptic response with 4.68-MHz bandwidth in the third-generation communications band (a fractional bandwidth of 0.0023). Full-wave simulations were conducted by using Sonnet software. A novel, compact, and low radiation resonator with a high-quality (Q) factor value was developed to reduce the parasitical coupling. In order to satisfy the demand of high band-edge steepness, three pairs of transmission zeros at finite frequencies were introduced in the cascaded quadruplet coupling structure. The filter was fabricated on a 2-in-diameter 0.43-mm-thick sapphire wafer with double-sided YBCO films. The measurements showed that the passband center frequency (f0) of the filter is 2.038 GHz at 67 K with a midband insertion loss of 0.67 dB and the return loss better than 15 dB. The measured response of the filter also exhibited ultra-high band-edge steepness of 140-220 dB/MHz. Better than 60 dB of out-of-band rejections for frequencies very close to the band edge (|f-f0|>2.7 MHz), better than 90 dB at frequencies 7.5 MHz away from the center frequency and up to 100 dB of wideband rejections were achieved

A 24-pole high Tc superconducting filter for mobile communication applications

This paper presents a highly selective 24-pole Chebyshev HTS bandpass filter. The filter was designed at 1748 MHz centre frequency with 75 MHz bandwidth, which was suitable for the GSM base station. The filter was fabricated using double-sided YBCO films on a 3 in diameter, 0.43 mm thick sapphire substrate. The simulation of the filter performance was carried out using Sonnet software. A novel resonator structure was proposed. The resonator exhibited a very high Q value of about 30 000 at 77 K. The filter showed an excellent selectivity. At the band edge of the filter, the slope was about 17 dB MHz(-1). Out of the band, the rejection level is better than -90 dB.

Superconducting filter with a linear phase for third-generation mobile communications

A linear phase filter using two cross- coupled quadruplet structures to achieve self- equalization was designed at 2012.5 MHz with 5 MHz bandwidth for a third- generation mobile communications system. This filter was fabricated using double- sided YBCO films on a 2 inch diameter, 0.5 mm thick MgO substrate. In the measurement, it showed good matching in the passband, with reflection better than - 15 dB. Moreover, the group delay variation is less than 50 ns over 89% of the filter bandwidth.

A HTS Bandpass Filter for a Meteorological Radar System and Its Field Tests

This paper presents recent progress of a high temperature superconducting (HTS) filter designed for a meteorological radar system (wind profiler) and its field tests results. The filter was designed to exhibit a ten-pole quasi-elliptic response with a fractional bandwidth of 0.35% in L band. It was fabricated using double-sided YBCO films on a 50-mm-diameter, 0.5-mm-thick MgO substrate. A HTS subsystem was assembled by connecting the filter with a cryogenic low noise amplifier (LNA), fixing them on a cryocooler and enclosing in a cryopackage. With the HTS subsystem substituting the corresponding conventional part (the conventional subsystem) of the wind profiler, two stages of experiments including field test were carried out. The first stage experimental results showed that while employing the HTS subsystem the sensitivity of the wind profiler improves 3.7 dB and the anti-interference ability improves 48.4 dB. The second stage experiment-field test results showed the improvement visually through the wind charts and wind profiles obtained in the field trial.

A Novel Quasi-Elliptic HTS Filter With Group-Delay Equalization Using Compact Quasi-Lumped Element Resonators in VHF Band

To produce a filter small enough to fit a 2-in wafer in the very high frequency (VHF) band while avoiding parasitic cross coupling among nonadjacent resonators, a novel quasi-lumped element resonator with interdigital capacitor, double-spiral inductor, and pad capacitor have been introduced. This resonator has not only a highly miniature structure but also a very weak far-field radiation. A ten-pole quasi-elliptic filter with group-delay equalization, which has a 7.1-MHz 1-dB passband and a center frequency of 257.5 MHz, is designed and fabricated on a 37.3 x mm x 30.1 x mm x 0.5 x mm LaAlO3 substrate. The measured results showed a 0.24-dB insertion loss, a 15-dB return loss, and a 70-dB out-of-band rejection. Moreover, the group delay variation is less than 50 ns over 70% of the 1-dB passband and the band where the phase error ripple is within plusmn5deg is more than 80% of the 1-dB passband. The overall experimental performance showed excellent agreement with the theory and simulation, which is a good proof of the advantage of our weak far-field radiation resonator. The result showed that the novel resonator is very suitable to fabricate narrowband ultrahigh frequency, VHF, or even lower frequency high-temperature superconductor filters on a 2-in wafer.

A COMPACT INTEGRATION OF HIGH-TEMPERATURE SUPERCONDUCTING BANDPASS AND BANDSTOP FILTERS

Integration of a high-temperature superconducting (HTS) narrowband bandpass filter and a HTS bandstop filter onto a single piece double-sided YBCO thin film with 0.5mm-thick LaAlO3 substrate has been carried out. The 8-pole bandpass filter was designed with a fractional bandwidth about 0.8%. A pair of transmission zeros was implemented, showing typical quasi-elliptical function characteristics. The bandstop filter has a high stopband attenuation (~70dB) to fulfill the special requirement of potential application in communications. Integration of the two filters was successfully achieved.

A New Coupling Matrix Extracting Method From the Frequency Response

Coupled resonators are widely used in many applications, especially for filters. It is necessary to know the coupling matrix of those resonators in order to further modify and/or optimize the existing design. In recent years, many efforts have been made to generate a coupling matrix. In this paper, a new method is proposed, which can be applied for both the synchronous and asynchronous coupled resonators. With this method, the eigenvalues and eigenvectors of the coupling matrix can be generated directly from the simulated frequency responses, and the coupling matrix can then be determined. Typical examples are illustrated for the cases such as a quadruplet with an image, real, or complex transmission zeros. The impact of loss is also discussed. As a matter of fact, this method has been successfully used in the design of high-temperature superconducting filters

An HTS microstrip equalizer for improving the group delay of an HTS filter for third-generation communications

This paper reports a high temperature superconducting (HTS) microstrip equalizer for improving the flatness of the pass-band group delay of an HTS filter for third-generation (3G) communications. The HTS filter to be equalized is a ten-pole quasi-elliptic function filter with a bandwidth of 9.6 MHz centered at 1946.5 MHz. The one-port coupled-resonator microstrip equalizers were designed to have three or four poles, and the calculated and simulated group delay response curves of the filter with the equalizers are presented and discussed. A three-pole equalizer was fabricated on a piece of 0.5 mm thick MgO wafer with double-sided YBCO films. The measured responses show that after connecting with the HTS equalizer, the group-delay effective bandwidth of the filter, defined as the ratio between the flat group delay pass-band width (a criterion of variation of pass-band group delay being less than 50 ns was applied) and the equal ripple pass-band width, increased from 50% to 70% without any noticeable degradation of the band-edge steepness of the HTS filter.

Demonstration of HTS microwave sub-systems with a pulse tube cryocooler

Abstract A special pulse tube cryocooler was designed and fabricated. Acceleration measurements show that the vibration of this cooler is much smaller than that of a Stirling machine. Two HTS microwave devices have been integrated with this cooler, which operate successfully as practical HTS sub-systems.

High Temperature Superconducting Microwave Filters for Applications in Mobile Communication, Satellite Receiver and Wind-Profile Radar

Three types of high performance high temperature superconducting (HTS) filters for different applications are introduced. The HTS filter for 3G mobile base station, which is constructed by multi-loop resonators, showed ultra selectivity with extremely small fractional bandwidth (narrower than 0.23%), extremely steep skirt slope (140- 220 dB/MHz) and excellent out-of-band rejections. The integrated bandpass and bandstop HTS filters for satellite receiver made by YBCO and TBCCO thin films achieved very small return loss (les -22.5 dB) and extremely high out-of-band rejection at certain frequency bands (> 110 dB) simultaneously and showed satisfactory results in the space qualification mechanical tests. Field tests of the wind-profile radar exhibited that with HTS subsystem an increase of 3.7 dB in sensitivity and an improvement of 48.4 dB in anti-interference ability of the radar were attained so that when conventional radar failed to detect the speed and direction of the wind above 2000 meters of the radar due to interference, the HTS radar can produce perfect wind spectrums and profiles.