Liang Sun

Dual-Band Superconducting Bandpass Filter Using Embedded Split Ring Resonator

In this paper, a superconducting YBa2Cu3Oy (YBCO) filter employs two sets of octagonal half-wavelength split ring resonators, which are designed to generate two passbands with compact size. The center frequency of the lower passband can be tuned by the outer resonators with loading spirals, and the center frequency of the upper passband can be adjusted by the inner resonators with interdigital structure. Both of them provide sufficient degrees of freedom to control the center frequencies and fractional bandwidths of the two passbands, independently. In addition, a pair of side-coupled stubs is applied to control the bandwidth of the lower passband whereas the interdigital structure is used to adjust the coupling strength between the inner split ring resonator (SRR). Based on the above-mentioned design methodology, a dual-band superconducting elliptic-function-response bandpass filter operating at 2.45 and 3.5 GHz is proposed in this paper. Simulated results show that the insertion losses in both passbands are less than 0.05 dB. Four transmission zeros are created close to the passband edges, resulting in high skirt selectivity. For fabrication, high-Tc superconducting YBCO films are deposited on double-side-polished 0.5-mm-thick MgO substrates. The overall size of this filter is 12.1 × 8.4 mm (about 0.25 × 0.17 λg, where λg is the guided wavelength at the center frequency of the first passband).

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 Wideband Superconducting Filter Using Strong Coupling Resonators for Radio Astronomy Observatory

A 12-pole wideband superconducting microstrip bandpass filter, which has a fractional bandwidth of 38% and a center frequency of 1455 MHz, is presented for the Miyun 50-m radio astronomy telescope, Beijing, China. A novel resonator, which can not only generate very large coupling, but also push its first spurious resonant peak away from the passband, is introduced. A new style interleaved coupling structure is proposed and successfully used in this study to realize the remarkably required strong coupling. To achieve high edge slope on the high side of the passband, as required, a single transmission zero was introduced. The filter was fabricated on a 36 mm times 30 mm times 0.5 mm double-sided YBa2Cu3O7 film deposited on an MgO substrate. The measured results showed that the filter had 0.05-dB minimum insertion loss, 0.08-dB passband ripple, and 23-dB return loss at a temperature of 40 K. The first spurious peak did not appear until 2632 MHz. The overall measured performance showed good agreement with the simulation.

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).

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.

Compact High-Temperature Superconducting Filter Using Multimode Stub-Loaded Resonator

A simple multimode resonator loaded by open- and short-end stubs is proposed in this paper. Its transmission characteristics and equivalent circuit models are investigated by even-odd mode analysis. In addition, the multiband filter design theory using the proposed resonator is explained, and the desired passbands can be conveniently allocated by properly choosing the dimension parameters of the stub-loaded resonator. For demonstration purposes, a compact high-temperature superconducting (HTS) filter operating at 1.57, 2.6, and 3.50 GHz is designed and fabricated. To sharpen the passband skirts of the filter, a source-load coupling configuration with interdigital structure is arranged to produce several transmission zeros. Then, multipath coupling diagrams are constructed, and the relative phase shifts of each path are studied to explain the responses of the triple-band filter. Furthermore, a grounding technique of the short-end stub is realized by subtly connecting with the metal wall packaging instead of via holes in the substrate. In consideration of the inaccuracy in HTS fabricating and packaging, an optimization scheme is proposed. The results of the sensitivity analysis revealed that the optimization scheme is viable. Finally, measurements are in good agreement with the electromagnetic simulations and verify the circuit design methodology.

Compact Triple-Band High-Temperature Superconducting Filter Using Multimode Stub-Loaded Resonator for ISM, WiMAX, and WLAN Applications

A compact triple-band high-temperature superconducting (HTS) bandpass filter using multimode stub-loaded resonator is proposed in this paper. The resonant characteristics of the multimode resonator are investigated by the even/odd-mode analysis. To sharpen the passband skirts, a source-load coupling configuration with a nonresonant node is arranged to produce several extra transmission zeros for realizing high-selectivity performances. For demonstration purposes, a triple-band filter operating at 2.45 GHz (ISM band), 3.5 GHz (WiMAX band), and 5.2 GHz (WLAN band) is designed, fabricated, and measured. Measurements are in good agreement with the electromagnetic simulations. The measured minimum insertion losses of the triple-band HTS filter are 0.16, 0.55, and 0.22 dB, whereas the return losses are greater than 16.7, 10.2, and 17.5 dB, respectively. Its overall size is only 8.3 mm

Design of Quad-Channel High-Temperature Superconducting Diplexer Using Spiral Stub-Loaded Resonators

times

Design of High-Temperature Superconducting Wideband Bandpass Filter With Narrow-Band Notch Resonators for Radio Telescope Application

8.6 mm.