Lan Fang

Compact design of high-temperature superconducting duplexer and triplexer for satellite communications

This paper presents a compact C-band high-temperature superconducting (HTS) input module duplexer, which can be scaled to a triplexer. The duplexer includes a common node as the input port, which is an extensible and effective structure for integrating a HTS multiplexer on a single superconducting film. The input node is realized by an open-loop microstrip line, which resonates at the frequency in the guard band between the two channels. In addition two four-pole bandpass filters consisting of rectangular spiral line resonators are used as output channels of the device. The duplexer is designed at 3995xa0MHz with a bandwidth of 226xa0MHz. The frequency ranges of the two channels are 3882–3942xa0MHz and 4048–4108xa0MHz, respectively. It is fabricated using double-sided Y Ba2Cu3O7 (YBCO) thin films on a piece of 30×xa0xa010xa0mm 2 MgO substrate. The experimental results show that the insertion loss is less than 0.1xa0dB for both channel filters and the isolation between the two channels is higher than 40xa0dB. Good agreement has been achieved between simulations and measurements to illustrate the effectiveness of the proposed approach. Moreover, the triplexer is also designed and measured and the scalability is verified by simulation and experiments.

The design of a linear phase superconducting filter with quasi-elliptic response

This paper presents the design of a linear phase superconducting filter with quasi-elliptic response. The coupling structure of the filter contains two trisections and one quadruplet. The two trisections are applied to generate two independent transmission zeros for high selectivity and are realized by meandered open-loop microstrip resonators; the quadruplet is applied for phase equalization and realized by four novel L-shaped microstrip resonators. The filter is designed at 1950 MHz with a bandwidth of 20 MHz. It is fabricated on a LaAlO3 wafer with double-coated Tl2Ba2CaCu2O8 films. The filter shows good selectivity together with flat group delay over 80% of the passband both in the simulation and measurements.

A computer-aided method for postproduction tuning of HTS filters

The empirical tuning of high temperature superconducting (HTS) filters is usually time-consuming and expensive. A computer-aided tuning method is presented in this paper. By means of optimization, the method diagnoses detuning of individual resonators quantitatively in the tuning process, and then by using neural network models the method is able to give the operator a decision on how much the corresponding tuning screws should be tuned. So, compared with the empirical tuning method, this method can be used to tune the HTS filters accurately with less time and cost.

Study on chaotic behaviors of RCLSJ model Josephson junctions

Chaotic behaviors of the dc-biased resistively-capacitively-inductively shunted Josephson junctions are studied numerically. The existence of the chaos is proved by the spectrum and strange attractor. We also find out the route to chaos is intermittence. The parameter space in which chaos exits is obtained, and different features of the chaos in different parameter range are also given.

Jc enhancement in Tl2Ba2CaCu2Ox thin films by introduction of CeO2 nanodots on substrates

Tl2Ba2CaCu2Ox (Tl-2212) thin films with enhanced transport critical current densities Jc were fabricated by using conventional dc sputtering and a post-annealing process. In order to employ artificial defects to improve the flux pinning strength, nano-sized CeO2 dots were deposited on the LaAlO3(001) substrates by radiofrequency (rf) magnetron sputtering from a cerium metal target prior to the growth of Tl-2212 films. The critical current density Jc (77 K) of the Tl-2212 thin film on the nanodot-introduced substrate reaches 6 × 106 A cm − 2 at self-field, which is 1.7 times larger than that on the normal substrate. The enhancement of the Jc in Tl-2212 film grown on the substrate with artificial defects is more obvious in magnetic fields. At 0.5 T dc magnetic field, a Jc (77 K) of 3.5 × 104 A cm − 2 is observed, which is about 13 times larger than that on the normal substrate.

HTS filter subsystem for future mobile communication system

A high-temperature superconducting (HTS) filter subsystem consisting of a 10-pole HTS filter with group delay self-equalization, a cryogenic low noise amplifier (LNA), and a cooling device is presented in this paper. The HTS filter has a 0.51% fractional bandwidth at 1955 MHz, simulated in Sonnet, and is fabricated using double-sided Tl2Ba2CaCu2O8 films on 0.5 mm thick LaAlO3 substrate. Measured responses show that the minimum insertion loss of the filter is 0.16 dB, and the out-of-band rejection is better than 75 dB. The slope is 27 dB MHz−1 at the low band edge and 22 dB MHz−1 at the upper band edge. The HTS filter subsystem has a gain of 19.3 dB and a noise figure (NF) of 0.8 dB. Furthermore, the phase distortion of HTS filters is considered, and an efficient design approach for self-equalized HTS filters is proposed.

Fabrication of CeO2 buffer layers for epitaxial growth of Tl-2212 films by the in situ two-temperature process

High-quality Tl-2212 superconducting films were prepared on CeO₂ coated r-cut sapphire substrates. An in situ two-temperature deposition process was introduced in the growth of CeO₂ buffer layers. XPS measurements showed that the deposition process can sharply decrease the mutual diffusion at the interface. The critical temperature T_c of Tl-2212 film grown on the buffer layer was 108.2 K, the critical current density J_c (77K, 0T) was above 6 MA/cm², and the microwave surface resistance R_s(77K, 10 GHz) was below 200 μΩ.

Growth of Tl-2212 Films on CeO2-Buffered Sapphire Substrates

Tl2Ba2CaCu2O8 (Tl-2212) films were prepared on r-cut sapphire substrates buffered with CeO2 by dc magnetron sputtering and post-annealing method. The in situ two-temperature process was used to grow CeO2 buffer layers. XRD and AFM measurements showed that CeO2 films deposited at temperature of 370-470°C were excellent c-axis orientation and had smooth surface. SEM observations demonstrated that the Tl-2212 films’ surface morphology was changed from condensing crystal structure to plate-like structure when the CeO2 deposition temperature was increased. The best Tl-2212 film’s critical temperature Tc can reach to 108.3 K, and critical current density Jc obtained at 5.33 MA/cm2 (77 K, 0 T).

Effect of CeO2 Deposition Temperature on the Properties of Tl-2212 Superconducting Films Grown on MgO Substrates

The preparation and superconductivity of Tl-2212 films grown on CeO2-buffered MgO substrates were investigated. AFM showed that the annealing of MgO substrates remarkably improved their crystal quality of surface layers, and led to the surface morphology of substrates evolving into unattached outgrowth structure with ultra-smooth surface. XRD measurements showed that CeO2 buffer layers grown on MgO annealed at the suitable conditions were pure (00l) phase. The 500 nm thick Tl-2212 films grown on these CeO2 films subsequently possessed excellent c-axis orientation and superconductivity. The best Tl-2212 film reached a low surface resistance of about 324 μΩ (10 GHz, 77 K), a critical current density as high as 3.5 MA/cm2 (77 K, 0 T) and a critical transition temperature of about 108.4 K.

Growth of Double-Side Tl-2212 Thin Film on CeO2-Buffered MgO Substrate

The double-side Tl-2212 films were fabricated on CeO2-buffered MgO substrates by dc magnetron sputtering and post-annealing method. The RF magnetron sputtering technology was used to grow CeO2 buffer layers. XRD and SEM measurements showed that the CeO2 films on annealed MgO substrates were highly c-axis orientation, and the Tl-2212 superconducting films on both sides had similar morphology and crystalline structure. For both sides of Tl-2212 films, the critical transition temperatures (Tc) were above 106 K, and the critical current densities (Jc) were above 2.2 MA/cm2 (77 K, 0 T).