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This paper presents a compact superconducting diplexer with conductor-backed coplanar waveguide (CBCPW) structures. The couplings of the CBCPW structure resonators are significantly weaker than those of traditional microstrip resonators. High isolations between two channels are therefore achieved by using the CBCPW structures because of their highly suppressed unwanted cross couplings. The CBCPW diplexer consists of two four-pole channel bandpass filters. The couplings in the CBCPW structures, in which the air layer below the substrate varies in height, are simulated and compared with the coupling simulations of microstrip structures. The comparison shows that the coupling intensities of the CBCPW structures are nearly one order of magnitude lower than those of the traditional microstrip structures. The fabricated diplexer exhibits high performance with a compact core size of only 20 mm × 14 mm, and its measurements agree well with the simulations. The measured insertion losses of both channels are less than 0.19 dB, and the isolations are over 53 dB.Index Terms-Bandpass filter (BPF), conductor-backed coplanar waveguide (CBCPW), diplexer, high-temperature superconducting (HTS).

Storing a very high frequency (VHF) band (30–300 MHz) electromagnetic wave has many potential applications, such as phase modulation, buffering, and radio frequency memory. It can be effectively achieved by applying coupled resonator-based electromagnetically induced transparency (EIT) due to its slow light effect. However, the wavelength in the VHF band is too long to design resonators, and the group delay is limited by the high resistive loss of metal. The practical application of EIT in the VHF band is still a big challenge. In this work, we propose and experimentally demonstrate EIT response in a high-temperature superconducting (HTS) microwave circuit with coupled-resonator-induced transparency. The chip size of the HTS circuit is only 34    mm × 20    mm with a very low transparency frequency of 198.55 MHz. In addition, we implement very large group delay higher than 12.3 μs and 16.2 μs with working temperatures of 65 K and 50 K separately, which is much longer than the previous reported works on slow wave. The fabricated circuit is planar with working temperature about 65 K, and thus can be easily integrated into other microwave devices under the cryogenic conditions provided by a commercial portable Stirling cryocooler. Our proposed method paves a way for studying EIT in the microwave region due to the high quality factor of the HTS resonator, which has great potential use for radio-frequency memory in the future.

The antennas were simulated using the commercial software package CST Microwave Studio and measured using an Agilent 8757D Scalar Network Analyzer. Surface Current DistributionThe simulated surface current distributions (L 1 at 18 mm and L 3 at 7 mm) of the antennas can be found in Figure 2. It shows that the length of the signal strip L 1 affects both the first and the second resonant frequency, whereas the length L 3 affects only the second resonant frequency. Simulated and Experimental ResultsThe surface current distribution shows that manipulation of the lengths L 1 and L 3 can possibly change the resonant frequencies of the antenna. Therefore, the reflection coefficients of the antennas were simulated by varying one parameter at a time while keeping the others at constant.Figure 3(a) shows the simulated reflection coefficient with various lengths of L 1 on FR4 substrate whereas keeping all other geometrical parameters at the initial value. Length L 1 has been varied from 12 to 24 mm with each increment of 3 mm. Figure 3(b) shows the simulated reflection coefficient with various lengths of L 3 using the initial geometrical parameters. Length L 3 has been simulated from 1 to 13 mm, with each increment of 3 mm.Similar patterns in the reflection coefficient have been obtained for simulation of the design on RO4350B substrate. Tables 2 and 3 show the difference between the measured and predicted resonant frequencies. It can be seen that the first equation produces a maximum error of 3.42% and the second equation produces a maximum error of 3.39%. Figures 5 and 6 depict the fabricated antennas on RO4350B and FR4. CONCLUSIONIn this article, two empirical equations were proposed to estimate the resonant frequencies of CPW-fed modified T-shaped microstrip antenna. The difference between predicted and measured frequencies is less than 4%. ABSTRACT: This article presents a novel six-pole high-temperature superconducting (HTS) UHF band filter that achieves a wide passband and a wide stopband simultaneously. This filter is designed with a new type of resonator that is composed of interdigital fingers and a vertical meander line. The center frequency of the filter is 357 MHz, and the fractional bandwidth is 28%. The measured out-of-band rejection is better than 55 dB up to 1438 MHz, which is four times higher than the fundamental frequency.