Keon-Shik Kong

YBCO superconducting ring resonators at millimeter-wave frequencies

Superconducting microstrip ring resonators operating at 35 GHz have been fabricated from laser ablated YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) films on lanthanum aluminate substrates. The circuits consisted of superconducting strips over normal metal ground planes. The circuits are measured from 20 K to 90 K and with microwave input powers ranging from 0.25 mW to 10 mW. The superconducting resonators show significant improvement in Q over identical gold resonators at 20 K, but only marginal improvement at 77 K. No variation in the superconductor performance is observed with varying input power. The lowest microwave surface resistance of the superconductors at 77 K is 9 m Omega . The change in the resonant frequency with temperature is analyzed and a value for the penetration depth computed. Double resonances were observed in some superconducting ring resonators and an explanation is advanced. Factors limiting millimeter-wave high-temperature superconductor circuits are explored and potential performance levels calculated based on current reported values for high-temperature superconductor surface resistances. >

Performance and modeling of superconducting ring resonators at millimeter-wave frequencies

Microstrip ring resonators operating at 35 GHz have been fabricated from laser-ablated YBCO thin films deposited on lanthanum aluminate substrates. They were measured over a range of temperatures, and their performance was compared to that of identical resonators made of evaporated gold. Below 60 K the superconducting strip performed better than the gold, reaching an unloaded Q approximately 1.5 times that of gold at 25 K. A shift in the resonant frequency follows the form predicted by the London equations. The phenomenological loss equivalence method is applied to the ring resonator, and the theoretically calculated Q values are compared to the experimental results.<<ETX>>

Effects of superconducting losses in pulse propagation on microstrip lines

An analysis of the effect of losses in the propagation of pulses on superconducting microstrip lines is presented. It is based on the phenomenological equivalence method (PEM) and the two-fluid model of superconductivity to calculate the propagation characteristics of the superconducting line. For most practical situations, it is shown that these losses do not introduce phase distortion, and the attenuation constant can be approximated by a quadratic expression of the frequency. Therefore, the effect of attenuation can be easily evaluated through a simple equivalent filter.<<ETX>>

Planar transmission lines with finitely thick conductors and lossy substrates

Various types of lossy planar transmission lines are analyzed by extending the spectral domain approach. Introduction of the finite metallization model and choice of the proper basis functions for the model not only overcomes the computational difficulty, but also reduces drastically the computation labor for the calculation of the conductor loss. Numerical results include the effective dielectric constants, characteristic impedance and total losses for slot lines, coplanar waveguides and strip lines. Numerical computations show that the currents on the side walls of the metal conductors make a considerable contribution to the conductor loss and cannot be neglected and that the quasi-static approximation gives reasonable results for the loss calculation of coplanar waveguides if the metallization thickness effect is taken into consideration properly.<<ETX>>

Conductor-backed coplanar waveguide resonators of YBa/sub 2/Cu/sub 3/O/sub 7- delta / on LaAlO/sub 3/

Conductor-backed coplanar waveguide (CBCPW) resonators operating at 10.8 GHz have been fabricated from laser-ablated and off-axis magnetron-sputtered YBa/sub 2/Cu/sub 3/O/sub 7- delta / (YBCO) high-temperature superconducting (HTS) thin films on LaAlO/sub 3/. These resonators were tested in the temperature range from 14 to 92 K. The unloaded quality factor (Q/sub 0/) at 77 K of the HTS CBCPW resonators was three to four times that of a similar gold (Au) resonator. To the authors knowledge, these results represent the first reported measurements of HTS-based CBCPW resonators.<<ETX>>

Analysis of the Superconducting Coplanar Waveguide

This paper presents a conductor loss calculation of the high Tc superconducting coplanar waveguide (CPW) by using Phenomenological Equivalence Method (PEM) and two fluid model. In this method, the equivalent strip line is obtained by calculating the equivalent width and thickness of CPW by considering the field penetration into the center conductor and ground plane of the CPW. Then, the conductor loss of CPW is calculated from the equivalent strip line. The theoretically calculted Q values are compared with the experimental results available. It is observed that the effect of the substrate loss becomes critical in superconducting coplanar waveguide because of the reduced conductor loss.

Conductor Loss Calculation of Superconducting Microstrip Line using a Phenomenological Loss Equivalence Method

A new approach is presented to calculate the conductor loss of the microstrip line with a superconductor. In this method, two-fluid model for a superconductor is combined with the phenomenological loss equivalence method. This method can be applied to calculate the conductor loss of the superconducting line that has the thickness comparable with the penetration depth. In this method, the geometric factor as well as the field penetration effect in the microstrip line are well considered. Also, its simplicity and the fast calculation give an advantage for its implementation in the computer-aided design of monolithic microwave circuits.

Design aspects and comparison between high-Tc superconducting coplanar waveguide and microstrip line

The high T sub c superconducting microstrip line and coplanar waveguide are compared in terms of the loss characteristics and the design aspects. The quality factor Q values for each structure are compared in respect to the same characteristic impedance with the comparable dimensions of the center conductor of the coplanar waveguide and the strip of the microstrip line. Also, the advantages and disadvantages for each structure are discussed in respect to passive microwave circuit applications.

Computer aided design of evanescent mode waveguide bandpass filter with non-touching E-plane fins

The authors present an efficient computer-aided-design procedure that systematically utilizes a lookup table containing the scattering parameters of E-plane fins. The algorithm incorporates the correlations between the design parameters and the filter characteristics. Using this algorithm, all the filter parameters are obtained directly from the specifications given for the center frequency and the bandwidth of the filter. The design algorithm was tested and shown to give results that are very close to experimental results.<<ETX>>

Evanescent Mode Waveguide Bandpass Filter with Non-Touching E-Plane Fins and Capacitive Iris

A design method based on an optimization is presented for an evanescent mode waveguide bandpass filter with non-touching E-plane fins. Broadband bandpass filters combined with a capacitive iris with a passband as wide as 15% are designed by this method. The theoretical design has been confirmed by the measurement of fabricated filters in the Ka band.