E. Belohoubek

Microwave properties of highly oriented YBa2Cu3O7−x thin films

We have performed intra‐ and extra‐cavity microwave frequency (1–100 GHz) measurements on high quality Y1Ba2Cu3O7−x superconducting thin films on (100) LaAlO3 substrates. The ∼0.3 μm thin films fabricated by the pulsed laser deposition technique exhibit superconducting transition temperatures >90 K, as determined by resistivity and ac susceptibility measurements, and critical current densities of 5×106 A/cm2 at 77 K. Moreover, ion beam channeling minimum yields of ∼3% were measured, indicating the extremely high crystalline quality of films grown on the LaAlO3 substrate. Microwave surface resistance values at 77 K for these films are found to be more than one to two orders of magnitude lower than for copper at 77 K for almost the entire frequency range explored. We postulate that the reason we observe such low surface resistances in these films is the virtual absence of grain and phase boundaries coupled with the high degree of crystallinity. Furthermore, we believe that the residual resistance measured b...

30-Way Radial Power Combiner for Miniature GaAs FET Power Amplifiers

A compact radial divider/combiner structure is described that combines 30 miniature GaAs FET power amplifiers. A power output of 26 W has been achieved at 11.3 GHz with a 0.5-dB bandwidth of 600 MHz. The combiner is small, lightweight, low loss and offers graceful degradation.

Performance of a narrow band microwave filter implemented in thin-film YBa2Cu3O7-δ with ohmic contacts

Using in situ deposited thin‐film Y1Ba2Cu3O7−δ on LaAlO3 substrates, we have developed a pseudo‐interdigital three‐pole stripline filter with a minimum passband loss under 3.5 dB at 9.5 GHz and 77 K. The passband is very narrow, having a bandwidth of only 50 MHz (0.5%). The filter occupies a volume of less than 0.1 cm3. An equivalent copper filter produced a loss of 18.5 and 28 dB at 77 and 300 K, respectively. The input and output coupling is achieved by ex situ sputtered Au thin‐film contacts defined on the Y1Ba2Cu3O7−δ by a lift‐off technology and ultrasonically bonded to hermetic K connectors. Some of the major concerns in the realization of narrow band filters such as air gaps between high dielectric constant substrates and uniformity of the substrate’s dielectric constant are addressed.

High temperature superconducting components for microwave systems

Abstract Starting with an overview of the various requirements placed on substrates for superconducting microwave applications, the current state of the art of high temperature superconducting thin films on different substrate types is discussed. Recent results for several superconducting microwave components that could form important building blocks for advanced microwave systems are presented, including performance data on experimental devices such as narrow band-pass and band-stop filters, superconducting circulators and miniature, low-frequency spiral resonators. Some examples of system types that can most likely benefit from high temperature superconductivity are identified.

Critical design issues in implementing a YBCO superconductor X-band narrow bandpass filter operating at 77 K

The implementation of a narrowband (0.5%) high-T/sub c/ superconducting filter operating at X-band and 77 K is discussed. The authors examine the effects of high-temperature superconductor (HTS) film thickness on the loss performance; kinetic and mutual inductance contributions to the center frequency drift with temperature; and nonlinearities associated with the generation of intermodulation distortion. It is concluded that, in order to design high-performance circuits with HTS materials, kinetic inductance effects and the generation of intermodulation products must be controlled. Film thickness and uniformity are key parameters to low-loss performance.<<ETX>>

Microwave properties and modeling of high-T/sub c/ superconducting thin film meander line

Meander lines have been utilized for characterizing laser-deposited, thin-film, high-T/sub c/ superconducting material. The dispersion characteristics of the meander line have been modeled and the power dependence of high-T/sub c/ materials as a function of frequency and temperature has been investigated. Measurements showed that magnetic fields as low as 0.1 Oe will affect the superconducting material, decreasing the Q of the meander lines. The Q deterioration is temperature and frequency dependent and the latter is less pronounced at higher frequencies.<<ETX>>

Microwave Measurements on Patterned High Temperature Superconducting Thin Film Circuits

The microwave surface resistance and dispersion of laser deposited YBaCuO films patterned in the form of a meander line have been measured from L through Ku-band at temperatures from 5 to 90K. Surface resistance values below 1 mΩ were demonstrated at 10 GHz and 79K. The results show great promise for the realization of effective high-Tc superconductive passive microwave components in the near future.

Miniature circulators for microwave superconducting systems

Ultraminiature high performance lumped element high temperature superconductor (HTS) circulators have been successfully demonstrated. Epitaxial HTS YBCO films have been deposited by pulsed laser deposition (PLD) onto buffered Yttrium Iron Garnet (YIG) substrates with measured surface resistance values (<1 m/spl Omega/ at 10 GHz @ 77 K) comparable to those of HTS films on lanthanum aluminate. The lumped element circulators occupy an area about an order of magnitude smaller in size than that of conventional disc junction circulators. Excellent low loss (<0.23 dB) and high isolation (>30 dB) over 5% bandwidth have also been demonstrated.<<ETX>>

Microwave characteristics of bulk high-T/sub c/ superconductors

Currently, most available high-T/sub c/ bulk material is in disk form that does not lend itself readily to microwave-loss measurements. A resonant measurement technique using low-impedance disk resonators is described. The configuration enhances the influence of conductor losses on the resonator Q and thereby permits the evaluation of disks as a function of temperature in a relatively simple test configuration with good accuracy. Measurements on bulk YBa/sub 2/Cu/sub 3/O/sub 6+x/ material are described with conductivities at X-band ranging up to 10 times that of Au at 65 degrees K.<<ETX>>

Microwave compatible YBa2Cu3O7−δ films on (001)MgF2 substrates

High quality YBa2Cu3O7−δ (YBCO) films have been epitaxially grown on low dielectric constant, low loss tangent (001)MgF2 substrates using a double buffer layer scheme. The YBCO films are (001) oriented, exhibit Tc’s of 88–89 K with transition widths ≤0.5 K and Jc’s of 4×106 A/cm2 at 77 K in zero field. Dielectric resonator experiments indicate unloaded Q values in excess of 30 000 at 77 K and 24 GHz in the unpatterned films. Films patterned into meanderline resonators and operating at 10 GHz, 79 K, exhibit surface resistance (Rs)<1 m Ω suggesting near‐future realization of low loss superconducting components in the millimeter‐wave region.