Balam A. Willemsen

HTS filter subsystems for wireless telecommunications

After many years of research and development, HTS filter subsystems for telecommunications are finally being manufactured in volume. Nearly 1,000 HTS filter subsystems are currently deployed worldwide with millions of hours of cumulative operation. An overview of the worldwide effort to commercialize HTS filter subsystems is presented. The essential technology elements required to manufacture HTS filter subsystems are discussed i.e., filters, cryogenic low-noise amplifiers, advanced cryopackaging, cryocoolers and control electronics. Currently sales of HTS filter subsystems are limited to existing analog and digital telephony networks. Planned third generation (3G) systems for wireless telephony and data communications require higher receiver performance to maintain high data rates with even lower-power handsets. The deployment of HTS filter subsystems in these 3G networks may be an excellent opportunity to achieve greater market penetration. Selected results of field trials of HTS filter subsystems are also presented.

Highly-selective electronically-tunable cryogenic filters using monolithic, discretely-switchable MEMS capacitor arrays

A low loss electronically tunable filter was demonstrated using HTS/Au MEMS switched capacitor arrays. The two-pole filter was tuned by simultaneously varying the capacitance of each resonator by equal amounts. A K factor of between 3,500 and 5,000 was demonstrated for single pole resonators. The total tuning range was about 25% with an average Q of 7,000 at 77 K.

UNUSUAL POWER DEPENDENCE OF TWO-TONE INTERMODULATION IN HIGH-TC SUPERCONDUCTING MICROWAVE RESONATORS

We study the power dependence of two-tone intermodulation arising in high-T-c superconducting microwave resonators as a function of each tone separately. In the regime where the intermodulation power varies as the square of the input power for equally strong tones, we observe unexpected behavior of the power dependence on the individual tones. We show that this behavior can be understood in terms of a nonlinear inductance which varies linearly with the magnitude of the input current. These findings provide a consistent phenomenological picture of the unusual power dependence and should place constraints on a microscopic description of nonlinear behavior in high-T-c films where the intermodulation products vary like the square of the input power

Microwave intermodulation of a superconducting disk resonator

We calculate the third order intermodulation products for the TM010 mode of a thin film disk resonator and discuss the particular case of a 1 GHz resonator in order to obtain a quantitative idea of the performance that can be obtained. The linear and nonlinear microwave responses of a TM010 disk resonator are then compared to that of an equivalent half wavelength microstrip resonator. This analysis allows one to independently quantify the contributions to the nonlinear device performance from the material properties, device size and field configuration.

Microwave intermodulation in thin film high-Tc superconducting microstrip hairpin resonators: Experiment and theory

We present experimental results for microwave intermodulation in a series of superconducting hairpin resonators. We find that geometry plays a dominant role in determining both the losses and intermodulation in these resonators. The experimental data can be reproduced using recent theoretical calculations with a single parameter, JIMD (77 K). We compare the response of the fundamental and the first harmonic modes of these resonators to find that the use of the first harmonic mode gives less intermodulation, but we also find higher losses due to the more extended fields of this mode.

Microwave intermodulation in high-T/sub c/ superconducting microstrip resonators

We present experimental results on microwave intermodulation measurements on a High T/sub c/ Superconducting band-reject microstrip resonator which exhibits unconventional 2:1 intermodulation products. We discuss unusual features of this 2:1 behavior that are uncovered by detailed frequency swept and unbalanced power measurements. We also introduce a phenomenological theory which arises from a nonlinear inductance of the form L=L/sub 0/+/spl alpha/|I| which quantitatively describes the observed response.

Nonlinear response of HTSC thin film microwave resonators in an applied DC magnetic field

The non-linear microwave surface impedance, Z/sub s/=R/sub s/+iX/sub s/, of patterned YBCO thin films, was measured using a suspended line resonator in the presence of a perpendicular DC magnetic field, H/sub DC/, of magnitude comparable to that of the microwave field, H/sub rf/. Signature of the virgin state was found to be absent even for relatively low microwave power levels. The microwave loss was initially found to decrease for small applied H/sub DC/ before increasing again. Also, non-linearities inherent in the sample were found to be substantially suppressed at low powers at these applied fields. These two features together can lead to significant improvement in device performance.

Nonlinear response of suspended high temperature superconducting thin film microwave resonators

The nonlinear microwave surface impedance, Z/sub s/(H/sub rf/) of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/(-/spl delta/) thin films is measured using suspended patterned resonators. We find that the nonlinear response is well described in terms of a single mechanism, namely the hysteretic ac response of the current-induced critical state.<<ETX>>

Phenomenological Theory of Intermodulation in HTS Resonators and Filters

Recent work on nonlinear effects in microwave resonators and filters from high temperature superconductors, focusing on intermodulations, is reviewed. We calculate the intrinsic nonlinear response of s-wave and d-wave superconductors. A phenomenological description of the lowest order nonlinear behavior in high-Tc films in terms of a single parameter, jIMD, is proposed. We show how this description can be used to calculate the intermodulation power arising in realistic microstrip resonators. These calculations show good agreement with measurements on hairpin resonators. This description can also be used for the modeling of nonlinear behavior of complex microwave filters.

Critical-state flux penetration and linear microwave vortex response in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} films

Z˜ s(H)5Rs(H)1iXs(H) of YBa2Cu3O72d thin films was measured using suspended patterned resonators. Z ˜ s(H) is shown to be a direct measure of the flux density B(H) enabling a very precise test of models of flux penetration. Three regimes of field-dependent behavior were observed: ~1! Initial flux penetration occurs on very low-field scales Hi~4.2 K!;10 mT, ~2! at moderate fields the flux penetration into the virgin state is in excellent agreement with calculations based upon the field-inducedBean critical state for thin-film geometry, parametrized by a field scale Hs(4.2 K);Jcd;0.5 T, and ~3! for very high fields H@Hs , the flux density is uniform and the measurements enable direct determination of vortex parameters such as pinning force constants a p and vortex viscosity h. However, hysteresis loops are in disagreement with the thin-film Bean model, and instead are governed by the low-field scale Hi , rather than by Hs . Geometric barriers are insufficient to account for the hysteresis loops. @S0163-1829~97!08641-4#