Jerald A. Weiss

Ferrite-superconductor devices for advanced microwave applications

Microwave devices comprising magnetized ferrite in contact with superconductor circuits designed to eliminate magnetic field penetration of the superconductor have demonstrated phase shift without significant conduction losses. The device structures are adaptable to low- or high-T/sub c/ superconductors. A nonoptimized design of a ferrite phase shifter that employs niobium or YBCO meanderlines has produced over 1000 degrees of differential phase shift with a figure of merit exceeding 1000 degrees/dB at X band. By combining superconductor meanderline sections with alternating T junctions on a ferrite substrate in a configuration with three-fold symmetry, a low-loss three-port switching circulator has been demonstrated.

New uniaxial-ferrite millimeter-wave junction circulators

The authors report on progress in the development of millimeter-wave junction circulators for the band near 31 GHz, incorporating the technique of exploiting the high effective internal magnetic anisotropy field of barium and strontium magnetoplumbites (hexagonal ferrites) to eliminate the external permanent magnet requirement. Microstrip and waveguide three-port junction versions have been built and evaluated, exhibiting good isolation and insertion loss performance, and requiring no magnet. Design considerations include the magnetic material parameters of remanent magnetization, anisotropy, coercive field, resistivity, and shape-dependent demagnetizing effects, as well as microstrip and waveguide junction circuit geometries, dissipative effects, temperature stability, and influences of coax-microstrip transducers.<<ETX>>

Superconductor ferrite phase shifters and circulators

We have previously demonstrated high-T/sub c/ superconductor/ferrite nonreciprocal microwave phase shifters that avoid dc magnetic-flux penetration of the superconductor through a novel design of the magnetic circuit, and thus operate with very low loss. Recently, a simplified magnetic structure has been introduced, and devices with approximately 0.1 dB insertion loss with 500 degrees of phase shift (figure of merit 5000 deg/dB) at 10 GHz and 77 K using YBCO have been demonstrated. The same operating principles have been applied to the design and fabrication of circulators. By combining three low-loss phase shifters and three T junctions on a ferrite substrate in a configuration with three-fold symmetry, a three-port switching circulator has been demonstrated using niobium at 4 K. The insertion loss is less than 1 dB, the isolation greater than 20 dB, and switching time less than 1 /spl mu/s. The switching circulator can serve as a low-loss, high-speed rf switch. Extension of this design to YBCO is discussed. Higher performance, reduced weight and volume, as well as lower cost are anticipated for microwave systems that can benefit from such circulators and phase shifters.

Quasi-optical ferrite reflection circulator

A quasi-optical Faraday rotation ferrite circulator for microwave or millimeter radiation is analyzed by a matrix formalism. Both reflection and transmission configurations at oblique incidence are examined. Numerical results are presented for the band centered at 35 GHz. Theory and experiment are compared over a 10%-20% band. Notwithstanding the complexities of oblique incidence, the reflection-type device promises favorable bandwidth, low loss, and isolation comparable to those of the transmission version now in system deployment, and offers the potential for much higher heat-dissipation capability. >

The ring-network circulator for integrated circuits: theory and experiments

The theoretical model of a ring network junction circulator introduced in 1965 is reexamined and further elaborated, in view of its prospects for compatibility with accomplished and anticipated advances in microcircuit technology. Following a brief review of the theory, solutions are presented to illustrate the potential for novel, efficient designs with options including miniature, self-magnetized, reversible, broadband, superconducting, or other advantageous characteristics. New experimental models are showing good conformance to theoretical predictions for this promising alternative circulator design concept.

Nonreciprocal magneto-optics for millimeter waves

The magnetooptical principles that form the basis for isolators and circulators at infrared wavelengths, i.e. 0.8 and 1.3 mu m, have been successfully applied at 1 cm (35 GHz). Unlike the infrared case, which functions on the wings of a crystal-field absorption line, millimeter-wave rotation originates from ferrimagnetic resonance, and its magnitude is directly proportional to the ferrite magnetization. The basic theory is adapted to interpret experiments over a band from 26 to 40 GHz, with unmatched iron-garnet rotation elements used in a Gaussian-beam spectrometer and with the addition of antireflection quarter-wave plates. An experimental demonstration of a 45 degrees rotator yielded an effective isolation greater than 40 dB, with a total insertion loss substantially less than 0.1 dB over a 20% bandwidth. >

Hysteresis loops modeled from coercivity, anisotropy, and microstructure parameters

By modifying the microstructure (a/H) and magnetocrystalline anisotropy (b/H2) terms of the approach‐to‐saturation (ATS) law, the range of fields over which these terms remain finite is extended to low fields and a good approximation to the hysteresis loop may be constructed in its entirety. The model involves the introduction of the coercive field Hc, the anisotropy field HK, and a reverse domain nucleation field Hn as bias fields that are included in the denominators of the a and b terms. With these phenomenological refinements, the remanent magnetization becomes a function of a/(Hn+Hc), from which Hn may be obtained once a and Hc are determined. Initial results from several different magnetic materials, particularly garnets and spinel ferrites with square hysteresis loops, indicate good agreement with experiment. In cases where ATS analysis is not available because of inadequate sensitivity or inability to reach sufficiently high fields, curve fitting to a lower‐field portion of the hysteresis loop is ...

Hysteresis Evaluation of Microwave Ferrites at Audio Frequency with Large Dynamic Range

The evaluation of ferrites and ferrimagnetic garnets for use in microwave switches and digital phasers requires, in addition to microwave examination, determination of saturation and remanent magnetization, coercive field, and a measure of squareness, including the dependence of these properies on amplitude of actuating fields, temperature, and internal and externally applied stresses. We have developed a novel method which combines the required accuracy and convenience, and by which we are able to examine, on a single specimen, both the low‐field details of hysteresis and the approach to saturation at high fields. The field is produced by a nickel—ferrite electromagnet excited at 60 or 400 Hz, generating a field at amplitudes up to 1000 Oe. The specimen may be a rod, toroid, or other shape. Flux sensing is conventional; sensing of internal field is done by a magnetic potentiometer of special design. Integration is performed by a system incorporating amplifiers which were selected for gain, bandwidth, noi...

A Switching Circulator: S-Band; Stripline; Remanent; 15 kilowatts; I0 microseconds; Temperature-Stable

A stripline, three-port remanence circulator switch has been designed for high-speed switching of time delay in a phased array RADAR at S-band (2.9 GHz). Special attention was devoted to minimizing switching time and energy through design of the magnetic circuit and suppression of eddy currents. Temperature stabilization of insertion phase was accomplished by means of a flux regulating magnetic circuit. Switching performance: time: less than 10 micro-seconds; energy: 450 microjoules. Circulator performance: bandwidth for >26 dB isolation, 8.9 percent; insertion loss, 0.35 dB. Temperature stability of insertion phase: one electrical degree per 10/spl deg/C. Peak RF power: 15 kW. The discussion includes details of the junction design and performance, techniques of eddy current suppression, temperature stabilization, and the method of switching energy measurements.

The Reggia‐Spencer Microwave Phase Shifter

The essential properties of the wave‐guide phase shifter reported by Reggia and Spencer are explained by means of a composite phenomenological model which incorporates the two dominating effects: the elliptic wave‐guide symmetry and a dielectric wave‐guide effect. The model provides an advantageous starting point for more precise calculations, as well as a qualitative guide to further device development. It also sheds further light on Faraday rotation and its associated interference effect under conditions of elliptic symmetry.