H. How

Integrated self-biased hexaferrite microstrip circulators for millimeter-wavelength applications

Planar microstrip Y-junction circulators have been fabricated from metallized 130-/spl mu/m-thick self-biased strontium hexaferrite ceramic die, and then bonded onto silicon die to yield integrated circulator circuits. The impedance matching networks needed to transform the low-impedance circulator outputs were deployed on low-loss alumina or glass dielectrics to minimize circuit losses. These magnetically self-biased circulators show a normalized isolation and insertion loss of 33 and 2.8 dB, respectively, and a 1% bandwidth for an isolation of 20 dB. Application of small (H<1.5 kOe) magnetic bias fields improved the isolation and insertion loss values to 50 and 1.6 dB, respectively. This design may form the basis for future monolithic millimeter-wave integrated circulator circuits that do not require magnets.

MMIC circulators using hexaferrites

MMIC circulators operating at K/sub A/-band have been fabricated from single crystal and polycrystalline hexaferrite platelets integrated into glass-microwave integrated circuit wafers. Measurements on circulators utilizing single crystal BaFe/sub 11.1/Sc/sub 0.9/O/sub 19/ showed two-band circulation, below-FMR (at 36 GHz) and above-FMR (at 24 GHz), while those using single crystal BaFe/sub 12/O/sub 19/ showed above-FMR circulation at 32-35 GHz. Self-biased circulators using SrFe/sub 12/O/sub 19/ ceramics showed above-FMR circulation at 32 GHz. All circulators showed reasonable insertion losses and isolation, with the best insertion loss of 1.2 dB at an isolation of 18 dB being found for a BaFe/sub 11.1/Sc/sub 0.9/O/sub 19/ circulator operating below-FMR.

Theory and experiment of thin-film junction circulator

We have calculated the S-parameters and losses in ferrite-film-junction circulators using a new effective-field theory assuming TEM-like propagation. Conductivity loss dominates the dielectric and magnetic losses in Y-junction circulators fabricated on ferrite films with thicknesses less than 200 /spl mu/m. It is plausible to fabricate Y-junction thin-film circulator at X-band with insertion loss less than 0.5 dB if the film thickness is larger than 100 /spl mu/m. The quality of the conductor plane is important in reducing the overall insertion loss of the thin-film-junction circulator.

The permeability tensor of composite consisting of magnetic particles

The demagnetizing energy of spheroidal magnetic particles dispersed in cubic lattices has been calculated. The demagnetizing energy contains contributions from the demagnetizing self‐energy and magnetostatic coupling energy between particles. The total demagnetizing energy can be conveniently expressed in terms of three demagnetizing factors whose sum equals unity. For low volume loading of particles the self‐energy contribution is the dominant one, which is insensitive to particle coordinations and can be approximated by that of an isolated particle. However, when particle loading increases appreciably, significant differences arise for different particle lattices (sc, bcc, and fcc). One advantage of our formulation is that the permeability tensor of the composite can then be calculated for either a magnetic nonsaturated or saturated state of the particle. In contrast to conductivity calculations at the percolation limit there is no divergence of the permeability.

Development of high frequency ferrite phase-shifter

A phase-shifter was fabricated on a c-texture Zn/sub 2/Y (Zn/sub 2/Ba/sub 2/Fe/sub 12/O/sub 22/) single crystal substrate, and tested over microwave frequencies from 2 to 35 GHz and for biasing magnetic fields from 0.2 to 5 kOe. The differential phase-shift rate was 90/spl deg//kOe.mm at a microwave frequency of 20 GHz and a magnetic bias-field of 1.3 kOe. This device showed that it is possible to reduce the bias-field requirement efficiently and simply by utilizing the large in-plane anisotropy in Y-type hexaferrites and magnetostatic modes. A simple model based on the conjugate method for a TEM wave gave a reasonable match with the measured performance of the device, when the uniaxial magnetic anisotropy and magnetostatic modes were included.

Microwave characteristics of high T/sub c/ superconducting coplanar waveguide resonator

A theoretical formulation has been developed to calculate the coupling coefficient, London penetration depth, and surface resistance of a coplanar waveguide resonator fabricated from films of superconducting YBCO material. Experimental data of the reflection coefficient as a function of temperature and frequency agree reasonably well with calculations. The formulation is of sufficient generality to be applicable to other guided structures. >

Microwave phase shifter utilizing nonreciprocal wave propagation

Novel microwave phase shifters are proposed and fabricated utilizing nonreciprocal wave propagation whose insertion loss is independent of the obtained angle in phase shift. The fabricated phase shifter consisted of a ferrite ring resonator whose feeder point can be mechanically adjusted to give 360/spl deg/ phase-shift angle at relatively constant insertion loss. Measurements are compared with calculations.

Steerable phased array antennas using single-crystal YIG phase shifters-theory and experiments

A phased array antenna containing four linear microstrip patch elements has been fabricated and tested. The elements were fed through single-crystal yttrium-iron-garnet (YIG) phase shifters. By varying the bias magnetic field, the input phases to the antenna elements can thus been tuned, resulting in steering of the radiation beam in one dimension. Measurements compared reasonably well with calculations.

Design of six-port stripline ferrite junction circulators

Circulation conditions for a six-port stripline ferrite junction circulator have been formulated. For external magnetic field biased above FMR it results in wider transmission frequency bandwidth compared to normal three-port devices. We surmize that six-port circulators can also be used as high power devices similar to the three-port counterpart. >

Generation of high-order harmonics in insulator magnetic fluxgate sensor cores

High-order harmonics generated in an insulator core of a magnetic fluxgate show insignificant attenuation at high frequencies. This suggests that coherent detection of the fluxgate signal can be applied to an insulator core, decoupling noise participation thereby enhancing the detection sensitivity.