James W. Mink

Global modeling of spatially distributed microwave and millimeter-wave systems

Microwave and millimeter-wave systems have generally been developed from a circuit perspective with the effect of the electromagnetic (EM) environment modeled using lumped elements or N-port scattering parameters. The recent development of the local reference node concept coupled with steady-state and transient analyses using state variables allows the incorporation of unrestrained EM modeling of microwave structures in a circuit simulator. A strategy implementing global modeling of electrically large microwave systems using the circuit abstraction is presented. This is applied to the modeling of a quasi-optical power-combining amplifier.

A quasi-optical dielectric slab power combiner

Real power gain from a quasi-optical power combining dielectric slab waveguide amplifier system is reported for the first time. The system employs four MESFET amplifiers located under the slab, and a small signal gain of 10.5 dB was achieved. Measurements of insertion loss and E-field patterns are presented.

Impedance matrix of an antenna array in a quasi-optical resonator

The power from numerous millimeter-wave solid-state sources can be efficiently combined using quasi-optical techniques. One technique is to place an array of active radiating sources within a quasi-optical resonator. The driving point impedance of each antenna is strongly affected by the presence of all other active antennas as well as by the mode structure and Q of the resonator. The impedance matrix for an array of antennas radiating into a plano-concave open resonator is determined here through use of the Lorentz integral. The resulting expressions include the effect of diffraction loss and are valid for arbitrary reflector spacing, source frequency, array location and geometry. The result can be used for impedance matching of each active source to its antenna, facilitating design of an efficient power combining system. Simulations using the impedance matrix in conjunction with an antenna impedance model are compared with two-port measurements. >

A dyadic Green's function for the plano-concave quasi-optical resonator

An approximate dyadic Greens function is derived for a quasi-optical resonator. The Greens function is comprised of resonant and nonresonant terms corresponding to coupling of the modal and nonmodal resonator fields. The effect of losses due to diffraction, finite reflector conductivity and radiation are included. Experimental one- and two-port measurements of antennas in an X-band cavity compare favorably with theoretical predictions.<<ETX>>

Electromagnetic modeling of finite grid structures in quasi-optical systems

A full-wave moment method technique developed for the analysis of quasi-optical systems is used to model finite grid structures. This technique incorporates an electric field dyadic Greens function for a grid centered between two lenses in free space which is derived by separately considering paraxial and nonparaxial fields. Results for the driving point reflection coefficient of a 3/spl times/3 grid are computed and compared with measurements.

Further Investigations with an Optical Beam Waveguide for Long Distance Transmission

Measurements made with an optical beam waveguide employing quartz lenses for the beam iteration demonstrate that a transmission loss of 0.5 dB/km is readily obtainable, and that this loss is solely determined by the absorption, scatter, and reflection losses of the lenses. The transmission loss and its variation depends on the air pressure along the light path. Photometric measurements of the energy distribution of the transmitted beam illustrate that distortions in the mode pattern of the laser are the major cause of the launching loss which for the available laser was measured to be approximately 0.4 dB.

Use of the moment method and dyadic Green's functions in the analysis of quasi-optical structures

A moment method using a dyadic Greens function is developed for the analysis of quasi-optical systems. The dyadic Greens function used has separate terms for the paraxial and non-paraxial fields and is much easier to develop than a mixed potential Greens function. The method is applied to the analysis of antenna elements in a quasi-optical resonator.<<ETX>>

Diffractional field distortion and cross-coupling in guided optical multibeam transmission

Abstract : Simultaneous transmission of several off-axis Gaussian beams through a lens-type beam waveguide is subjected to distortions caused by diffraction at the lens apertures and by imperfections of the lenses. The report is concerned with the diffraction effects which are inherent to the performance of beam waveguides and independent of the technological progress in producing high quality lenses. Theoretical information on the diffractional distortions of off-axis beams and the resulting cross talk is presented and numerically evaluated for typical examples. (Author)