M. C. Bailey

Integral equation formulation of microstrip antennas

The problem of a microstrip antenna covered by a dielectric is formulated in terms of coupled integro-differential equations with the current distribution on the microstrip patch as an unknown variable. Galerkins method is used to solve for the unknown patch current. Using the present formulation the resonant frequency and bandwidth of a rectangular microstrip antenna are determined and compared with experimental results.

Analysis of elliptical and circular microstrip antennas using moment method

A method of calculating the input impedance of either a circular or a slightly ellipitcal microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Greens function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented.

Input Admittance of a Circular Waveguide Aperture Covered by a Dielectric Slab

The input admittance of a circular waveguide opening onto an infinite flange with a homogeneous lossy dielectric coating is derived using integral transforms and assuming the dominant TE 11 mode as the trial field at the aperture. Admittance calculations for low-loss dielectric sheets of various thicknesses are given and compared with measurements obtained using ground planes of varying sizes. Excellent agreement with theory is obtained for the circular waveguide terminated into a square ground plane only 1\lambda to 2\lambda . on a side. A quantitative comparison of the surface wave contribution to the total admittance is also given.

Broad-band half-wave dipole

An ultrahigh frequency (UHF) fan-dipole is optimized for wide-band operation near the first resonance in order that the antenna could be used in a planar array of half-wavelength spaced elements operating over a conducting ground plane. The resultant voltage standing-wave ratio (VSWR) of the optimized dipole (with a 50 \Omega coax input) is less than 2:1 over a 37 percent bandwidth.

Mutual coupling in a finite planar array of circular apertures

Equations are presented for the calculation of the interelement mutual coupling in a finite size planar array of waveguide-fed apertures in an infinite flat conductor. The general mutual admittance expression is evaluated for circular apertures and the mutual coupling calculations are verified experimentally for two TE_{11} mode excited apertures. Qualitative agreement between calculations for a 183 element array and an infinite array establishes the validity of the finite array theoretical model.

The impedance properties of dielectric-covered narrow radiating slots in the broad face of a rectangular waveguide

An extension of Oliners theory is used to predict the impedance of slots with dielectric coatings. Theoretical curves are presented which show the change in impedance as a function of dielectric constant, dielectric losses, and dielectric thickness. The effect of a dielectric or plasma upon the resonant frequency is also included. The agreement with experimental dielectric-covered slot data justifies the extension of Oliners theory.

Analysis of finite phased arrays of circular microstrip patches

A method is presented for analyzing a finite planar array of circular microstrip patches fed by coaxial probes. The self- and mutual impedances between array elements are calculated using the method of moments with the dyadic Greens function for a dielectric layer on a ground plane. The patch circuits are determined by using the reaction integral equation. The active input impedance as well as the active element pattern of the array are computed from a knowledge of the resultant patch currents. The calculated results for two-element and eight-element linear arrays are in good agreement with experimental data. The active reflection coefficient and element pattern for the center and edge elements of a two-dimensional array as a function of scan angle are also presented. >

Design of dielectric-covered resonant slots in a rectangular waveguide

A summary is given of the effects of a dielectric cover upon the resonant frequency, the resonant conductance of a longitudinal shunt slot, and the power coupled out of a waveguide by a pair of near circularly polarized crossed slots. Typical data curves are presented which illustrate these changes due to variations in the dielectric constant and thickness of the cover. A simple modification of Stevensons free-space theory for resonant slots radiating into a homogeneous dielectric half-space is used in conjunction with the plane-wave reflection coefficient to predict bounds on the conductance and power variations for dielectric thicknesses greater than about one-quarter wavelength. The accuracy of this simple theory in predicting measurements on dielectric-covered slots is similar to the accuracy of Stevensons free-space theory within about 9 percent for the shunt slots and about 15 percent for the cross slots.

Mutual coupling between circular waveguide-fed apertures in a rectangular ground plane

A method is presented whereby the infinite ground plane analytical model for the self- and mutual admittances of waveguide-fed apertures can be supplemented (using the geometrical theory of diffraction) to include the edge effects of a rectangular ground plane. The H -plane coupling between two TE_{11} mode excited circular apertures is calculated and compared with measurements.

The development of an L-band radiometer dual-mode horn

A conical circularly polarized dual-mode horn, designed for the frequency range of 1400-1460 MHz, is described. This electrically shorter version of the Potter horn yields circularly symmetrical patterns over a broader frequency range (approaching 10 percent). A technique is described for matching the input over the design bandwidth with a VSWR < 1.05.