A planar conducting structure, an electrically small distance above a ground plane, can be constructed to radiate in the direction normal to its plane while still retaining its low-profile characteristics. A circular disc structure is analysed theoretically to provide aid in the design of such antennas. The currents, fields, total radiated power, directive gain, losses, Q-factor and efficiency are all calculated at several frequencies for various values of the thickness, permittivity, and loss tangent of the dielectric material that separates the antenna from the ground plane.

Theory of the circular-disc printed-circuit antenna

A one-point back-feed type circularly polarized microstrip disk antenna is investigated. To establish a design procedure, (1) the operating condition for circular polarization is studied and design formulas and data are presented and (2) the fabrication and radiation characteristics of arrays consisting of the present circularly polarized disk antenna element are discussed. It is demonstrated that this class of antennas can serve as a useful form of circularly polarized array element. Further, in order to analyze the mutual coupling of such antenna elements, the resonance and inter-element mutual admittance of an array consisting of two disk antennas located on the same plane are determined. The fundamental information on the mutual coupling thus obtained is presented for a design aid. Using these results, a circularly polarized array is realized with good axial ratio and boresight ratio less than 0.5 dB.

A design of back-feed type circularly polarized microstrip disk antennas having symmetrical perturbation element by one-point feed

Band broadening and optimization of a microstrip array antenna are investigated and a design method is presented for an S-band satellite marine communication antenna. Validity of this design is confirmed by experiment. Bandwidth as large as 13% is achieved with a parasitic element in which the VSWR remains less than 1.5. The coplanar arrangement, in which the radiator and feed circuit are in the same plane, permits simple, low-less structure. Based on these investigations a microstrip array antenna is fabricated for S-band satellite marine communications which has a relative bandwidth greater than 8.5%, gain greater than 18.8 dBi, efficiency above 62%, sidelobe level below -22 dB and VSWR less than 1.5.

Broadband circularly polarized microstrip array antenna with coplanar feed

The calculation of currents induced by a plane wave normally incident upon an infinite strip embedded in a grounded dielectric slab is used to infer the resonant width (or frequency) of rectangular microstrip antennas. By placing the strip inside the dielectric, the effect of a dielectric cover of the same material as the substrate can be included in the calculation of resonant frequency. A comparison with measured results indicated agreement of 1 percent or better for rectangular microstrip antennas constructed on Teflon-fiberglass substrate.

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Resonant Frequency of Microstrip Antennas Calculated From TE-Excitation of an Infinite Strip Embedded in a Grounded Dielectric Slab.

In this paper, we utilize a conformal finite difference time domain (CFDTD) code to predict the coupling between two coplanar radiators with complete feed circuits. The CFDTD has been parallelized to operate on a Linux cluster, allowing rapid simulation of large, complex problems. A wide variety of antenna configurations have been analyzed, and two representative examples are discussed herein. The first consists of circular microstrip patches operating at C-band, while the second is comprised of rectangular Ka-band patches. Numerical coupling data are compared against both measurements and theory. Input impedance characteristics are also evaluated to determine the radiation efficiency.

Coupling between planar microstrip patches in an array environment

The radio frequency characteristics and design parameters for microstrip disk antenna elements and planar arrays are presented. Two C-band model arrays (an 8 element linear and an 8 by 8 planar) were designed, fabricated, and tested to demonstrate the technique of using microstrip elements for array applications. These arrays were designed with a cosine amplitude distribution.

M. C. Bailey

Papers

Design of microstrip disk antenna arrays