Fast Analysis of Multilayer Conformal Antenna Structures and Networks

Abstract

Broadband satellite communications and precise navigation in safety-of-life ap-plications require high-gain terminal antenna arrays with an appropriate size. Drag reduction and aesthetical reasons make it necessary to smoothly integrate the array into the surface of vehicles, vessels or airplanes. For this purpose, the use of microstrip antennas offers several advantages. They are flexible and very well suited for the conformal integration since they can be adapted to almost any kind of structure. In aeronautics, new materials like GLARE (glass-fiber rein-forced aluminum) are composed of several thin layers resulting in a multilayer architecture, if stacked patches have to be integrated for broadband applications. To determine and control the radiation characteristics, every element in an array must be fed with accurate amplitude and phase and thus a good prediction of the characteristics of the microstrip or coplanar lines composing the feed network is needed. The incorporation of extra networks for calibration purposes or the distri-bution of local-oscillator signals results in additional thin layers. The analysis of these stratified structures using commercial simulation tools with full 3D-modeling is difficult and time consuming.

An alternative approach is the use of 2D-procedures like integral-equation tech-niques or discrete mode matching (DMM) that involve the dyadic Green’s func-tion of the layered structure in a suitable coordinate system. This paper presents a systematic way to set up the dyadic Green’s function for multilayer structures us-ing a full-wave equivalent circuit (FWEC) in curvilinear coordinate systems. The FWEC forms a basis for the efficient analysis of planar, cylindrical and spherical structures with the integral-equation technique in the spectral domain, and for the application of DMM on arbitrarily shaped structures (quasi-planar, quasi-circular cylindrical) in the space domain.

In order to test the applicability of the equivalent-circuit approach and demon-strate its excellent potential and versatility, dielectric cylindrical waveguides with an index profile have been investigated, where the profile has been approximated by up to 10,000 homogeneous layers with different permittivity.

Several additional examples are shown for the application of the FWEC like the analysis of patch antennas on a deformed (quasi-planar) substrate and of micro-strip lines on a three-layer cylindrical substrate using DMM, and the coupling of patch antennas on a cylinder using a method-of-moments approach.

All results have been validated as far as possible by using commercial software.