D. M. Kokotoff*, R. B. Waterhouse*, and J. T. Aberle**

One of the most robust techniques to feed a printed antenna uses a coaxial connector whose outer conductor is soldered to the ground plane and whose center conductor is attached to the patch. This method of excitation has several advantages including better isolation between the feed circuitry and the radiating element, but is more difficult to model. Multiple probe feeds are used to achieve circular polarization and to reduce cross-polarized levels. Shorting posts are introduced to control the resonant frequency and the polarization.

Accurate and efficient numerical modeling of printed antennas featuring probe feeds and shorting posts requires the development of appropriate full-wave solutions. The full wave solution of choice for many printed antenna geometries is the Green's function/Moment Method technique. In the case of probe-fed printed antennas, one must carefully consider both the continuity and the singular nature of the current at the point where the probe is connected to the patch. These conditions can be ensured by the proper choice of a singular expansion function in the solution. This expansion function is commonly referred to as an ``attachment mode.'' Although, different types of attachment modes have been described in the literature, we use attachment modes derived from the cavity model. Attachment modes have been obtained for rectangular, circular and annular ring patch antennas. These expansion functions have allowed us to develop a suite of accurate and efficient numerical models for the design and analysis of printed antennas. In the presentation, the approach used to develop these expansion modes and their advantages and disadvantages are discussed. Furthermore, comparisons between numerical and experimental results are presented.