A reciprocity approach for analyzing radiation from aperture and nicrostrip antennas.

by 1961- Arakaki, Dean Yasuo

Conformal antennas, used extensively on mobile communications systems, generally have complex configurations and are often times mounted on or used within large structures. Hence, the modeling of such antennas is a challenging problem. The most frequently used numerical techniques either require excessive computational resources or cannot effectively model such structures. Thus, hybrid techniques have recently been employed to take advantage of each method’s strengths, while minimizing weaknesses. To enhance computational efficiency, a new methodology is introduced in this thesis, based on a combination of the Finite Difference Time Domain (FDTD) and the Method of Moments (MoM) numerical techniques in conjunction with the Surface Equivalence and Reciprocity Theorems. Several antenna configurations are considered to illustrate the new methodology: 1) radiating slots on conducting cylinders, 2) microstrip patch antennas mounted on large conducting structures, and 3) reflector antennas with partial circular symmetry. In the transmit mode, the region containing the radiation source is first analyzed using either the MoM or FDTD technique to determine “equivalent currents” at the radiating aperture. The Surface Equivalence Principle is then applied, allowing the material in the radiating region to be theoretically modified to match its surroundings. This creates a homogeneous structure for the first two antenna types, and a circularly symmetric structure for the last type. iv The operation of the antenna system is then reversed to the receive mode, and the fields produced at the radiating aperture are determined. By analyzing this mode of operation, difficult integrals and asymmetric sources are avoided for antenna types 1 and 2, and 3, respectively. For antenna types 1 and 2, the MoM technique is used to compute the surface fields, which reduces computational resource requirements since the surface of the structure – as opposed to its volume – is modeled. For antenna type 3, the effective removal of asymmetric sources allows a 2-D FDTD simulation of the antenna structure, instead of a full 3-D model. Finally, utilizing the Reciprocity Theorem, the surface fields determined for the receive mode case are combined with the “equivalent currents” calculated in the transmit mode in order to compute far-zone fields. Through use of the technique, computational savings on the order of 95% are realized.