The problem of solving the inverse scattering problem using the inverse source method is discussed. It is shown that the method, in general. gives rise to inaccurate solutions when the number of unhowns in the problem is increased. ? l i s is~due to the presence of the non-radiating sources, and hi&-spatial-frequency currents that generate evanescent waves. Moreover. we show that the Green operator acrs as 3 low-pass filtering operator. removing highfrequency information. The same problem is shown to be endemic hom an operator viewpoint.

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simulated maximum realized gain is À9.8 dBi, and the measured gain is À13.9 dBi, which is a practical value for short-range wireless tags. This difference is probably due to fabrication error and a slight leakage current. The antenna gain can be improved by improving the antenna element structure. CONCLUSIONSA capacitive feed structure for small, low-profile antenna with ka ¼ 0.37 is simulated, fabricated, and measured. The proposed C-feed antenna provides good impedance matching characteristics even if the antenna is connected to larger grounds and shows a small leakage current on the outer surface of the coaxial cable. The proposed antenna has potential applications in RFID and mobile terminals.