Broadband FDTD analysis of Fermi antenna with narrow width substrate

It is desired to develop a receiving element suitable for a millimeter wave passive imaging array. The tapered slot antenna (TSA) meets the demands of such applications. TSA is well known as a thin structure which is of low weight, easy to fabricate and broadband. S. Sugawara et al. have proposed a TSA called "Fermi antenna" which has a taper profile of the Fermi-Dirac function and a corrugation on the side of the substrate (see MTT-S Int. Micro. Symp., vol.2, p.959-62, 1997). They found experimentally that the E-plane and the H-plane patterns of Fermi antenna are almost equal and they have low side lobe levels. However, the frequency characteristics of the Fermi antenna have not been investigated and the mechanism of the operation of the antenna has not been clarified. We present a broadband FDTD analysis of the Fermi antenna for millimeter wave imaging. The frequency characteristics are investigated to obtain the operating principles. The axially symmetric E-plane and H-plane patterns are obtained in the case of a Fermi antenna with a narrow substrate. Experimental investigation confirms that the radiation patterns obtained by numerical analysis almost agree with the measurements.