Slot Antennas

Abstract

The radiation pattern and conductance of a thin straight half‐wavelength slot are derived using an assumed electric field distribution over the slot. Subsequently, Babinet's principle, which provides a relationship between the input impedances of a slot and a conducting plate, both having the same shape, is derived. In addition, an antenna evaluation method based on the finite‐difference time‐domain method is briefly described. Using the finite‐difference time‐domain method, straight, bowtie, loop, curl, and spiral slot antennas are analyzed. The analysis reveals (1) the effects of the finiteness of the conducting sheet, in which the straight slot is cut, on the radiation characteristics; (2) the effects of the bowtie angle on the radiation characteristics; (3) the input impedance of the loop as a function of the circumference; and (4) the frequency responses of the curl and spiral slots, acting as circularly polarized radiation elements.