A design study for the basic TEM horn antenna

The basic TEM horn antenna consists of two identical triangular plates meeting at an apex of each. The angular width of each plate is /spl alpha/, and the angular separation between the plates is /spl beta/. The length of each plate (as measured along the side) is s. A key parameter is the characteristic impedance, Z/sub c/, of the spherical TEM wave on the infinitely long antenna (s/spl rarr//spl infin/), which depends only on the angles /spl alpha/ and /spl beta/. Z/sub c/ can be obtained by conformal mapping. For a particular choice of Z/sub c/, a set of possible angles can be found. We focus on the values most often used in practical designs: Z/sub c/ = 50 /spl Omega/ and Z/sub c/ = 100 /spl Omega/. Apart from the characteristic impedance, there is comparatively little other design information available. We examine the realized gain, G/sub r/, for TEM horn antennas. Specifically, we vary /spl beta/ (while adjusting /spl alpha/ to maintain a constant Z/sub c/) and the antenna electrical length, s//spl lambda/. Using this information, we produce design curves for the optimal antenna (highest G/sub r/) for a given s//spl lambda/. The results for Z/sub c/ = 100 /spl Omega/ are presented.