Unidirectional patterns of traveling-wave rectangular antenna

A traveling-wave rectangular antenna, for which the feeding point is placed at the center of a leg and the matching impedance is terminated at the opposite leg, is considered. This antenna has two kinds of quasi-nonsidelobe unidirectional patterns of cardioid shape; one is endfire and the other is backfire. Endfire patterns are obtained for leg lengths comparable with a wavelength, while backfire patterns are obtained when the antenna is small relative to a wavelength. In the former, the unidirectional antenna pattern for leg lengths of
\lambda
and
\lambda/4
has a beamwidth of about
180\deg
and very high front-to-back ratio (FBR). When the antenna lengths change by several percent from the ideal lengths, the variation of the beamwidth is in the range of
40\deg
and the FBR is in the range of about 5 (14 dB) to infinity. In the latter, for the rectangular antenna with a leg length of
\lambda/10
, the pattern in a plane perpendicular to the antenna has a beamwidth of
160\deg
and the pattern in a plane including the antenna has the beamwidth of
124\deg
. When the antenna lengths vary by about
\pm30
percent, the variation of the beamwidth is in the range of
30\deg
and the variation of the sidelobe level is about 4 dB. Although we used a suitable resistance instead of the matching impedance, the experimental results were almost coincidental with the theoretical patterns.