A two-element yagi-type array in a parallel-plate waveguide--Theoretical and experimental studies

A theory is developed for the current distribution, impedance, and radiation characteristics of a two-element Yagi-type array, consisting of a driven antenna and a tuned parasite in a parallel-plate waveguide. By optimizing the spacing between elements and the tuning reactance of the parasite, front-to-back ratios as high as +31 dB (parasite as reflector) or as low as -19 dB (parasite as director) can be obtained for antennas with
a=0.01\lambda
and
h=0.25\lambda
, where
a
and
h
are the radius and height of the antenna, respectively. Extensive experimental measurements have been made on the antenna array, and a brief description of the apparatus is included. The experimental results agree well with theory. Possible applications of this type of antenna array as variable power-dividers and attenuators in strip lines and other circuits are explained.