Mode-controlling waveguide-to-coax transition for TV broadcast system

摘要

A coax-fed slotted-cylinder (pylon) antenna for UHF television operation at power of 200 kW and above has a coaxial feed which is large enough to propagate higher TE.sub.11 mode as well as the desired fundamental TEM mode. The power fed to each slot and as a consequence the antenna array factor may be perturbed by the higher modes. It is important to reduce losses in the feed of the high-power signals from the transmitter or high power amplifier up the tower to the antenna. For lowest loss, a waveguide is used for the run up the tower. A waveguide-to- coax transition is used for adapting the waveguide to the coaxial antenna feed while suppressing the undesired TE.sub.1,1 mode. The transition has two short semicircular waveguides opening into the waveguide feed from the transmitter. The semicircular walls of the two waveguides are coupled to the outer conductor of the coax antenna feed. The semicircular waveguides have a common flat wall, the center of one core of which is coupled to the center-conductor of the coax antenna feed.