In UHF TV broadcast antenna systems, there are inner and outer feed conductors which are joined to inner and outer antenna conductors. The inner feed conductor is received within and concentrically aligned with the outer feed conductor. The inner feed conductor is joined to an inner antenna conductor by a T connector. The inner antenna conductor is `shorted` to the outer antenna conductor by the "shorts" which are typically comprised of a collar with electrical contacts (generally watchband springs) through which the inner antenna conductor rides. The collars are shorted to the outer antenna conductor usually by means of spokes. The location of the center line of these collars is nominally one wavelength away from the center line of the last radiating slot of each half of the antenna.
Referring to FIG. 1 a prior art antenna system is shown generally at 10 and comprises a lateral outer feed conductor 12 and an inner feed conductor 14. The entire weight of the inner conductor 14 is carried by centering pins 16 with bushings 18 received within the inner conductor 14 and in registration with the centering pins 16 to prevent crushing. An antenna 20 has inner and outer antenna conductors 22 and 24. The inner conductors 14 and 22 are joined by a T connector 26.
The differential expansion of the inner and outer antenna conductors 22 and 24 is accommodated by the inner conductor 22 being allowed to ride through the "short" 28. The "short" 28 allows for an electrical short. However, this design does not provide an efficient thermal short to ambient for the heat energy that is generated in the inner conductor 22. Also, the prior art design loads substantially the entire weight of the inner conductor 14 onto the T conductor 26. This results in the centering pins and bushings being required as just described.
The present invention embodies an antenna design that provides for an electrical short, a thermal short and mechanical support for the inner antenna conductor which design eliminates the need for bushings or the like to prevent crushing of the lateral inner feed conductor.
The inner antenna conductor is mechanically fastened to the antenna top. This provides an electrical short to the outer conductor and a thermal short to ambient. The weight of the inner feed conductor and inner feed antenna conductor is carried by a fastener which is easily sized to carry the load.