WHY SLOTTED CYLINDER ANTENNAS?
UHF slotted cylinder antennas gained prominence in NTSC broadcasting due to their combination of low wind loading and superior omnidirectional performance. Their small diameter construction, most within the 8″ to 14″ outside diameter range, provides the minimum wind load reducing the cost of tower structures. Small physical diameter also translates into small electrical radius (R/l ) for the slot radiators, which results in excellent circularity of the azimuth pattern. Figure 1 shows an overlay of two azimuth patterns. The smooth, nearly circular azimuth pattern, is typical for a slotted cylinder antenna with a circularity of 0.5 dB. Compare it to the typical azimuth pattern of a panel antenna with a circularity of 2.0 dB. When both are normalized to unity, the amplitude difference between the patterns at the minimum of the panel pattern reaches 3 dB. Considering approximately 1 mile of coverage loss per dB, this could mean 3 miles of service reduction in some directions for the panel.
