KLM's 435-18C Circular Polarized antenna brings ail the row advantages of circular polarity of UUF, for optimized satellite and terrestrial communications.
Although originally inspired and designed for the Phase III satellite, OSCAR 9, the 18C is finding wide appeal and acceptance among DX'ers, ATV'ers, and the 440-450 FM group. Totally new design and construction techniques were necessary for. the 18C because of the strict electrical requirements for good circularity at UHF frequencies.
The parasitic elements (3/16" 606.1-T6 rod) pass through the center of the boom in both planes, and are isolated from it with polyethylene insulators and locking snap rings.
Folded dipoles of 3/8" O.D. tubing are used for the driven elements. These provide excellent bandwidth, and, being looped around the boom, maintain perfect element symmetry.
Circularity is held within 1dB, 430-440 Mhz and 3dB, 420-450 MHz. Electrically, the 18C has nine elements in the vertical plane and nine in the horizontal.
Offset between them is 1/4 wavelength. Each dipole has a feed impedance of 50 ohms, and two coaxial baluns are supplied.