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.