To provide horizon to zenith reception coverage for Differential GPS
operations, two antennas with complementary patterns may be used. An
antenna for high-angle coverage includes a ring of four dipoles excited to
provide progressive-phase-omnidirectional (PPO) coverage. A cylindrical
(e.g., octagonal) structure, with an upper edge at the diode horizontal
centerline, extends upward from a ground plane section. An absorber
configuration having a serrated upper edge portion extends around the
dipoles above the cylindrical structure and has radiation absorption
properties. For an octagonal configuration, the absorber configuration may
include eight resistance card sections with triangular portions extending
above the wall structure. A conical antenna pattern expanding upwardly can
provide omnidirectional coverage above a selected elevation angle (e.g.,
above 55.degree. elevation).
