Robust antennae recommended for reception of DGPS spot beam services (with options for DGPS + L1 GPS, and L1 GPS + GLONASS reception) in areas where general purpose antennae are inoperable due to L-band interference.
The antenna body is machined in two parts from aluminium (dimensions shown in figure 1) and hard anodised resulting in a rugged grey finish resistant to salt water corrosion. An ‘O’ ring ensures a waterproof seal between the case halves to a minimum of IP67, the limiting factor being the seal between the N-type coaxial connectors (TNC optional) on the antenna and its cable.
A 4mm thick GRP pressure moulding, which can be painted to any colour required, provides a strong, but electrically low-loss radome. The mass of the antenna is 1.4kg.
The AD420 antenna element is a shaped dipole with RHCP and an omni-directional radiation pattern in azimuth. The AD422 is a variant with an RHCP quadrifilar receiving element designed to provide enhanced reception of geo-stationary satellites close to the horizon at polar latitudes. Radiation patterns are shown in figure 2.
The element is connected to a built in GaAs FET amplifier via a comb-line filter. The amplifier’s gain is factory preset within the range 25dB to 46dB (42dB typical) with a total noise figure of less than 2.5 dB including the filter. In order to suppress L band interference, a low loss comb lined filter is used, figure 3.
The amplifier is phantom powered via the coaxial output lead with a +5V to +20Vdc supply at typically 45mA. Either TNC or N-type connectors are available on request. The antenna complies with EMC requirements and is CE marked.
Operating temperature range for the antenna is -55°C to +70°C and storage temperature range is -55° C to +100° C.