A high performance antenna with enhanced interdigital filters for interference rejection in the frequency range 1626.5 to 1660MHz
The antenna case is machined from solid aluminium in two parts which are hard anodised resulting in a rugged 244mm diameter base with a medium grey finish that is extremely resistant to salt water corrosion.
The antenna is sealed to a minimum of IP67 with an ‘O’ ring preventing water ingress between the case halves; the limiting factor is the seal between the type N connector (TNC optional) on the antenna and the corresponding connector on the coaxial cable.
The radome is a 4 mm thick GRP pressure molding, which can be painted to any colour as required.
The mass of the antenna is 3.7 kg. Outline dimensions are shown in figure 1. Provision is made for an optional ground-plane extension.
Stacked antennae elements are used for dual band reception. The radiation pattern is RHCP (+/- 0.5 dB at zenith) and omni-directional in azimuth, whilst good reception can be achieved down to 5° in elevation, figure 2.
Figure 2. Antenna element response at 1575.42MHz (GPS L1) and at 1227.6MHz (GPS L2)
For combined DGPS/GPS/GLONASS reception in the L1 band, a tenth order interdigital filter with the response shown in figure 3 provides significant out of band attenuation over the frequency range 1626.5 – 1660 MHz.
A similar filter provides a passband for the frequency range 1164MHz – 1254MHz incorporating GLONASS and GPS L2 reception, figure 4.
A single low noise amplifier is used across both frequency bands. It employs a low noise GAsFet input stage followed by a silicon bipolar MMIC. The amplifier’s gain is factory preset to 43+/-2 dB, although other gains are available on request. A noise matching input circuit gives a total noise figure for amplifier and filter of 3.0dB (4dB max at 1610MHz) across each pass-band.
The supply voltage to the antenna is phantom fed via the coaxial down-lead and is in the range of +5V to +20Vdc with a supply current of typically 45mA usually sourced from the receiver.
Operating temperature range is -45°C to +70°C and storage temperature range is -55°C to +100°C.
The antenna is environmentally tested to EN60945 (clauses 8.2,8.3,8.4,8.7,8.8), and complies with EMC requirements for emissions EN55022 and immunity EN5008-1, and is CE marked accordingly.