AD540 combined L1/L2 GPS/DGPS and UHF antenna

Introduction

The AD540  (figure 1) combines an antenna for DGPS and L1/L2 GPS reception with a dipole antenna for connection to a UHF (458MHz) radio modem, without compromising performance. Interdigital filters are incorporated for use in areas where general purpose antennae are inoperable due to L-band interference. 

A single output is provided for GPS/DGPS and UHF, enabling connection to be made with one lead. An optional multiplexer is available to separate the signals at the receivers.

 

Electrical Specification

Patch antenna elements are used for both L1 and L2 reception. The patches are stacked with L1 topmost, consequently the phase centres are 59 mm and 51mm above the base of the antenna for L1 and L2 respectively. The radiation pattern is RH circular (+/- 0.5 dB at zenith) and omni-directional in azimuth, whilst good reception can be achieved down to 5° in elevation.

A dual interdigital filter is used for L2 (at 1227.6MHz), and DGPS and GPS (1530 to 1575.42 MHz) reception. A triple interdigital filtered option is available on request, with 12 MHz pass-bands centred at 1227.6,1536, and 1575.42 MHz. 

A single LNA is used for both L1 and L2 reception. It employs a low noise GAsFet input stage followed by a silicon bipolar MMIC. The amplifier’s gain is factory preset usually to 45+/-2 dB for both L1 and L2, although other gains are available on request. A noise matching input circuit gives a total noise figure for amplifier and filter of <2.5 dB across each pass-band, figures 2 and 3. Supply voltage to the antenna is in the range 5V to 20Vdc (or 3V to 20Vdc on request) with a supply current of typically 50mA.

The antenna complies with EMC requirements and is CE marked accordingly.

Mechanical Specification

The antenna case is a two part construction. Machined from solid aluminium blocks, both parts are hard anodised and dichromate and nickel acetate sealed resulting in a 21cm diameter base with an attractive green finish that is both very tough and extremely resistant to salt water corrosion.

The radome is a 4 mm thick GRP pressure molding, which can be painted to any required colour.

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 on the antenna and the corresponding connector on the coaxial cable.

Provision is made for an optional ground-plane extension.

Operating temperature range is -30°C to +70°C and storage temperature range is -40°C to +100°C.

The weight of the antenna is typically 3.2kg. Outline dimensions are shown in attached drawing.

 

Back to main introduction