AD410 L1/L2 GPS antenna

 

Introduction

The AD410 antenna (shown below) is a robust, lower cost alternative to existing L1/L2 models from other manufacturers.

 

Figure 1. AD410 antenna with mounting bracket. The base is 188 mm (7.4") in diameter. The fours holes around the periphery (plan view) are for an optional ground plane extension.

 

Electrical Specification

Low Noise Amplifier

Identical LNAs with ceramic filters are employed for both L1 and L2 reception. Each employs a low noise GAsFet input stage followed by a silicon bipolar MMIC. The amplifiers’ gain is factory preset typically in the range 38 to 48 dB at L1 and L2. A noise matching input circuit gives a noise figure of <2.5 dB across each band and dielectric filters are used to provide selectivity (figure 2). Supply voltage to the antenna is in the range 5V to 20Vdc with a supply current of typically 60mA. A single output is provided for connection to the receiver. The amplifier complies with EMC requirements and is CE marked.

Antenna

Patch antenna elements are used for both L1and L2 reception. The patches are stacked with L1 topmost, consequently the phase centres are 45 mm and 41 mm 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 degrees in elevation for L1 and L2.

Provision is made for an optional ground-plane extension.

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

 

 

Figure 2. Gain (black lines) and noise figure (red lines) of L1 and L2 ceramic filters with low noise amplifier used in the AD410. The L1 (1.57542 GHz) and L2 (1.2276 GHz) GPS frequencies are shown bracketed (+/-10 MHz) with the green vertical lines. Although the ceramic filters provide good noise figures across the bands, improved out of band attenuation requires comb or interdigital filters (e.g AD490)

 

 

Mechanical Specification

The antenna case is of a two part construction. Machined from solid aluminium blocks, both parts are hard anodised and dichromate and nickel acetate sealed resulting in a 8" diameter base with a green finish that is both very tough and extremely resistant to salt water corrosion.

The radome is a 4 mm thick GRP pressure moulding, 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 type N connector on the coaxial cable.

The mass of the antenna is 1.9 kg. Outline dimensions are shown in figure 1, above. Operating temperature range is -30°C to +70°C. Storage temperature range is -40°C to +100°C.

Antenna fixing may be by either a 5/8" UNC centre hole, eight M5 tapped holes spaced 45° apart on a 129mm PCD or with an L shaped bracket with V bolts supplied with the antenna.

 

'Car mounted antenna': An AD410 antenna supporting the back

quarter of a Volvo 960 estate car

 

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