AD316 DGPS and  DGPS/GPS comb filtered antennae

 

Introduction

A very robust, compact antenna, the AD316 and its variants (figure 1) are designed for reception of low power satellite transmissions down to -130 dBm in areas where general purpose antennae are inoperable due to L-band interference.

 

 

Figure 1. General arrangements of the AD 316 with a bottom mounted TNC (top left) and a side entry N-type connector (top right and bottom). An N-type connector can also be specified for the version shown on the left. The height of the antenna is 145mm.

 

 

Electrical Specification

The antenna element is a shaped dipole with right hand circular polarisation, an omni-directional radiation pattern in azimuth, and good reception down to 5 degrees in elevation.

The element is connected to a built in GaAs FET amplifier with a precision low-loss comb filter. Comb filters' frequency responses are shown in figure 2 for the band 1530 to 1560 MHz enabling DGPS reception, and the band 1530 to 1575 MHz for DGPS and GPS reception.

The amplifier gain is factory preset within the range 30 dB to 45 dB with an overall noise figure of less than 2.5dB. The amplifier is phantom powered via the coaxial output lead with a 3.3V to 20Vdc supply at typically 35 mA. The amplifier complies with EMC requirements and is CE marked.

 

 

Figure 2. Frequency responses of two comb filters with different bandwidths for DGPS reception (in red), and DGPS and GPS reception (in green).  The measurements were obtained over the frequency range 1500 to 1600 MHz with an Agilent HP8714ET network analyser. Comb filters are light-weight, very robust, and have low pass-band losses.

 

 

Mechanical Specification

The antenna base is milled from aluminium, hard anodised and then dichromate and nickel acetate sealed giving an attractive, but extremely rugged green finish offering superb resistance to salt water corrosion.  A 4mm thick GRP pressure moulding, which can be painted to any colour required, provides a strong, but low-loss radome.

TNC or N-type connectors are available with options for side or centre mounting (figure 1).

The antenna is sealed to a minimum of IP67, the limiting factor being the seal between the connector on the antenna and the connector on the coaxial cable.

The antenna complies with EMC requirements and is CE marked, its mass is 0.8 kg, operating temperature range is -30C to +70C, and storage temperature range is -40C to +100C.

 

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