AD512 Filtered Passive Iridium Antenna

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A rugged passive Iridium antenna with an interdigital filter designed to operate in harsh environments (figures 1&2). The antenna’s base is milled from aluminium and hard anodised to give a mechanically resilient medium grey finish resistant to corrosion. The radome is 4 mm thick GRP, and the mass of the antenna is 1.1kg.

Figure 1. A Passive Filtered Iridium antenna AD512 mounted on a mast with its supplied bracket and V-bolts
Figure 2. General Assembly of an AD512 antenna and mounting bracket with dimensions

The AD512 has a RHCP radiation pattern over the Iridium band (figure 3) and should be mounted to give an unobstructed view of the sky from horizon to horizon. Each antenna incorporates a low-loss interdigital filter to reject interference at frequencies neighbouring the Iridium band (figure 4) for example from Inmarsat uplinks or mobile phone masts. The bracket (AD510-2) provided with each antenna can be attached to a mast or spar up to 60mm in diameter using the V-bolts provided. Connection to the Iridium handset is made with a low-loss coaxial cable from a TNC (or optional N-type connector) on the underside of the antenna.

In order to meet the requirements of directive 1999/5/EC, the AD512 must only be used with Iridium systems that conform and operate within the Iridium frequency band harmonised throughout the Community. In particular, article 3.2 of the directive stipulates that effective use should be made of the system’s allotted spectrum with avoidance of harmful interference (e.g. those identified in ERC/DEC/(97)03 and ERC/DEC/(97)05), consequently the antenna must not be connected to a signal source generating spurious emissions.

Figure 3. Elevation response of the AD512 including insertion loss due to filter at Iridium band centre (1621.5MHz)
Figure 4. Frequency response of the AD512 interdigital filter with pass-band centre at 1621.5MHz