In conjunction with the USCG Automatic Identification System (AIS) requirements for commercial vessels, Digital Antenna created a series of 4Æ AIS antennas that meet the exacting AIS frequency requirements. Designed with a low 1.5:1.0 SWR ratio from 159-162 MHz, Digital AntennaÆs 4.5 dB gain AIS antennas offer unsurpassed durability and performance compatible with all AIS transponders. All 4' AIS Antennas Feature: Powerful brass radiators Soldered connections Power directing ferrite choke bead High gloss urethane finish 316 stainless steel ferrule 4.5dB gain