Iridium Certified Passive Antenna. The M1621HCT-P-SMA is a high performance antenna designed for the Iridium network, and built on proprietary Maxtena Helicore® technology. This technology provides exceptional pattern control, polarization purity and high efficiency in a very compact form factor. The M1621HCT-P-SMA is a screw-on design, featuring an integrated SMA connector and is rated IP-67 when mounted for added protection. This product is designed for applications requiring high quality reception of the Iridium network.