165 MHz of continuous coverage allows one antenna to serve both directions of an L-band data link. The design is entirely passive, so there is no bias line, no current draw and no radiation-sensitive device in the signal path. Axial ratio is 2 to 3 dB at boresight and specified at 8 dB maximum 90 degrees off boresight, which sets a predictable floor on polarization loss at the edge of coverage. VSWR is 2:1 across the band through an SMA female interface. The envelope is 97 x 97 x 18 mm (3.8 x 3.8 x 0.72 in) at 190 g. The antenna is designed for the harsh conditions of space operation across LEO, MEO and GEO, with a sealed and vented housing addressing corona, multipaction, atomic oxygen and MMOD over a five-year mission life. Qualification follows NASA GEVS (GSFC-STD-7000) with random vibration to 14.1 GRMS and humidity per MIL-STD-810 Method 507.6, across a -70 to +100 °C operating and storage range. ATH-L-004-RH is the matching test hat. Certain small-volume orders can ship within days rather than the months typically quoted for space-qualified hardware.