An isoflux pattern compensates for the fact that a ground terminal at the edge of the visible disc is significantly further away than one at nadir, flattening received flux across the pass rather than peaking it at boresight. Wide bandwidth allows simultaneous transmit and receive through a single port, eliminating a second antenna and its cabling. Axial ratio runs 1.3 to 3.3 dB across 2000 to 2120 MHz and 1 to 2.5 dB across 2200 to 2300 MHz, with VSWR at 2:1 through an SMA female interface. The envelope is 97 x 97 x 89 mm (3.8 x 3.8 x 3.5 in) at 170 g. The antenna is built to withstand the harsh conditions of the lunar environment over long mission durations, addressing corona, multipaction and MMOD. Qualification is to NASA GEVS (GSFC-STD-7000) with random vibration to 14.1 GRMS overall across a -70 to +100 °C operating and storage range. ATH-S-004-RH is the matching test hat, shaped around the isoflux geometry to give a repeatable coupling factor during integration.