Port isolation is the specification that makes a dual-port antenna work, and it is the one most likely to be degraded by an assembly error, a contaminated interface or a damaged connector. Verifying it before the spacecraft is closed out requires a fixture that addresses each port independently. Transmit coupling is characterised across 2200 to 2300 MHz at 5 dB typical and receive across 2025 to 2120 MHz at 4 dB typical, both at 2.5:1 VSWR. Measuring one port while terminating the other gives a direct bench check on the leakage figure the antenna is specified to. One fixture covers two antennas, the active dual-port CSA-S-003-RH and the fully passive CSA-S-005-RH, reducing the test hardware a programme flying both has to procure and control. The RF shielded enclosure mounts to features already on the antenna without a spacecraft bracket and dismounts without tooling. The envelope is 97 x 97 x 37 mm (3.8 x 3.8 x 1.45 in) at 240 g with an SMA female interface, rated -70 to +100 °C.