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Changes to Measurement Arrangement for Tests Performed With Rod (Monopole) Antenna
This technical note from Com-Power Corporation describes the significant change made to the monopole antenna test setup between MIL-STD-461E and MIL-STD-461F, which was released in December 2007. Under previous versions of the standard, the 1.04-meter rod antenna counterpoise was positioned at the same height as the EUT ground plane, with a bonding strap of sheet metal or aluminum foil bridging the gap between the two. In MIL-STD-461F, this arrangement was revised based on experimental findings that the bonding strap was distorting results — enhancing readings at some frequencies while suppressing them at others. In the new arrangement, the counterpoise height is decoupled from the ground plane height, with the vertical center of the rod element now fixed at 120 cm above the shielded room floor. The bonding strap is eliminated entirely, and the only ground connection is made through the coaxial antenna output cable shield, which is bonded to the floor directly beneath the antenna. A ferrite with 20 to 30 ohms of impedance is also required on the output cable between the antenna port and the floor grounding point. The standard additionally requires that antennas with isolated coaxial bulkhead connectors be modified to allow electrical contact between the connector shell and the matching network enclosure.