dsc50050.jpg

Detail of the aft S-Band in-flight antenna, located on the aft face of the ascent stage, below the aft aft VHF in-flight antenna and to the left of the reaction control system quad. The LM had two S-Band in-flight antennas; the forward antenna appears at dsc50011.jpg. These antennas were used to communicate with Earth over the Manned Space Flight Network (MSFN).

As described by the Lunar Module News Reference,

The two S-band in-flight antennas are omni-directional; one is forward and one is aft on the LM. The antennas are right-hand circularly polarized radiators that collectively cover 90% of the sphere at -3 db or better. They operate at 22.82.5 mHz (transmit) and 2101.8 mHz (receive). These antennas are the primary S-band antennas for the LM when in flight.