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.