dsc50011.jpg

Detail of the forward S-Band in-flight antenna, located on the front face of the ascent stage, between the tracking light and the rendezvous radar antenna. The LM had two S-Band in-flight antennas; the aft antenna appears at dsc50050.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.

Below the antenna, just above the forward hatch, is the tracking light.