Based on @OrganicMarble's answer I did some further reading. @William-Rem's comment asks:
Is that a quadrafilar antenna with... a ground plane?"
and the answer appears to be yes; the four rods pointing radially below the quadrafilar "cloverleaf" are labeled as a ground plane in Figure 6.
As @OrganicMarble already points out, the VHF antennas were used for voice, data and ranging with the CSM (ranging up to 200 km) and voice to "extravehicular (EV) crewmen on the lunar surface". An electronic diplexer and an antenna switch allowed two VHF receivers and two transmitters to access either VHF Antenna A or B.
VHF A voice 1296.8 MHz
VHF A ranging 1296.8 MHz
VHF B voice backup 1259.7 MHz
VHF B data 1259.7 MHz
VHF B ranging 1259.7 MHz
I found NASA Technical Note NASA TN 0-6974 Apollo Experience Report - Lunar Module Communications System. Figure 6. Shows the various antennas on the LM and Figure 7. shows a rather complicated "simplified" block diagram
Two VHF inflight antennas were used for communications with the CSM. The
antenna was designed to produce right-hand circular polarization. The radiation pattern
provided approximately 47r -steradian coverage with a minimum gain of -6 decibels (with
respect to the CSM linearly polarized VHF antenna) when the antenna assembly was
terminated in a free-space environment. This requirement was accomplished by manual
switching between the two antennas.
[...] Audio inputs from the commander or LM pilot were hardlined to the respective
audio centers located in the SPA. If a VHF transmitter was selected, the audio center
routed the voice input to the correct VHF modulator and provided keying of the transmitter. After amplification to a peak power of approximately 7.6 watts, the signal was
routed through the VHF diplexer to the selected VHF antenna. Any received RF signals were routed through the VHF diplexer to the receiver section. The detected output of
the receiver was routed to the PMP in the SPA, which further amplified and routed the
signal to the audio centers. The transmit/receive selector switches and volume controls on the crewmen's control panels controlled headset audio signals. The VHF communication modes between the LM and the CSM are shown in figure 1.
I also found AS10-34-5053 - Apollo 10 - Apollo 10 Mission image - VHF Antenna Array on LM
Cropped, zoomed, sharpened and higher contrast:
Additional Information About this Item
National Archives Identifier: 16682061
Local Identifier: 255-AMP-AS10-34-5053
Creator(s): National Aeronautics and Space Administration. Lyndon B. Johnson Space Center. 2/17/1973- (Most Recent)
From: File Unit: Apollo 10 - AS10-27-3855 through AS10-35-5290, 11/9/1967 - 12/19/1972
Series: Photographs of the Apollo Space Program, 11/9/1967 - 12/19/1972
The original database describes this as:
Description: View of Very High Frequency (VHF) Antenna Array on Lunar Module (LM). Image was taken of translunar coast during the Apollo 10 mission. Film magazine was M,film type was SO-368 with 80mm lens. Film type was 70mm color.
Original: Film - 70MM CT
Also, cropped from AS09-20-3069 Apollo 9, David R. Scott spacewalk:
and cropped from AS09-20-3064 Apollo 9, David R. Scott spacewalk: