bbnn wrote:
"I know that a 1/4 antenna needs one to work but do the 1/2 and 5/8 ant
need a metal ground plane?"

A radio has a pair of RF signal connections. It isn`t the length of the
antenna which determines the need for a counterpoise. Balanced antennas
have a pair of connectors. These are interchangeable and may be
connected to the radio`s pair of RF connections. If the transmission
line wires are close-spaced, they don`t tend to radiate much.

An unbalanced antenna works against the earth, a ground plane, or a
counterpoise. It may have only one insulated connector. But the radio
requires two RF connections to make a complete circuit. The unbalanced
antenna needs a connection between the grounded side of the radio, or
one of the ungrounded RF terminals if there is no grounded terminal, and
the side of the antenna meant for a ground connection, such as its
ground-plane. This connection frequently is made by a coax`s external
shield.

If you have an unbalanced antenna, it needs something like a ground
plane so that you have something to connect the grounded side of your
radio to for a complete circuit. Otherwise the transmission line becomes
part of your radiator.

A balanced antenna, such as a dipole or a loop, has interchangeable
terminals and needs no connection to the earth for a complete RF signal
path. A ground plane would be superfluous.

Best regards, Richard Harrison, KB5WZI