redhat wrote:
Hello All,
should the antenna ground be connected to the transmitter circuit
ground? i saw a microstrip antenna that has only a feed pad but no
ground pad .
Regards

The short answer is yes. But such a connection isn't usually
infinitesimally short, so current will flow along the path and the path
will become part of the antenna and radiate.

An antenna is a circuit, and like any circuit it has two terminals. Our
calling one of these "ground" doesn't give it any special or magical
properties -- it's simply one of the two connections. However much
current flows into one of the antenna terminals must flow out of the
other. If we connect, for example, a piece of coax from a transmitter to
an antenna and connect only the center conductor to the antenna, then
the outside of the coax becomes the other half of the antenna. If one
amp flows into the antenna, one amp flows along the outside of the coax
shield. This would be the case for the microstrip antenna you describe,
if you're really describing it accurately.

Follow the current from the "hot" side of the transmitter to the
feedline, along the feedline to the "antenna", back from the other
terminal of the "antenna" to the "ground" side of the transmitter.
Anywhere the current is flowing right beside an equal current going in
the other direction (to simplify a bit), like it does on the inside of a
coaxial cable, there won't be any significant radiation. But anywhere a
current is flowing where there isn't a very nearby, opposite current,
the conductor is actually part of the antenna and will radiate.

Roy Lewallen, W7EL