Where is the antenna located on a 2006 Honda Civic EX?

2006 Honda civic antenna

The antenna is located in the rear windshield. It looks like its part of the rear defrost wires but the top (non-heating section) is actually the antenna.

Well, that answers why reception is so marginal when compared to vehicles w/an external, vertical antenna.

The AM signals are highly attenuated AND highly directional; AM-station antennas are vertically-polarized...in most cased the entire vertical tower is "hot".

The FM stations' antennas are horizontally-polarized, thus better for reception in HONDAs.