A direct antenna modulation (DAM) transmitter with a switched electrically small antenna

The first demonstration of a DAM transmitter with an electrically small antenna is presented in this paper. Traditionally efficiency-bandwidth product of an electrically small radiation system is inversely proportional to radiation Q of the antenna, which is high in nature according to radiation wave properties. However, a DAM transmitter operates in time-variant mode so that its efficiency-bandwidth product is not limited by Q. The key to improve the efficiency-bandwidth product is to decouple far-field radiation energy from near-field reactive energy. In DAM scheme, far field radiation is directly turned on and off to represent information, while a maximum reactive energy is circulated within system to enhance efficiency-bandwidth performance. To prove the concept, a traditional and a DAM transmitter have been tested and compared under the same condition. Results show that information tone received from the DAM transmitter is significantly higher in magnitude when signal bandwidth exceeds bandwidth of the traditional transmitter.