| The electrical size of an antenna can not be minimized in a conventional way beyond a certain degree due to the well known high radiation Q limit dictated by the radiation physics. For a linear, time-invariant radiation system, the higher its radiation Q becomes, the smaller the efficiency-bandwidth product is limited to be. Nevertheless, the relationship linking high Q to small efficiency-bandwidth product does not apply to a non-linear time-variant system. Direction Antenna Modulation (DAM) is one technique that can be used to create efficient radiation beyond the usual limit of the antenna's bandwidth. The proposed system integrates switches with antennas and directly modulates the radiation energy in time domain. With the proposed pulse modulation schemes, one can achieve a radiation bandwidth beyond the 1/Q limitation because the radiation energy and the near field storage energy are decoupled in the modulation process. No fundamental loss of energy is expected caused by the switching on and off actions, as the system best circulates the stored energy. This is to assure that the system efficiency is not traded-off for bandwidth. Therefore, both efficient and wideband radiation can be achieved from such switched electrically small antennas. |
