Operation Problems of the EER Transmitter with Narrowband Antenna

High efficiency power amplifiers, using switching modes of active elements operation and Envelope Elimination and Restoration (EER, also known as Kahn technique) "synthetic" amplification method are most preferred for use in onboard devices where the power supply is limited. When it is not possible to place a full-sized antenna, it becomes narrow-band. The operation of the EER transmitter on the narrowband antenna is accompanied with increasing out-of-band emissions. Physical description of the processes when the EER transmitter is operating on a narrow-band antenna was considered. It was shown that with a rapid change in the transmitted signal, the input impedance of the antenna may become negative. At these times, antenna sends energy back to transmitter. The performed simulation of the modulator's LPF characteristics shows the reasons for the growth of out-of-band emissions when operating on a narrow-band antenna.