Automatic impedance matching of an active helical antenna near a human operator

This paper, presents an automatic impedance matching technique for normal mode helical antenna technique for a normal mode helical antenna near a human operator in the 150 MHz band. The helical antenna incorporating varactor diodes for changing impedance maintains a good matching condition regardless of the distance between the helical antenna and the operator. This eliminates a power loss caused by the impedance mismatch due to the human body. The technique makes use of the steepest gradient algorithm that can achieve an adaptive control algorithm of the impedance condition.