Electronic beam tilting using a single reactively loaded circular wire loop antenna

The near-field current distribution along a circular loop wire antenna is modified by the inclusion of an electronically controllable reactive load, a varactor diode, into the antenna to provide beam pattern shaping. Modifications to a 4:1 balun are shown which permit varactor biasing while facilitating the impedance match of the circular loop, VSWR 1.3 to 1.9; this VSWR is superior to that previously reported for a reactively loaded wire antenna. In addition, it is shown that a reactively loaded dipole structure can provide only 10° beam tilt while the circular wire loop structure provides up to 27° beam tilt.