Compact directional v.h.f. antennas

The prototype of a compact directional antenna for geophysical diagnostics from a borehole has been constructed and tested. The prototype consists of a wire monopole antenna placed next to a ferrite cylinder which loads the antenna thereby changing its characteristics. At its resonant frequency of 230 MHz, the ferrite-loaded antenna has an input resistance of 19 ¿, and is physically shorter by a factor of 2.57 when compared to an unloaded monopole resonant at 230 MHz. The antenna radiation pattern is directional with a front/back ratio of 8.5 dB, and a¿3 dB beamwidth of 146° at 249.6 MHz.