Date Added: Jan 2013
In High Frequency (HF) communication, both sky wave and ground wave plays an important part. During a communication trial, it was observed that duplex communication was established over the range of 250 kilometers using dipole and rod antenna. There is null in the vertical direction of rod antenna and hence sky wave communication theoretically is not possible. Thus there is a need to study the radiation pattern in null direction as effect of main lobe is already known. This phenomenon needs to be understood so as to stop unintended transmission in the null direction. This paper describes the simulation of radiation pattern of HF antennas and proposes a hardware blocking model to stop them from emission in the null direction.