Propagation effects on a VHF radar

An ONERA study is presented of the propagation effects of VHF radars, which offers such advantages for airborne surveillance as nonambiguous pulse-Doppler capability and improved power balance in the presence of active or passive countermeasures. While a region of interference between the reflected and direct rays extends almost to the horizon in conventional microwave radars, VHF radar fields decrease more smoothly from the last interference lobe, which is closer to the transmitter, at a distance which is approximately proportional to the frequency. Attention is also given to low elevation defocusing behavior and near-ground effect comparisons between microwave and VHF radars. None of the advantages and disadvantages identified by the present study seem decisive.