Patent ID: 7292202

Claim:
A range limited antenna, comprising: a) a first pair of antenna elements and a second pair of antenna elements; b) RF signal processing network connected to said first pair and second pair of antenna elements; c) said network having a function, F(Ξ,x)=Φ A (x)−Φ B (x), where x is a signal, Φ A (x) is the phase angle of signal x at said first antenna element pair, Φ B (x) is the phase angle of signal x at said second antenna element pair, and Ξ contains all additional parameters which bear on the system; and d) said network is configured to pass a signal for which F(Ξ,x)>ε, where ε is a threshold amount, adjustable to vary a radius from the antenna for which the antenna will have gain for emitted signals within said radius and has attenuation outside said radius.