Patent ID: 7642986

Claim:
A range limited antenna, comprising: a) at least two sets of antenna elements; b) RF signal processing network connected to the at least two sets of antenna elements; c) the RF signal processing network having a function, F (Ξ, x )=Φ A ( x )−Φ B ( x )+Φ C ( x )−Φ D ( x ) . . . +Φ N−1 ( x )−Φ N ( x ), where x is a signal, Φ A (x) is the phase angle of signal x at the first antenna element set, Φ B (x) is the phase angle of signal x at the second antenna element set, Φ C (x) is the phase angle of signal x at the third antenna element set, Φ D (x) is the phase angle of signal x at the fourth antenna element set, Φ N−1 (x) is the phase angle of signal x at the N− 1 st antenna element set, Φ N (x) is the phase angle of signal x at the N th antenna element set, and Ξ contains all additional parameters which bear on the system; and d) the RF signal processing 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 the radius and has attenuation outside the radius.