Highly decoupled cosited antennas

DETAILED DESCRIPTION It is the primary object of the present invention to provide high interantenna isolation between closely spaced antennas.
A related object of the invention is to obtain a very high decoupling (e.
g.
, 35 dB isolation) between antennas separated by only a fraction of a wavelength (over the operative frequency band) without significant impairment of the equatorial plane radiation pattern.
The achievement of the foregoing objects is based on significantly minimizing the radiation couping between cosited antennas by separating the antenna near-fields, and by suppressing extraneous parasitic rf currents on the outer conductors of the coaxial cable antenna feed lines.
In a preferred embodiment of the present invention two cosited omnidirectional biconical antennas are respectively tilted plus and minus 45 degrees (.
+-.
45.
degree.
) with respect to the vertical and, therefore, are 90 degrees with respect to each other to effect polarization mismatch and near-field decoupling.
In combination with the described antennae orientation, a plurality of high impedance cable chokes are added in series with the coaxial cable antennae feed lines to suppress induced parasitic rf currents.
The cable chokes increase and smooth the interantenna isolation by eliminating extraneous coupling due to scattering from the transmission lines.