Analysis and design of highly decoupled colinear antennas

In communication systems used for simultaneous transmission and reception on adjacent frequencies cross-talk interference often occurs as a result of the strong mutual coupling of the collocated transmitting and receiving antennas. To solve this problem, a colinear antenna array consisting of two independently fed vertical half wavelength dipoles and a feed line 'isolator section' was designed. The colinear antenna arrangement minimizes radiation coupling. The isolator section, which is a new concept, practically eliminates parasitic currents induced on the outer surface of the feed line connected to the upper dipole. As a result, the inter-dipole coupling is greatly reduced and the dipoles operate independently and as if the feed line were not present. Moreover, field pattern distortion is practically eliminated since the feed line does not contribute to the antenna radiation.