Parasitic Current Reduction on Electrically Long Coaxial Cables Feeding Dipoles of a Collinear Array

The reduction of parasitic currents induced on the outer conductor of electrically long coaxial cables feeding the dipoles of a collinear array is addressed. Firstly, an experimental model is presented, and its appropriateness has been verified through validation with simulations data. The above model has been used to show the effectiveness of a low-cost technique to suppress the RF currents induced on the coaxial cables running inside the metallic mast of a collinear dipole array. The proposed solution consists of a dielectric-loaded coaxial choke, realized as a shorted quarter-wavelength coaxial cylinder mounted on the external conductor of the coaxial cable, and filled with Polytetrafluoroethylene (PTFE) to reduce its physical length. The PTFE-loaded choke performance is shown through both numerical simulations and measurements on prototypes, in the 200-400 MHz frequency range. Finally, a numerical parametric analysis is performed to get some design criteria for more complex multiple-choke arrangements.