Preliminary Study on Suppression Rate of Unbalanced Sheath Current of Coaxial Cable Using Sleeve Choke

An approximate analysis method for estimating the spurious radiations from unbalanced sheath current on a coaxial cable is presented and validated. The coaxial cable is vertically connected to a horizontal planar, quasi-isotropic magnetic dipole antenna. The spurious radiation generated by the unbalanced sheath current can be approximately calculated by the superposition of two radiated, high-order resonant electric dipole modes: In that way, the measured patterns of magnetic dipole antenna can be approximately “calibrated” by excluding the dual-mode, spurious cable radiations. Both coaxial cables with/without sleeve choke have been studied to yield the concept of “suppression rate of unbalance sheath current” (SRUSC). As is validated at 3 GHz-band, the SRUSC of a quarter-wavelength sleeve choke is about 14 dB at the centered frequency.