Theoretical and experimental investigation of box-to-antenna coupled EMI noise on an helicopter under the influence of rotors

In this work, a specific box-to-antenna EMI coupling problem in an helicopter platform is investigated. The problem is reduced to an antenna-to-antenna coupling problem by modeling the EMI source with a monopole antenna. The VHF high band blade antenna was chosen as the victim antenna. The effect of the main and tail rotors on the coupling is also considered and the rotor modulation effect on the coupling is analyzed. The investigation consisted of two stages; numerical analysis and scaled model measurements. The analysis and measurement results are compared for both maximum coupling and for different rotor positions. A good agreement is found between the numerical analysis and measurement.