In-Band Radar Cross-Section Reduction of Slot Antenna Using Characteristic Modes

In this letter, a methodology for achieving in-band radar cross-section (RCS) reduction of slot antennas is proposed. This method is based on the characteristic mode (CM) analysis of the slot antenna to distinguish radiation modes and scattering modes. Several CM indicators, including the modal currents, the modal significance, and the modal weighting coefficient (MWC), are calculated to provide systematic guidelines on suppressing scattering modes while keeping the radiation modes work properly. Following the specific mode characteristics, two techniques are proposed to reduce the MWC for each scattering mode. First, reactance components are placed at optimal locations over the antenna to shift the resonant frequency of a particular scattering mode out of the operation frequency band. Second, additional slots are introduced to disrupt the current path and thus reduce the bandwidth of the scattering mode. The proposed methodology is validated through the design of a low RCS T-shaped slot antenna. The experimental results show that the design has not introduced deterioration in radiation characteristic, while show remarkable RCS reduction. The proposed antenna achieves at least 5 dB reductions over the wide operation frequency band (59.6% bandwidth) of the T-shaped slot antenna.