Wideband, Circular Polarized Sum and Difference Pattern Coaxial Antenna

We present a compact coaxial flared antenna for communication and tracking applications with a broad instantaneous RF bandwidth greater than alternatives like a circular horn. To solve the free space impedance mismatch due to the small aperture, a flared, impedance transforming outer conductor is proposed. Modal analysis is applied and modal coefficients, as a function of the number of excitations, are assessed; a circular polarized TE
₂₁
difference mode with the same cutoff frequency as the TE
₁₁
sum mode via impedance matching and specified mode coupling points resulted in a 2.4 to 1 bandwidth. The polarization diverse antenna exhibits linear or circular polarization and is well suited as a direct radiating element or as a feed for low f/D lens or reflector applications.