Influence of antennas on the radar cross section of camouflaged aircraft

The radar cross section (RCS) of sensitive military aircraft has been considerable reduced in the last 10 years. The improvements were mainly achieved by geometrical shaping and the usage of new absorbent materials. The only equipment that can not be RCS-reduced during operation are the various antennas of the different onboard sensor systems (RADAR, EW, communication). Antennas have to receive or radiate electromagnetic energy and need a certain aperture size to produce a desired radiation pattern. The maximum antenna RCS is about the same as that of flat plates, having equal effective areas. A minimum can be achieved, when the structural scattering is compensated by the reflection at the load impedance. Depending on frequency and polarization, any value between is possible. Therefore the antenna RCS may exceed the structural RCS of stealth aircraft. The paper analyses the antenna radar cross section for arbitrary polarization and arbitrary impedance match over wide frequency ranges. Examples for waveguide and planar antenna types are given and reduction and minimization of antenna scattering are discussed