Figure 1: Model of crow's-nest antenna
The Crow's-Nest Antenna (CNA) is an omnidirectional phased array system comprised of elements distributed in a sphere. It is a patented antenna, developed by the Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR (FHR). The single radiating elements are randomly arranged to avoid the rising of grating lobes. A rotationally invariant density distribution of the radiating elements into the imagined sphere allows the realization of a uniform pencil-beam for full azimuth and elevation coverage. The necessary phase shifts for a directional radiation are calculated by a beam steering computer. Using digital beamforming a sharply focused pencil beam can be organized with this antenna in almost all directions simultaneously. The feeding lines are fixed in a ground plate and are stabilized with a dielectric having a relative permittivity of εr≈ 1 to avoid a decreased propagation speed of the electromagnetic waves within the antenna.
This antenna realized for applications in X-Band has got a diameter of 6 feet containing about 2,000 single radiating elements. The name of the antenna was derived from the designation “crow's nest” for the specially designed platform in the upper part of the mainmast of a ship that is used as a lookout point to observe all directions too.