More complex antennas increase the directivity of the antenna. It behaves essentially as a dipole antenna. Skywave signals can be detected at distances exceeding from the transmitting antenna. The radar receive antenna is located far from the radar transmit antenna in bistatic radar. Another with a mounted rotating slab-shaped radar antenna. The reflected radar signals captured by the receiving antenna are usually very weak. The equipment originally used a long trailing wire antenna. The amount of power passing through any sphere centered on the transmitting antenna is equal. A completely uniform omnidirectional antenna is not physically possible. It functions as a quarter-wave monopole antenna. Another type is the Omnidirectional Microstrip Antenna (OMA). It consists of a rotating ground antenna and transponders in aircraft. The tower acts as a support structure for an antenna. The polarization of a commercial antenna is an essential specification. They have linear polarization (except for the helical antenna).