Design of Off-Center Fed Windmill Loop for Pattern Reconfiguration

In this letter, a low-profile pattern-reconfigurable antenna has been designed. The antenna is modified from a conventional windmill loop antenna, with the radial arms disconnected at the center and a shorting via added between the top and bottom layers. Three different patterns are controlled by three p-i-n diodes, which are located at the center of the bottom layer and operate as switches. A half-wavelength bent dipole with a reflector provides a boresight radiation with directional pattern on the azimuth plane. The second boresight pattern is obtained by a coupled fed half-wavelength dipole together with another one-wavelength dipole. The radiation nulls of the two boresight patterns are complementary to each other on the azimuth plane. A third pattern with omnidirectional radiation on the azimuth plane is obtained when the current is uniformly distributed along the arcs, forming a typical magnetic dipole. The antenna operates at 2.4 GHz wireless local area network (WLAN) band (2.40-2.485 GHz), with the measured average efficiencies of 82%, 82%, and 80% for the three modes, respectively.