A Single-Layer Planar Antenna Unaffected by a Possibly Close-by Metal Surface

A planar antenna on a single metal layer is proposed, whose feed remains matched at the frequency of operation of 4.85 GHz, no matter if there is a metal ground plane close-by, or at some distance, or far away. In free space, the proposed antenna acts like a slot antenna. Otherwise, if a metal plane is located close to the antenna, a current will flow in the ground and the antenna behaves like a coplanar waveguide patch antenna. For the first case, dipole-like omnidirectional radiation occurs, while for the second case, the typical patch-like radiation pattern is observed. In both cases, the complex feed impedance is about the same. If the metal ground is located at intermediate distance, the feed impedance variation remains small. Measurements of a prototype show that for the distance between antenna and metal ground ranging from 4 mm to 250 mm, a feed match better than -12dB is achieved at 4.85 GHz.