Method for designing an antenna

A method for designing an antenna characterized by a target centre frequency, fc, and fitting within a maximum footprint of λmin/2 by λmin/2 wherein λmin is a given minimum free-space wavelength associated with a highest frequency of operation, fmax, the method comprising:

• determining dimensions of a fractional-mode, FM, air-filled, AF, antenna cavity, an FM-AF cavity, resonating around the target centre frequency characterized by a conductive ground cavity layer, a conductive top cavity layer, conductive cavity sidewalls between the top and ground cavity layer, and a side opening resulting from the fractional-mode;
• adding a guard trace for shielding radiation from the side opening by adding sidewalls at a distance from the side opening;
• wherein the conductive top cavity layer is at least partially open over said distance thereby obtaining a radiating slot between the guard trace and the FM-AF cavity;
• wherein the FM-AF cavity and radiation slot form an antenna cavity;
• matching the impedance of the antenna cavity around the target centre frequency by adjusting the FM-AF cavity and/or radiating slot dimensions within the maximum footprint.