Radiation refers to the transmission of electromagnetic energy through propagating waves in free space.
There are two components to an EM wave – electric and magnetic.
A radiation source will inevitably be dominant in either electric or magnetic fields.
Magnetic Sources
A magnetic field is generated by current, and loop geometries emphasize magnetic fields.
A coil geometry strengthens magnetic fields by the square of the number of turns.
These structures are associated with inductance and low impedance.
Example magnetic sources:
-multi-turn coils
-loops
-apertures (openings) in metal structure
Electric Sources
Electric field is generated by voltage between conductive elements. This is the most common antenna type.
Larger surface areas tend to increase electric field.
These structures are associated with capacitance and high impedance.
Example electric sources:
-monopoles and dipoles
-parallel plates
-horn antennas
-wire antennas