Antenna is a set of conducting wires that allow electric current to pass. When the electric current fluctuates, the lectromagnetic wave radiation occurs. The antenna radiates the wave energy into space or receive energy from the space.
The radiation ability depends the wire’s length and shape. For example, if the two wires are very close, the electric and magnetic field are trapped between them and the radiation is very weak (figure 1a). As the two wires are apart further, the radiation becomes stronger, meaning more energy is radiated into the space (figure1b, figure1c)