For surface wave transmission, it is desirable to have an antenna of size comparable to the wavelength of the transmitted signal due to the phenomenon of diffraction. Diffraction refers to the bending or spreading of waves when they encounter an obstacle or pass through an opening.
When the size of the antenna is comparable to the wavelength, it allows for efficient coupling of energy between the antenna and the surface wave. This is because the dimensions of the antenna interact with the surface wave in a way that maximizes the transfer of energy.
If the antenna size is much smaller than the wavelength, the surface wave will not efficiently couple with the antenna. This can result in poor transmission efficiency and weaker signal strength.
On the other hand, if the antenna size is much larger than the wavelength, it can lead to excessive diffraction and scattering of the surface wave. This can cause signal degradation and loss of energy.
By matching the size of the antenna to the wavelength, the diffraction effects are optimized, resulting in better transmission efficiency and stronger signal reception for surface wave propagation.