Dipole antennas

Much of the work of Spectrum Planning Group is based on well established principles of ‘antennas and propagation’. Propagation matters have received a lot of attention over the years and much has been written on the topic but the ‘antennas’ part, although arguably simpler, may lack a suitable written reference that gathers much of the relevant material into one place. The primary purpose of this White Paper is to take a step towards correcting this state of affairs, but a huge amount of underlying complexity comes to light when one ‘scratches the surface’ of a topic like this. A secondary objective, then, is to present some of the more interesting and useful facts, and to provide simple, physical explanations wherever possible. In summary, this White Paper is intended to provide a compendium of well-known and obscure facts about dipole antennas and isotropic sources including effective aperture areas, coupling factors, radiation resistances and link budget equations. What began as a simple case of looking up the effective aperture area of a dipole developed into a quest for the whole story about dipole antennas and has resulted in this re-working of a small part of a very-old, but intriguing story. Of course, spectrum planning for terrestrial broadcasting involves many more-complicated antennas such as log-periodic dipole arrays and Yagi-Uda arrays, not to mention the multitude of clever transmitting antenna designs based on slots. It wouldn’t be possible to do these justice as well in a document of this size so I’ve deliberately limited the scope. Additional key words: antenna, dipole, antenna gain, effective aperture area, link budget, radiation resistance, cage dipole, folded dipole, balun, monopole, biconical dipole, discone