Even the law states that the Effective Radiated Power (ERP) will not exceed.There is this concept that, the moment they exhibit gain, antennas magically create power within themselves.If one examines an antenna it will be noted it is constructed of basic materials, the best being gold, silver, copper, then aluminium following on.
Gain has a positive value, loss has a negative value, and is equal to. The reference is known as 0dBD (zero decibel referenced to dipole). An antenna with the effective radiated power of twice the input power would therefore have a gain of 10log(21) 3dBD. ![]() It increases the antenna gain figure by 2.14dB, this being the gain of a dipole over an isotropic antenna; But this is not a head start This is covered more in the paper Cheating with Antenna Gain. The graph is usually circular, the intensity indicated by the distance from the centre based in the corresponding angle. Using anything other than 3dB does not do an antennas reputation any good as this could give the impression the antenna has a widernarrower beamwidth and if a serious engineer looks at this he would, rightly so, discredit the design. The radiation pattern of this antenna is typically referred to as the doughnut as shown in the adjoining figure. Here the shape of the radiation was changed such that the outer most energy was focused to compliment the middle half, the result being a doubling of the radiated energy along the required plane or effectively a 3dB gain. ![]() There is, however, one further method of focusing, to now intensify the radiation in only one direction. This makes all the energy appear in only one hemisphere and thus results in a doubling of radiated energy in this direction or 3dB gain. The effective angle, however, of such an antenna is small (typically 10 degrees). ![]() The reflector is usually just a single rod, maybe a collection of them. Even if a bunch, the reflector is not going to stop every scrap of energy from escaping between the cracks Some will be radiated towards the rear (or, in the case of reception, bypass the reflector and be intercepted by the dipole). Antenna Dbi Explained Free Space TheRemember, when in free space the dipole is just as sensitive to this direction as it is to the front of the antenna, and has a natural tendency to want to continue with the doughnut pattern. Yip, the very tips of the metal will cause some signal to bend on the edges of the reflector and toward the rear (or, in the case of reception, from the rear toward the dipole). The higher the gain of an antenna the smaller the effective angle of use. This is the part people forget i.e. Choosing the correct antenna is dealt with in Choosing the correct antenna.
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