I agree with other answers that the relevant part is reflections. If you mean by height the length of a dipole antenna, this will affect the emission/reception pattern, and reflections will depend substantially on this pattern. A longer than half-wavelength antenna will have lobes downward and upwards. If it is height above ground, it is ground reflections that constitute the main contribution,and also determine how different from an optimal half wavelength antenna it is.
Hi Sangam!
Basically it is not the noise it is fading, we have different types of fading such as log normal, Rayleigh, raician etc.,
Hi, Types of noise vary, basically, the word noise used to refer to the thermal noise. Thermal noise, or sometimes called white because of its flat spectral power density, is the result of thermal agitation of charge carriers. Thermal noise power depends on bandwidth and temperature and is ideally irrespective of antenna height, unless, of course, with temperature going down as going up, thermal noise goes down.
Other than that, noise is not any more white, sometimes called colored. Generally, other noise types can be reduced or sometimes mitigated. Sources of other noise types vary. In current multiuser communications the signals of others are interfering with our signal at the receiving antenna. Such interferences add to the thermal noise to get the total noise. The signal itself can interfere with itself causing what is called inter-symbol interference (ISI). This results from the multipath environment due to the different scatterers and reflectors, where the signal is received over different paths with varying amplitudes and delays. Having the antenna at heights much above scatterers reduces this multipath effect. Of course, ISI is dealt with differently in different communication systems, e.g. the use of equalizers.
In communication between 2 nodes, e.g. a microwave link, it is necessary to have LOS. The higher the antennas, the more the LOS is confirmed. In such systems the conceptual zones (Fresnel Zones) are evaluated to insure clear LOS, e.g. by insuring that no building or other structure on the path between the two antennas has its roof top within the 1st zone (or better the 2nd or higher order zones). This will insure that no diffracted signal interferes destructively with the original signal.
In summary, I would say the going up in the skies for an antenna is generally better. Probably the only difference will be lower reflections from reflectors surrounding the antenna. Multipath Interference due scatterers and reflectors increases when antenna height decreases. Hope this dealt with your question. Thanks. @AlDmour.
Dear Sangam.
What do you mean with height? Do you mean the distance between the ground plane and the feeding point of the antenna. This other than the antenna dipole length or size.
Transmitter antennas covering relatively large area as that of mobile base stations are installed on antenna towers with heights in the order of few tens of meters. The antennas themselves are lambda/2 dipoles.For GSM operating in 900 MHz band the wave length of the electromagnetic radiation will be 1/3 meters.
A receiving antenna may receive the the radiation from the transmitting antenna directly or indirectly through reflections from the surroundings or the reception may be a mix of the two. IN the first case it is a line of sight reception and in the second case it is a non-line of sight reception.
The non line of sight reception suffers as the colleagues indicated from multipath interference leading to severe fading of the signal. The experts developed effective methods to overcome the impairments of such transmission type.
There is a type of antenna noise not mentioned in details in the previous answers. It the thermal noise of the antenna that many engineers over look it, the thermal noise of the antenna,
The thermal noise of the antenna comes from that it receives any electromagnetic radiation in its frequency range from its surroundings i.e. the earth and the sky. In order to come to thermal balance, the bodies emits radiation called the black body radiation. Part of this radiation lies in the radio wave frequencies. Such noise power can be expressed by; N= 4 k Tn. BW, where Tn the equivalent noise temperature, BW the bandwidth of the receiver antenna and k the Boltzman constant.
IN addition, the antenna can generally pick up any foreign interfering signal in its band width .
Thank you for your questions.
Wish you success.
The height of the antenna must be greater that λ/4. If not, Interference will be experienced among the horizontal and vertical plane waves.
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