Assuming a constant gain receiving antenna in any case, the power received will be proportional to the transmitting antenna's gain from equation 1 , multiplied by the reciprocal of the free space path loss equation from the question :. In other words, irradiance is proportional to the inverse-square of distance, regardless of frequency. However, the 5 GHz antenna will have a smaller beam width, thus focusing the transmitted power over a smaller area.
This means the 5 GHz case will have a higher irradiance than the 2. If the receiving antenna has an equal effective aperture rather than a constant gain at any frequency, the receiving antenna will then be subject to a greater radiant flux with increasing frequency. Effective aperture can be expressed as a function of the antenna gain and the wavelength.
On pages 7. It is the capture area of the [antenna] that determines its effectiveness in absorbing the incoming radiation: it means that as the wavelength is reduced it becomes increasingly important to design the [antenna] to have a higher gain. We make contact with a distant station on MHz, who has an identical phased array and height as our antenna. The gains and patterns are identical.
Signals are just readable. We then attempt to make contact with this station on MHz with a scaled-down version of the MHz array with the same gain and pattern. The statement above from that book implies that we will not succeed! Part of the reason is that the received power at the receiver input will be significantly less on the higher band, even though the gain of both antennas is the same! If we want to communicate with that distant station on the higher band, then we need to increase the gain of the MHz array so that its aperture is the same as the MHz antenna.
It goes without saying the band conditions will vary; but we are assuming that the conditions are the same for both tests. Sign up to join this community. Small-scale fading: Due to the constructive and destructive interference of the multiple signal paths between the transmitter and receiver.
This occurs at the scale of the order of the carrier wavelength, and is frequency dependent. The fading characteristics vary over different spaces, frequencies, and times. Our research shows that destructive interference and multipath fading can be eliminated by using reference phase to control LOS beam phase.
In slow fading channels, the coherence time of the channel is long and encoding can be performed only over a single or a few fading states e. While encoding still averages out the randomness of the noise, it may not be possible to fully average out the randomness of the channel.
In wireless communication environment, many copies of the signals get combined at the reciever side and some of them constructively combines and some of them destructively combines. Fast Fading: It occurs mainly due to reflections for surfaces and movement of transmitter or receiver.
High doppler spread is observed in the fast fading with Doppler bandwidth comparable to or greater than the bandwidth of the signal and the channel variations are as fast or faster than the signal variations. Rayleigh fading is most applicable when there is no dominant line-of-sight propagation between the transmitter and receiver. Rician model considers that the dominant wave can be a phasor sum of two or more dominant signals, e.
Ultraviolet rays are one of the causes of fading because they can break down chemical bonds and fade the color in an object. Other major contributors to fading include visible light and solar heat. Other objects may reflect the light more, which makes them less prone to fade. Sunlight causes some foods to fade. Frequency selective fading occurs when the symbol length is shorter than the delay spread, or equivalently when signal bandwidth is larger than the channel bandwidth.
Explanation: Slow fading can be minimized by using error correcting codes and also by using diversity technique to get additional uncorrelated estimates of a signal. Explanation: The zero forcing algorithm has the disadvantage that the inverse filter may excessively amplify noise at frequencies where the folded channel spectrum has high attenuation. CDMA systems use a signal fast chip rate for spreading the spectrum. To use the free space path loss calculator, enter the figures as required and press calculate to provide the answer.
The calculator below is a path loss calculator because it includes the antenna gains. To make it a free space path loss calculator, antenna gains of 0 should be entered into both gain boxes. Using the path loss calculator, it should be remembered that the calculations have been scaled to accept distances in terms of kilometres and frequencies in terms of MHz.
All antenna gains are expressed in decibels relative to an isotropic radiator and not a dipole which has a gain of 2. It should also be remembered that although the calculator is for path loss and is not strictly a free space path loss calculator, the calculation assumes there is free space between the two and no other effects affect the signal apart from the reduction due to signal distance and the antenna gains.
A free space path loss calculation does not include the antenna gains and only looks at the path loss itself. Free space propagation basics The free space propagation model is the simplest scenario for the propagation of radio signals. As the ripples move outwards their level reduces until they finally disappear to the eye. Free space propagation signal level It can be shown that the level of the signal falls as it moves away from the point where it has been radiated.
Reflective antennas, that is dish antennas, of a given size have higher gain with decreasing wavelength. Systems that use stick antennas therefore benefit from lower frequencies while dish-antenna systems will attain higher system gain at higher frequencies. Remember to use this knowledge for good and not for evil, although it should be possible to impress smug colleagues if the topic ever comes up.
For example, quantum background noise increases substantially above about 70GHz. This does not effect "propagation" in that it does not impede a wave or photon, but it does interfere with its detection in a receiver. See Section 4. See Section I'm sure other texts have good treatments as well. To post reply to a comment, click on the 'reply' button attached to each comment. To post a new comment not a reply to a comment check out the 'Write a Comment' tab at the top of the comments.
Registering will allow you to participate to the forums on ALL the related sites and give you access to all pdf downloads. Blogs Eric Jacobsen. Basics Wireless Communication. Introduction It seems to be fairly common knowledge, even among practicing professionals, that the efficiency of propagation of wireless signals is frequency dependent.
Comments Write a Comment Select to add a comment [ - ]. Great Article! It may be even better if you may add a figure of wave propagation in air channel within 5Mb to Ghz. Good article! It reminds me of bad statistics-- the defnintion of the parameters can be manipulated to make the final result say anything you want. Hi, I just read your article and found it to be very interesting. I had a slight doubt, you say if we only consider propogation exluding antennas, then it is frequency independent.
But my doubt is when electromagnetic waves propogate, they have a propogation coefficient, which is definitely frequency dependent. Can you please share your thoughts on this. Anurag, could you clarify what you mean? There are propagation effects through materials e.
Strictly speaking, air is a material and is lossy, but it is a small enough effect to generally be neglected. I remember I had this issue during my college assignment. The way I see it is, there are two dimensions one is Electrical and other Physical. If you increase the frequency f, electrically effective aperture increases. This effectively increase the Gain of the antenna by the same factor.
Hence they cancel out and the end result is no dependence of frequency. I am at peace with this and correct intuitively. Hi, wonderful article, it cleared my long pending question on this topic. For any given antenna, that antenna will have a bandpass frequency response.
As you move the signal frequency the gain then depends on the antenna's frequency response. Thanks for the clarity! I spent hours trying to understand how that equation made sense from a physics perspective.
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