isotropic radiation patter equation
isotropic radiation patter equation
(OP)
I'm trying to plot an ideal isotropic radiation pattern (meters vs dB). So far, I've managed to find some equations in order to do this...
ReceivePower(RxP) = TransmitPower(TxP) - FreeSpaceLoss(FSL)
*Assuming that there is no loss internally within the receiver or transmitter, and that there is no gain between either of the systems.
TxP = InputPower / 4*Pie*Radius^2
FSP = -27.55 dB + 20*log[frequency(MHz)] + 20*log[distance(m)]
Given the transmit frequency, the only variable would be the distance from the signal origin.
The isotropic pattern should be a sphere, but it seems that the 1/R^2 is heavily influencing my graph. So instead of a steady decline in power, I immediately see a steep drop as the power goes to zero as distance increases.
Are these the equations I should be using to calculate the propagation data?
ReceivePower(RxP) = TransmitPower(TxP) - FreeSpaceLoss(FSL)
*Assuming that there is no loss internally within the receiver or transmitter, and that there is no gain between either of the systems.
TxP = InputPower / 4*Pie*Radius^2
FSP = -27.55 dB + 20*log[frequency(MHz)] + 20*log[distance(m)]
Given the transmit frequency, the only variable would be the distance from the signal origin.
The isotropic pattern should be a sphere, but it seems that the 1/R^2 is heavily influencing my graph. So instead of a steady decline in power, I immediately see a steep drop as the power goes to zero as distance increases.
Are these the equations I should be using to calculate the propagation data?





RE: isotropic radiation patter equation
By the way, tomorrow is 'Pi Day' (3/14). Happy Pi Day.
The number I learned was 32.25 (instead of your 27.55), but it depends on your units.
Wiki link:
http://en.wikipedia.org/wiki/Free-space_loss
It's only a sphere in 3-D, and even then only for a given power density value. On a flat graph it is a square-law decline. Compared to short distance (near field), the power does actually approach zero (essentially) fairly quickly depending on your scales. In other words, adjust your X and Y scales.
Hint: try a log scale on the power (amplitude) axis.
RE: isotropic radiation patter equation
RE: isotropic radiation patter equation
Just so that I have this straight, the isotropic 3d graphs that I'm viewing (that show a sphere) only demonstrate distribution of the signal and not the distribution of power? (http://w
When I graph my isotropic signal, it in a 3d space, it looks more like rotating a 1/R^2 function around the y-axis. Hopefully I'm seeing this properly.
Lastly, I'm not entirely sure what you meant by trying a log scale on the amplitude axis, but I am unable to take the log of most of those numbers since, most of those consist of negative values. I appreciate all the help.
RE: isotropic radiation patter equation
To plot all values in 3-D you need to introduce colour as the fourth axis.
If your path loss is giving negative values (which is fine), then assign an absolute power (say 1 watt) to the source and calculate the smaller-but-always-positive power levels all the way out. Then you can convert the scale to log if it helps.
(If you still find negative power, then the Universe will implode shortly anyway...
RE: isotropic radiation patter equation
If you get very close to an antenna, the simple formulas in the antenna near field don't work. Hence, beware if for exampley you want results from 0.1" to 1" from an antenna that's radiating at a wavelength of 4 inches.
kch
RE: isotropic radiation patter equation
You had it in your first equation for TxP, although that formula gives power flux density at a distance from the antenna (watts per metre squared).