antennagainradiationRF
I was doing an experiment for finding the radiation pattern of Pyramidal Horn Antennas at RF frequencies(as part of my course curriculum). There I came across the Friis Transmission Equation
What I don't understand here is the two terms Gt and Gr. What does these gain terms refer to? Gain is something associated with active devices like amplifiers. But how come antennas have gain? They don't have any source of energy so that they can amplify the power, they are transmitting or receiving.
For a compound box antenna the formula is similar and this might be useful: -
Obviously they are not using A and B to denote the aperture dimensions but, I suspect that "r" is going to be exactly the same i.e. distance between centre of aperture and measurement point.
Your requirements will never be met.
A dish antenna is the best for providing focus and if you looked at voyager II, it used a 3.7 metre dish at about 3 GHz. This would give a 3dB half-beam-width of about 0.91 degrees.
I'm using the example of Voyager II because they would not ship something to the planets that had not been thought about (o-rings excluded from this statement).
At 1 GHz this half beam angle increases to 2.74 degrees
At 1 GHz and a 1m dish this increases to 10.2 degrees
See this calculator to check. To help you get further ideas about this follow these rules: -
Best Answer
The gain is an indication of directionality. IF you have an isotropic emitter that sends , say 1 W, into complete sphere you are emitting radiation over \$4\pi\$ steradians solid angle. If you make the antennae more directional and emit over a smaller area then the energy is concentrated (per steradian) in a smaller solid angle. This increase is a gain, gain in an active amplifier is a dimensionless number, and so is this.