An antenna is just a passive impedance-matching device, nothing more or less. It matches 377 ohms to whatever the feedline impedance is. Making the antenna's effective area larger is the only way to capture more arriving energy from the transmitter.
At the same time, as its size grows, the area of the antenna that's not exposed to the transmitted wavefront increases even more rapidly than the area that is, making it a losing proposition to keep increasing the size alone. Instead, we use directive and/or reflective elements whose geometry allows a smaller antenna element to receive more energy from one direction at the expense of others.
Just like a lens, in other words. A larger lens or mirror captures more light than a smaller one (focal length considerations aside), but that's not all there is to making a good camera or telescope. The right combination of smaller optical elements can do almost as well as a single huge lens, while being much more practical to work with.
One key point is that in neither case is any amplification or "gain" present. It's just a matter of which approach captures more of the limited number of photons available. Another is that the size of the lenses or antenna elements has to be expressed in terms of wavelength, not absolute spatial dimensions, if you want to compare them directly.
That's ultimately what the path loss equation describes, albeit awkwardly. Path loss increases at shorter wavelengths simply because the exposed areas of the antennas get smaller while the wavefront doesn't.
We can sometimes compensate for that by making the antennas bigger in terms of the number of wavelengths. Mathematically, the path losses involved in the Deep Space Network would be much lower if they could use LF/HF frequencies instead of microwaves, for instance... but to take advantage of that, the antenna sizes would have to increase to ridiculous dimensions, on the order of miles. Microwaves end up being a much better fit in practice. Even if lower frequencies were usable, the resulting increase in atmospheric noise (and decrease in available bandwidth) would swamp any advantages.
> At the same time, as its size grows, the area of the antenna that's not exposed to the transmitted wavefront increases even more rapidly than the area that is, making it a losing proposition to keep increasing the size alone.
And this is based on frequency correct? So frequency is direct component.
>One key point is that in neither case is any amplification or "gain" present. It's just a matter of which approach captures more of the limited number of photons available.
Gain: the factor by which power or voltage is increased in an amplifier or other electronic device, usually expressed as a logarithm.
Gain does not require amplification, the transmission gain of antenna is not based on it, nether is reception. In both transmission and reception it is based on how efficient the antenna is and it's directionality. Both are directly tied to frequency and geometry together, you cannot ignore frequency as the GP said.
This paper seems to be a great resource and helped reaffirm my understanding of frequency being a key component in antenna design and it not being "shoehorned" in. Gain and effective area are proportional to each other and therefore the term gain is used for receiving antennas because it matches it transmission characteristics, hence reciprocity:
"Many antenna properties are the same for both transmitting and receiving. It is often easier to calculate the gain of a transmitting antenna than the collecting area of a receiving antenna, and it is often easier to measure the receiving power pattern of a large radio telescope than to measure its transmitting power pattern. Thus this receiving/transmitting “reciprocity” greatly simplifies antenna calculations and measurements. Reciprocity can be understood via Maxwell’s equations or by thermodynamic arguments.
Burke and Graham-Smith [20] state the electromagnetic case for reciprocity clearly: “An antenna can be treated either as a receiving device, gathering the incoming radiation field and conducting electrical signals to the output terminals, or as a transmitting system, launching electromagnetic waves outward. These two cases are equivalent because of time reversibility: the solutions of Maxwell’s equations are valid when time is reversed.”
And this is based on frequency correct? So frequency is direct component.
Right, frequency and wavelength are inverses of each other. You can turn one into the other by dividing the velocity by either, f=c/m or m=c/f. Of course c isn't really c, but depends on the transmission media.
Gain does not require amplification, the transmission gain of antenna is not based on it, nether is reception.
By default, power gain is what an RF engineer refers to when s/he talks about "gain." And that does require amplification. You can increase voltage or current through impedance transformation, but never both at once.
By default, power gain is what an RF engineer refers to when s/he talks about "gain."
Really they never use that term with antennas without amplifiers? Seems like its all over the literature, again back to previous material:
3.1.3 The Power Gain of a Transmitting Antenna
The power gain G(θ,ϕ) of a transmitting antenna is defined as the power transmitted per unit solid angle in direction (θ,ϕ) relative to an isotropic antenna, which has the same gain in all directions. Frequently, the value of G is expressed logarithmically in units of decibels (dB):
(3.31)
For any lossless antenna, energy conservation requires that the gain averaged over all directions be
⟨G⟩=1
(3.32)
Consequently, all lossless antennas obey
∫sphereGdΩ=4π.
(3.33)
Different lossless antennas may radiate with different directional patterns, but they do not alter the total amount of power radiated. Consequently, the gain of a lossless antenna depends only on the angular distribution of radiation from that antenna. In general, an antenna having peak gain G0 must beam most of its power into a solid angle ΔΩ
such that ΔΩ≈4π/G0
This motivates the definition of the beam solid angle ΩA
ΩA≡4πG0.
(3.34)
Thus the higher the gain, the smaller the beam solid angle.
Directional antenna direct more power to the receiver they do not add more power through amplification. You could also say they waste less power toward no receiver. Reciprocally it works for the receiving antenna as well and is again referred to as gain everywhere I have seen.
Key phrase: "relative to an isotropic antenna." They can call it power gain all they want, but it's still not power gain. The literature is full of imprecise language, and it sounds like that's an example.
If an antenna exhibited power gain, you could build a perpetual motion machine with a pair of them. It's not power gain. Instead, it's just less power loss.
Please point me to precise language that describes antenna gain without using the word gain rather than making a vague declaration. You seem to be trying to pigeon hole the word gain to mean only electronics gain [1] while the word gain has various related meanings [2] and in the RF world antenna gain is precisely defined and does not involve amplification [3].
Antenna gain relative to an isotropic radiator is a thing. Absolute power gain from a passive antenna is not. There is no such term as electronics gain.
I really don't know how to explain this any more clearly; we're probably talking past each other. In engineering, we don't use the M-W dictionary. Things have to be spelled out more precisely, such as (in this case) exactly what the reference is for a given gain figure.
When you see the term 'dB' used in technical writing, it's only a unitless ratio, not a power level, unless explicitly associated with a reference power level. In typical RF discussions, you'll frequently hear 'dBm' or 'dBw' used to describe absolute power levels relative to one milliwatt or one watt, for instance. But the antenna people are more likely to use 'dB' by itself to refer to the gain of one antenna over another, or perhaps 'dBi' to refer to gain over a theoretical isotropic antenna. The latter quantity normally does exceed zero, but only by focusing the existing RF power, not by generating or amplifying it.
A related term is ERP, or effective radiated power. Imagine connecting a 1-watt transmitter to the 70-meter dish at a Deep Space Network tracking station. The ERP will be over ten million watts, but it won't even cook your lunch. It's effective power, expressed relative to what you could deliver to a target antenna with an isotropic radiator. Not actual physical power, in the sense of work divided by time.
In electronics, gain is a measure of the ability of a two-port circuit (often an amplifier) to increase the power or amplitude of a signal from the input to the output port
What game are you playing here, are you really just redefining the english language to win an internet argument?
At the transmitter there are two kinds of gain. The first is simply crack up the power and more signal energy will be received at the receiver. The other "gain" is where the physical shape of the transmitting antenna directs more of the energy it receives in one direction (usually straight ahead) rather than a different directions. The amount of gain due to the physical shape will vary with the frequency of radio wave relative to the physical shape the antenna.
Think of a flashlight. The beam is brighter in the middle and falls off towards the sides. That's "gain" compared to a flashlight that beams light in all directions equally, like a sphere.
So while the transmitter can "shape the beam" to create gain, the receiver cannot (though the path lose equation implies that it does). The receiver can physically just trap the amount of watts per square metre that it receives and this amount depends only on its size and not on the frequency of the incoming radiation.
So the transmitter and receiver antennas are very different in their physics of how the operate but the Path Loss Equations fudges things to make it look like they are the same ie that the gain of either is equally dependent on the frequency/wave length when in fact that's false and the two antennas are asymmetric in how they respond the carrier frequency.
So while the transmitter can "shape the beam" to create gain, the receiver cannot (though the path lose equation implies that it does). The receiver can physically just trap the amount of watts per square metre that it receives and this amount depends only on its size and not on the frequency of the incoming radiation.
So radio telescopes don't shape the incoming radiation? You can't just have a big flat antenna with a lot of area, they use dish reflectors and wave guides to shape the incoming radiation down to the actual antenna that has a size determined by guess what, FREQUENCY.
"Figure 3.3: Most high-frequency feeds are quarter-wave ground-plane verticals inside waveguide horns. The only true antenna in this figure is the λ/4 ground-plane vertical, which converts electromagnetic waves in the waveguide to currents in the coaxial cable extending down from the waveguide.
According to the strict definition of an antenna as a device for converting between electromagnetic waves in space and currents in conductors, the only antennas in most radio telescopes are half-wave dipoles and their relatives, quarter-wave ground-plane verticals. The large parabolic reflector of a radio telescope serves only to focus plane waves onto the feed antenna. (The term “feed” comes from radar antennas used for transmitting; the “feed” antenna feeds transmitter power to the main reflector. Receiving antennas used in radio astronomy work the other way around, and the “feed” actually collects radiation from the reflector.)
Conservation of energy directly leads to the role of frequency in antenna reception and reciprocity:
Figure 3.5: A cavity in thermodynamic equilibrium at temperature T containing a resistor R is coupled to an antenna, also at temperature T, through a filter blocking electromagnetic radiation but passing currents having frequencies in the range ν to ν+dν.
Imagine an antenna inside a cavity in full thermodynamic equilibrium at temperature T connected through a transmission line to a matched resistor (whose resistance equals the radiation resistance of the antenna) in a second cavity at the same temperature (Figure 3.5). A filter between the cavities passes only currents in a narrow range of frequencies between ν and ν+dν. Because this entire system is in thermodynamic equilibrium, no net power can flow through the wires connecting the antenna and the resistor. Otherwise, one cavity would heat up and the other would cool down, in violation of the second law of thermodynamics.
The article casually equates gain to change in "power or amplitude of a signal." While not wrong per se, this is one of the drawbacks of using lay references in specific fields. Power and amplitude mean the same thing to 99% of people, but they are not the same thing at all. Amplitude is measured in volts, while power is measured in watts. Voltage doesn't do work, convey information, or obey conservation laws; power does.
As a result, when engineers refer to gain in voltage alone, they will (or should) go out of their way to use the term "voltage gain." Otherwise it's a power ratio, in which the denominator is typically a given number of watts or the power present at the feedpoint of a hypothetical isotropic antenna.
Antenna people rarely care about voltage gain outside the context of impedance matching or regulatory matters. Voltage is useful when discussing field strength in volts per meter, but at the end of the day, the antenna engineer's job is to deliver power, not voltage. (Also, to avoid embarrassing Steve Jobs.)
You casually provide nothing contradictory to what I have stated and have multiple times dismissed power gain in antennas, electronic amplifiers have electronic gain, antennas have gain not dependent on electronic amplification, gain is the correct word. With antennas it is power gain not voltage gain, but gain non the less, thank you for confirming GAIN is the correct term in the most ridiculous concession possible...WTF.
Really no directionality, no resonance? Just make bigger area antenna out of whatever and it collects more energy regardless of geometry?
Please go on this is new information to me.