6 ms·

> 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

> 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.” https://www.cv.nrao.edu/~sransom/web/Ch3.html https://www.cv.nrao.edu/~sransom/web/Ch3.html

CamperBob2 5y ago
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.
- SigmundA 5y ago
  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.
  - CamperBob2 5y ago
    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.
    - SigmundA 5y ago
      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]. [1] https://en.wikipedia.org/wiki/Gain_(electronics) https://en.wikipedia.org/wiki/Gain_(electronics) [2] https://www.merriam-webster.com/dictionary/gain https://www.merriam-webster.com/dictionary/gain [3] https://en.wikipedia.org/wiki/Antenna_gain https://en.wikipedia.org/wiki/Antenna_gain

CamperBob2 5y ago

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.

SigmundA 5y ago
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.
- CamperBob2 5y ago
  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.
  - SigmundA 5y ago
    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]. [1] https://en.wikipedia.org/wiki/Gain_(electronics) https://en.wikipedia.org/wiki/Gain_(electronics) [2] https://www.merriam-webster.com/dictionary/gain https://www.merriam-webster.com/dictionary/gain [3] https://en.wikipedia.org/wiki/Antenna_gain https://en.wikipedia.org/wiki/Antenna_gain