How Antennas Work(antenna-theory.com)
antenna-theory.com
How Antennas Work
http://www.antenna-theory.com/m/index.php
75 comments
I admit that I have never had the nerve to use simply in the same sentence as with a set of simultaneous three dimensional second-order partial differential equations.
Also, see my comment about reciprocal: https://news.ycombinator.com/item?id=22790001
Also, see my comment about reciprocal: https://news.ycombinator.com/item?id=22790001
>2. Antennas are reciprocal. They receive as well as they transmit.
While true, this could be really misleading in practical application. A really good transmitting antenna doesn't always (or even usually) make a really good receiving antenna.
While true, this could be really misleading in practical application. A really good transmitting antenna doesn't always (or even usually) make a really good receiving antenna.
You are absolutely correct. See http://www.arrl.org/shop/Receiving-Antennas-for-the-Radio-Am...:
Receiving Antennas for the Radio Amateur Receiving Antennas for the Radio Amateur Transmitting and receiving antennas have different jobs to do. Although the fundamental characteristics of antennas apply to both transmission and reception, the requirements and priorities of receiving antennas can be vastly different from those of transmitting antennas. Receiving Antennas for the Radio Amateur focuses entirely on active and passive receiving antennas and their associated circuits. There are relatively few cases where a radio amateur cannot benefit from a separate, well-designed receiving antenna or antenna system. On the low bands, including our new allocations at 630 and 2,200 meters, heavy emphasis on the receiving end of these radio paths is essential for success.
There is a long, fruitfull discussion of the reciprocity properties of receiving and transmitting antennas.
He discusses at some length how, even at HF, variations in polarization of arriving waves can vastly influence the received signal legibility.
Receiving Antennas for the Radio Amateur Receiving Antennas for the Radio Amateur Transmitting and receiving antennas have different jobs to do. Although the fundamental characteristics of antennas apply to both transmission and reception, the requirements and priorities of receiving antennas can be vastly different from those of transmitting antennas. Receiving Antennas for the Radio Amateur focuses entirely on active and passive receiving antennas and their associated circuits. There are relatively few cases where a radio amateur cannot benefit from a separate, well-designed receiving antenna or antenna system. On the low bands, including our new allocations at 630 and 2,200 meters, heavy emphasis on the receiving end of these radio paths is essential for success.
There is a long, fruitfull discussion of the reciprocity properties of receiving and transmitting antennas.
He discusses at some length how, even at HF, variations in polarization of arriving waves can vastly influence the received signal legibility.
The reciprocity of receiving and transmitting antennas is in fact fundamentally incorrect. They behave very asymmetrically in their physics.
In terms of the properties of the antenna itself, it is reciprocal -- the "How Antennas Work" part. You comment is more along the lines of "How to Use Antennas", that is a different question.
The places where there is a benefit to having different antennas for receive and transmit depends on the characteristics of the channel and on the application. The classic example being where a receiving antenna that reduces reception of local noise can give a better signal-to-noise ratio than an antenna that has been optimized for the best transmitted signal footprint at the location of the other station.
So, while I agree that in practice there are plenty of times where separate receive and transmit antennas have a benefit, it isn't because of antenna physics.
The places where there is a benefit to having different antennas for receive and transmit depends on the characteristics of the channel and on the application. The classic example being where a receiving antenna that reduces reception of local noise can give a better signal-to-noise ratio than an antenna that has been optimized for the best transmitted signal footprint at the location of the other station.
So, while I agree that in practice there are plenty of times where separate receive and transmit antennas have a benefit, it isn't because of antenna physics.
Case in point is my ham radio station.
I have an active magnetic loop for HF RX. This allows me to null out near field interference (a few dB from the transformer in the back yard) and provides very broad bandwidth (VLF thru HF). It is 75 feet from the house, away from that near field interference.
TX is an inverted L, up the side of the house, with a tuner at the base. I don’t have electrical length, but I do have power, so I can trade off efficiency for a power amp, and the bandwidth with the tuner. Interference is irrelevant, but I can see some 60 Hz cross modulation on a monitoring receiver, due to coupling to the house wiring.
I have an active magnetic loop for HF RX. This allows me to null out near field interference (a few dB from the transformer in the back yard) and provides very broad bandwidth (VLF thru HF). It is 75 feet from the house, away from that near field interference.
TX is an inverted L, up the side of the house, with a tuner at the base. I don’t have electrical length, but I do have power, so I can trade off efficiency for a power amp, and the bandwidth with the tuner. Interference is irrelevant, but I can see some 60 Hz cross modulation on a monitoring receiver, due to coupling to the house wiring.
I think this is incorrect. See my comment at https://news.ycombinator.com/item?id=22790001
As far as I can tell, you are agreeing with me. It is the channel that is not reciprocal, which is why there is a benefit to separate antennas.
Do not confuse the analysis of an antenna in free space with real-world deployment with real ground, noise sources of various kinds, and asymmetrical propagation.
Do not confuse the analysis of an antenna in free space with real-world deployment with real ground, noise sources of various kinds, and asymmetrical propagation.
I would say it's the other way around: A really good transmitting antenna is necessarily a really good receiving antenna (at least at the frequencies it's tuned for), but a purpose-built receiving antenna might make a poor transmitting antenna because of power handling and matching considerations.
Honest question: in what way? As in it might make sense to have an omni-directional antenna for the transmitter but a directional antenna for the receiver rather than omni-directional for both?
The correct answer is, it’s complicated. (Of course) It depends greatly on the definition of the output, for example, which can vary by application.
Easy answer is, for a fixed load (I.e. a resistor) and frequency, one varies amplitude with power. (perhaps absolute value of area under the curve might be a better description)
For more information see here: http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/powstr.html This is for a physical string, which I think is easier to wrap your head around. The math is very similar for electrical waves.
Easy answer is, for a fixed load (I.e. a resistor) and frequency, one varies amplitude with power. (perhaps absolute value of area under the curve might be a better description)
For more information see here: http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/powstr.html This is for a physical string, which I think is easier to wrap your head around. The math is very similar for electrical waves.
Yes, and additionally, the return signal, for example on 160 and other low bands may actually follow a different path due to phenomenon of grey line propagation, and other more complicated paths.
Ha ha, well I take issue with the “simply” part. There are several expensive, EM field solvers. If it were simply, they would be cheap.
I am glad that at least one person recognized my attempt at humor.
The cheap-skate's antenna modelling package is NEC2, which is public domain. It is a Method-of-Moment solver, not FDTD which is much more useful at microwaves. But for UHF and below, NEC2 is great as long as you know how to dodge the (reasonably well understood) deficiencies. The downside is that it is from the age of FORTRAN, so the native interface is column-sensitive punch card images. People have done free or low-cost wrappers, though, to take the misery out of it.
NEC4 fixes a number of the model bugs in NEC2, but the last I heard NEC4 fell under ITAR, so requires a license.
I don't know of a freebie FDTD EM package, though.
The cheap-skate's antenna modelling package is NEC2, which is public domain. It is a Method-of-Moment solver, not FDTD which is much more useful at microwaves. But for UHF and below, NEC2 is great as long as you know how to dodge the (reasonably well understood) deficiencies. The downside is that it is from the age of FORTRAN, so the native interface is column-sensitive punch card images. People have done free or low-cost wrappers, though, to take the misery out of it.
NEC4 fixes a number of the model bugs in NEC2, but the last I heard NEC4 fell under ITAR, so requires a license.
I don't know of a freebie FDTD EM package, though.
One insight that may help non EE educated people understand what an antenna does: The simplest form of an antenna would be just a simple point emmiting electromagnetic waves. These waves would be transmitted all around that point distributed as sphere. All points of a sphere will have the same power. Now, an antenna has a different geometry than a point that helps somehow "focus" the EM waves, so their power is not distributed around the sphere uniformally but some directions get more power depending on the antenna design.
Now the thing to keep in mind is that an antenna is a passive device. It does amplify the signal but it does not add any power to it, it just collects the power to specific points. This may be easier to understand with a receiving antenna (which collects the signal).
For example, consider the satellite dish which is of course an antenna. Due to its design it should be conceptually easy to understand that the power of the transmitted field is all gathered in a very small area in the front of the dish. The largest the dish, the smaller the point where all the transmitted power is pointed, so less power would be needed to cover largest distances (and more difficult finding where the dish needs to point).
Now the thing to keep in mind is that an antenna is a passive device. It does amplify the signal but it does not add any power to it, it just collects the power to specific points. This may be easier to understand with a receiving antenna (which collects the signal).
For example, consider the satellite dish which is of course an antenna. Due to its design it should be conceptually easy to understand that the power of the transmitted field is all gathered in a very small area in the front of the dish. The largest the dish, the smaller the point where all the transmitted power is pointed, so less power would be needed to cover largest distances (and more difficult finding where the dish needs to point).
Great explanation! Maybe I'm asking a dumb question but I'll shoot anyway: what is power? I mean, when I change the power of a signal what physical variable am I playing with? Amplitude, frequency, or wavelength are intuitive to visualize, but power?
Power is how "strong" a signal is. I think it's the easiest one to understand, that's why everybody's talking about dbm!
In all electric circuits to change the power a component will consume you either change the voltage you apply to it or change its resistance, based on the P=VI & R=V/I equations.
In all electric circuits to change the power a component will consume you either change the voltage you apply to it or change its resistance, based on the P=VI & R=V/I equations.
I really cannot get my head around it. What is "strong" in a signal? What physical variable is stronger? I assume "strong" or "more power" means that the signal attenuates less over time/distance, but what is causing this lesser attenuation?
No, the attenuation is exactly the same no matter the power and is analogous to the square of the distance. So a signal that has power X in a point 10 meters from the source it will have X/100 20 meters from the source.
The analogy of the waves that another comment mentioned is a nice one (since we talk about EM waves).
Another thing that may help you understand that more power means that the electrical charge to the protons/electrons in the air where the EM field is transmitted will also be more.
The analogy of the waves that another comment mentioned is a nice one (since we talk about EM waves).
Another thing that may help you understand that more power means that the electrical charge to the protons/electrons in the air where the EM field is transmitted will also be more.
Thank you.
The amplitude of the wave is bigger to begin with. I think the waves in water analogy is suitable here: drop a stone in water and there'll be very big ripples just around the point where it drops, but they'll get smaller the further out they are. Drop an even bigger stone, you'll get bigger ripples. That's power.
Power roughly correlates to amplitude.
On the transmitter side keeping the signal linear means you generally don't see great efficiency in terms of power in -> power radiated.
On the transmitter side keeping the signal linear means you generally don't see great efficiency in terms of power in -> power radiated.
An antenna doesn't amplify a received signal. It takes an actual electrical amplifier to do that. When an antenna's gain is being mentioned, that gain is actually how much better the antenna is at taking in more of the signal than the standard candle isotropic antenna, e.g., one that transmits and receives equally in any direction.
Well it amplifies the signal by the Q of the antenna. The issue is that high Q resonators make lousy radiators, as the radiation resistance is very low compared to the reactance, and bandwidth is 1/Q. But you can certainly get amplification by a high-Q resonator inserted in a field.
This is why electrically small antennas have an effective aperature much, much larger than their physical size. That ferrite rod antenna in an AM radio can have a massive electrical aperature (antenna gain) since it is narrow band (high Q). The resonance is amplifying the signal.
You can also transmit through it if you can keep it cool. It may have 0.1% efficiency, radiating 1W for 1 kW of input power, if you have a nuclear reactor (say a VLF antenna on an aircraft carrier where you can’t have wire antennas), you can trade power for size.
This is why electrically small antennas have an effective aperature much, much larger than their physical size. That ferrite rod antenna in an AM radio can have a massive electrical aperature (antenna gain) since it is narrow band (high Q). The resonance is amplifying the signal.
You can also transmit through it if you can keep it cool. It may have 0.1% efficiency, radiating 1W for 1 kW of input power, if you have a nuclear reactor (say a VLF antenna on an aircraft carrier where you can’t have wire antennas), you can trade power for size.
Yes I tried to make that clear by mentioning that an antenna is a passive device. I just wanted to clarify that antennas help both at the transmitting and receving end. English are my 2nd language so maybe I could have explained it better...
It’s not a question of focus at all; by Birkhoff’s theorem it can’t be a sphere
One thing I have always struggled to understand about antennas --
Of course I know that an antenna is most efficient at radiating power when its length is some fraction/multiple of the emitted wavelength. But I cannot for the life of me intuit how the electrons are being excited and behaving.
If I use the bathtub analogy of sloshing water, it cannot be (I believe) that the electrons are sloshing in bulk up and down the antenna and "accumulating" at one end at the speed of light.
On the other hand, if each electron along the length of the antenna is oscillating in its own relatively stable position, what then does the length matter to the electron at one end versus the other?
Or should I understand it as, energy is being transmitted out of the antenna, like it is in a flute being played, and the electrons are most constructively-interference being reinforced to resonate at the frequency desired (by standing waves in the conductor) if the length of the material matches the wavelength?
This has always been hard to visualize.
Of course I know that an antenna is most efficient at radiating power when its length is some fraction/multiple of the emitted wavelength. But I cannot for the life of me intuit how the electrons are being excited and behaving.
If I use the bathtub analogy of sloshing water, it cannot be (I believe) that the electrons are sloshing in bulk up and down the antenna and "accumulating" at one end at the speed of light.
On the other hand, if each electron along the length of the antenna is oscillating in its own relatively stable position, what then does the length matter to the electron at one end versus the other?
Or should I understand it as, energy is being transmitted out of the antenna, like it is in a flute being played, and the electrons are most constructively-interference being reinforced to resonate at the frequency desired (by standing waves in the conductor) if the length of the material matches the wavelength?
This has always been hard to visualize.
Page 296 of this book has a good illustration of the field changes around a transmitting antenna: https://archive.org/details/principlesunderl00unit
(It's almost 100 years old but the physics have not changed. If anything, these early books often have far more detailed explanations because they assumed far less about the reader.)
(It's almost 100 years old but the physics have not changed. If anything, these early books often have far more detailed explanations because they assumed far less about the reader.)
Wow, amazing to see that book is from 1918 and the basics were all already laid out.
Need to think about charge displacement and fields rather than electrons. The electrons moving in wire (direct current) circuit only move, on average, a few cm/sec. Now the charge displacement moves at the speed of light.
Think of a tube stuffed tightly with marbles. Push the marbles at one end, and they move near instantly at the other end. The force transfers instantly, but the marbles may hardly move.
Now imagine the marbles connected with stiff, little springs. Push on one end, and the compression wave moves through the charges quickly (the speed depends on the spring constant). It hits the other end, yielding a little more charge accumulation, then bounces back, yielding a little less charge. Do that a 2.5 billion times a second and you have a WiFi antenna. The charges don’t move much all; it’s the charge displacement that moves, which is the E and H field. The key is also that the displacement must have acceleration (harmonic motion) to have a derivative. Accelerating charges radiate; constant velocity charges (direct current) don’t.
The jist of it is that all the energy is contained in the fields. That metal rod has charge that is easily displaced.
Now as to how an accelerating charge radiates; I can’t remember, but Feynman covers it in his 3 volume lectures.
Think of a tube stuffed tightly with marbles. Push the marbles at one end, and they move near instantly at the other end. The force transfers instantly, but the marbles may hardly move.
Now imagine the marbles connected with stiff, little springs. Push on one end, and the compression wave moves through the charges quickly (the speed depends on the spring constant). It hits the other end, yielding a little more charge accumulation, then bounces back, yielding a little less charge. Do that a 2.5 billion times a second and you have a WiFi antenna. The charges don’t move much all; it’s the charge displacement that moves, which is the E and H field. The key is also that the displacement must have acceleration (harmonic motion) to have a derivative. Accelerating charges radiate; constant velocity charges (direct current) don’t.
The jist of it is that all the energy is contained in the fields. That metal rod has charge that is easily displaced.
Now as to how an accelerating charge radiates; I can’t remember, but Feynman covers it in his 3 volume lectures.
Another nice thing to think about is spherical symmetry, ie can one have it in an antenna. Some thought with Maxwell’s equations will lead you inexorably to Birkhoff’s theorem.
Ha ha, way over my head. I had one modern physics course; a little special relativity but mostly quantum behavior.
If you mean a perfect, isotopic antenna; I don’t believe it exists. Though I suppose it could, if you consider an antenna pattern to be a wave function. A spherical mass should be emitting black-body radiation with an isotropic pattern. Maybe only noise can be isotropic. If you try to encode information, it can’t.
If you mean a perfect, isotopic antenna; I don’t believe it exists. Though I suppose it could, if you consider an antenna pattern to be a wave function. A spherical mass should be emitting black-body radiation with an isotropic pattern. Maybe only noise can be isotropic. If you try to encode information, it can’t.
That is helpful!
If you're more interested in a practical approach to designing and building antennas for radios, find a recent copy of the ARRL Handbook, the source of information about ham radio. In it, you'll find some theory, a little math, but mostly, how to build and deploy a wide variety of antennae to cover frequency ranges from 2 MHz to 10 GHz. They also offer a stand-alone book on nothing but antennas with more details and examples.
> and deploy
Thats one of the things that made the ARRL Antenna handbook so valuable to me; they have some solid advice on weatherproofing and dealing with things like wind and snow loads.
Its easy to make an antenna; its just a bent length of wire at the end of the day. Making it be the same length of bent wire today, tomorrow and beyond, when its mounted outside and /or in harsh conditions, thats difficult.
Thats one of the things that made the ARRL Antenna handbook so valuable to me; they have some solid advice on weatherproofing and dealing with things like wind and snow loads.
Its easy to make an antenna; its just a bent length of wire at the end of the day. Making it be the same length of bent wire today, tomorrow and beyond, when its mounted outside and /or in harsh conditions, thats difficult.
That would be http://www.arrl.org/arrl-antenna-book
This is a neat website Y an antenna engineer with lots cool info, but the big picture is buried. From that page, click on “antenna basics” then scroll all the way to the bottom where you can find “why do antennas radiate?”
http://www.antenna-theory.com/basics/whyantennasradiate.php
That answers the fundamental question of how antennas work.
Edit: looks like kawfey’s comment answered the issue already, I didn’t scroll down far enough: https://news.ycombinator.com/item?id=22787249
http://www.antenna-theory.com/basics/whyantennasradiate.php
That answers the fundamental question of how antennas work.
Edit: looks like kawfey’s comment answered the issue already, I didn’t scroll down far enough: https://news.ycombinator.com/item?id=22787249
The only thing not on the web-site is how antennas work, even in theory.
As an antenna engineer, I've referred to this site hundreds of times. To be fair, it's almost an eli5 version of how antennas work, but it's been a good reference for basics.
http://www.antenna-theory.com/basics/whyantennasradiate.php is as deep as it gets.
For DEEP antenna theory, I can't recommend the Balanis book high enough. https://www.amazon.com/Antenna-Theory-Analysis-Constantine-B...
http://www.antenna-theory.com/basics/whyantennasradiate.php is as deep as it gets.
For DEEP antenna theory, I can't recommend the Balanis book high enough. https://www.amazon.com/Antenna-Theory-Analysis-Constantine-B...
I think the biggest take-away, that especially Hollywood needs to take note of, is what everyone gets wrong -- you don't point a whip antenna at something to get the highest gain, you want to be at a right angle to the source. Remote controls often have the antenna oriented the wrong way for distance/gain, and I've seen people orient wifi router antennas to "point" to usage areas, etc.
Depends on the polarization. You want the antenna at 90 degrees to the direction of the field. A vertical whip radiates horizontally, a horizontal whip radiates vertically!
The reason you usually put them vertical is so that you can use the Earth as a ground plane, leading to less wasted power. A horizontally positioned whip antenna will lose a fair bit of power to the ground.
The reason you usually put them vertical is so that you can use the Earth as a ground plane, leading to less wasted power. A horizontally positioned whip antenna will lose a fair bit of power to the ground.
It all depends what the polar patterns look like for the access point. In a omni directional antenna being 90 degrees is generally the best because it puts out a donut shaped pattern. But with a directional antenna you want to be inline with it, or whatever the direction is pointing.
If by remote control you mean TV remotes, those usually work via an IR LED. The radiation pattern is pretty much what you'd get with visible light, i.e. the highest intensity zone is directly in front of the LED.
> If by remote control you mean TV remotes...
They don’t mean that.
They don’t mean that.
Do you know what they meant? Absent any context I don't think ``remote control'' has another well known device. I'm assuming that the person I responded to doesn't have a background in this stuff as this is was their first introduction to antenna radiation patterns.
Not sure if you’re joking or trolling, but for example ‘remote control car’, ‘remote control helicopter’, ‘remote control boat’, ‘remote control bomb disposal robot.’ The handset you use to control them is itself called the ‘remote control.’ That's what they mean.
No, I'm serious. Thank you for explaining.
I've heard people talk about tv remotes as ``remote controls'' several orders of magnitude more times than RC gear.
I've never seen someone have to reorient their RC transmitter to get a better signal. Modern RC airplane/car/helicopter/boat transmitters have multiple fixed antennas (as do the receivers) and have for many years (since people switched from 50MHz radios to 2.4GHz spread spectrum radios). The range is long enough that it you'll generally lose sight of your vehicle before you lose the radio connection.
I've heard people talk about tv remotes as ``remote controls'' several orders of magnitude more times than RC gear.
I've never seen someone have to reorient their RC transmitter to get a better signal. Modern RC airplane/car/helicopter/boat transmitters have multiple fixed antennas (as do the receivers) and have for many years (since people switched from 50MHz radios to 2.4GHz spread spectrum radios). The range is long enough that it you'll generally lose sight of your vehicle before you lose the radio connection.
Brace yourself for an onslaught of garish advertisements. If the content is truly exhaustive, a book would be a far better presentation format. I didn't survive long enough to find out.
You must install uBlock Origin and live in a completely different and serene internet. :-)
Excerpt:
"Specifically, consider this statement: Complexity is not a sign of intelligence; simplify. I have found this to a priceless amount of wisdom."
"Specifically, consider this statement: Complexity is not a sign of intelligence; simplify. I have found this to a priceless amount of wisdom."
Not complete without atomic antennas:
https://www.technologyreview.com/s/611977/get-ready-for-atom...
https://www.technologyreview.com/s/611977/get-ready-for-atom...
A thread from 11 months ago: https://news.ycombinator.com/item?id=19708982
This topic is uncommon enough that we won't call this a dupe (this came up yesterday: https://news.ycombinator.com/item?id=22781498).
This topic is uncommon enough that we won't call this a dupe (this came up yesterday: https://news.ycombinator.com/item?id=22781498).
It's mildly irritating that the concepts of explanations like this (and almost all others) are based on a false understanding, through the path loss equation and the law of reciprocity, of the underlying physics of antennas.
While this kind of approach allows for the proper engineering of antenna systems it is at least 50% wrong regarding the underlying physics.
While this kind of approach allows for the proper engineering of antenna systems it is at least 50% wrong regarding the underlying physics.
some past comments, https://news.ycombinator.com/item?id=19708982
Can somebody explain why I can send high definition video over WiFi, but not over an average quality USB 3 cable that is extended to a 6m length?
In a nutshell:
If you have to guide an EM wave without dispersion (e.g. TEM propagation), it takes at least two conductors; those have loss. The smaller they get (think a thin coax) the more lossy they become.
If you need a wide bandwidth, you need a smaller conductor arrangement to keep it from “over-moding” (becoming non TEM). Once it’s non-TEM, you get dispersion and corrupt your signal.
So there is a fundamental trade-off of bandwidth versus loss. Free space propagation is always TEM, so plenty of bandwidth, but now you must direct it with antennas as opposed to guiding it with conductors.
You can get 110 GHz of bandwidth on a 1 mm coax, but it is very lossy, so much so that the microwave industry/research is looking into non-contact wafer probing for mmWave and THz applications.
Fiber has similar issues. It’s extremely low-loss, and non-TEM, but that dispersion is small enough you can multiplex in multiple channels without much dispersion across a single channel. Over long runs, still the dispersion is large enough that it needs to be compensated with various tricks.
A 10G Ethernet copper cable is at most 3 meters, and hard-wired to the SFP modules. But you can buy a 10G mmWave radio and get 10 km. Now several km of that copper cable would be hundreds dB loss.
If you have to guide an EM wave without dispersion (e.g. TEM propagation), it takes at least two conductors; those have loss. The smaller they get (think a thin coax) the more lossy they become.
If you need a wide bandwidth, you need a smaller conductor arrangement to keep it from “over-moding” (becoming non TEM). Once it’s non-TEM, you get dispersion and corrupt your signal.
So there is a fundamental trade-off of bandwidth versus loss. Free space propagation is always TEM, so plenty of bandwidth, but now you must direct it with antennas as opposed to guiding it with conductors.
You can get 110 GHz of bandwidth on a 1 mm coax, but it is very lossy, so much so that the microwave industry/research is looking into non-contact wafer probing for mmWave and THz applications.
Fiber has similar issues. It’s extremely low-loss, and non-TEM, but that dispersion is small enough you can multiplex in multiple channels without much dispersion across a single channel. Over long runs, still the dispersion is large enough that it needs to be compensated with various tricks.
A 10G Ethernet copper cable is at most 3 meters, and hard-wired to the SFP modules. But you can buy a 10G mmWave radio and get 10 km. Now several km of that copper cable would be hundreds dB loss.
Fiber guys are lucky that they can cheat with things like Raman amplification that us poor RF souls have no real equivalent for.
https://en.wikipedia.org/wiki/Raman_amplification
https://en.wikipedia.org/wiki/Raman_amplification
I suppose parametric amplifiers would be similar in the RF realm. At least we have distributed amplifiers, which I suppose could be an amplifying medium if you could make them fine enough.
The full-justification formatting makes for some badly mutilated paragraphs when trying to read that site in portrait orientation.
Recommended reading - Antenna Theory Analysis and Design, by Constantine Balanis
wow, I thought I would get some nice tips to position my wifi routers and repeaters antennas, but it too much information. Useful for who wants to get deep knowlegde, but I think I still need an easier guidance for my routers.
To be fair, it's antenna theory, not propagation theory. That by itself is another realm of electrophysics.
https://en.wikipedia.org/wiki/Radio_propagation
There are some ray-tracing and wave theory solvers out there that will readily accept a 2D floor plan, but 3D full wave solutions are intensely complicated computational problems that probably won't even resolve to real-life just because of the complexities of the real world. The biggest problem for AP (router) placement is multipath interference, which either creates a null or node at any given location, compromising of basically infinite paths between the AP, bouncing off of walls, furniture, people, animals, and everything,
The network engineer's rule of thumb is to ignore multipathing completely, and start at 0dB a foot from the router, and subtract 10dB for passing through drywall, 15dB for brick walls, 8dB for glass, and 6dB for every doubling of distance between the wireless AP and the desired client locations. As long as you stay above around -20- -30dB, you should have good signal. I've come up with these numbers in my own experience as an RF engineer. Typical software usually uses n-bounce ray tracing to determine deadzones or optimum placements, but that stuff is expensive and only as accurate as the 2D or 3D model of your space.
An even less intense rule of thumb is place as close to common client locations then move them by trial and error until it works best. I place a single AP on the ground in the center of my home, and another mesh node for my back yard, and my whole house is covered. (I use ubiquiti unifi gear, which are far more powerful than a router/AP-in-one, and it gives you a lot of insight on how well the clients are connected, interference, and other useful data).
This is also why mesh wireless is getting popular, so you can dot mesh APs around the home in just about every room, and ignore the whole problem.
https://en.wikipedia.org/wiki/Radio_propagation
There are some ray-tracing and wave theory solvers out there that will readily accept a 2D floor plan, but 3D full wave solutions are intensely complicated computational problems that probably won't even resolve to real-life just because of the complexities of the real world. The biggest problem for AP (router) placement is multipath interference, which either creates a null or node at any given location, compromising of basically infinite paths between the AP, bouncing off of walls, furniture, people, animals, and everything,
The network engineer's rule of thumb is to ignore multipathing completely, and start at 0dB a foot from the router, and subtract 10dB for passing through drywall, 15dB for brick walls, 8dB for glass, and 6dB for every doubling of distance between the wireless AP and the desired client locations. As long as you stay above around -20- -30dB, you should have good signal. I've come up with these numbers in my own experience as an RF engineer. Typical software usually uses n-bounce ray tracing to determine deadzones or optimum placements, but that stuff is expensive and only as accurate as the 2D or 3D model of your space.
An even less intense rule of thumb is place as close to common client locations then move them by trial and error until it works best. I place a single AP on the ground in the center of my home, and another mesh node for my back yard, and my whole house is covered. (I use ubiquiti unifi gear, which are far more powerful than a router/AP-in-one, and it gives you a lot of insight on how well the clients are connected, interference, and other useful data).
This is also why mesh wireless is getting popular, so you can dot mesh APs around the home in just about every room, and ignore the whole problem.
It’s definitely more of theory site. This talks about enterprise WiFi, but it might be helpful: https://www.accessagility.com/wifi-design-guide
Home routers are dipoles - if you want to get into wifi look at the cisco press books
The big thing to see if you can find is the polar pattern for your access points. That shows how the signal radiates and you can aim your stuff better.
Had to turn the zoom to 66% to make it readable, yikes.
Is there an index of all the pages on this site?
1. Accelerate an electron, get a photon. A good transmitting antenna is something that is an efficient structure for accelerating electrons.
2. Antennas are reciprocal. They receive as well as they transmit.
3. Resonant structures are often used because you can keep more electrons accelerating with less energy -- the damp finger on the rim of a wine glass effect.
4. Power can be directed by appropriately phasing the radiating sub-structures to create constructive and destructive interference in the radiated energy.
The rest is modeled simply with a set of simultaneous three dimensional second-order partial differential equations.