So what do the professional antennas use, for impedance matching? I'd guess there is just an RF transformer (great, but not much for transmitting above a couple watts), or a spooled thin teflon coax to make the classical hairpin balun. I do not see many options past these two, that could be fitted in the small space available.
No problem with your title, you can call it whatever you want as long as it is somewhat understandable what kind of antenna it is about, but if a unskilled beginner wrongly tells me what name to use for a classic antenna as he else will become irritated at me, is a bit too hilarious.
It can be pretty hard to design your own antenna and balun without proper tools. A Yagi-Uda is as complicated as an antenna can be. You want as beginner to build a precise designed ladder without tools in a dark room.
When using a VNA for designing antennas and baluns is VNA used as a design tool during whole development phase.
It is not something that you measure final result with as a kind of design confirmation.
It do not differ much from when designing a RF stage. Much tuning and design adjustments must be done based on measurements and not seldom must design take a few steps backward if intended goal not i reached. Knowing when to take these steps backward without tools is not possible.
Transformer exist for any power level. More then 100 kW is no problem but we keep the biggest coils in steel cages so that they not tries to knock down the house due to fast changes in power or antenna load. Such wild thing have actually happen.
Simplest is to design a dipole such that it is a perfect conjugate match relative radio impedance+antenna cable.
Then is no additional balancing element needed. Different kind of baluns can ensure better dipole balance and ferrite tubes can absorb power that is reflected.
A balun can improve impedance matching by transforming an impedance for better fit of antenna relative radio and it can make it harder for reflektions to reach cable braid at cost that it also affect antenn impedance.
An optimal effective antenna is conjugate matched but various baluns can be added to for example allow wider frequency range.
A Yagi antenna, what kind of balun to select is much a question about frequency, needed frequency range and type of dipole.
If you look at a professional antenna is balun part often self-described.
Some baluns can be more complex to understand.
Bicone antennas are designed to be very wideband. Antenna element must be designed to be impedance stable over a wide range at expected impedance. Same for balun part that must have wider frequency range then what a quarter wave transformer allows for.
A such balun can be seen here: [url]http://www.gtemcell.com/wp-content/uploads/2012/02/DSC02335.jpg[/url]
This is a kind of balun very common in many kinds of Yagi-Uda antennas: [url]https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSmRjQyXCOF7QoPZSoxkaSDjUiuHHIOTOgrudU558EXZrwim9hM[/url]
Size differs with frequency. It is a cheap and simple design that is "good enough" and easy to design for conjugate match.
Also professional antennas us quarter wave transformer in several ways. This one is popular as it can be designed for very precise performance with aid of a simple tuning and because of that used as reference when measuring other antennas.: [url]http://www.antennamagus.com/images/Newsletter2-1/Roberts-balun-large.png[/url]
Especially for higher frequencies can it be an advantage to design dipole and sometimes a whole Yagi-Uda antenna diretly at PCB: [url]https://www.scribd.com/doc/73556375/Printed-Dipole-Antenna-With-Integrated-Balun[/url]
Main problem is if you want to design a high performing antenna without doing any measurements.
It will fail. Big.
I have designed antennas as professional for 30 years and I will fail if trying to design an Yagi-Uda without using tools.
A less experienced will fail bigger.
It is no absolute need for an VNA and it is in any case needed time to learn how to use it. It is very easy to measure but it is sometimes complex to measure correct.
VNA and measurement cable, when to notice or take action to avoid that they maybe will extend antenna ground plane resulting in false impedance readings, and what actions to do are such examples.
Measure with correct port forwarding is another common problem.
Without VNA do trial and error method remain. It is not nessary wrong and it is possible to reachgood result but it will take a factor 100 longer time comparing to use a VNA.
Design a simple oscillator with controlled impedance, sama as intended for antenna, and connect directly to antenna without cable or balun. Place a receiver 10 meters away in antenna directions and measure received signal level. Use a cable to extend signal reading so that you can read it while adjusting antenna.
Now tune extremly systematic. Paper and pen and tune in small steps. For impedance is it two unknown variables that should be adjusted for optimal result and it can take some time to get a feel for what is what.
When setting oscillator impedance without tools, do I use three resistors in similar fashion as when designing resistive attenuators. Allow for a 5-6 dB attenuation and your designed impedance.
That gives you a stable TX impedance without need for tool to measure impedance.
When antenna is final optimized , replace oscillator with intended balun and connect oscillator either directly at balun, now adjusted for assumed radio impedance+cable impedance, and tune the balun, if it is a tunable version or else can it be needed to continue to tune at the antenna.
If none of above seems doable for you, you want to design something fast and simple, with some directive gain, you accept that it will be few dB loss, then can a biquad be a possible solution. It is a very uncritical antenna where 8 dBi gain is reachable with a measuring tape as the only tool and basic skill in doing nice soldering and effective connections from RF view. If VSWR meter is used can antenna height adjust impedance. Adjust by brutal bending with you fingers. Is much tuning needed is it something wrong in the design. Find out and redo.
If you want to know more about innards of the antennas and antenna-shapes, do as I do, reverse engineer every antenna within reach and investigate why thing looks as they do. Most basic antenna shapes and baluns are technically described in books like [url]https://www.wiley.com/en-us/Antenna+Theory%3A+Analysis+and+Design%2C+4th+Edition-p-9781118642061[/url]
That book is in antenna world the only book you need.
I was in the Radio transmission business for more than 40 years before I retired, & have seen, & tested more antennas than I care to remember.
The antenna designed by Mr Yagi & Mr Uda was called a "Yagi" by every professional I ever met in that time.
We only have your own chest beating to vouch for your great antenna design skills.
Steel cages will interact with any any RF coil.
Twaddle!
Dipoles are balanced antennas, & coaxial cables are unbalanced feeders-- no amount of "conjugate matching" will change that.
That is not the function of a balun!
Then the quarter wave transformers in TV transmission antenna arrays don"t work?
A simplified example: A resistor is a balanced load, comparable with a well balanced dipole.
Assume you have a ideal coaxial able with characteristic impedance 50 Ohm, feed by a 50 Ohm radio and solder a 50 Ohm resistor at coaxial cable end using real short wires.
Will it be any reflections along cable braid? No it is not possible. It is much comparable with adding a termination load at coaxial cable.
Will it be any practical change how resistor and cable current is flowing if placing a ideal 1:1 balun between cable and resistor? No.
Can the resistor be replaced with any else 50 Ohm resistive load, such as a well matched dipole without causing any changes in load sensed by coaxial cable? Yes.
Will it be any unbalanced current causing reflections along cable braid? Still no.
You get it now?
QuoteI was in the Radio transmission business for more than 40 years before I retired, & have seen, & tested more antennas than I care to remember.
The antenna designed by Mr Yagi & Mr Uda was called a "Yagi" by every professional I ever met in that time.
You have never read or written a white paper or a patent application related to antennas where this antenna is referrred?
Basic antenna bible, Balani Antenna theory, should be known by any professional as a minimum. Open it at chapter 10 and read.
QuoteWe only have your own chest beating to vouch for your great antenna design skills.No meaning to boast but I do not like your way doing insinuations about me.
For that reason have you have got PM about my patent portfolio for a wide range of antennas. My antenna design software is used in most bigger RF labs developing cell phone antennas or other embedded antenna. You will get a link to its homepage.
Do expect similar portfolio from you. Fair deal?
QuoteSteel cages will interact with any any RF coil.I am sure you have seen them, common in old shortwave stations, always in steel cages and sometimes with motorized tuning equipment mounted at the cage. Commonly known as antenna loading coil and often used at bigger commercial shortwave transmitter stations. Typical 100 mm solid copper wire winded as a coil. Example of a such old coil under delivery Today would that amount of copper cost just as much as all other equipment together.
These coils could cause a lot of mechanical power if heavy modulated. We are talking about 100kW magnetic loss only in coil. A such transmitter was always ramped up slowly to not destroy its coils.
QuoteTwaddle!
Dipoles are balanced antennas, & coaxial cables are unbalanced feeders-- no amount of "conjugate matching" will change that.
Long experience and not knowing this kind of stuff?
A simplified example: A resistor is a balanced load, comparable with a well balanced dipole.
Assume you have a ideal coaxial able with characteristic impedance 50 Ohm, feed by a 50 Ohm radio and solder a 50 Ohm resistor at coaxial cable end using real short wires.
Will it be any reflections along cable braid? No it is not possible. It is much comparable with adding a termination load at coaxial cable.
Will it be any practical change how resistor and cable current is flowing if placing a ideal 1:1 balun between cable and resistor? No.
Can the resistor be replaced with any else 50 Ohm resistive load, such as a well matched dipole without causing any changes in load sensed by coaxial cable? Yes.
Will it be any unbalanced current causing reflections along cable braid? Still no.
You get it now?
QuoteThat is not the function of a balun!In most of today very compact electronic and embedded antennas do we seldom have the luxury to avoid this.
<boastmode on>One of my currently most selling antennas (~10k/month) is the groundplane part of the balun for low frequencies while it is a conventional ground for the upper frequencies.
Works very well and is class leading, markets best performing antenna in its class. It is an antenna for IoT in need of maximal coverage whatever frequency.<boastmode off>
You will get a link in PM to that antenna as well so that you not insinuate that it is made up.QuoteThen the quarter wave transformers in TV transmission antenna arrays don"t work?That belongs almost to way too basic knowing to not even comment if you have long experience about antennas.
They do work to some degree. For UHF band is a such transformer typical centered at 630MHz and must then cover additional +/- 25% (470-800MHz). It will create a rather big phase error at band edges and poor balance as a quarter wave at 630MHz not any longer is a quarter-wave at bandedges. Count with some losses and a balun up to 90 degrees out of phase. Good enough to sell to consumers.
UHF Yagi-Uda for improved TV reception have been sold in two versions. One for lower half of UHF band and one for upper UHF band.
Upper frequency part is in many countries now reserved for cell phones and UHF for TV have become more narrow.
A real wide band antenna usable over a frequency decade such as some bicone antennas or logperiodic antennas can not use a quarterwave transformer as already at 2*f0 have it become a halfwave transformer which not is usable.
Why so much hate? I have even tried to name the antenna correctly in the thread title.
I do not own any VNA (sure, pretty expensive instrument just for home toying), neither do I own any of the "simple china" ones everyone has hype over. I rather go and beg on places, where they have proper VNAs (up to 3GHz) to get a proper measurement.
So what do the professional antennas use, for impedance matching? I'd guess there is just an RF transformer (great, but not much for transmitting above a couple watts), or a spooled thin teflon coax to make the classical hairpin balun. I do not see many options past these two, that could be fitted in the small space available.
you must look here:
http://www.iw5edi.com/technical-articles/6-element-for-432-mhz
The key point of these is that they are easily reproducible: if you've ever done much antenna work, much of the prescribed publications seem to be based on unicorn technology that might have worked once, but are not reproducible because some detail or other is missing.
I think it is fair to say I've done what you could call antenna design in the past. Can't really chip in on the entire balun-business since the near field of my antennas is expressed in millimeters. I've never been able to use a VNA as a design tool since I can't just go about changing my antenna designs by hand, they are too small for that. As a result, I have noticed I have a different approach to many things than most - not better, not worse, just different.
Of course, near-field and far-field are just things we like to come up with to make our life easier. There is no hard line where it suddenly stops influencing the antenna - I have seen this in cases where metal objects hundreds or even thousands of wavelengths away from the antenna impacted antenna impedance to the point where the circuit performance was influenced significantly.
As to the matching: The way I have understood matching of dipole antennas and similar is always as a resonating element - when you think about it, you have a current wave that is 0 at the ends and maximum in the middle, and a voltage standing wave that is opposite - the voltage is highest at the ends and lowest (well, 0) in the middle.
You can then just choose how far along you end up feeding this entire structure. The V/I ratio at that location determines the impedance.
Needless to say, this is a simplification, and parasitic elements, the fact that you can't have ideal standing waves, and the fact that your antenna is never exactly the right length, all cause errors here. And yes, if you feed a dipole exactly in the middle, you will indeed see that magic impedance people keep talking about - but if you shift those feed points a bit, you will influence that impedance, and you can actually play around with it to better match your transmission line (this is what inserts are doing in the case of microstrip-fed patch antennas)
I think in the case of a yagi, since the elements should all be designed in such a way to co-resonate to some extent, you don't see them in the impedance that much. Hence the impedance is still similar to that of a dipole. (could be totally wrong, I have never designed a yagi)
The key point of these is that they are easily reproducible: if you've ever done much antenna work, much of the prescribed publications seem to be based on unicorn technology that might have worked once, but are not reproducible because some detail or other is missing.
Not to mention all of the 'we added a slot here and 'tada' better performance. Oh but we forgot to mention we kinda let our EM solver optimize over 12 different parameters for 2 weeks to get this and we have no clue why it works but here is a plot of the currents on the ground because I guess everyone puts them in their papers so we probably should too!'
Regarding the feelings expressed by some here towards HAMs: I can understand where you are coming from. This is the same with all somewhat technical hobbies: Unfortunatly a lot of people are not experts, and just do stuff because they are told or because that is how it has always been done, and use poor terminology, etc. I have learned to somewhat accept this, and instead of fighting it, trying to help and perhaps explain more clearly. The only point when I really can't restrain myself is when HAMs (or makers or whatever) talk like they are all engineering experts
and know everything or worse still make statements like 'why go to school when I can make these things at home'. There is a few of those I see here on the forum and on youtube etc, and to be blunt, I usually just think: "well if it is so easy and you don't need school, howcome you are the technician and I'm the one designing the things you are a technician for?"
Just to be clear: I have a great amount of respect for the practical and hands-on knowledge technicians and similar have. It just bothers me that sometimes, they don't seem to respect the theoretical and design knowledge I have spent years building up.
kinda don't know where I was going with this but whatever, do with it as you please.
You are wrong, the impedance of the yagi driven element is affected by the presence of the other elements, & by the spacing of such elements both away from the DE & between themselves.
In the website I linked, https://www.qsl.net/dk7zb/6m/212.htm
DE impedances of 12.5, 18.0 & 28.0 Ohms are referred to, (with matching methods described)---all a far cry from approx 73.0 Ohms for a dipole in free space.
Most simple dipoles are not "in free space", the closer they approach the Earth's surface, the more the impedane drops, so that the wire dipoles commonly used by Hams are often a good match for 50.0 Ohm coaxial cable.
If the dipole impedance is affected in this way, is it surprising that parasitic elements small fractions of a wavelength away from the DE of a yagi will affect that element?
QuoteRegarding the feelings expressed by some here towards HAMs: I can understand where you are coming from. This is the same with all somewhat technical hobbies: Unfortunatly a lot of people are not experts, and just do stuff because they are told or because that is how it has always been done, and use poor terminology, etc. I have learned to somewhat accept this, and instead of fighting it, trying to help and perhaps explain more clearly. The only point when I really can't restrain myself is when HAMs (or makers or whatever) talk like they are all engineering expertsMany Hams are Engineers with similar qualifications to yourself, & with extensive experience with the design, testing & construction of antennas.
Many of the rest of us have worked with antennas of various kinds over decades, so maybe, just maybe, do know a little about such devices.
Quote
and know everything or worse still make statements like 'why go to school when I can make these things at home'. There is a few of those I see here on the forum and on youtube etc, and to be blunt, I usually just think: "well if it is so easy and you don't need school, howcome you are the technician and I'm the one designing the things you are a technician for?"Where do you get the idea that technicians don't go to school?
Without a reasonable amount of technical knowedge, we would not be able to do our job!
I very much doubt I have ever worked on anything you designed, but I have encountered many silly design blunders on the part of EEs, ones which with a few minutes of reflection, or perusing other EE's designs would have been avoided.
Techs do see a lot of other designs, & can usually have a good handle on which designs are poor, & which aren't.
QuoteJust to be clear: I have a great amount of respect for the practical and hands-on knowledge technicians and similar have. It just bothers me that sometimes, they don't seem to respect the theoretical and design knowledge I have spent years building up.I, similarly, have a great deal of respect for EEs, but expect of them a higher level of knowledge, & will "call them out" on it when they are demonstrably wrong on factual matters.