How can I make my Yagi-Uda antenna smaller???

[rocket100]

I am trying to build a Yagi antenna for 900mhz and I am using this formula:

**broken link removed**

Length:

Reflector length = 0.495 x wavelength

Dipole radiator = 0.473 x wavelength

Director D1 = 0.440 x wavelength

Director D2 = 0.435 x wavelength

Director D3 = 0.430 x wavelength

----------------------------------------------

Spacing:

R-DR = 0.125 x wavelength

DR - D1 = 0.125 x wavelength

D1 - D2 = 0.250 x wavelength

D2 - D3 etc = 0.250 x wavelength

--------------------------------------------------------------------------------------------

But the problem is, when I use this formula with 900mhz the antenna ends up being huge. What I need to do is make it smaller. Would it work if I took all of the lengths and spacings then divide it by, say four?

 

[transistor495]

Wavelength is calculated by 300 divided by frequency in MHz. Then calculate the element values by applying on each. I got 16.5cm as the reflector length for the 900MHz center frequency.

Googling the same returned the link: Tony’s Cafe

 

[tytower]

The yagi above is based on 1/4 wavelength theory. Meaning an upright stick antenna of 1/4 the wavelength properly grounded will receive the best signal . I have found so far that if you double it to 1/2 wave it won't work , 3 times will work but its called 5/8ths because there is an electrical end effect that means you must cut it shorter.

So even multiples dont seem to work but odds do ?
The other 1/2 of this antenna is a ground reflection which in effect makes it a 1/2 wave dipole. Confusing .

So if you try to go smaller it just simply don't work. The best signal is received by a "resonant" antenna ,resonant at the frequency you are using .
There are interesting developments in smaller antennas for mobile phones and the like but you will have to Google for them.

I heard of an "H" pattern antenna which was resonant on all frequencies up to a point but I could not get one to work. I found one on a TV antenna and I'm convinced it was a con.

Dick Smith put out a good 900MHz mobile whip about 2 foot long which I have and it works well. Not as well as a Yagi properly tuned would.

Oh just a little about the spacing - The space between D and D1 should also be about .25 This might be a typo somewhere.To keep the signal adding to the Driven element the 1/4 spacing enhances the signal in phase. The reflector at the rear is out of phase only to stop signal coming in from the back. It is sometimes useful to keep this at .25 also so signal still comes in in phase from that direction. Specially if you are in the geographical middle of a three way conversation.

You can play with the spacing and I have found .20 to be better than .25. The different lengths of the elements other than the driven are to slightly detune them on the chosen frequency. I found the above post of Tony's cafe interesting and the spacing mentioned more so but I have not had time to check it out yet. Its not built how I would do it but that's not important ,rather does it work well?

 

[trash]

3 times will work but its called 5/8ths because there is an electrical end effect that means you must cut it shorter.

3 x 1/4 = 3/4 not 5/8

5/8th works not because of the velocity factor.
If this were the case you would have a velocity factor that changes with frequency.

Still not up with the basic laws on the universe tytower ?

The reason why 1/2 wavelength doesn't appear to work for you and 5/8ths is because of impedance of the antenna. In particular the fact that you're end feeding that antenna. A 1/2-wave end fed has a feedpoint high impedance: A 1/2 wave is resonant so it is non reactive. But the impedance of the antenna is kilohms. The return loss on the mismatch with 50 ohms is terrible. With 1/8th added the feed impedance drops close to a low impedance. Capacitive reactance is added which ballanced by the inductive reactance in series with the radiator so that antenna is resonant much like a half wave.

Confusing .

Only confusing because you're looking at a circuit without basic understanding of reactance and impedance.

I heard of an "H" pattern antenna which was resonant on all frequencies up to a point but I could not get one to work. I found one on a TV antenna and I'm convinced it was a con.

A "Collins Receptor" .... haha. I met the guy who designed it. He was a con-artist. Just not a very good one. He was too convinced of his own importance without results. While his antenna works (he used to get very pissed if you called it an "antenna") it's just another shape feeder like a dipole, or a quad, or a slot or any other combination inductive and cross field antennas.
I even have an antenna which uses the H feeders, it's not currently in use.
The basically don't perform any better than a slot feed. You can expect a default 5.8dBi from them with a reflector.


My question is to Rocket is;
Why is this antenna too big ?
Are you trying to mount it on the phone itself ?
What are you trying to achieve by using the yagi ?

 

[trash]

Ah, here's the insertion loss of a 1/4 - 5/8 wave antenna.
**broken link removed**

While this example was built at microwave frequencies, the response is typical at whatever length the antenna.

 

[tytower]

3 x 1/4 = 3/4 not 5/8

5/8th works not because of the velocity factor.
If this were the case you would have a velocity factor that changes with frequency.

Still not up with the basic laws on the universe tytower ?

Only confusing because you're looking at a circuit without basic understanding of reactance and impedance.

You are another of these " I know everything" types who can't but pick on everyone else's posts .

Leave mine alone and give your interpretation or views by all means but the disparaging posts are unnecessary .
The first part is rubbish above . Better look it up hey !
"Confusing" is to anyone looking at it as a learner !
Anyway for the OP the important part is even multiples of an antenna don't work so when planing it out work on odd multiples.

As I said elsewhere trash becomes landfill at some point , hopefully soon

 

[trash]

You've got some real issues there tytower.
The information you gave is wrong and I explained why.
Actually this is a common theme. You post something incorrect, I correct it, you get upset.

You are another of these " I know everything" types who can't but pick on everyone else's posts .

Sounds like you have a gripe for anybody who has put the time in at university and actually bothered to make an effort to learn or conduct valid research.
I don't pick on anybody else's posts. I stick with what I know and what I'm good at.
I don't get upset if somebody proves me wrong. I pick up that information, learn from it and add it to my own knowledge. It's a continual process of learning and correction.
You won't find me posting anything in the audio sections etc. I can't hear the difference between an LP and MP3 and wouldn't claim so.

I would suggest rather than posting incorrect information about subjects you think you know something about and clearly don't. Rather then getting embarrassed when other people (not just me) correct your mistakes, that you learn from your mistakes. Not try and blame others for highlighting your stupidity.

"Confusing" is to anyone looking at it as a learner !

Which is what you're doing. For anybody who is not familiar with the subject, you're filling their head with ****. It's then up to the rest of us to clean up your mess.

You don't have the guts to admit your mistake and even now, you're insisting it is still correct. It's actually pretty clear you have absolutely no understanding of subject else you would have been easily able to understand what I have said about impedance and explained why it might be incorrect.

If I had any doubt, I'd fire up the VNA and print you out a smith chart to back up what I've said. But we both you know have never seen either of these things and have no hope in hell of understanding any evidence presented to you.


So, back to the antenna. What tytower has said about velocity factor is completely incorrect. While velocity factor needs to be considered when making an antenna. It is not the reason why antenna lengths of 5/8 wavelength work. And certainly not because they are behaving as 3/4.

It is due to the impedance of the antenna at it's feed point.

 

[tytower]

You've got some real issues there tytower.
Sounds like you have a gripe for anybody who has put the time in at university and actually bothered to make an effort to learn or conduct valid research.
I don't pick on anybody else's posts. I stick with what I know and what I'm good at.
I would suggest rather than posting incorrect information about subjects you think you know something about and clearly don't. Rather then getting embarrassed when other people (not just me) correct your mistakes, that you learn from your mistakes. Not try and blame others for highlighting your stupidity.
Which is what you're doing. For anybody who is not familiar with the subject, you're filling their head with ****. It's then up to the rest of us to clean up your mess.

Well that pretty well exposes your real gripe doesn't it ?
Most of what you have to say is a ***** at me .
Are you saying I hav'nt been to Uni ? - Wrong -3 yrs
Are you saying I have no experience with antenna building - Wrong 35 yrs so get stuffed !

Wake up , stop the constant attack and get on with it elsewhere .
For any other readers if you are making a Yagi look carefully at what I have said above . I've made and used quite a few

 

[trash]

Hahaha.... I didn't know they teach antenna building in a Bachelor of Attendance.

Most of what you have to say is a ***** at me .

Still got some issues there tytower. You know (and I've said it many times before) that I treat every post of yours like it's the first and disregard all the stupid **** you've said in the past, unless it's on topic.
In this case, the subject of antennas, and your claims to know something about them. You clearly don't. Even the most simplest of antennas you got it completely wrong and even when you were corrected, you're still defending your failing.
You lack understanding of any sort of basic engineering maths, so any claims of having attended university was not in science or engineering.

Even in other treads your advice was ...

Errr---Use a black one

With respect to a VHF output transistor. To even suggest something simple like a 2N2222A was too hard.
I suspect the only thing you know about transistors is that some of them are black.

Wake up , stop the constant attack and get on with it elsewhere .
For any other readers if you are making a Yagi look carefully at what I have said above . I've made and used quite a few

My advice to the readers is to check anything you say. You have a history of saying stupid **** and giving people incorrect information.

So I'll say it again...
I treat every post of yours like it's the first and disregard all the stupid **** of topic you've said in the past.
If you say something new and incorrect, don't be surprised if I or somebody else corrects you.
I'm not surprised by your comments, you seem to get upset with everybody that corrects you.
Hey, what do those four red pips mean ?

 

[tytower]

Here you go rocket100
I was looking for designs on 900Mhz some time ago and bookmarked this to have a look at
Personally I would reduce the spacings a bit, but not under 20% , and cut the thing off right at the last director.
You could play around with 2 more reflectors in a semi-circle behind the driven element, exact same spacing though.

https://girasoli.org/?p=64

Read it through to the second page though as he fiddles with impedance a bit
Its cheap enough to build and play with

 

[tytower]

For anyone interested in making a good antenna this is as good an explanation of resonance as I have seen

http://www.intuitor.com/resonance/radioTVres.html

 

[Willen]

I am trying to build a Yagi antenna for 900mhz and I am using this formula:

**broken link removed**

Length:

Reflector length = 0.495 x wavelength

Dipole radiator = 0.473 x wavelength

Director D1 = 0.440 x wavelength

Director D2 = 0.435 x wavelength

Director D3 = 0.430 x wavelength

----------------------------------------------

Spacing:

R-DR = 0.125 x wavelength

DR - D1 = 0.125 x wavelength

D1 - D2 = 0.250 x wavelength

D2 - D3 etc = 0.250 x wavelength

--------------------------------------------------------------------------------------------

But the problem is, when I use this formula with 900mhz the antenna ends up being huge. What I need to do is make it smaller. Would it work if I took all of the lengths and spacings then divide it by, say four?

I want to transmit FM RF with high gain antenna like Yagi, help me in basic way plz:

1. I should have to feed rf in two ends of dipole rediator only, isn't it?
2. I am confusing in Main Rod (which connects reflector, dipole rediator and directors) component. Does it should have to be conductor? Are they all small rods and main rod connected electrically via Main Rod?
3. It is too much directional antenna with high gain. May I know, in which direction it can transmitt? And how to stand this Yagi in the sky to transmit horizontally?
4. Impedance matching Balun (75 ohm - 300 ohm) is necessary for Yagi too, isn't it?

 

[KJ6EAD]

This is a datasheet for commercial Yagi antennas. The boom lengths vary from 33cm to 136cm depending on the number of elements/directionality/gain. Why not compare your results to a known good commercial product?

https://www.lairdtech.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=3560

 

[trash]

I'm not sure why you consider this antenna too big ?
Too wide or too long ?

If it is too wide, then you can halve the wide by using a loop yagi or a quagi.
If it is too long, then switch to a phased array of short yagis.

1. I should have to feed rf in two ends of dipole rediator only, isn't it?

I don't quite understand the question. Is it a standard dipole, or a folded dipole and how are you feeding it ? Balun or gamma match etc ?

Does it should have to be conductor?

No, it doesn't. I am not aware of how it effects the performance. It's something I have not considered for a long time.

It is too much directional antenna with high gain.

This depends on your application.

May I know, in which direction it can transmitt?

It only transmits in one direction.

And how to stand this Yagi in the sky to transmit horizontally?

Mount it straight on a pole like a TV antenna (which are usually yagis).

Impedance matching Balun (75 ohm - 300 ohm) is necessary for Yagi too, isn't it?

This depends on your transmitter impedance, coax impedance and driven element.

Is this antenna for receive only, or transmit and receive ?
What sort of transmit power ?

 

[Willen]

I'm not sure why you consider this antenna too big ?
Too wide or too long ?

If it is too wide, then you can halve the wide by using a loop yagi or a quagi.
If it is too long, then switch to a phased array of short yagis.


I don't quite understand the question. Is it a standard dipole, or a folded dipole and how are you feeding it ? Balun or gamma match etc ?


No, it doesn't. I am not aware of how it effects the performance. It's something I have not considered for a long time.


This depends on your application.


It only transmits in one direction.


Mount it straight on a pole like a TV antenna (which are usually yagis).


This depends on your transmitter impedance, coax impedance and driven element.

Is this antenna for receive only, or transmit and receive ?
What sort of transmit power ?

I have a 500mW-1.5 watt FM transmitter with 50 ohm output. Actually i want to transmit all around the area with long....range. Which is the right decision and how to make it?

 

[trash]

All around the area.
Ok, well that sounds like you want an omni directional antenna. Not a yagi.

I'm assuming that you have already taken into account your local laws regarding FM radio transmitters.
Some places in the world they won't care and in others they had a special big boot for stamping bums.

Start simple !
A quarter wave ground plane antenna. Like this one.
**broken link removed**
It's 75 ohm typical impedance but feeding it with 50 ohms and wearing the ~1dB insertion loss will work fine.
Bending the radials down helps bring the impedance down to 50 ohms, but I think it mentions that in the article.

Increasing the driven element to 5/8 wavelength will also bring the impedance down to ~50ohms and increase the gain of the antenna.

That should be all you need.

 

[alec_t]

Post deleted

 

[Willen]

How dipole determines the direction (only 2 direction?) if I keep it vertically. Which two directions has strong signal? All FM stations has dipole but how they are transmitting all around the area??

 

[davenn]

How dipole determines the direction (only 2 direction?) if I keep it vertically. Which two directions has strong signal? All FM stations has dipole but how they are transmitting all around the area??

a vertical dipole is omni directional
its only once you incorporate it into a Yagi does it become directional

Dave

 

[DJAE]

Em this already seems to have got heated, thats electronics for you! Rf is the worst because so much is subjective and circumstantial. Often simulations can be meaningless....
Anyway just want to add(in case someone hasn't already) allow for velocity factor of free space such that wavelength actually becomes 300/frequency x 0.975(approx).

Also bear in mind that diameter of radiators etc affect bandwidth, thinner will be much more selective. So using a larger material will make the design much more forgiving!

If you use a folded radiator the impedance is affected by the presence of other elements.

Hope that is some help.

Sorry if covering old ground here!