Patch and dipole antenna

Baluncore
2019 Award
There are two quite independent waves propagating on the TL. One is in the forward direction from the source, the other is the reflected component travelling back towards the source. The sum of those two propagating waves will vary along the line and will form a standing wave pattern. That standing wave can be seen by measuring the total voltage across, or current flowing in the line, which will show nodes or nulls in fixed positions along the line.

The propagating waves cannot see each other and do not influence each other, they are travelling waves, propagating in opposite directions on the same line.

davenn
legyptien21
This is not a competition.
!! I never said or thought it s a competition. I do try to understand you. That s why I wanted to know (and asked) why did you say "A standing wave is not stationary in the sense of propagation.". I m not saying you are wrong, I just wanted to understand what do you mean by that.

sorry if I offended you...

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legyptien21
The sum of those two propagating waves will vary along the line and will form a standing wave pattern. That standing wave can be seen by measuring the total voltage across, or current flowing in the line, which will show nodes or nulls in fixed positions along the line.
excellent !!!! We are touching here something which drives me crazy for a long time. We were saying in all what we said until now that in the general case of interference between the incident and reflected wave, we will have a standing wave PLUS a propagating wave. If we measure the total voltage as you say, it will give the standing PLUS (addition mathematically) a propagating wave.

Im stuck with that for a long time, I have to understand that. To me the nodes or nulls won t be fixe in the general case (partially reflection).

Baluncore
2019 Award
in the general case of interference between the incident and reflected wave, we will have a standing wave PLUS a propagating wave.
No. There is an incident wave and a reflected wave, both of which are propagating, but in different directions. The sum of those is a fixed standing wave pattern. There is no "PLUS a propagating wave" as you put it.

legyptien21
Vi*sin (wt - kx ) + Vr*sin (wt + kx ) = Vr*(sin (wt - kx) + sin (wt + kx)) + C*sin (wt + kx) with Vi = Vr + C

Vr*(sin (wt - kx) + sin (wt + kx)) represent a standing wave if we use the Simpson formula...

Do we agree ? if not why ?

Baluncore
2019 Award
Do we agree ? if not why ?
No.
Where do the equations come from ?
What do the symbols mean ?

legyptien21
No.
Where do the equations come from ?
What do the symbols mean ?
the equations come fro my mind. Vi and Vr are the amplitude of the incident and reflected wave. K: wave number. w=2*pi*f with f the frequency. C is the amplitude of a wave which is part of the incident wave since we decide Vi = Vr + C. I hope it s ok now.

Baluncore
2019 Award
C is the amplitude of a wave which is part of the incident wave since we decide Vi = Vr + C.
So you are saying that the part of the incident wave that is not reflected, but which passes through the impedance mismatch, is reflected as C.
That is nonsensical.
If Vi = Vr + C, then C is not reflected and so is no longer propagating on the line. It is lost from the line.

legyptien21
So you are saying that the part of the incident wave that is not reflected,
I never said such a thing nowhere, sorry. I did a simple derivation, and I don t think I did a mistake mathematically. Then I interpretated the results as a superposition of standing wave and propagating wave. You may not agree with this physical interpretation but at least we should agree on the mathematical derivation... Do we ?

thanks

Baluncore
2019 Award
No.
Then I interpretated the results as a superposition of standing wave and propagating wave.
You cannot have a superposition of a standing wave and a propagating wave.

legyptien21
do we agree on the mathematical derivation ?

Baluncore
2019 Award
do we agree on the mathematical derivation ?
No.

legyptien21
Is it possible to have soe details about the reason of this no...?

why mathematically it s wrong ?

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Baluncore
2019 Award
For a lossless line with a characteristic impedance that is real, terminated in a resistive load.
Avoiding common scale factors.
The incident wave at the load will be Ei = Sin(t).
At a point a time x before the load, Ei = Sin(t+x).
The reflected wave will have an amplitude, A, between –1 and +1, determined by Zo and R.
The reflected wave at the load will be Er = A*Sin(t).
At a point back up the line, a time x after reflection from the load, Er = A*Sin(t–x).
Then the sum of the incident and reflected waves is Es = Ei + Er = Sin(t+x) + A*Sin(t–x)
For values of x = wave period * n / 4 ; there will be maxima and minima in Es.
Es = Sin(t+x) + A*Sin(t–x) represents the standing wave.
Vr*(sin (wt - kx) + sin (wt + kx)) represent a standing wave if we use the Simpson formula...
That should be Es = Vi * Sin(wt + kx) + Vr * Sin(wt - kx)

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sophiecentaur
Gold Member
If we have NOT full reflection on the wall so it means there is no standing wave in the cavity right ? the max and mins are moving ?
If you ever had a 'complete' reflection at the ends of a cavity, the amplitude of the standing wave would build up until it was infinite. A cavity, just like a resonant wire (as in a tuned dipole) will have a resonant frequency but, because of its finite Q factor, it will: 1. have a finite standing energy and 2. a finite bandwidth.
There will be power entering the cavity at one end and power leaving the cavity at the slots, resulting in a standing wave (when the frequency and dimensions are appropriate) but the (stationary) nodes of the standing wave will not be perfect because of the net power flowing through them.

legyptien21
a finite bandwidth.
You mean a bandwidth different than 0 ? because if we had a full reflection as you said, we would have had a infinite quality factor (with bandwidth = 0) if we suppose a lossless cavity right ?
We agree on these two points ?

There will be power entering the cavity at one end and power leaving the cavity at the slots, resulting in a standing wave (when the frequency and dimensions are appropriate) but the (stationary) nodes of the standing wave will not be perfect because of the net power flowing through them.
Sophie please can you tell me if you agree with my mathematical derivation at message 30 ? If so I would like to know your opinion about the speed of the sum of the standing wave and propagation wave ?

Thanks

davenn
Gold Member
2019 Award
you have already been told that your workings in post # are incorrect

Baluncore corrected them in post # 39

legyptien21
you have already been told that your workings in post # are incorrect

Baluncore corrected them in post # 39
And ?

1) I can be wrong, he can be wrong, we are all human.
Most importantly,
2) the justification of Baluncore doesnt make sense to me because his equation have no sense. Where is the wave number, where is the angular speed... Can you guess the wavelength of his equations... ?

If the equations are right then we take the most general case to do a derivation not a case where we add time in sec with X in meters...

davenn
Gold Member
2019 Award
when are you going to stop your own misunderstandings and listen to people who know what they are talking about ??

to me because his equation have no sense.
then you need to get back to the textbooks and start learning the real stuff and not what you make up out of your head

I trust what Baluncore says cuz I know he has had a lot of history working in RF electronics

Baluncore
2019 Award
If the equations are right then we take the most general case to do a derivation not a case where we add time in sec with X in meters...
If you go back and look you will see that I clearly defined x as a time relative to incidence at the load. That eliminates the velocity factor from the equation.
At a point a time x before the load, .....
.... At a point back up the line, a time x after reflection from the load, .....
Can you guess the wavelength of his equations... ?
The period T is sufficient. Wave number and angular speed are the same for all.

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legyptien21
If you go back and look you will see that I clearly defined x as a time relative to incidence at the load. That eliminates the velocity factor from the equation.
if you start to switch all letter and their meaning, noboday will follow easily. Anyway, I m open to talk about that :

Ei = Sin(t) this is your incident wave I beleive ? in every incident wave there is X which represent the distance. so where is the distance in your equation, where is the propagation. there is no point to write it that way and to eliminate the velocity...

If you wanna write your derivation with letters and their meaning as your asked me then I will follow you otherwise no one will be able to...

It s late for me now I will answer tomorrow

Baluncore
2019 Award
Ei = Sin(t) this is your incident wave I beleive ?
I clearly defined the incident wave at the load when I wrote ...
The incident wave at the load will be Ei = Sin(t).
if you start to switch all letter and their meaning, noboday will follow easily.
I clearly defined x as a time. You chose to ignore it.

in every incident wave there is X which represent the distance. so where is the distance in your equation, where is the propagation.
The incident wave will be a sine wave at the load, Ei = Sin(t). Earlier on the line it will have a time shift of x, giving Ei = Sin(t+x).
Ei does not exist after it has reached the load as it is a forward travelling wave.
The distance in my equation is measured by time along the transmission line from the load.
The time x, is an analogue of distance, just like "Light Years" in astronomy.
I keep t and x separate so as to show the time shift of the incident and reflected waves at any travel time x from the load.
The time shift of Ei and Er is 2 * x. That explains the n * T / 4 standing wave pattern, where n is an integer and T is the period of the wave.
The sign of the reflection amplitude parameter, A, is also important because it may invert the reflected wave.

Drakkith
Staff Emeritus

davenn
berkeman
Mentor
if you start to switch all letter and their meaning, noboday will follow easily. Anyway, I m open to talk about that :

Ei = Sin(t) this is your incident wave I beleive ? in every incident wave there is X which represent the distance. so where is the distance in your equation, where is the propagation. there is no point to write it that way and to eliminate the velocity...

If you wanna write your derivation with letters and their meaning as your asked me then I will follow you otherwise no one will be able to...

It s late for me now I will answer tomorrow
Thread cleaned up some and reopened for now. @legyptien21 -- What exactly are you asking about in this thread? You started asking about antennas, and then moved more into asking about transmission lines with resonant cavities on the end. What exactly do you want to ask about? What is the physical application? It is better to deal with real physical systems when discussing antenna systems, versus abstract questions. Especially when there is a bit of language translation issue.

BTW, it would be best if you would use "want to" instead of "wanna" -- the word wanna has very negative connotations in scientific discussions. Thanks.

legyptien21
As you may know, patch antenna, dipole antenna, transmission line, resonance, quality factors, all that are related. And when you start a conversation and ask about antenna, you notice that we don t agree with some more fundamental stuff. If we are not using the same mathematical langage and we do not agree on a very simple matheatical derivation then not need to go further.

I m sure you have good background in physics and you will notice that Sophie has an answer who is not the same at all than Balunchore (position of nulls/nodes are moving around a position because of the flow of energy). It s now very clear, many thanks to Sophiecentaur.

I m done with this post.

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