[SOLVED] gain in a monopole wire antenna

[ghasem_008]

Hi.
I have one question.
as we know,in a λ/4 monopole wire antenna above ground plane,gain is 5.16 dB.
also,in antenna,we can use from: dB=dBi. (if we don't use from dBd).
but in a reference book,we saw gain of monopole antenna in a frequency range is 0 dBi (as attachment)

in this book:
height = h = 50mm
radius = 0.5 mm
why in this book,gain is 0 dBi?

 

[ghasem_008]

is there anyone who help me?
why in this book gain of λ/4 monopole wire antenna is 0 dBi???

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alos,I have another question.
among dipole wire antenna,which of them have largest gain?λ/2 dipole antenna?

 

[Alan0354]

Is it possible that the book consider gain differently? In antenna books, they put D0 in the gain equation to specify directivity which make it larger than 1.
\[G_0=e_{cd}D_0\]
Where \[e_{cd}\] is the efficiency. For ideal lossless antenna, it is 1. So gain is just D0. D0 is 1 for isotropic antenna, any other antenna is bigger than 1.

But in real life, the antenna is passive and you really don't have gain. Take me a while to get use to it.

 

[ghasem_008]

dear alan!
everyone know that antenna is a passive element!
for example,maximum gain of a ideal dipole is 1.67 db.while a dipole antenna in free space is 2.156 dBi.and if dipole is above the earth,gain can be 8.5 dBi.
now my question is:
for example compare maximum gain in a 3λ/2 and λ/2 monopole.it's clear?

 

[Alan0354]

If you already know all these, then review Balanis Antenna Theory p191 to 193 on monopole.

 

[ghasem_008]

Ok.I saw it.
what is your mean?you think that G in there is antenna gain?

 

[Alan0354]

Two separate definition of gain is defined in P66 of Balanis. One only include efficiency in equation (2.49a) as what I posted. The other even including the input mismatch to the driving source....called Absolute Gain. in equation (2-49b).

 

[ghasem_008]

So,page 191 and 193 was wrong.
now with (2-49b),can you compare maximum gain in a 3λ/2 and λ/2 monopole?

 

[Alan0354]

I am not expert, I just studied the chapter. I looked at my notes. For λ/4 monopole on gnd. \[G_0=D_0\] for lossless antenna. The D0 is same as λ/2 isolated dipole and is 1.643 from my notes. So Gain in db is 10 log D0= 2.16dB.

Look at section 4.6 p182 to 184 for all the info on λ/2 dipole. As for the other length, you are going to have to do the calculation yourself using equations in p 172 to 179. It is long using sine and cosine integrals. Use Wolfham special function calculator to get those numbers and plug in.

 

[ghasem_008]

thank you.
but these books are very simple.also,you have a mistake.because:
Directivity(λ/4 monopole) = 2*Directivity(λ/2 dipole)=2*1.643 = 3.286=5.167 dBi.
good luck

 

[Alan0354]

thank you.
but these books are very simple.also,you have a mistake.because:
Directivity(λ/4 monopole) = 2*Directivity(λ/2 dipole)=2*1.643 = 3.286=5.167 dBi.
good luck

No, Dierectivity is the same. Read P193 at the top, for 0<θ<Π/2, you use equation (4.84) and (4.85) which is for E(θ) and H(Φ) for λ/2 dipole for calculating Wav(θ), Prad, which in turn calculate D0.

Well, this question is sure very simple if I can answer. It's all explained in the first few chapters. If you are that good in antenna, please help me in this, it should be very simple:

https://www.edaboard.com/threads/292284/

 

[ghasem_008]

dear allan.
in antenna we have:
Zin(λ/4 monopoel) = 0.5*Zin(λ/2 dipole) = 0.5*(73+j42.5)=36.5+j21.25
actually,a λ/4 monopole antenna focus on half space.So it's radiation strength in a specific direction is doubled.SO:
Directivity(λ/4 monopole) = 2*Directivity(λ/2 dipole)=2*1.643 = 3.286=5.167 dBi.

 

[Alan0354]

You are right, it's even written in my notes, just did not read all the way when I saw the E and H are the same. Prad is half because it's only half space, so D double.

You have a chance to look at my other question?

 

[Bob60]

Very funny 8-O. Directivity(λ/4 monopole) and dipole are same. It looks like China antenna gain. Typically they calculate LNA and antenna gain together, whatever you wants, whatever you need and got for instance 40dB gain from one patch.
On the picture 5/8λ symmetrical, possible non, gain is same.

 

[ghasem_008]

what is your mean Bob60?
Who says directicity monopole and dipole are same????????? Please read a few books antennas!!!!

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why gain of monopole antenna is 0 dBi?

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why in theory it is possible to make a monopole 1/4 wave radiator antenna that would give 0 dBi gain???

 

[davenn]

Who says directivity monopole and dipole are same????????? Please read a few books antennas!!!!

They both have an omni-directional pattern in azimuth

Dave

 

[ghasem_008]

can you say that why gain is 0 dBi?

 

[ghasem_008]

is there anyone who know ANTENNA?
why is my figure,gain of a monopole antenna is 0 dBi???
while gain of isotropic antenna is 0 dBi!

 

[Alan0354]

Ghasem, I think you should tone down on your put down and sarcasm. I don't know your book that talked about dBi, nor do I really care at this point. I pointed out to you in an "EASY BOOK" everything to be said and to calculate the gain. For someone that claimed it's so easy, you sure don't quite seems to grasp the very basic theory of this.


To moderator, My experience is that this forum is highly technical forum, people are very friendly and courteous. I don't think this is in line with the forum here.

 

[ghasem_008]

in my posts,there is not any sarcasm,at all.
I mean that in my posts,please give me reply that is related on my question.
best regard
ghasem