What is transmission Line

[sumit007]

transmission line theory 101

What is transmission line and how is it related to antennas ?

Thanks

 

[the_risk_master]

Hi,

A simple answer: a transmission line is any conducting path connecting the link between the source(voltage or current) to load(antennas can be considered as a load). antennas impedances are matched to that of the transmission line or medium in order to have a maximum power(signal strength) transfer to the load or a receiving end.

 

[safwatonline]

the diffrence bet. a wave guide and a T.L is that T.L has two conductors

 

[konarkk]

Transmission line work on ckt or network theory wheras waveguide on electromagnetic wave theory

 

[suvendu]

In short,Transmission mission line is a guided medium where as antenna is an unguided medium.

 

[my_books]

http://www.williamson-labs.com/xmission.htm

http://www.tpub.com/neets/book10/41.htm

 

[shaikhsarfraz]

Hi,
Transmission lines are the conducting medium between the soutce ans the load.
In transmission lines the impedance are matched so that there is maximum power transfer and there is no reflection as reflection can produce standing waves.
Moreover in transmission line Ohm's law cannot be applied as due to low wavelenth of signal(comparedto the length of transmission line ) the V and I relation cannt be considered linear, so be use the concept of Distributed components where be distribute the line into infinitessimal parts and get the current and the voltage relation.

They play important role in IO circuit design where many a times we have to simulate the circuit with Transmission line load.

For more refer any book on transmission line

Thanks
Shaikh Sarfraz

 

[itzikhaim]

Hello, sumit007 !

I hope you got an idea of what T.L. is , by now !

If you don't, here is a link for the chpater of Transmission Line by Sophocles J. Orfanidis at Rutgers University NJ :

https://www.ece.rutgers.edu/~orfanidi/ewa/ch09.pdf

you can download the whole book - its free for now (draft copy).

There you can find topics which covers the most of Antenna theory and design, as well.

And last, you have to know that every Antenna is a wave guide but not all wave giodes are antennas (note thate some say wave guide is not T.L. - I prefer to consider it as T.L. because its transfers power from one side to another - like coax or microstrip line which are "the classical" T.L.)

Hope you understood this topic -
Itzik !

Added after 3 minutes:

Hello again !

I got wrong with the last sentence in the previous reply,

I meant that every Antenna is a Transmission Line (T.L.) but not vice versa.

bye, for now

Added after 47 seconds:

Hello again !

I got wrong with the last sentence in the previous reply,

I meant that every Antenna is a Transmission Line (T.L.) but not vice versa.

bye, for now

 

[shaikhsarfraz]

Hi,
I forgot to add that transmission lines are used for high frequencies, where the lumped circuit components donnot hold good, so instead distributed component approach is used.

Thanks
Shaikh Sarfraz

 

[electronics_kumar]

if the signals wavelength is comparable or less than that of conductors length, then it is called as transmission line...
thumb rule is L>= (LAMDA/10)....
HOPE IT HELPS...

 

[eng_hamdy]

transmission line is the medium which connects point to point in a specified communication systems like co-axial cable,pair cable,fiber cables each have its transmission bandwidth if transmitt data or if we talk about communication sys.
if we talk about high voltage we care about transmisted voltage and current .
thanx
it my first replay in edaboard

 

[catchamitpal]

transmission line is an interface point betwwen any tow networks.
It also serves the purpose of transmiting the power from source to destination
impedance matching benefits from the power pouint of view making it maximum

 

[Euler's Identity]

"What is transmission line and how is it related to antennas ?"

I'll make a stab at it...

The Transmission Line (TL), with respect to an antenna, matches an antenna to a source or load, usually for maximum power transfer. A TL is a complex impedance that looks like Z = R±jX. However, where lower operating frequencies allow for the use of discrete components for the creation of an impedance, as normally the wavelengths are much larger than a component's leads or a circuit's interconnecting traces, the operating frequencies of TL's require impedance creation by way of geometry and materials -- the length of a wire, its diameter, and its distance from the reference, for examples, are factors of its impedance.

TL line theory is based on Maxwell's equations, the equations behind the more familiar Ohm's and Kirchhoff's Laws. No longer are equations based on functions of time but on wavelength as well To successfully work with Maxwell's equations requires knowledge of Multivariable/variate Calculus. I remember very little TL theory and so will be of little more help than this brief overview. However, at all times TL theory is in practice, as at all times Maxwell's equations apply. Therefore, every electronic circuit is a transmission line. It's just that usually the frequencies (the wavelengths involved) are low enough that the simplifications of Ohm's or Kirchhoff's Laws suffice for producing successful designs.

Now the not so professional view...

TL analysis and circuit design is some freaky stuff and, though many more knowledgeable folks will disagree, is almost black magic. When a coax line is shorted to ground but still develops a voltage drop at certain wavelengths being transmitted, it's magic. When the coax is RG-59 in a black outer casing, it can be called black magic. Then, when one gets a look at some of the microwave microstrip circuits that join amp A to amp B, one could even say it's art.

Years ago I was introduced to a branch of TL design called "microstrip." I kid you not when I say TL engineering is magic. When you substantially increase the bandwidth of a transmitter by building up a mound of solder on a pad connected to the lead of a microwave device, you are no longer in Kansas. "...but that makes the board look bad...but it actually works very well now!...luckily it's all hidden by a metal cover, so the customer will never see it..." ;-)

Take a look at a microwave frequency microstrip interdigital bandpass filter some time. Working with TL theory is an art. May the Schwartz be with you.

 

[funster]

when electrical connection's length is long than device's size,

we should treat the connection as transmission line than a lump device.

transmission line's radition ls less than antennas.

best regards

What is transmission line and how is it related to antennas ?

Thanks

 

[a_aziz]

Hi.
A transmision line is a way to flowing the elcramagnetic waves that may be a two-pair wire, coaxial, or printed microstrip line. We can use them as a feed network to fed the antennas.