Why do we take antenna length lambda/2 and lambda/4?

[hiyan]

i wantto ask why we take Antenna length lemda/2 and lemda/4?




2nd in the end of antenna why resiatnace high?


3rd length of transmission line is depends on the wavelength of the signal being transmitted why?




4th how the standing waves are genrated in transmission line?



i hope all members who know guide me and explain me briefly.thanks

b/c i was search but no answer reasonable .

 

[brahma]

Re: why

have you read the book regarding these topics or mearly asking after attending any lecture? these are very well available in any antenna book.
Any way, λ/2 length is used because it is the shortest length by which high radiation could be obtained for the particular freq, bcoz the in an antenna current distribution will not be uniform, only time varying field can give rise to radiation. the electrons get accelerated for quater of the cycle and then suddenly chages its direction and moves in the opp direction, the same action is performed for quater cycle (i.e. λ/2 length) thats why the minimum length required is λ/2.

i couldnt answer all your question- short of time. you better go through books...

 

[electronics_kumar]

Re: why

i wantto ask why we take Antenna length lemda/2 and lemda/4?




2nd in the end of antenna why resiatnace high?


3rd length of transmission line is depends on the wavelength of the signal being transmitted why?




4th how the standing waves are genrated in transmission line?



i hope all members who know guide me and explain me briefly.thanks

b/c i was search but no answer reasonable .

standing waves are generated when there is mismatching between load and circiut impedance.....some of waves wiill be reflected back instead of getting absorbed....that wave in combination with incident wave will a new wave called as standing wave ..it is a unwanted phenomena..
at antenna height lamda /2 we will get maximum radiation

 

[hiyan]

Re: why

currect is MAx at center and voltage at teh end of Antenna wil be MAx and after 1/2 and 1/4 sec get the max teh only this reason .



after attending a lecture i was read but above messge always got i REad FRanzel and 2 books .also.so is it right ?

2nd kindly explain the answer of all remaining my question .Thanks

 

[hiyan]

Re: why

:?:

 

[nik_harsha]

Re: why

hey ,
the high impedence is for matching purpose .. to get max radiation with minimum standing waves . other q's were answered .
read text books for detailed explanation .

regerds ,
nix.