why

Discussion in 'Homework Help' started by hiyan, Dec 7, 2005.

  1. hiyan

    Thread Starter Member

    Sep 23, 2005
    26
    0
    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
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    I think if you do some looking on the topic of resonance, most of your questions will be answered. All the things you mention have to resonate at the transmit/receive frequency in order to function efficiently. A little antenna theory will explain why quarter- and half-wave antennas work.
     
  3. hiyan

    Thread Starter Member

    Sep 23, 2005
    26
    0






    i read but i did not found above questions answer so kindly tell me and explain me thanks.
     
  4. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,158
    Visit http://www.phy.davidson.edu/instrumentation/NEETS.htm

    Locate and download

    Module 10 - Introduction to Wave Propagation, Transmission Lines and Antennas, presents the characteristics of wave propagation, transmission lines, and antennas.

    That book has the answers your seeking.
     
  5. n9xv

    Senior Member

    Jan 18, 2005
    329
    1
    "i wantto ask why we take Antenna length lemda/2 and lemda/4?"

    Lamda/2 & Lamda/4 denote the physical half-wave & quarter-wave dimensions for the antenna in question. The quarter-wave antenna is the building block from which all antenna systems are designed.

    The half-wave antenna is the fundamental design by which all antennas are ultimately compared.


    "2nd in the end of antenna why resiatnace high?"

    In a half-wave antenna, the current nodes are at minimum towards the ends of the antenna. Thus, minimum current = highest impedance.

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

    This is due to velocity factor. In other words, the speed of electricity is slower through any "medium" than it is through a vacuum.

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

    Standing waves or standing wave ratio (SWR) is due to an impedance mismatch between feedline and antenna. Standing waves are the waves or energy reflected back towards the transmitter due to the mismatch. Standing waves are the "leftover" waves that did'nt get transmitted or radiated.
     
  6. hiyan

    Thread Starter Member

    Sep 23, 2005
    26
    0










    Thank u all :)
     
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