why antenna is of quarter wavelength
Maximum power transfer.
Quarter wave one direction....reflects back another quarter wave= 180 degrees
combines witth the incoming wave....therefore it cancels. All the energy is transmitted.
I think it probably evolved from a 1/2 wave horizontal dipole which has an approximate impedance of 75 ohms. 1/2 wave is chosen since it presents a reasonable real impedance at the feed point. Replace one half of the dipole with a ground plane and you have a 1/4 wave length antenna fed against a ground plane with an approximate impedance of 37 ohms.
Actually, a 5/8 wave length vertical is the best length because the major lobe of radiation is the lowest angle to the horizon, hence you get the longest distance. However, it needs a matching network to transform the feed impedance to something common like 50 ohms.
At the length half lambda, the antenna resonates. The antenna reaches
a maximal radiation resistance, so the antenna works optimal.
If you bring the antenna above a metallic plate of 'infinite' extent, you
can save the length to the half
regards
yendori
Maximum power transfer.
Quarter wave one direction....reflects back another quarter wave= 180 degrees
combines witth the incoming wave....therefore it cancels. All the energy is transmitted.
hai yendori ,
i am unable to visualize it.. could u plz explain it some aids
antenna is a transmission line!
Now on web,so search, can be some transmission lines similation tools that you can easily viasualize on each instance how it looks like.