antenna-theory.com

[Abu Maria.]

hi

firstly thank you for all your answers...

I read an interesting link in this forum

http://www.antenna-theory.com/antennas/patches/patch4.php

but i have questions:

1-why PHYSICALLY when we increase height of the substrat in patch antenna we increase the bandwith ?
2-why PHYSICALLY when we increase height of the substrat in patch antenna surface wave will be excited ?

thank u and sorry

[splendor]

Hi, Abu,

I would like to try to answer 1st question. Please feel free to figure it out if I am wrong..

Thicker patch antenna, or smaller eps, usually means that antenna is less reactive (capacitive usually):

from the energy point of view, this means less stored energy in near field, leads to lower Q, larger bandwidth

from the impedance point of view, this means the impedance will vary slower, especially for the imaginary part crossing zero. So the matching bandwidth will be wider.

Bigsteve, if I am wrong,can you point it out for me? I am not sure by myself. Thanks

[bigSteve]

I think that is a good answer. Definitely when you have a lot of capacitance (as in a capacitor) or a transmission line, the fields are tightly bound - and therefore the energy is stored in the near field. This is the "reactive fields" you speak of.

To get radiation, we do need to move out of the capacitance region and into the antenna region. Now on the subject of bandwidth - a higher substrate height does lead to wider bandwidth. It is the same analogy as in a fat dipole - the fields have a larger degree of freedom. This yields more bandwidth.

Alternatively, reducing the capacitance lowers the Q, which is higher bandwidth as you say.

[Abu Maria.]

thank u all
splender you say"...Thicker patch antenna, or smaller eps, usually means that antenna is less reactive (capacitive usually)"

why?
Normally, when you have a high thickness, we have field lines that will be bigger, so better or radiation



from the energy point of view, this means less stored energy in near field, leads to lower Q, larger bandwidth ..."

i dont understand this!sorry