theoretical gain of monopole

Hi all,

I would like to know the antenna gain for Monopole, some article post it as 2.1 dBi because it is a one kind of half-wave dipole. Someone mentioned it is 5.1dBi. Please clarify for me.

Thanks in advance!

Dear Rayengine!

If we consider lambda/2 dipole for example, it has directivity 2.15 dBi.
Monopole with infinite ground causes radiating only to upper half space, so that directivity of monopole=directivity of relevant dipole+3dB

In our case of lambda/2 dipole, its counterpart is lambda/4 monopole with D=2.15dBi+3dB=5.15dBi

In practite you don't have ideal infinite ground, directivity is less than theoretical value..

Best,

Eirp

Thanks for your answer!

But if I am talking some small hand-held devices, will it have significant change on it ?

BR

Hi,

various factors will now affect the gain, Mainly the operating frequency in relation with the size of your ground plane. If I remember correctly,

In the condition that the length of d monopole stays constant and grounding is to the metal casing of hand-held device:

Note: perfect electic conducting gnd then gain of monopole approx 5.15dBi

Note: where the size of gnd plane (e.g. ur hand-held device) is =/>> lambda / 2 then gain of monopole again approx 5.15dBi.

where size of gnd plane < lambda / 2 then effective gain will start to degrade slightly and then rapidly when lambda is < lambda/4. If your antenna is vertically placed, the gain will also depend on the length of your hand-held device. I can't really tell what the gain will be now but usually in the range of 0 to -2 dBd (e.g. 2.15 dBi to 0.15dBi) depending on the size of your ground.

Hope this helps.

Cheers,
Element7k

Gain of monopole is mainly affected from distance to ground ( it is very difficult to installa amonopole right on the ground ) and ground resistence.
Sometimes we use for some our applications monopole antennas and we made some test long time ago and we always assume gain as 0 dBi.

Mandi