why do we need ground plane ?for antennas?

do all monopole antennas need ground planes

can some explain me why do we need ground plane for the antennas , plz tell how does its effects in the case of mobile terminal antennas?

why do we need grounding

The ground plane, decrease the influence of external noises, Because the electric (and so magnetic) field is weak on the ground plane, and so near that plane.

what are ground plane terminals

The purpose is to complete the circuit. Planes less than a few wavelengths wide affect the impedance and radiating pattern as well. A plane one wavelength in radius causes most of the antenna radiation to go up at 45 degrees.

why do antennas need a ground plane

as far as i could remember ground plane increase directivity , i remember that the mono-pole on a ground plane has double "as far as i can remember" the directivity of the normal dipole.

how big a ground plane do i need

for dipole, no need ground plane
because E-field is formed with anther pole

for monopole, it acts as a reference level(mirror) to form E-field with solo pole

Added after 1 minutes:

but the ground plane location is very important

otherwise it will become a microstrip transmittion line rather than antenna

for helical antennas ground plane reduces the size of the back lobe and hence the power wastage. larger the ground plane more reduction. hence improved directivity also.
basically the ground plane is meant for providing a closed circuit. they are just like the common ground we select for bread boards.

i think that in RF point of view, transmittion line and ground is not viewed as "circuit"

I may consider the pairs(transimttion line and ground) as a waveguide. It is like a optical fiber which allows light wave propagate

One reason to have a ground plane(GP) is it is easier to feed such antennas.

For instance, a dipole antenna needs a balun/coupler to have a balanced feed for the two arms. This balun can be eliminated by designing a monopole on ground plane, where a coax can directly feed the antenna. The outer conductor is connected to GP and inner conductor extends as monopole arm.

Note that ideal ground plane has infinite loss and is a perfect electrical conductor. As a consequence of image theory, a lambda/4 monopole standing vertically on a infinite ground plane has equivalent radition characteristics as of a lambda/2 dipole, in the region above the ground plane. In practice however, infinite GP is approximated by sufficiently large finite GPs. Effect of this finite size of GP does affect the input impedance and gain (directivity).

~ Venkat

tender_006 wrote:

"can some explain me why do we need ground plane for the antennas , plz tell how does its effects in the case of mobile terminal antennas?"

In the case of mobile terminal antennas, most antennas used in e.g. mobile phones utilizes the terminal chassis as a part of the antenna. Due to the finite size of the chassis, it acts more like a fat dipole-type resonator than a ground plane, especially at lower frequencies (like 900 MHz). This is the reason you can achieve fairly large bandwidths (~10%) with internal phone antennas, even though they use patch-type elements (usually something called PIFA) which are known for their small bandwidth (~1%). The patch element in effect mainly couples power to the chassis dipole-type mode.

In short, the groundplane is in fact the main radiator for mobile terminal antennas.

Best regards,
Peter

To all that need simple explanation

Our eyes detect electromagnetic waves that oscillate 10exp16 HZ. coming from source of light.
Antenna is "source of light" that our eyes can't see because of the lower frequency, comparing to light frequency. So when we want to increase the amount of light that comes from source of light to one direction we put mirror that behave like reflector. and we get twice the amount of light because the second half sphere of light energy added to the first one.
Like at electromagnetic light waves. In Electromagnetic microwaves, Ground plan is just a mirror to reflect the back energy.
We have to put the ground plan in the right place because the electromagnetic waves like vectors needs to be sum in phase otherwise, out of phase they will cancel each other.
with this gnd. plan we can change the direction of the beam like we do in simple
mirror.

for PIFA, we need to use 3D simulation..
but is it ok if we use 2D simulation to simulate the top patch only?

We have to put the ground plan in the right place because the electromagnetic waves like vectors needs to be sum in phase otherwise, out of phase they will cancel each other.
with this gnd. plan we can change the direction of the beam like we do in simple

Click to expand...

hello plasma,
thank u for the nice explanation, but can u please help me with how do i decide what is the right place for grounding as in my design we have a SMA connector and ground plane under it and also around the signal track.. but is it the right direction?

Simple it improves the output power of the arial by providing a return path for transmited and recieved signals

plasma said:

To all that need simple explanation

Our eyes detect electromagnetic waves that oscillate 10exp16 HZ. coming from source of light.
Antenna is "source of light" that our eyes can't see because of the lower frequency, comparing to light frequency.
mirror.

Click to expand...

I have a question about monopole antenna. If Ground plane(GP) is "mirror" like what you describe. Why ground plane dont exist under monopole antenna? monopole antenna has only one feed point,without ground point. and it must have clearance area under antenna.
Could you explain it. Thank you very much.
Regards
Fan Yi

Several people to answer here...

If you have a vertical electrical vector AT the surface of a perfect electrical conductor (PEC) the vertical vector is mirrored by the currents in phase and it radiates like a dipole, if the electrical vector is horizontal AT the surface, it is mirrored out of phase by the currents on the surface and cancels in the far field.

The ground plane (GP) carries currents which replicate the vector. These currents radiate like and antenna (if you don't know this you will learn this because EVERYTHING IS AN ANTENNA of some type-Even you bit heads! ;-) ). These being the case the radiating elements antenna pattern is affected because you've created an antenna array in effect.

If you put a horizontal dipole 1/4 wavelength over a GP, the mirrored image will look like a dipole 1/4 wavelength below the ground plane, but in opposite phase. These means the original and the mirrored image are now a 2 element array, spaced 1/2 wavelength appart, but radiating in opposite phase so at boresight in the far field they radiate reinforcing each other and creating a main lobe in that direction.

If you now take that horizontal dipole and put it 1/2 wavelength above the ground plane you get a null or zero radiation at boresight (directly above the dipole). All the power that was radiating directly above the dipole is now pushed out into the side lobes. You can use the logic in the paragraph above to figure out why they cancel in the far field in this case.

As for the quote from Waltz fan, you've connected the outer conductor from the cable to the ground plane sealing in the radiation from the cable to the region above the GP. To build the monopol you make a hole big enough that the center conductor for the cable comes through the GP, big enough so the insulation from the cable would come through the GP, but the outer conductor connects to the GP.

CntrCond>|
________ | _____________ < GP
over thr> | | |
over thr> | | |
thecable> | | | <outer conductor

I hope this drawing comes out. Maybe someone else is smart enough... I'm too lazy to product a pdf.

Aren't antennas fun!

Waltz_Fan said:

plasma said:

To all that need simple explanation

Our eyes detect electromagnetic waves that oscillate 10exp16 HZ. coming from source of light.
Antenna is "source of light" that our eyes can't see because of the lower frequency, comparing to light frequency.
mirror.

Click to expand...

I have a question about monopole antenna. If Ground plane(GP) is "mirror" like what you describe. Why ground plane dont exist under monopole antenna? monopole antenna has only one feed point,without ground point. and it must have clearance area under antenna.
Could you explain it. Thank you very much.
Regards
Fan Yi

Click to expand...

anyone know that in HF, VHF and UHF how we could simulate the ground plane (Earth)!
i used perfect Conductor and a rectangular plane with permitivity and conductivity of the earth for dry earth but the simulation results is too much different from each other!
regards!