why farfield pattern has more ripple

[parameswari]

Hi
my antenna beamwith is 70degree. I simulated by placing 3 of my antenna at 10lambda seperation between them in free space. I could see more ripple in my far field pattern. Why more ripple? can any one explain?

Thanks

 

[volker_muehlhaus]

https://en.wikipedia.org/wiki/Side_lobe

 

[tallface65]

This likely has nothing to do with single element side lobes as are alluded to in above post. What you are seeing is the interference effects of placing three antennas within close proximity of one another. When you have individual, coherent sources, like RF antennas, they will interfere with one another. This interference is essentially the superposition of each of their fields which includes the phase due to the difference in electrical propagation distance. Look up interference or even for this case, just look up array factor.

If you know your single element uncoupled antenna pattern, you can then multiply it by the array factor induced by having three antennas separated by 10 lambda.

Have fun :>)

 

[volker_muehlhaus]

This likely has nothing to do with single element side lobes as are alluded to in above post.

The relevant section in my link above is:
"For discrete aperture antennas (such as phased arrays) in which the element spacing is much greater than a half wavelength, the aliasing effect causes some sidelobes to become substantially larger in amplitude (...)"

The distance between the patches (10 lambda) is too large.

 

[parameswari]

Hi

but antennas are at very far distance and it wont act like array. each one of it is a individual element

 

[volker_muehlhaus]

but antennas are at very far distance and it wont act like array. each one of it is a individual element

It is not that simple.

You miss the important point: the antennas are driven by the same signal. These coherent signals will interfere in the far field, even if the antennas are at far distance.

The large distance between the antennas causes this alias effect -> grating lobes that are mentioned in my link.