The "distortion" you're seeing is the sum of the fields from the two
antennas, which vectorally add to produce a total pattern. This is a
"phased array". The pattern of a phased array depends on the relative
phase and magnitude of currents in the elements (in your case, the
antennas), the spacing between elements, and their relative
orientations. So if you don't want to change antenna positions, the only
alternative is to alter the relative magnitude and/or phase of the
currents in the two. One source of information about this topic is
Chapter 8 of the _ARRL Antenna Book_.

Roy Lewallen, W7EL

Rohit wrote:
Hi all,
I have placed 2 similar antennas (3 dB beamwidth = 90deg,
Polarization= LHC) on a PEC box with a small spacing between the 2.
Both antenna's are tilted and the first one is at 45deg and other at
135 deg from the horizontal so that both can cover 180 deg.

With this setup, in the simulation result i am observing heavy
distortion (about 10dB ripple or more) at 90 deg. What is the reason
for this heavy distortion. Is there any way i can remove the
distortion in the pattern without changing the antenna's position??

Thanks in advance,
Rohit