Hi Santheep,
Thanks for your post, this is very interesting. We’ve not made any changes to the antennas we use on the emonPi for a long time. I can see from your photos that the two antennas as the same, it’s very strange that one is performing better than the other. This is the antenna we use:
The only thing I can suggest is that the new antenna could be faulty in some way? Seems unlikely, but we would be happy to send you another antenna to test with?