Ah - so it's your box that we're seeing round there - I've done lots of airport outlines for your surrounding airfields recently, including San Bernadino just a couple of days ago.
Your results look pretty good for an indoor aerial. The ADS-B signals are easily blocked by walls, buildings, and even modern coated window glass, so you'll probably see a big improvement by getting the antenna outside, unless yu're surrounded by taller buildings.
DPD aerials are well respected by many RadarBox users, but they still can't see through walls!
I've got 15m (nearly 50ft) of high quality cable up to my outside aerial, and, thanks to also living on top of a hill, get really good results despite any cable loss (and I don't have a pre-amp).
By the way, the polar diagram will build up over time (you can clear/reset it on the File...Preferences dialogue box).
Rod