Need Antenna Design and CST Help

Hi everyone, I have designed a dual-band microstrip patch antenna for LTE and WiFi application. The antenna operate at 2.6GHz for LTE and 5.0GHz for WiFi. I have started the design process by designing the 5.0GHz WiFi then introduce two inverted U slots to generate the second 2.6GHz. The impedance matching for the first 5.0GHz WiFi is okay, but I cannot achieved impedance matching for the second 2.6GHz LTE. That is why the bandwidth, return loss and gain for 2.6GHz is not okay.

Please advice on dual-band impedance matching especially for second 2.6GHz impedance matching.
Thank you in advance.