IFA FOR 865-867 MHz, bandwidth and resonance

HI,

I am currently designing an Inverted - F - Antenna (IFA) FOR 865-867 MHz band using CST 2015 version. I will be thankful if you could help me out for the following questions.

1. Which portion of the antenna i am supposed to optimize in order to get the resonance?
2. What is the effect of adjusting the distance between the shorting pin and the feed?
3. what are the ways to increase the bandwidth?

kindly help me out !

1. Length of horizontal part and height. Plus length of ground plane
2. Shorting pin is like matching inductor - changes the impedance
3. Increase height. Change length of ground plane

- these are 'first order' ideas. All the parameters are inter-dependent. And depend on your specific geometry. You have to play with geometry to see how it reacts.

Increase antenna size. Electrical small antennas (< lambda/4) have a limited bandwidth by nature.