monopole simulation

Hi, friends. I am a greenhand in mobile Ant design. here I simulate a monopole Ant, but there are error or mistakes. I remember the ant should work as the lambda/4. I want it to work at GSM 900MHz, DCS 1800MHz and PCS1900MHz. what should I do to modify the design?
Please give me some advice~!
thanks~!

Why don't you use PIFA? Your design is more or less close to PIFA without the shorting pin.

Anyway, in your simulation, the feeding was not correctly setup. I tried to change the feeding to get some results. However, it's not the best way to do it. Take a look at the attachement. you need to change the dimensions to get better results at your design frequencies.

Regards,
Shameem

Thank you very much Shameemkabir for your advice and your reply~!
As for the differences between PIFA and monopole, I have read some articles on it. For monopole there is no GND plane in the PCB and no shorting pin. Pifa antenna may have narrower bandwith. monopole can be made at a smaller package compared to Pifa at the same frequency.
Is there any more differences between them?

Added after 18 minutes:

By the way, how to create the model and simulate the monopole antenna on this paper? why there is a 50 Ohm microstrip line across the FR4 substrate? In the actual mobile phone, I think there is not enough space for that long microstrip line.
Could anyone please upload or send me the .HFSS file for this paper? I am
thanks and best regards~!

How can you use a monopole without a GND plane? I guess, what you mean by without GND plane is, there is no GND plane just under the monopole whereas PIFA antenna has it.
I'm not quite sure whether these statements are true. you have some rule of thumb to increase the bw of PIFA. Moreover, you don't need any external circuit to match the PIFA.

Added after 15 minutes:

it is just as you did in your simulation. Just try it. it would work I guess.
you are right. however, this microstrip line is only for measurement purpose. In the actual mobile phone you feed it at the indicated "feed point".
it should be the other way around :D. design the antenna and upload, if there are some problems for us to solve.

regards,
Shameem

first, I want to thank Shameem for his warmhearted reply and explanations to my question.
I have changed the monopole size to fit the required work band. there are two band maintained GSM and DCS. however the return loss is is not small enough. I upload the modified file here, so that those who will be puzzled with modeling monopole antenna can refer to mine.
the simulation of the attached paper will be made later as I am a little busy with my work recently~!
best wishes~!