ads momentum pifa antenna

hi,

guys i'm tasked to design a low-profile small printed antenna that operate in 915MHz for GSM application. i have this book "planar antennas for wireless communications" by kin lu wong. there was a reference design on CPW-fed PIFA. what i have is ADS 2004a Momentum. I have been really struggling with the proper application of PORTS and truncated GROUNDS noting the limitation of ADS to infinite groundplane and substrate...
below is the image of my layout in ADS with the following dimensions and specs.

the middle port is the CPW-fed port single, 50 ohm port. the other two ports at the sides are GROund reference port to 1.

http://usera.imagecave.com/krazooom/...telayerdef.JPG
http://usera.imagecave.com/krazooom/...nlayer.bmp.jpg

according to the book, the resonant frequency should be about 2045MHz with a 20%BW as shown by the response , however it is different from the result above

please help me verify such design if you have ANSOFT HFSS to layout such structure and compare the response..
i would greatly appreciate your help on this!

thanks!

blue_electron,
There is a section in ADS' Momentum help file dealing with CPW port. You should read it carefully. I suggest you read the Appendix A and you will find a topic on "Internal Ports with a CPW Structure." It says that CPW ports set-up is very tricky, and different set-up of the ports can result in very different simulation output.

Honglin

Hello blue_electron,
In my experience with simulating CPW's with momentum. I used to define the slots as metal lines and specify them as slots in the substrate setup and didn't have problems with the results matching with HFSS. Unfortunately, I don't have access to ADS anymore and hence can't send you an example file. I'll try to find one and send it to you but can't promise.

Ananth.

Hello,

Upload your ADS project file.We can help you better.

PS:
Hello,

Upload your ADS project file.We can help you better.

By the look of your layout you have attached three ports to your structures. This enables you to excite the two modes of your CPW, the quasi-TEM mode and the slot mode. Now the mode which you probably mean to be excited in your prototype is the quasi-TEM mode. In other words, your prototype will include an element such a bridge which will short the slot mode and prevent it from propagating into the rest of your system, radio or what have you...

This is where your simulation layout may differ from your prototype. Indeed, depending on how you excite / load the ports in your simulation file, the slot mode might be excited in a way which does not correspond to reality.

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