Huge Discrepancy between simulated and fabricated Antenna

I have an antenna design, which I simulated on CST and gave very promising results , then when fabricated it gave a totally different response.What could be the reason for that ? Where should I look for problems?

--Simulated

--Actual

-- The Antenna
Any Help would be greatly appreciated.

Do you mean the connection from the network analyzer to the sma connector ?

If you mean the connection from the network analyzer to the sma , I didn't model that ,I only used a waveguide port on CST to model the microstrip line feeding. How should I model that ?
How do I isolate the feedline , isn't the cable on a network analyzer already isolated ?

How did you model the feed line? Did you try to isolate the feedline in real measurement?



No. I'm talking about the cable effect, as discussed e.g. in this thread https://www.edaboard.com/thread129541.html

An asymmetrical feed line becomes part of the antenna and changes S11 and radiation diagram completely. This is actually a two-part question, 1. which feed configuration did you simulate, 2. what is the real measurement configuration?

I presume that you performed correct VNA calibration to a reference plane at the antenna input, or apply at least port extension.

Another point would be to check the plausibility of your simulation.



I'm not sure which configuration you are describing here. I don't see a microstrip line with your antenna.

In fact the simulation would be designed to fit best the real application. That's not typically the VNA measurement setup, at least it isn't for a portable device antenna.

The VNA measurement needs additional means to avoid wrong results by cable effect, like the ferrite tubes discussed in the linked thread, more have been discussed at Edaboard in other previous threads.

That's how I simulated the port .



Thanks, I will try to check isolating the cable.



The question that's bugging me, however, before trying the cable problem: is that on the same VNA another (hilbert curve) fractal antenna around the same total dimensions was measured and it wasn't affected as much as this one when I touched the cable?

get a bunch of these:
http://www.ebay.com/itm/13mm-Inner-D...item4ad06a7c9a

which antenna is this?