CST Impedance matching of basic rectangular patch using feeding line

So basically these are the steps I used in impedance matching.

1. Find impedance of square patch.
2. Add a feedline to eliminate the imaginary part of the impedance
3. use calculator to obtain the width and length of quarter wave feedline
4. Add Quarter wave .

Based on the result, i've obtained a total impedance approximately of 49+j1 impedance. I supposed this is a matched patched antenna, but the problem is that, my total efficiency simulated keep on getting -5db which is not good.

Below attached is the file. Can some1 enlighten me which part is wrong?

I haven't checked your file.
But, what S11 do you get? This indicates how well the port is mached to the antenna.
And what is your gain or radiation efficiency? This will indicate how well your antenna radiates.
These two "sum up" to the total efficiency, thus when your total efficiency is to low you have to check if is your gain or the S11.

flanello said:

I haven't checked your file.
But, what S11 do you get? This indicates how well the port is mached to the antenna.
And what is your gain or radiation efficiency? This will indicate how well your antenna radiates.
These two "sum up" to the total efficiency, thus when your total efficiency is to low you have to check if is your gain or the S11.

Click to expand...

my S11 is -26db at 2.4GHz, which is at my desired frequency.
my gain is 1.65dB.
I've tried numerious time and still couldnt figured it out. :sad:

What is your directivity and the radiation efficiency?

flanello said:

What is your directivity and the radiation efficiency?

Click to expand...

my directivity is 6.765db and radiation efficiency is -5.1db. still couldnt solve this problem

An efficiency is -5.1db means ~32%. Thus your antenna is only radiating 32% of the power it gets.
You would have to increase these value in order to get a better total efficiency.
Can you post your antenna structure?
What is your frequency? What is substrate material and how tall is it? What is the size of your patch?

flanello said:

An efficiency is -5.1db means ~32%. Thus your antenna is only radiating 32% of the power it gets.
You would have to increase these value in order to get a better total efficiency.
Can you post your antenna structure?
What is your frequency? What is substrate material and how tall is it? What is the size of your patch?

Click to expand...

my desired frequency is 2.4 GHz. FR4 board, er 4.4 with 1.6mm height and tan lost of 0.019. dimension of patch is 27.5mm x 28.5mm, which is a square patch. currently using a quarterwave feedline.

I'm trying to get a matched square patch before i start to design my antenna..

With a S11 of -26dB you have a matched antenna. It seems that your structure doesn't radiate good enough. You should get a radiation efficiency of above 80%, then your total efficiency is better since it is the product of the matching efficiency and the radiation efficiency.
It seems your patch is fine. How large is the ground plane?

flanello said:

With a S11 of -26dB you have a matched antenna. It seems that your structure doesn't radiate good enough. You should get a radiation efficiency of above 80%, then your total efficiency is better since it is the product of the matching efficiency and the radiation efficiency.
It seems your patch is fine. How large is the ground plane?

Click to expand...

the ground is same size as the substrate.. where its length = 80mm , width = 60mm