Hi everyone,
I need to achieve a wideband result from an SIW Leaky Wave Antenna. I've tried tapering the microstrip feedline but results for S11 are not appropriate yet. Also, I put patches into the structure but still no good results!
What are the methods for decreasing the magnitude of S11 and getting wideband results???
Thanks
I am little surprised that you are not getting wideband results in SIW. The main factor to achieve wideband s-par is impedance matching with source. So, if you have used tapering then you should have got the results, I think you have some mismatch in there. Did you check the impedance versus frequency curve? and how much bandwidth you are getting right now?
Two images attached. One for reference impedance extracted from CST & another for S11 par. Maybe I'm seeing wrong figure for impedance?! Because again with the simple microstrip feedline my reference impedance was the same! How could I sure that my tapering works right?
To increase the bandwidth, you want to decrease the Q-factor of the antenna, which means that you have to decrease the stored energy in the substrate. So to increase the bandwidth, you have to increase the substrate height, increase the patch widths or decrease the relative permittivity.
Thank you for your reply dear Mohammad. In the case of height and permittivity I have to say that I'm not able to change them because of fabrication limitations here now I'm using RT5880 with the permittivity of 2.2 & the height of 1.575 mm, so for this height & permittivity the width of the patch can not be changed. Now I'm looking for some tricks in order to escalate bandwidth.
You can then use multimoding techniques, such as using stack elements, co-planar parasitic elements. There are other broadening techniques such as using an impedance matching network in the feed part of the antenna, or by introducing losses in the antenna (resistive loading), but at the expense of decrease in radiation efficiency. The losses can be in the form of lossy substrate materials, layer of lossy film, or a discrete chip resistor.
A good reference: "R. Garg, P. Bhartia, I. Bahl and A. Ittipiboon, Microstrip Antenna Design Handbook, Artech House, 2001."
I guess you have used the slots for the radiations. I think your slots are not acting like the radiating slots. Play with the dimensions of the slots (Len, breadth and orientation.). Looking from your S para curves, your SIW is just acting like a transmission line not a leaky wave antenna. Tapering should be done at last when the final design is ready. Dont bother about tapering its very easy job. Let me know more about your design so that i can help you out in designing...
Plot port impedance Z0 without normalizing it to 50 Ohms. Let's see how it behaves. Rahul Agrawal will definitely help you with this as he has good experience with SIWs and LWAs.@Rahul agrawal
Dear Rahul Agrawal, you were right about the changing the position of the slots it helped to better radiation but as my structure is a special one I have to consider other issues too. Anyway, thank you so much...
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