The problem could be due to mismatch between the feed line and the antenna, between the antenna and free-space, or both. Check the impedance of your feed and the antenna and make sure they're matched, if not you can use an impedance transformer or lumped components to match the two. Alternatively, there are online calculators that can help you with the antenna and feed line dimensions.
Thanks Ghanshyam sir and Mohamed K.Emara sir, but please tell me how to design impedance transformer
As mentioned by Mohamed K. Emara Sir, you go for online calculator and you tube videos
Hello Shally Gujral Madam,
Try to improve impedance matching between feed line and antenna patch. Use online calculator to find the dimension of the feed and patch for matched condition and use them. Also, you can use or incorporate some basic modification, like parasitic and extended patch, slots, metal posts to increase the impedance matching. This may also help to increase the S11 of the antenna.
Best Regards
Anik
There is one and only one technique to improve the matching. It is nothing but "Impedance matching". T = (Zin - Zo)/(Zin + Zo) and S11 is obtained by taking the logarithm of T. It is impossible to obtained Zin = Zo, but Zin can be nearly equal to Zo. Hence, (Zin - Zo) term is minimized, as a result of that T is minimized and it tends to zero, which gives more negative value of S11. Therefore, try to match your antenna input impedance with your feeding system.
Dear @shally Gujral : We can give more detail, if you can provide the details of your antenna geometry including the feeding system. Because, if we have rectangular or circular MA, we have some thumb rule, in case of triangular antenna, there is no thumb rule. Please, give more details
Respected Sudipta sir ,I am using rectangular shape patch antenna with microstrip feed line. And high permittivity substrate. I think due to high permittivity substrate ,s11 is not as per requirement.
I have tried many things like increased substrate height,dgs, parasitic patch,stacked substrates ,but no results.
Anik sir, I have tried parasitic patch, I will try metal post also.
Thanks
Parasitic patch will act as loading on the antenna system. Hence, impedance matching is possible
Why don't you change the microstrip feeding. Suitable position, width of line, placement of feeding line etc provides matching.
The width may vary due to er and thickness of substrate.
But, due to high er, matching is poor, is not correct.
Usually width of patch controls the impedance bandwidth. That can be tried out (Increase width of patch as well).
Some times slots, inset feed mechanism, increased substrate dimensions can also be used for enhancing the S11.
you can use different slots or slits on your patch.
and also check the feed line or adjust the feed point to have 50 ohms matching.
Among the operations and methods to be taken into consideration:
-Adjust the power point to have 50 ohms corresponding,
- You can use different locations or slots on the patches to achieve better performance,
- The choice of substrate type and antenna dimensions also play a very important role,
- antenna networks: Parasitic patchea will act as a load on the antenna system (the case of reconfigurable antennas). Therefore, impedance matching is possible (for example: increasing the number of patches),
- Also the choice of switches and their polarizations in case of reconfigurable antennas can meet the requirements,
- ....
Having s11 above -10dB is low matching. In patch antenna with coaxial feeding, it happens due to
1. Wrong dimension of the inner conductor or
2. Wrong positioning of th coax
Solution
1. Make sure that the dimension of the inner conductor is correct to give 50 ohm..you can use https://www.everythingrf.com/rf-calculators/coaxial-cable-calculator to confirm
2. Try to sweep the position of the coax along x/y axis....from my experience in cst 0 and -2 are good start
If you are simulating using a coax or inset feed you should select the feed point at the midpoint along width and approx one third along the length of the patch. It is always better to use a optimization technique like PSO to have a set of values for length, width of the patch and feed position( normally these are the parameters chosen for resonant frequency/50ohm matching optimization). You then have a set of values of these parameters to choose from and play with. For coax feed while fabricating, poor soldering sometimes causes feed reactance which in turn deviates the matching. For inset feed feed line width plays a important role.
Numerous factors control the return loss. They are:
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