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why coupling-feed microstripe antenna has larger BW?

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antenna_abc

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microstripe antenna

Hi, I have a question about the coupling feeding technique of microstripe antenna.

Why the EM coupling or Aperture Coupling can increase the microstripe antenna bandwidth? The microstripe antenna structure indicates its narrowband, so why the coupling effect can help to improve bandwidth? is it the capactor loading or other lump-component matching technique can also be used to improve bandwidth? Thanks
 

aperture coupling in patch antennas

The capactor loading or other lump-component matching technique could improve bandwidth .

I think the reason for it is due to the material loss and surface loss.
 

antenna bw

Hi, antenna_abc:

There are two type of coupled fed antennas: (1) aperture coupled fed and (2) proximity coupled fed with multiple elements. For aperture coupled fed antenna, normally, there is more space between the slot and the patch. The more space for storing energy makes it wider bandwidth. Dr. Pozar and colleagues published many papers on aperture fed antennas. I noticed that only those with a big separation between the aperture and the patch show very wide bandwidth. Those with small separations do show similar bandwidth as regular patch antennas. For multiple coupled elements, the resonaces of the different elements are coupled together to form wider bandwidth. Again, it basically increases the space for storing the energy (not the total energy). Regards.
 
coupling feeding antenna

Thanks for all your replys.

Dr. Jian, I am not quite sure what you mean that separation between the aperture and the fix? is it the thickness of the antenna patch substrate? So do you mean that aperture coupling patch antenna is nothing but just a conventional patch antenna with thicker substrate, and that is the reason why bandwidth of it is better?

And do you mean that when the stored EM energe can be spread out in the antenna structure, the bandwidth can be improved? Is it related to Chu-Criterion for small antenna?

One more question is that I am a little confused that by adding tuning network, the RF systems bandwidth should be decreased since tuning network introduces extra Q into the systems, but by adding coupling in microstrip antenna, it seems the bandwidth can be improved... So what is the trick insides this phenomenon?

Once again, thank you very much for your help, and I appreciate all your reply~~
 

aperture coupling

Hi, antenna_abc:

A typical aperture coupled antenna is like the following:

-----------------patch

air or foam

------------------
substrate
-----aperture on ground----------------
substrate
--------------------feed line

Normally, people want to have a thick layer of air of foam. From what I see, the big space there allows the antenna to store energy. Then, the antenna has larger bandwidth. I am not sure about "Chu-Criterion for small antenna" and I could not comment on it.

From what I see, bigger space to store energy should improve the bandwidth. A dipole antenna has wider bandwidth than a typical patch because it has more space. An oval shaped antenna even has wider bandwidth because it occupies even more space.

Regarding tuning network, it can make a structure wider bandwidth or narrower bandwidth. It really depends upon how you make it. In fact, for any passive structure with no matter how little radiation, as long as Re(Zin) > 0, you can find a response of a passive network to make its bandwidth to be infinity. However, you may not be able to synthesize the passive network because it normaly is an anti-phase element over a very wide frequency range or the ANG(S21) is increasing with frequency. A normal passive network's ANG(S21) is decreasing with frequency except near resonances. The difficulty to synthesize a network with increasing ANG(S21) in a wide band is not smaller than tuning an antenna element for wider bandwidth. Regards.
 
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