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Yagi-Uda antenna slot placement

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turuk

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Hello all,

I wanna ask what happens if i put L shaped slot at the ground of this type Yagi-uda antenna shown in figure.(1st picture is the antenna w/o slots, other one shows the places of slots-a bit primitive yea :lol:) I've never seen any paper that uses slots at the back of 180 degree phase delay but when i tried, i get better sparameter results.

Is there any reason why this design is not used?

Would be appreciated if u answered, thank u :)

balun.png

slot-balun.png
 

I've never seen any paper that uses slots at the back of 180 degree phase delay but when i tried, i get better sparameter results.

Funny idea, what is the idea/concept here? What is the phase difference at the two arms with/without your slots? Ideally you have -3dB and 180° without the slots, and can't get any better than this.

I guess you have created a phase/amplitude imbalance, with will result in a tilted radiation pattern.
 
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    turuk

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I wanna ask what happens
if i put L shaped slot at the ground of this type Yagi-uda antenna shown in figure.
Equivalently series discontinuity composed of Resistance//Reactance.
Resistance is due to back-radiation.

I've never seen any paper that uses slots at the back of 180 degree phase delay but when i tried,
i get better sparameter results.
S11 seeing from feeding point might be improved for effect of Resistance//Reactance.
However Resistance causes loss.

Is there any reason why this design is not used?
Loss due to back-radiation.
 
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    turuk

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how can i find the phase difference? Im using CST.

Simulate the microstrip part (without the antenna part) as a 3-port, and look at difference between S21 and S31.

coupler.png
 
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    turuk

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    turuk

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thank u so much for clear explanation.

- - - Updated - - -

Thank u so much for the recommendations. Since i am new for antenna design, i thought this balun type would be easy to design cuz there are so many documentations and detailed explanations about how to make it. I saw other balun designs but seem complicated to me so I was kinda afraid to go with those ones. However, i will definitely try them.

Based on your experience, can u recommend me directional antenna type other than yagi? Cuz i thought printed yagi is directional but i ended up w/ low gain and radidation pattern is not very good also.
 

The reason could be that the printed balun dimension is greater (or comparable) with the elements of the Yagi antenna.
I know, there is some ground involved, but I found that the solutions presented in the links above works much better, and with less headaches..
 

This printed Yagi has been around for about 25 years. Was first presented in an issue of Applied Microwave & Wireless magazine.
Myself I never got decent antenna pattern results with this printed Yagi, and the reason is the printed balun.
I recommend to use for feeding the printed Yagi the approach used in the links below:


https://www.hindawi.com/journals/ijap/2012/612170/fig1/
https://www.ti.com/lit/an/swra350/swra350.pdf?ts=1587932817601


Thank u so much for the recommendations. Since i am new for antenna design, i thought this balun type would be easy to design cuz there are so many documentations and detailed explanations about how to make it. I saw other balun designs but seem complicated to me so I was kinda afraid to go with those ones. However, i will definitely try them.

Based on your experience, can u recommend me directional antenna type other than yagi? Cuz i thought printed yagi is directional but i ended up w/ low gain and radidation pattern is not very good also.
 

Printed Yagi antennas may have lower gain compared to their non-printed equivalents.
An option to get a good gain, and narrow beamwidth is to use a linear array with patch antenna elements (at least 8 elements).
For a single broadside beam (perpendicular to the axis of the array) the antennas need to be fed with equal amplitude and the same phase, which may not be very complicated.

https://www.scielo.br/scielo.php?script=sci_arttext&pid=S2179-10742017000200460
 
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    turuk

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Hi Turuk,

I always liked the quote that was attributed to Einstein and went something like this: "If we knew what we were doing we would not call it experimenting."

Simulate it both ways, or even better, build two versions in hardware to see if something useful happens. Then go on to see if you can figure out what is going on and how to control the effect.

I would be careful about improved s parameters. Just because less energy is being reflected, that does not mean that more is being radiated. Improved s parameters most often are a consequence of increased internal loss. S parameters are more easily measured.
 

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