I am learning multiband and metamaterial based patch antenna designing on HFSS. Kindly guide me how to achieve 50 ohms matched condition while designing. What is the feed line calculation procedure? Is there any other method as well to get 50 ohm impedance matched condition?
The patch antenna usually is fed at the end, and this typically yields a high input impedance. In order to reduce the input impedance, the patch antenna would be better to be fed closer to the center since the current is higher closer to the center. One method of doing this is by using a inset fed (I believe this technique must be discussed in Balanis Antenna book).
It can also be matched to a 50 Ohm transmission line by using a quarter-wavelength transmission line. This technique, however, will have narrow bandwidth. In order to increase the bandwidth, you have to use a multi-section transformer (read section 5.5 - 5.8 of Pozar Microwave Engineering book).
Finally, these are some hints, and you would find different techniques of feeding a patch antenna in different antenna books such as Stutzman Antenna Theory and Design. However, let me know if you have any more questions, and I hope that I have answered your question well enough.
Thank you Mohammad Mousavi.
I have one more clarification, in order to miniature a printed antenna, we go for various odd and unique designs. In this case it is difficult to go for center fed (inset feeding). So is there any other way to achieve good impedance matching? In few paper and commercial antennas I have observed 50 ohms matched feed line in the design. Do you have any idea on feed line dimensions or anything related to get the matched condition?
You may use probe fed microstrip patch antenna. For calculating feeding point, you can use the formula as given below :
Yf=W/2
Xf=L/[2*sqrt(Ereff)]
Where Xf, Yf are feeding points
W-Patch width
L-Patch Length
Ereff-effective Dielectric Constant of patch
Further, these parameters can be calculated using Section 3.8 Microwave Engineering by Pozar https://www.google.co.in/url?sa=t&source=web&rct=j&url=http://hasanahputri.staff.telkomuniversity.ac.id/files/2016/09/Microwave-Engineering-2nd-Ed-David-Pozar-OCRed.pdf&ved=2ahUKEwijodCN9OrZAhXJa7wKHQwKBmYQFjALegQICBAB&usg=AOvVaw1jtK4fIQWHmqCPPZU3LkBh
Hope this helps, let me know if further queries.
Thank you Neeresh Kumar, I will go with the procedure and if there is any confusion I will post the query .
Hi Mohammad Saadh:
You can easily match your antenna to a 50 Ohm line using a quarter-wavelength transmission line (QWT), and the dimensions depends on the input impedance of your designed patch antenna. As I said this technique would be really narrow band since you are using one section of QWT, and it only matched at the single resonance frequency. As far as I understand from your design, I recommend using a multi-section transformer such as taper line would be better. But still it is just a recommendation, and you should find the best matching for your specific design. Do not hesitate to ask more questions if you have any.
Bests,
Mohammad.
Assume patch antenna is operating in TM_10, then at centre of patch the impedance of the patch antenna is zero and at the edge of the patch the impedance is maximum ( near about 200 ohm practically). So you can optimise the location of feed point between centre and edge along x-axis where the impedance is 50 ohm. Please check slide no.17-21 from attached ppt
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