Design a Yagi with 4 to 1 Balun
I'm designing a Yagi antenna with a folded dipole as a radiating element. Now I've designed a 4 to 1 Balun which transforms 200 ohm to 50 ohm.
Now, the situation is: the simulation of both separately gives good results at 53MHz but whenever I design and simulate it together it gives s11 at 68.2MHz.
What kind of Balun have you designed ? Double Aperture Ferrite Core ?
A lambda/2 transformer..https://www.marcelpost.com/wiki/imag...Coax-balun.jpg
-Input Impedance of Yagi antenna is really 200 Ohm ? Or a bit mismatch is observed ?
-Have you ever checked Phase Balance of the Balun ? How did you simulate it ?
Can you post your simulation results ?
Hi,
Yes,the i/p imp. of a Yagi antenna is around 200ohm, I guess.I'm going to attach the pic.VSWR=1.0031.
Now for the second part of your question, what is phase Balance and what it tells us? And I think it'll be faster and easier if we communicate over mail.
You also should check the Phase balance/imbalance of the Balun.Because The Input/Output Impedance of the Balun may be good but Phase balance between the Differential Ports may not be fine.
In order to check this, Balanced Ports of the Balun should be terminated by 2x 100 Ohm Port and other Single Ended Port is terminated by 50 Ohm as usual.Then check s-parameters' Magnitudes and Phases. Magnitudes should be as low as possible ( less reflection loss), Phases should be as close as possible to 180 Degree between P1(SE) and P2 (D1) and P3 (D2) at the mid-band frequency.
Yes,I've terminated the balanced side by 200ohm and the other by 50ohm...The magnitude of s-parameters seems good but phase...just look at it...
By the way,now I'm getting the result of "both-combined" i.e,yagi with the balun around 53mhz but the efficiency is pretty bad(around -3db) and gain is not so high(5.8).I'm attaching those pics too.
Phase of S21 and S31..
I've 2 ports..one for differential..
Your methodology is not so correct.You have to do EM simulation with 3 ports in order to obtain 3-port s-parameters.Each port will have standard 50 Ohm .
After obtaining this 3-port s-parameters, you should do a schematic simulation in a any RF simulator by connecting 50 Ohm Port to Single Ended side,100 Ohm to Differential Side for each
So you will obtain practical operating condition for your Balun.Then you have to check S11,S22,S33 Magnitude in dB, S31,S21 Magnitude and Phase
I hope you understand.
Hey,
Good suggestion..actually I completely forgot about the 180 phase-shift at the differential end but I'm wondering how can I design i.e. how to create 2 differential ports for 3 ends?
The impedance of a folded dipole is about 300 ohms..
http://www.radio-electronics.com/inf...ded_dipole.php
try searching for "Ruthroff baluns"
Yes, that is correct, but when put into a Yagi, as the OP is doing, its impedance drops significantly
the 200 Ohm figure is quite a common figure used and a 4 : 1 balun to get to 50 Ohms
That said, I have read comments in days gone by that spacings and numbers of elements significantly affect the feed impedance
to the point where is can drop well below 200 Ohms
Dave