how can i design a balun for 50 ohm line??

hello!

i need to design a coaxial balun to produce a balanced output from an unbalanced 50ohm transmission line...
can anyone help in balun deigning????
its urgent
i have no idea


thanxx

There are some preliminar questions you have to answer.
What's your systems frequency?
Is your system narrow or broadband?

Take a look at the book Antenna Theory from Balanis, you will certainly understand better the theme.

Good work.

actually i m designing a balanced antenna for WLAN [2.4 GHz and 5.2 GHz]... shape of antenna is just like dipole. it is fed from center. i just need a balun to feed this antenna with coax....
i think its simple narrow band antenna radiating for above WLAN bands...

It's pretty easy. Make a section of coax long enough that you develop enough inductance on the shield to give you >Zload*10 ohms of input impedance looking into the shield conductor (increasing common-mode impedance). Since you are using a coax balun, the balanced output impedance will be 25 ohms per-side, so use Zload=25 ohms.

Example for 1 GHz.
Zload*10 = 250 ohms
ZL = jwL.... 250 = j*2*pi*1e9*L, so L = 40 nH
Assuming approximately 10 nH/inch of metal self-inductance... 40 nH / 10 nH/inch = ~4" of coax.

At 2.4 GHz you'd need 16.6 nH and 5.8 GHz that would fall to 6.9 nH. Going with the larger value, that would give you a coax of 1.66"+.

The coax can be coiled to make it smaller, and improve the response by increasing the inductance due to the number of turns. Also, you could shorten the coax by adding a ferrite sleeve or looping the coax through a binocular core... again, by boosting the inductance to get Zload*10+.

I commonly use this analysis approach for narrowband solutions, so I'm not sure how well it's preform over an octave. Go to your favorite simulator and mess around with the balun models to see how behaved that design will be from 2.4-5.8 GHz.

ok...brother

thanks..