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Printed Wideband Balun

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freqzt

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wideband balun

Hi all,

I've simulated a equiangular spiral antenna. The antenna bandwidth is 50 MHz - 5 GHz, and the impedance is around 200 ohm. As you know, this antenna is include in a balance antenna category. I want to feed this antenna using unbalance cable. The problem is, how to make a wideband balun using microstrip. I've found a literature about it, and the link is here. But I still can't to figure it. Does anyone can help me to design a printed wideband balun with the above constrains?
 

It's not verifiable, that the balun design suggested in your literature is actually operational as such in the lower frequency range. Measuring two baluns back-to-back proves nothing, unfortunately. You have to use a single balun and correct differential (and additional common mode) termination to check the real characteristics with a VNA.

In my opinion, it's obvious, that a balun for e.g. 100 MHz must either have large dimensions or use a magnetic core (a transformer). I'm sure, that a printed balun without a core isn't feasible for the intended frequency range.
 

Hi FvM,

Thank you for your answer. Could you give me the example of balun that using magnetic core? If the balun using magnetic core, is it can fulfill the bandwidth requirement?
 

Hello,

You should be able to design in Multilayered Broadside CPW Coupled-Line Balun for wideband (using AWR MWO)...

See the attached paper...


---manju---
 

The said multilayered design is said to have a bandwidth of 2.45 +/- 0.65 GHz. Although it offers considerable improvements above simple microstrip, it can't be a solution for the requested low frequency range. One may doúbt if the specification is feasible at all.

I can't answer your question, if and how a balun with magnetic core can achieve the high frequency specification. Possibly a transmission line transformer design. Or a combination of a transformer for the 50 MHz .. 1 Ghz range and a transmission line balun for the high frequency range.
 

This is a tough one. 10:1 bandwidth is not impossible. but the problem is the low frequency of 50MHz.
At such low frequency, you wont want to use planar structure as the size will be very very big. Yet when using lump elements don't allow you to reach the higher frequency portion.
 

In your opinion, what is possible solution to make a wideband balun?
 
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