How to make a small microstrip balun ？

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hausn

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how to reduce the size of microstrip balun,when it works at 2-6G ,but i just have 25mm ?i have try with the klopfstein taper but its result of s11 seems not good enough. do you have any good ideals?help
 

If you use high di-electric coefficient substrate ( for instance Alumina), the dimensions will be smaller.Marchand Balun can also be used so that it has many variants.
 

BigBoss said:
If you use high di-electric coefficient substrate ( for instance Alumina), the dimensions will be smaller.Marchand Balun can also be used so that it has many variants.
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i use the fr4 as substrate，the result is not well at the2-3G，other higher freq is ok
 

hausn said:
i use the fr4 as substrate，the result is not well at the2-3G，other higher freq is ok
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FR4 is not very much recommended substrate for beyond 1-2GHz even it looks like working.A high quality and high dielectric substrates should be choosen for precise and application specific structures.Balun is one of them because here Gain and Phase balance is important for a proper performance.FR4 has also poor fabrication tolerances and di-electric coefficient shows some variations between manufacturers.
For 3GHz, lambda/4 will be 11.9mm for FR4 ( Er=4.4) substrate, 7.9mm for Alumina ( Er=9.8 ) and losses will be much less than FR4.
 


thanks，but i do not understand why you use lambda/4.may books say balun size should more lambda/2 .
 



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