Bandwidth of Transmission Lines

Hello,


How to calculate the bandwidth of "TRANSMISSION LINES", In many books, the formula for calculating the bandwidth of antennas is given, Please let me know how to calculate the bandwidth of STRIPLINES AND MICROSTRIPLINES, Is there any specific formulae ? Also, I have constructed a stripline to microstrip transition with a good return loss of 20dB and insertion loss less than 1dB. How to calculate the Bandwidth of the transition, Please help.

Regards,
Avi

Transmission lines don't have bandwidth, instead they have "cut-off" frequency.The cut-off frequency is defined as attenuation level of the transmission line at certain frequency for a defined length,let's say 50dB@10GHz for 100m etc.
That means, beyond this frequency and length it's not practical to use this transmission line whatever type is..
But in practice MS Lines have very high cut-off frequencies and they can be used up to few tenth of GHz on low loss substrates.

Either how you determined these values, by simulation or real measurement, you surely know, that they are frequency dependant. If you simulate/measure the loss values for higher frequencies, you'll know the "bandwidth".

Hello, Please explain, I am sorry, I did not get the answer, If transmission lines do not have bandwidth, then why does pozar text book on page 174 chapter 3 -transmisson lines and waveguides gives the comparison between different kinds of lines and compares the bandwidth of each of these lines.

Secondly, If percent bw is calculated as fh-fl/fc * 100% ?, then what will be the bandwidth at s-band (2-4 Ghz) ? Because th transition model which i have constructed has 3 and 4ghz as start and stop frequency with solution freq. of 3.5ghz. that is, i have plotted the response of s11 v/s freq. in this range. Now what will be the bandwidth ?

Regards,
Avi

because you took pozar's comment out of context without acknowledging the comments around it.
see the response you got in the microwaves 101 forum where you also asked this same Q

as was also commented in the other forum.... cutoff freq and moding is of more concern in a given transmission line at a given freq.

Dave

I like rectangular waveguide the best. It can easily pass signals up to thousands of GHz! Hard to beat that for bandwidth!

A rectangular waveguide has a lower frequency limit and will block signals below that cut off frequency.