Could someone please elaborate on this example. I don't see the equations as they relate to LCOUP and NA. Also, how do you set a tuning variable to integer? I am trying to design a coupler that has different turns ratios for the two transformers and I need to be able to set the coupling factor and determine the turns ratios of the two transformers. Can someone tell me how the equations were setup in this example to do this?

The secret of broadband transformers is as follows. The inductance of the windings must be large enough that the reactance is several times the terminating impedance. This factor limits the low frequency response. The inductance of the windings must be low enough that the leakage inductance created by finite winding coupling (k) is small with respect to the terminating impedance. This limits the high frequency response and is best improved by tight windings and good magnetic core materials. Winding coefficients above 0.95 are achieved only with careful design and test.

I'm not sure I understand your questions because they seem to be answered by the equation block itself. If you do not see the expressions for Lcoup and Nb, you might reload the example from your original disk, in case someone has modified the equation block. Here is what the original equation block looks like:

R1=?50

C1=?0.01

Lpri=100

Lcoup=?7

Na=?5

Nb=Na*SQR(10^(Lcoup/10))

Nb=FIX(Nb)

Lsec=Lpri*Nb*Nb/Na/Na

In the example, the user enters R1 and C1. Ideally, R1 should equal the termination resistance and C1 should be zero. That's where you should start. In real couplers, due to leakage and other factors, modified values for R1 and C1 may yield better results. When you get close, experiment with (or optimize) these values to improve the specifications you are interested in.

Next you specify the primary inductance in nanohenries. This will set the low frequency response. As small a value as possible, that achieves the desired low frequency response, should be entered.

Next enter Lcoup, the desired coupling value in dB. Because line 7 converts Nb to an integer, as the coupling value is tuned, the displayed responses will not change continuously, but will jump when Lcoup is tuned to reach the next interger value for Nb.

Na is the number of turns for the primary. This parameter and the characteristics of the core material will determine the inductance of the primary. So Lpri and Na are actually dependent parameters. If Na is small, the integer function will cause large steps in available coupling values. If Na is large, it is difficult keeping parasitics low and the high-frequency response will suffer. This example models the impact of the coupling coefficient, k, but not winding stray capacitance. You may add stray capacitance to the schematic to match measured results. Stray capacitance will modify the high frequency responses, paraticularly yhr RL and directivity.

I hope this helps. Of course, the best learning tool is to experiment with the input parameters and watch what happens.

Clear skies and high Q