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Sonnet User's Guide - Sonnet Software

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<strong>Sonnet</strong> User’s <strong>Guide</strong><br />

For evaluation on a computer, a polynomial for K(k) is available in Abramowitz<br />

and Stegun, Handbook of Mathematical Functions, pp. 590 - 592. (Be sure to<br />

note the errata, m1 = 1-m2, not 1-m.):<br />

b<br />

w<br />

k<br />

η 0<br />

Z 0 ε r = ----- Kk' ------------<br />

( )<br />

4 Kk ( )<br />

π<br />

= tanh -- w ⎝<br />

⎛ 2<br />

--- b⎠<br />

⎞ k' = 1 – k 2<br />

η 0 = 376.7303136<br />

The expression for K(k) cited above provides an accuracy of about 1 x 10 -8 . When<br />

programmed on a computer, the following values are obtained for three different<br />

transmission line impedances (unity dielectric constant):<br />

Table 1 Stripline Benchmark Dimensions<br />

Z 0 (ohms)<br />

w/b<br />

25.0 3.3260319<br />

50.0 1.4423896<br />

100.0 0.50396767<br />

For a length of stripline, there are two parameters of interest: characteristic impedance<br />

and propagation velocity. With the w/b given above, we know the exact answer<br />

(to within 1 x 10 -8 ) for Z 0 . With a dielectric constant of 1.0, we also know<br />

the exact answer for the propagation velocity. It is the speed of light, known to<br />

about 1 x 10 -9 . Any difference from these values is error, or, DMAC.<br />

340

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