
Network Synthesis and Realisability 513
Limits
Sign of P
0
(x) Sign of P
1
(x) Sign of P
2
(x)
Sign Changes
x = 0 positive negative negative 1
x = ∞ positive positive negative 1
Therefore, overall sign changes = 1 − 1 = 0.
Since there is no overall sign change, the given function is a PRF, that is, positive real functions.
12.4 SYNTHESIS OF NETWORKS BY FOSTER’S
AND CAUER’S METHODS
The Foster’s method of network synthesis uses the partial fraction expansion of the driving point
immittance function. Foster is of two types: Foster form-I and Foster form-II. When the driving
point function is an impedance, it is referred to as Foster form-I. Foster form-II ...