Patent ID: 8768993

Claim:
A direct current (DC) compensation method for S-parameter rational functions, the method comprising: reading S-parameters f(sk) which are generated at given frequency sk from a storage unit, the S-parameters indicative of an n-port network; supplementing an S-parameter, which is generated at frequency sk=0, into the S-parameters f(sk) using an interpolation method, upon the condition that there is no S-parameter which is generated at the frequency sk=0; generating an S-parameter rational function according to the S-parameters f(sk) using a vector fitting algorithm; compensating a DC level of the S-parameter rational function to generate a compensated S-parameter rational function, comprising: (a) computing the pole values p m using first formulas as follows: p 2 ⁢ u = u / 100 + j · u s N - s 1 , p 2 ⁢ u - 1 = u / 100 - j · u s N - s 1 , where u=1˜M/2, and M is a total number of the pole values; (b) generating a matrix X: X : [ r 1 … r M d r ~ 1 … r ~ M ] using unknown variables r m , d, and of functions (σf) fit (s) and σ fit (s), wherein the functions (σf) fit (s) and σ fit (s) are shown as follows: ( σ ⁢ ⁢ f ) fit ⁢ ( s ) = f ⁡ ( 0 ) + s ⁡ ( ∑ m = 1 M ⁢ r m s - p m + d ) , σ fit ⁡ ( s ) = ∑ m = 1 M ⁢ r ~ m s - p m + 1 ; (c) substituting the pole values p m and the S-parameters f(sk) into matrixes A and B, wherein the matrixes A and B are shown as follows: matrix ⁢ ⁢ A = [ s 1 s 1 - p 1 … s 1 s 1 - p M s 1 - f ⁡ ( s 1 ) s 1 - p 1 … - f ⁡ ( s 1 ) s 1 - p M … … … … … … … s k s k - p 1 … s k s k - p M s k - f ⁡ ( s k ) s k - p 1 … - f ⁡ ( s k ) s k - p M … … … … … … … s K s K - p 1 … s K s K - p M s N - f ⁡ ( s K ) s K - p M … - f ⁡ ( s K ) s K - p M ] , ⁢ matrix ⁢ ⁢ B = [ f ⁡ ( s 1 ) - f ⁡ ( 0 ) … f ⁡ ( s k ) - f ⁡ ( 0 ) … f ⁡ ( s K ) - f ⁡ ( 0 ) ] ; (d) computing the unknown variables r m , d, and using a formula X=(A T A) −1 A T B, to get the functions (σf) fit (s) and σ fit (s); (e) recording the got (σf) fit (s) as (σf) fit — old (s) upon the condition that steps (b)˜(d) are only executed one time, and computing the pole values p m again using second formulas as follows: σ fit ⁡ ( s ) = ∑ m = 1 M ⁢ r ~ m s - p m + 1 = ∏ m = 1 M ⁢ ( s - z m ) ∏ m = 1 M ⁢ ( s - p m ) , where p m =z m , m=1˜M; (f) repeating steps (b)˜(d), determining if |(σf) fit (s)−(σf) fit — old (s)|<tol, wherein the tol is a predetermined error, and regarding the got (σf) fit (s) as the compensated S-parameter rational function; and storing the compensated S-parameter rational function into the storage unit.