H. Oraizi, OPTIMUM DESIGN OF MULTIHOLE DIRECTIONAL-COUPLERS WITH ARBITRARY APERTURE SPACING, IEEE transactions on microwave theory and techniques, 46(4), 1998, pp. 331-342
A numerical procedure based on the method of least squares is presente
d for the optimum design of multihole directional couplers with a spec
ified number of apertures and their arbitrary spacing in a desired fre
quency band for a given coupling coefficient (C) together with maximiz
ation of the mean value of isolation (I) or equivalently directivity (
D) across the band and also specified values of (C) and (D) (or equiva
lently isolation I), An error function is constructed in the band for
optimization of C and D or I, which after minimization gives the best
values of the hole radii and spacing, The proposed method is quite sui
table for computer-aided design (CAD) and has several advantages over
common design methods for multihole directional couplers, such as simp
licity of analysis and development of the numerical algorithm, flexibi
lity of hole spacing, specification of the desired values of C and D o
r I, and actual optimization of the coupler design in the desired freq
uency band. The proposed method is potentially applicable to the desig
n of other couplers.