A New Approach in the Computation of Ultrahigh Degree Equal-Ripple Polynomials for 90°-Coupler Synthesis

An improved efficient numerical method for the computation of ultrahigh degree equal-ripple polynomials, necessary for the synthesis of multielement 90° coupler, is presented. The highest degree computed was N=201 with an accuracy better than 10^-20. For the calculation of the impedances of the equivalent stepped impedance filter an optimization procedure is also described. Finally, based on the N coupling factors k_i of the sections, the continuous coupling curve is achieved using spline interpolation. Experimental results of a continuously tapered 8.34-dB coupler constructed in three-layer polyolefin stripline are presented.