hi, i want to design a 3dB coupler (to be specific LANGE coupler) using microstrip, and hence want to compute w/h and s/h for the same. The laminate which i m using has dielectric constant = 2.94. The first step for the above design is to compute even and odd mode impedance, and from these impedance we need to compute w/h and s/h (width and spacing of microstrip lines). I have searched extensively but most of the work is done for material with dielectric constant = 10 (graphs are available for this value). Please help me with this. :-[