Optimim design for a broadband microstrip balun

The letter reports calculations of Marchand balun performance which show that bandwidths approaching 50:1 (for a V.S.W.I.¿2:1) should be achievable with overlaid microstrip structures. The bandwidth limits (¿8:1) reported by previous writers appear to reflect only the inaccessibility of the true optimum to the semiempirical design methods used and the limitations of fabrication on single-thickness card. Preliminary experimental results confirm the theoretical indications.