Design of broadband lumped element baluns

Paper in proceeding, 2004

This paper reports on a small size broadband lumped element balun suitable for integration in MMICs. The design is an extension of the well known lattice balun, which independent of frequency has 180 degrees phase difference between the output ports, but suffers from a narrow amplitude bandwidth. It is shown how the amplitude bandwidth of the lattice balun may be improved by replacing inductors with low-pass T-sections, and the capacitors with high-pass T-sections. Scalable closed-form design equations for various bandwidths are derived. To validate the concept a prototype operating at 1 GHz has been fabricated with SMT chip components soldered on a PTFE laminate. It exhibits amplitude balance better than +or-0.25 dB and phase balance better than +or-8 degrees , over more than one octave bandwidth. The effective chip-area is 7*9 mm/sup 2/