Spiral transmission-line baluns for RF multichip module packages

We describe a design method and lumped model for a circular spiral transmission-line balun. All lumped values are extracted from the geometric parameters of the balun. From simulation, the design parameters with well predicted characteristics are defined. The balun is fabricated using multi-chip module processing technology, which is suitable for integration in RF packages. Measurements show a wide bandwidth of 1.5-4.1 GHz and excellent balanced outputs. Amplitude imbalance less than 0.5 dB and phase imbalance less than 4/spl deg/ are achieved. The simulation results are compared with the measurement. The model captures all important properties of the balun with reasonably high accuracy.