A new technique to estimate the effective bandwidth of the asymptotic waveform evaluation (AWE) method is proposed, which guarantees the reliable application of AWE in a certain region. Furthermore, based on the effective bandwidth estimation, we develop a novel broadband AWE method, which is an extension and improvement of the conventional AWE method. The new method selects the multiple expansion points automatically by a simple compare algorithm and then implements the AWE process on every expansion point, thereby expanding the variable bandwidth of the AWE greatly. The variable here can be frequency, structure dimension, material parameter, etc. In the end, two examples of parameter extraction of microwave structures are given, which demonstrate that the new method has high efficiency and good accuracy in a broad band. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.