Automatic generation of passive equivalent circuits for broadband microstrip antennas

In this paper, we propose an efficient method for extracting passive equivalent circuits of broadband antennas. To fully automate the extraction, the vector fitting in B. Gustaven and A. Semlyen (1999) is modified such that the order of the rational approximation can be determined automatically for a given error bound. Then, the approximation is corrected by quadratic programming for enforcing passivity. The passive model is further synthesized by RLC components using algorithms in G. Antonini (2003). As a result, simulated or measured frequency responses of a broadband antenna can be fit with minimum fitting error over a wide range of frequencies.