A Practical Method for Wideband Matching of Antennas Based on Filter Design Techniques

This article shows several practical improvements on impedance matching methods based on modern filter network theory. New conclusions about matching have been obtained using the Bode-Fano limit, adding frequency-independent reactances (FIRs) to the formulation for the first time. Moreover, a matching limit can be obtained analytically before building the network, thus providing a performance limit in advance. A lumped network is obtained analytically as a first attempt with the reflection coefficient bounded between two limits with equiripple behavior for a maximum bandwidth. Then, this network model is modified by adding frequency-independent reactances (FIRs) to provide a better match even for asymmetric responses. The lumped network is converted into a distributed network where the dispersion of the lines is accounted for. The next improvement is the conversion into an electromagnetic model, where dispersion is also considered in the inverters modeled with irises. Three examples with increasing bandwidths are considered, and a manufactured prototype is measured to test the good behavior of the proposed matching method.