Integration of devices is a trend of modern RF front-end design. To shrink the required area and enhance overall performance, the passive components can be co-designed into an antenna to deliver a so-called multi-function antenna, possessing not only the function of radiation but also filtering, impedance matching, and/or balanced-to-unbalanced transforming. In this paper, we presented the design of such a multi-function antenna based on a typical filter synthesis process. In the approach, the antenna serves as the last-stage resonator and load of a filter, while circuit resonators embedded in the antenna structure behave as the filter's front stages. Without increasing circuit area and sacrificing antenna gain, the accomplished antenna exhibits better band-edge selectivity and flat passband response. Several design examples will be addressed.