Millimeter wave (mm-wave) and microwave frequency has become a hot research topic in recent years. Comparing to traditional wireless communication frequency, microwave possesses larger available bandwidth, which is up to tens of gigahertz, so that it can support advanced digital services with ultra-high bit rate. To support the transmission rate over 100Gbit/s in an optical wireless system, forward error correction (FEC) is adopted in real-time communication systems to correct bit errors. Polar code is a kind of FEC which can theoretically achieve channel capacity as the code length tends to infinity. In this paper, we experimentally demonstrate a photonics-aided microwave communication system at K-band. With polar coding, 20-Gbit/s signal is transmitted over 20m wireless link. Our experimental results show that BER performance of such optical wireless system can be improved largely after we employ polar coding.