This paper presents field experiments on open-loop transmit diversity in downlink OFDM based radio access conducted in a measurement course in Yokosuka city near Tokyo. The experimental results obtained under actual propagation channel conditions show that Space Frequency Block Code (SFBC) and the combination of SFBC and Frequency Switched Transmit Diversity (FSTD) (or Cyclic Delay Diversity (CDD)) are the most promising open-loop transmit diversity schemes for two- and four-antenna transmission, respectively, from the viewpoint of the required average received signal-to-noise power ratio (SNR).