Abstract-Two opposite uni-directional radiation bands with good circular polarization (CP) characteristics are achieved in an Archimedean Spiral Antenna (ASA). A sandwich configuration is formed by utilizing two resonance based reflectors (RBRs) at the bottom and top sides of the ASA. Owing to the resonance characteristic, the RBRs do not act as reflectors at the other operational band, then, opposite uni-directional radiations are obtained, and the two uni-directional bands can be tuned independently. The proposed ASA with two uni-directional bands (ASA-TUB) has a wide impedance bandwidth about 4.4 : 1 (1.8-8 GHz), while its front-fire band (FFB) ranges from 1.8 GHz to 2.2 GHz (20.0%), and its back-fire band (BFB) is 4.4-7.1 GHz (46.9%) for front-to-back ratio (FBR) larger than 5 dB. The maximal FBRs for the FFB and BFB are 11.3 dB and 20 dB, respectively. Moreover, good CP performances are also obtained for the FFB and BFB. Besides, the whole profile of the proposed antenna is only 0.16λ at the lowest operational frequency. The proposed antenna has the properties of dual opposite uni-directional radiation bands, low profile, good FBR and CP.