This paper presents an analysis of a stripline Archimedean snail antenna on its impedance properties and radiation mechanism. The Archimedean snail antenna has similar structure to the spiral one but with asymmetric spiral turns on arm structures. Power can be transmitted from stripline mode to spiral radiating mode because of impedance matching between the two transmission line structures, i.e., stripline and parallel elevated slot-lines. The radiation occurs when the two elevated slot-line modes are in-phase, namely, common mode radiation. A design process can then be developed by impedance matching for the stripline Archimedean snail antenna. A compact (45mm × 40mm × 1:016mm) stripline-fed snail antenna is fabricated for demonstration. The measurement shows a good agreement with the simulated result from 2 GHz to 20 GHz. The snail type antenna has better performance than the spiral antenna due to its radiation mechanism. Compared to the traditional spiral antenna, this antenna design is a completely planar antenna, which provides a platform for integration of impedance matching circuits or other circuit elements easily inside the antenna structure without additional need of wideband balun and matching circuit designs.