According to super minimal electronic product technology development, the illegal usage and theft from domestic of minimized electronic device such as semi-conductor, USB memory chip and etc., has been issued. These devices are frequently used for the illegal purpose such as hidden wiretapping, hidden camera, bomb and threat of terror [1]. Many countries including the United States have been developed steadily Non-Linear Junction Detector (NLJD) system which searches the hidden small device such as semi-conductor without metal and with oxidized metal for solving this problem. The NLJD system performances are mainly determined by an antenna gain and power, even though various functions of the NLJD devices exist to realize high performance. In order to minimize the effect of power reduction by coupled wave from the hidden device, circular polarization (CP) antenna has been mainly used for NLJD system application [2], [3]. In this paper, authors designed the spiral antenna with archimedean slit ground structure to realize the circular polarization. The gain of spiral antenna proposed by reference [2] had been decreased due to multi resonance characteristics. In order to solve an above problem, authors has proposed triple band spiral antenna that it is improved antenna gain, axial ratio and return loss by the optimum spiral turning number design. A proposed antenna has small size and a few turning number with comparison of reference [2]. Narrow bandwidth problem at interested band of reference [2] has been also solved by the optimized feeding position design.
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