In this paper, the effects of a metal plane on the performance of a meandered slot RFID antenna are evaluated in a real environment, and 3 metal plane cases are considered (the most likely scenarios in which metal conductive materials are placed near the tag antenna). The metal plane effects can be categorized as matching degradation and antenna gain variation. First, matching degradation due to the antenna's induced mutual impedance is experimentally investigated. In addition, the gain variation is investigated to figure out the change in the radiation characteristics. With the derived antenna parameters, the read range is calculated with the Friis transmission equation and measured to analyze the effects of a metal plane on RFID system performance. The calculated and measured read range varies from 9.3 m to 19.1 m as the distance between the RFID antenna and the metal plane changes.

In this letter, a novel miniaturization method for 3 dB 90 hybrid coupler is proposed. The proposed structure is composed of a conventional structure with a coupled line section inserted in the low impedance section. The proposed coupler occupies an area of only 9.6% compared to a conventional branch-line coupler, and reveals comparable -parameter characteristics in the operation band. Furthermore, the proposed structure demonstrates a harmonic suppression property due to the a periodicity at odd order harmonics.

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