A Zeroth-order Resonant Antenna with Bandwidth Extended by Merging the Zeroth-order Mode with the First-negative Mode

In this paper, a novel miniaturized antenna based on Composite left/right handed (CRLH) transmission line theory with bandwidth extended is presented. The proposed antenna is constructed by two CRLH unit cells, and feeding by the copalnar waveguide (CPW). The dispersion diagram of CRLH unit cell is studied in this paper, for the purpose of further miniaturization, left-hand area of the dispersion diagram is considered. When the antenna is design as open end transmission line by two unit cells, the zeroth-order resonant (ZOR) mode and the first-negative order resonant (FNOR) mode will be excited simultaneously. After we removed one side ground plane of the CRLH unit cell, the slope of dispersion diagram increased, thus, the ZOR mode and FNOR mode could merge with each other. As a result, the bandwidth of the antenna could be extended. Moreover, since we remove one side ground plane, the unit cell occupies a smaller area, then miniaturization could also be satisfied. The antenna is designed on a 1.6 mm thick FR-4 substrate with a relative permitivity of 4.4 and loss tangent of 0.02. The overall size is 16 x 24 x 1.6 mm(3). The proposed antenna is fabricated and measured, the measurement results have a reasonable agreement with the simulation results. From the measurement results, the bandwidth of the proposed antenna is 2.30 GHz to 2.53 GHz, the relative bandwidth is approximately 9.5%. And the peak gain is around -3 dBi in the operating band. Good radiation characteristic is obtained. Due to the small profile and operates in the ISM 2.45 GHz band, the proposed antenna can be used in several mobile wireless communication systems such as WLAN, RFID system and so on.