The World Radiocommunication Conference 2007 meeting (WRC-07) [1] decided to use the 3.5GHz frequency band for IMT-Advanced. This follows the trend to use the microwave band for the mobile communication systems. Broadband transmission and the use of high frequency bands make covering the service area difficult due to propagation loss, feeding loss, etc. To address this, the usage of small cell attracted lots of attention. On the other hand, a dual-band configuration is effective in reducing the number of antennas at the base station establishment sites. One technique of the dual-band configuration is the using of parasitic elements for target high frequency band. An omni-directional antenna required multiple parasitic elements in same horizontal plane. But the deviation of radiation characteristics degrade because of the asymmetry in horizontal plane of antenna structure.
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