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A wideband printed antenna with unidirectinal radiation characteristics

Aiming to achieve wideband and unidirectional radiation, a planar printed antenna with two closely spaced strips is proposed and fabricated. This antenna consists of a printed rectangular loop and two metallic strips. The rectangular loop has a good direction but has a drawback of narrow band. According to the closely spaced loading theory, the impedance at the upper frequency will decrease when the two metallic strips is placed at the maximum radiation direction of the rectangular loop. This improves the impedance matching. Thus the impedance bandwidth is greatly expanded. In order to demonstrate the effectiveness of the double strips, a prototype of the antenna is fabricated and tested. Experimental results show good performance of the proposed antenna. It has a 62.7% measured bandwidth, ranging from 2.29 to 4.38 GHz. The measured F/B (front-to-back) ratio is larger than 8 dB in the whole frequency band.