This paper presents an ultra-wideband (UWB) rectangular ring antenna excited by a circular disc monopole (CDM) with a\r\nconducting rod and two double ridges to radiate bidirectional pattern with constant beam direction along the entire UWB\r\nfrequency range of 3.1ââ?¬â??10.6 GHz. The conducting rod and double ridges at the upper wall of the ring are added to solve the\r\ntilted beam problem at the higher edge frequency whereas the double ridges at the lower wall are used to enhance the impedance\r\nbandwidth. The dimensions of the rectangular ring and the CDM are initially considered to achieve the bidirectional pattern with\r\nthe suitable resonant frequencies and bandwidth. Then, the parameters of copper rod and two double ridges are determined by\r\nparametric study using CST Microwave Studio simulation software. The prototype antenna was fabricated, and the measured\r\nresults show good agreement with the simulated ones. The obtained bandwidth of |S11| < -10 dB can cover the UWB frequency\r\nrange as well as the bidirectional beam radiation with constant beam direction (? = 0?, 180? and f = 90?). The minimum and\r\nmaximum measured gains are 3.1 dBi to 5.3 dBi, respectively. The proposed antenna possesses compact size with good radiation\r\nperformance that can be a promising candidate for UWB applications.
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