A diversity monopulse antenna is presented in this paper. This monopulse antenna is based on a dual frequency dual mode rat-race coupler that has been designed by using Composite Right/Left Handed (CRLH) Transmission Lines (TL). The device has two input ports while the (Σ) and (Δ) outputs are interchangable at either of the two operating frequencies. In this way the monopulse antenna can work at two different frequencies with two sets of radiation patterns, Σ and Δ. In addition, there is no need of diplexing to separate the (Σ) and (Δ) radiation patterns since these patterns at either frequency are directly obtained at different ports. The dual frequency dual mode rat-race requires that the phase delay of the CRLH lines must be different at either working frequency. As an example of an application, a 950 MHz/1.8 GHz dual-band dual-mode rat-race coupler is shown.
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