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Abstract
A compact directional coupler with high directivity is presented. The coupling passbands characteristics of the multisections coupler which cascades two coupled lines via transmission line are analyzed. In addition, asymmetric coupled line and stepped impedance matching method are used to generate the isolation zero. A 2.45 GHz coupler is designed and implemented. The 3 dB bandwidth of the coupling is from 1.2 to 3.55 GHz with the corresponding fractional bandwidth (FBW) of 98%, and the directivity is better than 20 dB from 0.5 to 3.5 GHz. The proposed coupler presents small size and excellent directivity compared with the traditional parallel coupled line coupler.