Design of broadband microstrip‐to‐CPW transition

A broadband microstrip‐to‐CPW transition is presented. In the proposed structure, the upper microstrip ring is vertically coupled to the central conductor of the lower circular CPW via electromagnetic coupling. To obtain a wide bandwidth of operation, a short‐ended stub is introduced. The introduced short‐ended stub combined with the open‐ended microstrip ring constructs a quarter‐wavelength resonator. A sample transition has been designed and measured. Experimental results indicate that over 129% bandwidth with better than 10 dB return loss and below 1.7 dB insertion loss can be obtained.