A Novel Dual-Mode Microstrip Ring Coupler for Low-Cost Balanced Frequency Doubler Application

A dual-mode ring coupler is proposed for balanced frequency doubler application based on the microstrip technology. The proposed coupler can operate in a quasi-hybrid ring coupler mode and a T-junction power divider/combiner mode at two frequency bands with center frequencies of f
₀
and 2 f
₀
, respectively. The operating principle is analyzed, and the design procedure is described. To verify the proposed concept, a 3-/6-GHz dual-mode ring coupler is developed and fabricated. Measured results demonstrate that the proposed coupler achieves good performances with bandwidths up to 20% at both lower and upper bands. The measurements agree well with the simulations. Finally, as an application demonstration of our proposed dualmode coupler, a 19-/38-GHz balanced frequency doubler based on this structure is also designed and fabricated. Measured results show that the conversion loss of the fabricated multiplier is less than 8.9 dB with the input frequency ranging from 17 to 21 GHz, and the minimum conversion loss is 7.3 dB at 19 GHz.