Design realization of an improved high directional coupler with ultra wideband

A novel improved high directional coupler with super wide frequency band was designed in this paper. The device is composed of a coaxial-cable balun and a resistance power divider circuit. The coaxial-cable balun make signals transfer from unbalance to balance, and the power divider redistribute the two signals outputted from the balance ports of coaxial-cable balun. The two sections together realized signals directional transmission. To improve the wideband performance we introduced coupling capacitor design technique and thick film workmanship. The coupling capacitor design introduced into the device can repair the lower frequency response error of the coaxial-cable balun balance ports. The printed resistance can improve the high frequency working performance of the power divider. We firstly emulated the design using Serenade. The schematic model was built using thick film models and coupling capacitor chosen from the passive device library. The simulation results met our expectations that the working band was expanded. Then the assuming was verified in experiments. The directional coupler was tested using vector network analyzer. The test result showed that the novel directional coupler expanded the low work frequency limit to 100 kHz and the high work frequency limit to 40GHz. The directivity in the whole frequency range was larger than 15dB. The directivity was larger than 20dB in low frequency section (100 kHz~45MHz). The thick film also elevated the power capacity and the fighting against static wearing ability. In conclusion, resistance power divider has significant influence on the final character of the directional coupler, effective mend on resistance circuit and fair matching of resistance power divider circuit with coaxial-cable balun are available ways to improve the directional coupler.