UWB asymmetric multi-section directional coupler with improved directivity

An ultra-wideband (UWB) asymmetric multi-section directional coupler is proposed and demonstrated. In order to obtain broadband frequency response an asymmetric offset parallel-coupled strip transmission line coupler has been chosen. The influence of discontinuities in the regions of coupled and transmission line connections, as well as intersection connections, has been taken into account in the design stage. The proposed procedure allows to achieve a very significant improvement, particularly for the directivity and return loss characteristics by using the recently developed capacitive compensation technique to compensate the parasitic reactance associated with the discontinuities. A 15-dB coupler over the frequency range from 2 to 18 GHz is designed, fabricated and measured. The compensation technique has been applied for the design of directional couplers with the coupling value of 15 dB. Design consideration and simulated as well as measured results are presented and discussed.