A new broadside-offset coupler using CPW and microstrip lines

A new passive MMIC structure, the Broadside-Offset Coupled CPW-Microstrip Coupler (BOC-CPW-MS) is introduced using the multilayer, uniplanar MMIC technology. Computer simulations and large scale measurements are presented. The control of the coupling in the 2-30 dB range with 60-80% bandwidth at 30 GHz center frequency is shown in this paper. Introduction Different coupler structures have been presented already in earlier papers: in [1] the CPW line was realized on the second metal layer, only strong coupling was achieved. In [2] three metal layers were necessary to realize the coupler using broadside coupled Thin Film Microstrip lines. The authors in [3] presented resonators, using CPW lines in the multilayer structure. In our work we deal with the coupling between the CPW line (realized on the first metal layer) and the microstrip (MS) line (realized on the second metal layer). The coupling in our version can be easily controlled with the distance of the microstrip line from the CPW one (offset, see Figure 2.). We consider this structure as an original one. For computer modeling first we used Sonnet´s Em (commercially available 2.5 dimensional structure simulator) [4]. Accuracy test had been carried out on single CPW lines to find the necessary numbers of subsections for getting accurate results in the fastest running time. To get better than 1% accuracy for the characteristic impedance of the line taking 15-20 subsections was necessary over the line width, this took about a 10 minute running time at one frequency by a HP9000/730 workstation.