Differential to common mode coupling in microstrip lines; calculation and improvement

Differential signalling thru parallel printed lines has been recently focused because of its low noise transmission characteristics. But differential to common mode coupling is occurred due to any discontinuities in the structure. The coupled line structure can not be analyzed using microwave conventional simulating soft wares directly since the ports are too close to have good accuracy. And this accuracy is needed since the coupling is not a large value. In this paper, the even and odd modes of propagation and their mutual coupling are calculated using generalized two dimensional MOL. A technique is introduced to overcome the problem of close ports in simulation. And finally, a method for decreasing the odd to even mode coupling and improving the transmission characteristics are presented.