Abstract
Communications require the separation of the transmitted and received signals, which can be made by using ferrite materials for its non-reciprocity. When an external DC magnetic field is applied, the magnetic dipoles will align with the DC magnetic field. Right-hand and left-hand circularly polarized waves will experience different effective permeability and then have different propagating constant, resulting in the non-reciprocity. A stripline circulator is developed by using the ferrite material of yttrium iron garnet. The geometry of the central stripline is optimized for its insertion loss and bandwidth. In this article, a circulator was developed for 4G LTE communication band 3 of 1710 - 1880 MHz. With a maximum insertion loss of -0.35 dB, minimum reflection and isolation of -20 dB, the bandwidth of the developed circulator is 384 MHz, much better than the required value of the 4G band 3. We also have done the theoretical analysis at the same time and give explanation to broad bandwidth. Base on the previous experience, we set a design procedure of stripline circulator for different frequency ranges and successfully design a stripline circulator for another frequency range by following the procedure. Finally, we’ve proposed a way to decrease the applied DC magnetic field in the circulator and keep the working bandwidth simultaneously through researching the effect of magnetic properties of the YIG.