Study of a Ferrite LTCC Multifunctional Circulator With Integrated Winding

Abstract

This paper shows a study of a new ferrite low-temperature cofired ceramic (LTCC) circulator with integrated winding. The external magnets used in traditional circulators must be strong to overcome the ferrite’s demagnetization factor. The novel circulator presented herein uses an embedded winding within the ferrite to magnetize the material from the inside, thereby significantly reducing the demagnetization effects. Because of the controllability of the bias field, the resulting device is also multifunctional: when the windings are energized by a current, the device operates as a dynamic circulator in which the circulation direction can be changed by switching the direction of the current. If an external magnet is placed on the circulator, its operating frequency can be changed by adjusting the bias current. Unlike other LTCC circulators with external magnets, the proposed device can even operate as a power splitter by removing the bias current. A circulator prototype has been characterized in three states: unbiased, biased by windings, and biased by windings and external magnets. When no current is applied, the transmission of each port is about −5 dB with a return loss better than 20 dB at 14.8 GHz. When a current of 300 mA is injected into the windings, the measured insertion loss and isolation of the circulator are approximately 3 and 8 dB, respectively, whereas the return loss is better than 20 dB at 14.2 GHz. When external magnets are added in addition to a current of 200 mA, the insertion loss and isolation improve to 1.6 and 23 dB, respectively, at 14.2 GHz. The variation of the circulator’s working frequency is 0.6 GHz. This is achieved first by the change of internal magnetization $\boldsymbol {M}$ when current is less than 120 mA, then the heat due to the winding increases the ferrite’s $\mu _{\textrm {eff}}$ , leading to more frequency shifting. The total size ( $L \times W \times H$ ) is $8~\textrm {mm} \times 8~\textrm {mm} \times 1.1$ mm.