A compact directional coupler with high directivity using ferrite cores

In this paper, a wideband directional coupler is proposed for high-power applications, which is composed of a transformer and lumped elements. The introduction of the transformer greatly improves the directivity of the coupler. The measurement results demonstrate that the proposed design has an excellent return loss (>17 dB), small insertion loss (<0.4 dB), and high directivity (>22) over a wide frequency band (10-350 MHz). Meanwhile, it can achieve a flat coupling level of 32 dB with the imbalance less than 0.5 dB.