Investigation of miniaturized ultra-wideband circulator based on composite ferrite

This paper presents the design and implementation of an ultra-wideband ferrite circulator. The main transmission line of the circulator adopts the form of Y junction and quarter-wavelength impedance converter. To extend the lower-frequency operating bandwidth, the design adopts double-Y and single-stub (DYSS) matching technology. DYSS is equivalent to parallel LC resonance and plays the role of reactance compensation. In addition, the composite ferrite (CF) technology is introduced innovatively which broadens the high-frequency working bandwidth effectively. CF effectively improves the magnetic vector distribution in the center of the circulator. Considering the actual magnetization state of ferrite, non-uniform simulation of ferrite is also carried out in this paper. The results of non-uniform simulation are more consistent with the test results. In the operating frequency range of 2.3 GHz-6.5 GHz, the insertion loss is controlled within 0.7 dB, and the return loss and isolation are better than 15 dB. In particular, the circulator has a compact size of 0.37λ₀ × 0.37λ₀ (λ₀ is the free-space wavelength at 4.4 GHz) and an impressive relative bandwidth of 95%, which is rare among its counterparts. This design approach provides a reference for the miniaturization and broadband design of microstrip circulators.