Design of high-power folded substrate integrated waveguide circulator

Background The ferrite circulators are essential nonreciprocal components for achieving transmit-receive isolation in radio frequency (RF) systems. As airborne and missile-borne communication and radar systems evolve toward higher frequency bands, higher integration, and greater power, the power capacity and physical dimensions of circulators have become key metrics that constrain the performance of RF front-ends. Conventional waveguide circulators suffer from bulky volumes and are difficult to integrate with planar circuits. Substrate integrated waveguide (SIW) technology provides a promising approach to realize planar microwave components with reduced footprint while retaining high-power capacity. However, it is still a significant challenge for SIW circulators to achieve miniaturization and high-power capacity simultaneously.

Purpose This paper aims to design a compact folded substrate integrated waveguide (FSIW) circulator while maintaining high peak power capacity (PPC) for X-band applications.

Methods The proposed circulator adopts a compact FSIW transmission line, and the FSIW forms a closed-like waveguide cavity through the upper and lower metal layers and the metallized through-holes, thereby enhancing the power capacity of the circulator. A ferrite disk is loaded at the center of the three-port junction to realize nonreciprocal wave propagation. The power handing capability of the FSIW structure is analyzed, and the FSIW circulator is designed and verified through full-wave electromagnetic simulation. Key performances including insertion loss, isolation, return loss, and peak power capacity, are evaluated.

Results The simulation results show that within the frequency range of 7.88-9.20 GHz, the insertion loss of the circulator is less than 0.5 dB, while the isolation and return loss are both better than 20 dB. The size of the circulator is 5.88 mm × 6.17 mm, and the peak power capacity is 2200 W.

Conclusions The proposed FSIW circulator exhibits distinct advantages in both miniaturization and high-power capacity, which can be well applied to compact high-power X-band RF front-end systems.