A Broadband Circular Waveguide Rotary Joint With Substrate Integrated Coaxial Line Feeder

This letter proposed a broadband circular waveguide rotary joint with substrate integrated coaxial line (SICL) feeder. The SICL feeder can effectively convert TEM mode in the SICL into TM
₂₁₀
and TM
₀₂₀
modes in the multi-mode substrate integrated circular cavity (SICC). The annular slot on the surface of SICC can provide strong coupling between the SICC with TM
₂₁₀
and TM
₀₂₀
modes and the circular waveguide cavity with TM
₀₁₀
and TM
₀₁₁
modes. All the modes show symmetric electric field distribution. Thus, a wide bandwidth can be obtained due to six modes and strong coupling, and stable performance can be achieved while rotating because of symmetric field distribution. Comparing with reported circular waveguide rotary joints, the proposed design has the advantages of wide bandwidth and planarization of feeder. A prototype centered at 9.35 GHz is fabricated with a 10 dB impedance matching bandwidth of 24.6% and the insertion loss between 0.82 and 1.65 dB.