Design of a Dual-Mode Waveguide CP Antenna with a Symmetric Beamwidth Using Short Stub for Low-Orbit Satellite TC&R

In this study, a dual-mode waveguide circularly polarized antenna for TC&R (telemetry, command, and ranging) was proposed for the communication between a low-orbit satellite and a ground station. The proposed antenna required both a wide -10 dB bandwidth and axial ratio bandwidth of 7.1–7.3 GHz and 8.0–8.4 GHz. The antenna was designed with a stepped septum inside a square waveguide to obtain circular polarization and the axial ratio wide bandwidth. Next, a dual-mode synthesis method was adopted for link budgeting by combining square and circular waveguides. The requirement was that the co-polarization level with a symmetric -3 dB beamwidth of 39° must be -5 dBic or higher at ±76.5°, and the cross-polarization level must average -15 dBic or lower at ±76.5°. Finally, the corrugate structure attached to the outside of the extended circular waveguide was offset in multiple steps to suppress the back lobe of the crosspolarization As a result, the axial ratio maintained an average of 1.8 dB at 0° within each band of the required frequency. In addition, the co-polarization obtained an average of -4.52 dBic in the 7.2 GHz band and -5.31 dBic in the 8.2 GHz band at ±76.5°. Finally, in the case of the cross-polarization pattern, the back lobe level was suppressed by 9.89 dB at 7.2 GHz by the corrugate structure, and an average value of -19.9 dBic or less was obtained at ±76.5°. The proposed antenna was confirmed to be effective as a Korean low-orbit satellite TC&R antenna with a radiation pattern of a symmetric beamwidth.