Eight-channel directional coupler of orthogonal H21 modes in circular waveguide for X-band quasi-monopulse antenna systems
Keywords:directional coupler, waveguide H21-mode coupler, higher-order modes, quasi-monopulse antenna system, tracking system
The paper presents results of the development and performance optimization of 8-channel directional coupler (DC) of orthogonal type H21 modes in a circular multimode waveguide. This DC is designed for a high precision autotracking quasi-monopulse system of low-orbiting satellites for Earth remote probing. The design and testing of a prototype operating in the X-band 8–8.5 GHz were developed. The proposed simple and reliable DC design simultaneously performs an almost ideal power division of H21 mode into four equal parts. We obtain the coupling ratio –6.04…–6.2 dB, good matching (VSWR < 1.12), high isolation (I > 31 dB), and directivity (D > 25 dB). Transformation ratios of the working H21 mode into other types of modes in a circular DC waveguide are less than –70 dB. A manufactured prototype of the developed 8-channel DC is tested in the extended X-band of 7.7–8.5 GHz. The measured VSWR values do not exceed 1.25 for H11 modes with orthogonal circular polarizations. The measured isolation ratio of rectangular waveguide channels of tracking signal with respect to information signal in circular waveguide exceeds 32 dB.
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