Design of a broadband millimeter-wave quasi-optical mode converter for the low power test platform of the ECRH system on J-TEXT

For the low power test platform of the ECRH system on J-TEXT, a broadband millimeter-wave quasi-optical mode converter from TE
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mode to HE
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mode is studied. The mode converter is a corrugated horn antenna with the sine-parallel profile. The effects of different slot numbers in the mode converter and slot picth on the bandwidth of corrugated horns are compared and the appropriate parameters were determined using mode matching method. The simulation results show that in the frequency from 90 GHz to 120 GHz, the relative power of the HE
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mode can reach more than 97%, where the relative power of HE
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mode at the center frequency 105 GHz can reach more than 98.8%. The designed sine-parallel profile has the advantage that the output beam waist radius is at the output port.