Synthesis of Broadband Oversized Smooth-Walled Horn for High-Power Millimeter Wave

This article proposes a synthesis method based on phase modulation to design broadband oversized smooth-walled horns for high-power millimeter-wave applications. The bandwidth of oversized smooth-walled horn is confined by the mismatch of the relative phase between TE 11 mode and TM 11 mode. By analyzing the mode conversion along horn, it is found that the phase of the generated TM 11 mode can be influenced by the TE 11 mode. Therefore, the synthesis method uses a slow waveguide taper, in which the generated TM 11 mode is in a small fraction and its phase is efficiently influenced by TE 11 mode, to modulate the relative phase of TE 11 mode and TM 11 mode. Using the proposed method, an oversized smooth-walled horn is designed, of which the phase mismatch is ±10° in the range of 32-38 GHz. The simulation results show that the proposed horn has a highly symmetric far-field pattern with a peak gain greater than 28 dBi in the range of 32-38 GHz and the sidelobe level has −19 dB decline compared with the peak gain. A prototype is fabricated and the near-field pattern measurement is carried out. The high correspondence of the simulated near-field patterns with the measured ones proves that the proposed method is an appropriate option to design broadband feed horns for high-power millimeter wave.