Synthesis of Oversized Smooth-Walled Horns via Phase Rematching Method

Smooth-walled horns realize efficient radiation by introducing high-order modes meeting the requirements for both proportion and phase. However, the excitation of high-order modes depends on the relative phase of hybrid modes, and the modulation of the relative phase is limited by the frequency dispersion. The dependence between the excitation and phase modulation poses considerable challenges in synthesizing smooth-walled horns. This article reveals the hybrid modes conversion mechanism in smooth-walled horn and proposes a phase-rematching method to synthesize oversized smooth-walled horns for high power millimeter-wave applications. In this method, the excitation and phase modulation are independently realized: utilizing a slow taper near the input to modulate the relative phase and compensate for the frequency dispersion and employing a nonmonotonically increasing radius to control the amplitudes of hybrid modes. To verify the proposed method, a W-band highly oversized smooth-walled horn is designed, fabricated, and measured for gyrotron traveling-wave tubes.