Synthesis of Broadband, Oversized, Multimode Horn with Frequency-Invariant Radiation Patterns

The radiation pattern of an oversized waveguide horn typically changes considerably with frequency, which may result in waveform distortion when transmitting or receiving wideband signals. An approach for designing a broadband oversized waveguide horn with a stable radiation pattern is proposed by synthesizing a mixture beam. By analyzing the radiation characteristics of waveguide modes, a method is proposed for generating a mixture mode that varies with frequency to offset changes in radiation patterns caused by waveguide dispersion. To obtain the desired output modes over a broad bandwidth, a two-level optimization algorithm based on mode matching theory and particle swarm optimization is developed. A smooth-wall oversized multimode horn is designed, fabricated, and validated via measurements. The measurement results indicate that the horn can output highly symmetric fields. The radiation patterns are highly consistent within±8° range, and the gain change is less than 0.4 dBi in the frequency range of 32–38 GHz. The frequency-invariant output of the horn contributes to the stable working of antennas, thus improving the efficiency of broadband high-power millimeter-wave systems.