摘要： Traditionally, corrugated conical horn antennas have been the main choice for use in astronomical receivers in the range of millimeter and submillimeter waves. They present low cross-polar level and high coupling efficiency into the fundamental Gaussian mode. However, this type of antenna is difficult to manufacture, inevitably increasing its price and extending the production process. In this work, we present two kinds of feed horn antennas, aimed for use in a frequency range equivalent to ALMA Band 6 (211-275 GHz), which can be fabricated in a much simpler way with conventional machining tools. Specifically, we present the design and performance comparison of smooth-walled spline-profile horns in two geometries, diagonal and conical. Optimization of the designs has been made by means of an algorithm that allowed us to obtain models whose electrical and mechanical characteristics make them competitive when compared with corrugated horns. In particular, they are 40% shorter than conventional corrugated horns suited for this band, representing an advantage given the stringent space constraints of most astronomical receivers. We also demonstrate that they can be coupled efficiently to an astronomical-grade optical system, using ALMA Band-6 receiver as an example. Furthermore, we have constructed the diagonal horn and characterized it thoroughly. Experimental results of the radiation pattern at room temperature show a good cross-polar performance with levels below ?20 dB and gaussicity above 96%. Our calculations show a good antenna-efficiency level with losses less than 1%. All these properties demonstrate the feasibility of this type of horns to become the main option at the time of choosing a feed system for cutting-edge astronomical applications.