Amplitude methods for forming frequency-independent radiation characteristics of multibeam reflector antennas
Authors: Bobkov N. I. , Prozhivalsky V. V. , Dementiev L. A. 
Published: October 2024

The trend towards expanding the operating frequency ranges of radio-electronic equipment has led to an increasing interest in recent years in the study of ways to constructing multi-beam frequency-independent reflector antennas, which requires systematization of the principles and methods of their construction. When constructing reflector antennas, methods based on the selection of the directional properties of the feeds and methods based on the selection of the frequency-selective properties of the reflectors are used. Methods based on the choice of directional properties of feeds are divided into methods using horn feeds and methods using feeds in the form of cluster arrays with intersecting apertures. Horn feeds are used to create single-beam reflector antennas. Using cluster arrays, it is possible to form a plurality of beams of frequency-independent partial radiation patterns. Using the example of a hybrid reflector antenna, the possibility of forming nine beams in the azimuthal sector of 20° with a beam width of 3.2° ± 0.45° in the frequency band from 2 to 8 GHz is shown. The level of side lobes outside the working sector in the operating frequency band does not exceed –35 dB, the slope of the direction-finding characteristics varies from 4.8 to 9.8 dB/deg. Among the methods based on the choice of selective properties of reflectors, there are methods using frequency-selective surfaces and methods using corrective coatings on the working surface of the reflector. Frequency-selective surfaces are made in the form of wire meshes with variable pitch, in the form of a set of parabolic plates and in the form of a set of square waveguides with a side size ranging from half-wave at the upper frequency in the middle part of the reflector to half-wave at the lower operating frequency at the edges of the reflector. The disadvantages of using frequency-selective surfaces are the complex and expensive design of the reflector, low antenna efficiency, high side lobes and the need to use a large absorbing screen. When implementing the method using corrective coatings, the separate functions of a frequency-selective surface and a radio-absorbing screen are combined in one structural element – a frequency-dependent corrective coating applied to the working surface of the reflector. Among the advantages of this method, it is worth noting the simple design of the reflector and the possibility of its operation at any polarization, since the reflection characteristics of the coating are practically independent of the type of polarization. A common disadvantage of reflector antennas based on the choice of frequency-selective properties of reflectors is distortion of the shape of the main lobe of partial patterns and a larger range of scatter in the pattern width in the operating frequency band, which prevents the formation of linear direction-finding characteristics and reduces direction-finding accuracy. Due to the low efficiency of multibeam mirror antennas built using amplitude methods for forming frequency-independent radiation characteristics, their use as transmitting antennas is impractical. The completed review and identified features of methods for constructing frequency-independent radiation characteristics can become a methodological basis for the design of broadband multi-beam reflector antenna systems for advanced radio-electronic equipment.