N.I. Bobkov – Ph.D.(Eng.), Head of Research Sector, JSC «VNII «Gradient» (Rostov-on-Don)
When designing broadband multibeam antenna arrays (MAA), the actual problem is forming of frequency-independent partial radiation patterns in the band of operating frequencies. It is known that the compensation of radiation pattern width change with increasing frequency can be achieved by introducing a frequency-dependent phase distribution with a decreasing amplitude distribution in the aperture. However, in some cases, e.g., when designing transmitting active multibeam antenna arrays (MAA), it is required to form a frequency-independent radiation patterns with uniform amplitude distribution in the aperture. It is known that for some forms of aperture the amplitude distribution of an equivalent linear radiator, corresponding to a uniformly excited aperture, is decreasing. It is possible to achieve the effect of radiation pattern parameters stabilization in frequency band, by setting the corresponding frequency-dependent phase distribution in a plane of equivalent linear radiator. Thus, for uniformly excited array with a circular aperture of radius R, the amplitude distribution of an equivalent linear radiator is decreasing:
With the introduction of a one-dimensional frequency-dependent phase distribution «cosine to a power of 0.35», with an initial phase dephasing of 200° for the lower operating frequency f0, the MAA forms the frequency-independent radiation patterns.
For the example given in the article, radiation pattern width at −3 dB level is 5.7°±0.6° in the frequency band with a 16:1 overlap. For the partial radiation patterns deflected from the normal to aperture, their width and shape are also preserved in the specified frequency band. The article shows features of forming the frequency-independent radiation patterns for broadband MAA with a circular, elliptical, octagonal and hexagonal configurations of aperture, special phase distributions creation issues were also considered. The appropriate choice of the aperture shape and the use of special phase distributions can extend a potential MAA operating bandwidth up to four octaves. For receiving MAA, a constant level of intersection for partial radiation patterns and steepness of direction finding characteristics are maintained. The uniform amplitude excitation of array units allows to maintain high energy potential and efficiency of the transmission system in the frequency band.
The proposed method of broadband MAA construction with a frequency-independent partial radiation patterns and the results of the research can be applied in the development of broadband antenna systems for advanced electronic solutions.
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