N.I. Bobkov1, I.N. Bobkov2

1 JSC «All-Russian Scientific Research Institute «Gradient» (Rostov-on-Don, Russia)

2 Institute of Radio Engineering Systems and Control of the Southern Federal University (Taganrog, Rostov Region, Russia)

The relevance of the development of multibeam antenna arrays, partial directional patterns of which are maintained constant in a wide frequency band, is due to the tendency to continuously expand the working frequency range of modern radio electronic systems and the use of broadband signals. The conditions for the formation of frequency-independent radiation patterns of aperture antennas and antenna arrays are formulated as:

a frequency-independent falling continuous amplitude distribution should be formed in the aperture; a frequency-dependent even phase distribution, in which the decrease of the beamwidth with growing frequency is compensated by a misphasing increasing, must be introduced in the aperture.

The amplitude condition in active arrays usually performed by choosing transmitting coefficients of the amplifiers such a way that at the inputs of a beam forming network amplitudes of signals on extreme elements are decreased. However, when designing a transmitting active broadband multibeam antenna array, the formation of declining amplitude distribution on elements of an array by a forced reduction of the output amplifiers power is accompanied by a decrease in their total output power by 2 dB compared to the total power of microwave amplifiers operating in the maximum output power mode.

For linear multibeam antenna arrays with a uniform amplitude distribution, the implementation of the amplitude condition can be achieved due to the irregular placement of radiators with monotonously increasing spacings between them at the edges of the aperture, i.e., by constructing non-equidistant antenna arrays.

The model of a 32-element linear array with an aperture size L = 2.5λ0 (λ0 is the wavelength at a lower operating frequency f0) was simulated to prove the suggested method. Simulated partial radiation patterns in the 90° sector were calculated for frequency band with an overlap of 4:1. Radiation patterns were calculated for an additional frequency-dependent phase distribution in the form of a power function with an exponent of 2.2 with an initial dephasing of 100° at the lower operating frequency f0. The beamwidth for central radiation patterns is 22.2° ± 1.6° in the frequency band with 3:1 overlap and 23.2° ± 3.6° in the frequency band with 4:1 overlap. Patterns are frequency independent in width and shape of the main lobe up to minus 10 dB level.

To confirm the possibility of frequency-independent patterns forming, a prototype of the passive non-equidistant linear multibeam antenna array was built and tested. The results of physical experiment confirming the possibility of forming frequency-independent radiation patterns for a linear antenna array in the frequency band of up to two octaves.

Frequency-independent uniform amplitude distribution for active transmitting multibeam antenna arrays ensures the preservation of high energy potential and efficiency of the transmitting system in the frequency band. For receiving multi-beam arrays, a constant level of intersection of partial radiation patterns and a steepness of direction-finding characteristics are maintained.

Bobkov N.I., Bobkov I.N. Frequency-independent linear multibeam antenna array. Radioengineering. 2021. V. 86. № 11. P. 54−59. DOI: https://doi.org/10.18127/j00338486-202111-09 (in Russian)

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