V. P. Kortnev – Ph.D. (Eng.), Senior Research Scientist
E-mail: valery.kortnev@yandex.ru
The broadbandness of phased array antennas (PAA), as you know, depends on: angle-frequency sensitivity of the PAA aperture; broadbandness of the control devices for the angular position of the directional pattern (DP) of PAA; broadbandness of the distribution system (excitation system) of PAA.
The purpose of this work is to assess the possibility of increasing the level of PAA (APAA) broadbandness due to: increasing the angular-frequency sensitivity of PAA by means of “compression” of PAA DP; creation of circuits of broadband DP control devices. The angular-frequency sensitivity of a digital PAA with a relatively small aperture for a given wavelength can be increased by using the DP “compression” algorithm in about 10 times and more without changing the size of the aperture and frequency range, and when using Doppler filtering to increase the signal-to-noise ratio, the DP “compression” can be increased in several times more.
The second limitation of PAA broadbandness is narrowbandness of controlled antenna phase shifters, which is associated with the impossibility of forming the required phase simultaneously for each frequency of the broadband signal spectrum. A multifrequency antenna array (MFAA) is known in the literature. Its aperture consists not of individual emitters and phase shifters coupled to them, but of groups of emitters with phase shifters. Each phase shifter in the group, together with its emitter, operates at one harmonic of the signal. Thus, the group covers the entire operating frequency band.
However, the combination of radiators with different frequencies in one group leads to deterioration in the directivity characteristics of the PAA due to interaction of radiators of different frequencies.
The second version of broadband DP control systems is a controlled delay line (time control). The article deduced a formula for a narrowband PAA DP, which uses delay lines (DL). The DP equation has been used as a mathematical model of PAA, scanning in the ±60° sector (±1 ns). As a result of simulation, the effect has been obtained that was not previously encountered in the domestic literature – absence of any deformation of PAA DP when space scanning even at the boundaries of the working sector ±60° (±1 ns). The analysis has showed that the time-controlled PAA operates as a matched space-time filter (transversal one). In the materials of the article, an equivalent PAA circuit has been presented, showing that the phase characteristic of the signals received by the emitters is complex-conjugated with the phase characteristic of PAA – a matched complex-conjugate filter.
The frequency properties of the temporary control device have not been investigated, since its broadbandness, as it is known, is determined by the independence of the delay τ from the frequency, in contrast to the phase shifter, where the phase φ = ωτ (linear function of frequency ω).
At the same time, it is known that a temporary control device at DL is a complex and expensive equipment, therefore, the development of a broadband phase shifter does not lose its relevance. This paper describes a variant of the circuit using nonlinear processing and shows the positive test results of the analog broadband phase shifter, which can be used in inexpensive devices.
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