Synthesis of Simultaneous Multiple-Harmonic-Patterns in Time-Modulated Linear Antenna Arrays

Abstract

Abstract-In time-modulated antenna arrays (TMAAs), as a result of periodical switch-on and switchoff of the antenna elements, including operating frequency (termed as center frequency) signal, sideband signals are appeared at either sides of the center frequency in integer multiples of the modulation frequency. In this paper, it is shown that without using phase shifters, just by suitably controlling the on-time instants (OTIs) and on-time durations (OTDs) of a time-modulated linear antenna array (TMLAA) elements, simultaneously, along with a pencil beam pattern at the operating frequency, a shaped beam pattern can be obtained at both the first positive and negative harmonics of the timemodulation frequency. The important advantage of such a technique is that realization of multi-beam pattern in conventional antenna array (CAA) system generally requires complex feed network, whereas by using simple radio frequency (RF) switching circuit in the feed network of TMLAA, by virtue of the properties of harmonic radiations, synthesis of a shaped pattern at either (positive or negative) harmonic results in generating the same pattern in its opposite harmonic, and the synthesized patterns at different harmonics can be simultaneously used as independent communication channels. By employing a differential evolution (DE) based optimization method, numerical results for a 16-element TMLAA with uniform excitation show that in conjunction with a pencil beam pattern at the center frequency, a flat-top or a cosec square pattern at first positive and negative sidebands of side-lobe levels (SLL) −20 dB can be synthesized by suppressing the higher sideband level (SBL) to below −10 dB.

Pattern Synthesis in Time-Modulated Arrays Using Heuristic Approach

“…By taking into account the additional degree of freedom, namely, on-time instants of the antenna elements, improved array patterns can be observed. For example, more sideband reduction as compared to VAS approach is obtained when the same array pattern is synthesized at the center frequency [18][19], and electronic beam steering [9] and harmonic beam patterns of different shapes [7,8] can be realized without phase shifters.…”

“…In such cases, sideband signals and associated power losses are suppressed to improve the radiation efficiency at the operating frequency of the antenna array [5,6]. Presently, it is investigated that sideband signals are also effective in synthesizing multiple patterns and researchers are interested to exploit the same in some specific applications of the modern-day communication systems like harmonic beam forming [7], generation of multibeam radiation pattern [8], beam steering [9,10], direction finding [11], wireless power transmission [12], etc. The interested readers may refer to Reference [13] for the stateof-the-art overview, applications, and present research trend on time-modulation theory and techniques.…”

Research on Multibeam Pattern Synthesis of Time Modulated Array Based on Convex Optimization

“…In some research, various optimization algorithms have been applied to optimize the static excitation and RF switch sequence and realize the multibeam pattern synthesis of TMA. e differential evolution algorithm (DE) is used to realize the sideband beamforming of time modulated linear array in [15] and is applied to the time modulated circular aperture array to obtain the first-order sideband beam pattern in [16].…”

Differential evolution to synthesize low sidelobe thinned isophoric time‐modulated planar array with increased directivity

“…In Reference , PSO is used to generate circularly polarized shaped beam pattern in nonuniform concentric square and circular aperture arrays of disk patch antenna elements. Also, the SBR of TMA has been exploited to generate simultaneous multiple harmonic patterns of desired shaped beam that are used for scanning, surveillance and tracking applications …”

“…In the previously reported approaches, to realize the desired low sidelobe patterns, different array synthesis techniques such as amplitude tapering, thinning, time‐modulation, and nonuniform distribution of element spacing are employed across the elements of whole array aperture. Consideration of all the elements of the array in synthesizing the array patterns leads to increase the dimension of the optimization problems and hence computational complexity.…”