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A novel method of utilizing the repetitive self-similar propertyof the cantor set fractal (CSF) pattern in synthesizing a time-modulated linear array (TMLA) with multiband characteristics, applicable for interband communication, is proposed. The fractal pattern of different growth stages is used to constitute subarrays (SAs) and each group of the subarrayed elements is periodically modulated via a single radio frequency (RF) switch. A closed-form array factor (AF) expression of the proposed CSF–TMLA is derived, and through representative results, it is shown that a Pth stage CSF-TMLA is eligible to be functional at “P” intercommunication bands with power patterns of the same sidelobe level. It is further investigated that the number of RF switches and, hence, the unknown optimization variables essentially entailed to synthesize the array are drastically reduced. [ABSTRACT FROM AUTHOR]

A new technique for fast and accurate extraction of faulty element position from multipatterned time-modulated arrays (TMAs) has been proposed in this article. The strategy incorporates a novel rank-based population (RBP) for generating nonrepeated integers from the continuous population set of differential evolution (DE) algorithm. This enables to solve the discrete optimization problem of finding the defective elements in antenna arrays. Instead of considering the conventionally used single pattern, the degraded dual-beam patterns of TMA are utilized to enhance the convergence speed in detecting the faulty elements. Finally, a phasor matrix that stores the phasor components of the array factor is defined for the fast computation of error-free and failed array factors. Through rigorous simulation results, it is shown that the combination of the two—the RBP-based DE (DE-RBP) and fast computation of array factor—are more efficient in diagnosing faulty elements in multipattern TMA. This brings forth higher convergence speed, improved success rate, and less computation time than the previously reported methods. [ABSTRACT FROM AUTHOR]

This article investigates radiation characteristics of a new type of fractal shaped antenna array based on Haferman carpet geometry. An iterative feed matrix eases the complexity of array factor calculation that makes the array factor suitable for the application of any evolutionary optimization techniques. It is seen that Haferman carpet array produces peak side lobe level (PSLL) better than Sierpinski carpet that produces −10 dB PSLL at every stage of growth. Optimization techniques have been applied for array element reduction and PSLL minimization at different stages of growth. Here, PSLL is minimized by turning off array elements and also by varying inter element spacing between the array elements. The optimized version of Haferman carpet array produces better characteristics (49.38% thinning with −20.5 dB PSLL for stage-2, 46.3% thinning with −22 dB PSLL for stage-3 and 42.3% thinning with −21dB PSLL for stage-4) than its original counterpart in terms of reduced element count and PSLL. Numerical results for obtaining optimized array performance exploit both DE as well as PSO. A comparative study on the performance is also presented. As a whole, Haferman carpet is seen to be more effective approach than Sierpinski carpet in fractal antenna paradigm. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:719-729, 2015. [ABSTRACT FROM AUTHOR]

A wide band iris excited fractal slotted array has been realized and experimentally verified at X band. The design starts with a centered plus shaped slot in the broadwall of a rectangular waveguide and the same has been used in second iteration for fractal configuration, which exhibits dual resonance. The fractal unit cell is optimized for bandwidth by carrying out parametric study of slot-iris combinations and 2.4 GHz bandwidth is achieved for both radiation pattern and impedance response. An empirical expression for conductance of the unit cell has been developed to facilitate design of antenna array using the unit cell as an element. The optimized unit cell has been used for designing a four element array, which exhibits a pattern bandwidth of 1.4 GHz and impedance bandwidth of 2 GHz. The array is simulated in commercial fullwave 3D FEM simulator. The designed array has been fabricated and measured response has been compared with simulated data. [ABSTRACT FROM PUBLISHER]

This paper presents a novel technique to design a time-modulator that can be used as a discrete component to generate different patterns in time-modulated antenna array (TMAA) system. The technique quantizes the modulation period into a number of levels with equal step size between the consecutive levels and rounds off the on-time of the antenna elements to nearest quantization levels to obtain quantized on-times (QOTs) of the corresponding elements. In order to realize the time modulation technique, a representative block diagram of a time-modulator defined as “quantized time-modulator” is presented. It is shown that the effect of quantization errors on the synthesized patterns can be diminished by selecting a suitable number of quantization states by using artificial bee colony (ABC) as a global optimizer. Accordingly, two previously reported examples based on simulated annealing (SA) algorithm, optimized by using continuous search space of on-time are considered, and ABC optimized results using discrete search space of QOT are compared with those obtained by SA. Finally, a fully digitally controlled, low side lobe flat-top pattern with low dynamic range ratio of static amplitude is synthesized by considering discrete search space of QOT. [ABSTRACT FROM PUBLISHER]

In time-modulated antenna arrays (TMAAs), as a result of periodical switch-on and switch-off 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 time-modulation 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. [ABSTRACT FROM AUTHOR]

In this paper, a novel optimization method based on single objective, that is, minimization of sideband radiation (SBR) of ultra-low side lobe, narrow beam patterns in time modulated antenna arrays (TMAAs) is proposed. The proposed method utilizes the weighting vectors of the low side lobe Dolph-Chebyshev/Taylor series patterns as the dynamic excitation coefficients of the desired pattern at fundamental radiation. Differential evolution algorithm is employed to distribute the static amplitudes and switch-on time durations in such a way that in the optimization process, dynamic excitation distribution remains the same. Static amplitudes are perturbed in a predefined search range of (0.25, 1), whereas the weighted values of switch-on time durations are obtained by dividing dynamic excitation coefficients by static amplitudes. The technique greatly simplifies the difficulties of multi-objective TMAA synthesizing problem by reducing it to a single-objective optimization problem. Numerical examples for a 32-element linear array are presented to produce ultra low side lobe Taylorand Dolph-Chebyshev pattern with low value of maximum sideband radiation (SBRmax). The optimization results of the proposed method are also compared with those obtained by other optimization techniques, which have been reported previously. [ABSTRACT FROM AUTHOR]

In this article, a novel method for synthesizing rectangular planar array through thinning and time‐modulation is proposed. A new differential evolution based approach that generates a rank based population is adopted to find out the optimum element off position for thinning and ontime duration to modulate the antenna elements in time domain. The proposed synthesis method defines a preservative boundary at the array center where the antenna elements are not thinned and time‐modulated rather uniformly excited. It is shown that this proposed thinning and time‐modulation strategy with an optimum preservative boundary helps to realize low side lobe radiation pattern with increased directivity by controlling less number of optimization variables as compared to traditional approach. It also reduces the feed network complexity specifically for large antenna arrays. [ABSTRACT FROM AUTHOR]

This paper numerically proposes and experimentally investigates a compact coplanar waveguide fed two element ultra-wideband (UWB), multiple-input–multiple-output (MIMO) antenna array accompanying peak isolation and triple band notch mechanism. The proposed antenna consists of two identical printed monopole elements along with the incorporation of multiple 2nd order Hilbert defects in the ground structure and proposes to incorporate three different mechanisms to reduce the electromagnetic interference of the UWB antenna with existing narrowband systems. The measured impedance bandwidth for the intended antenna ranges from 2.7 GHz to 11.22 GHz. The incorporation of notch mechanisms provides interference suppression at the C-band (3.7–4.2 GHz), WLAN (5.15–5.825 GHz), and X-band communication (7.9–8.4 GHz). The overall size of the intended UWB MIMO antenna is 30.75 mm × 37.80 mm. Moreover, the diversity parameters of the proposed UWB MIMO antenna are numerically calculated and empirically investigated, these calculations and investigations depicts high diversity performance. It is noteworthy to observe that the spacing between the elements is staggeringly reduced to 2 mm. The concurrence among the diverse numerical and experimental outcomes supports the candidature of the suggested layout for portable UWB as well as UWB MIMO systems. [ABSTRACT FROM AUTHOR]