In this article, a concept of a phased antenna array based on substrate integrated waveguide (SIW) technology for 5G base stations is proposed. The array has a cosecant radiation pattern in the vertical plane for uniform illumination in a sector area. The array itself consists of 16 SIW traveling wave subarrays of 12 slot-coupled microstrip patch antennas associated with a pair of reflection-canceling vias and phasing elements to get the tapered distribution both in amplitude and phase for the cosecant-shaped radiation pattern. The array is designed to be operational at 28 GHz with a bandwidth of more than 10%, a candidate mm-wave frequency band for 5G. The phased antenna array supports wide-angle scanning of +/-60° in azimuth and exhibits good active impedance properties. The array design is successfully verified experimentally.

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This paper discusses the advantages and an example of using shaped elevation patterns for 5G base stations. A simple iterative power synthesis method involving the phase of shaped patterns, and suitable for both center- and end-fed sub-arrays, is used. Numerical simulations and some experimental results for an array of linear sub-arrays with cosecant squared patterns are presented to validate the concept.@en

The effect of forming single and multi-lobe beam
patterns at mm-wave base station antennas on the received signal
strength and co-channel interference is studied for mm-wave urban outdoor environments. A sample, simplified urban city model is used with randomly selected user positions. Ray tracing simulations are performed to analyze the channel’s directional characteristics towards the test users. Depending on the number of dominant paths, single or multiple main lobes are created in the appropriate directions. Through the simulations, it is observed that in comparison with the multi-lobe beam option, the single-lobe beam provides similar or better received power results (unless the ray phases are equalized at the transmitter or receiver with perfect channel information or there is an unexpected sudden blockage in the main path), while providing better interference cancellation capabilities towards other cochannel users.@en

An unconventional, yet quasi-modular base station phased array architecture synthesis technique is proposed for multiuser fifth-generation applications. By keeping uniform amplitudes and linearly progressing phases at the elements of an optimal irregular array, power-efficient side lobe suppression is achieved for effective inter-user interference mitigation. The layout irregularity is achieved within a slice of an array, which is repeated rotationally. The sequential rotation technique is applied to obtain modularity and improve the circular polarization characteristics. A modified k-means clustering algorithm is used to form the optimal subarrays. The simulation results indicate that the proposed quasi-modular topologies provide a good compromise between the side lobe performance and integrated array design complexity.

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The impact of reducing the total number of elements in passively-cooled, chip-integrated and space-tapered 5G base station antenna arrays on inter-beam interferences and chip temperatures is investigated for multi-user spacedivision-multiple-access applications. A convex element position optimization algorithm is used to synthesize the array layouts with minimized side lobes within a pre-defined cell sector. The multi-beam radiation patterns are computed to study the average trend of the maximum side lobe level with the element number. Thermal simulations are also performed by considering the same EIRP for all the arrays. The results indicate that, after an optimal number of elements, adding more elements to an array does not help reduce the inter-user interference further or provide significant advantage on decreasing the chip temperatures.@en

The future fifth generation (5G) systems will aim to design low-cost phased array base station antenna systems at mm-waves for simultaneous multiple beamforming with enhanced spatial multiplexing, limited interference, acceptable power consumption, suitable processing complexity, and passive cooling. In this study, a multi-user space division multiple access (SDMA) model is developed to investigate the trade-off between the quality of service (QoS), computational complexity in beamforming and cooling requirements for various use cases, and a number of users. The QoS at the user ends is rated by assessing the statistical signal-to-interference-plus-noise ratios (SINRs). Two beamforming algorithms, namely conjugate beamforming (CB) and zero-forcing (ZF), are considered and compared. Depending on the deployment scenario, rotated and optimised array layouts are proposed to be used in CB with the least computational complexity while providing relatively good QoS. Different reduced-complexity ZF algorithms are introduced as a compromise between the SINR performance and computational burden. The impact of the number of simultaneously served users on the thermal management in active integrated 5G base station antenna arrays is investigated as well.

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A novel basic antenna element for travelling-wave substrate integrated waveguide (SIW) arrays is proposed in this study. The antenna element is based on a transverse slot and newly complemented by a pair of vias used for matching and a phase shifter. By changing the geometries of the slot and the phase shifter, the amplitude and phase of a radiated wave can be controlled. The proposed approach extends the potential of transverse slots in SIW-based travelling-wave antenna arrays. To verify the capabilities of the antenna element, the authors demonstrate a six-element array with −30 dB side-lobe suppression, intended for a 24 GHz radar system. The measured results show good agreement with simulations.

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This paper presents a 5G downlink system model for a hybrid multi-user beamforming technique at the base station. The presented technique employs power flux equalization in the elevation plane using a fixed analog cosecant-shaped beam and digital beamforming in the azimuth plane. The system performances of various beamforming algorithms are investigated via Monte-Carlo simulations by creating simultaneous co-frequency beams towards the randomly-located users. The simulation results show that the proposed cosecant subarray hybrid beamforming statistically performs better than the state-of-the-art hybrid beamforming techniques and provides reduced complexity.

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An extended-feature, system-driven convex algorithm for the synthesis of uniform-amplitude, irregular planar phased arrays with simultaneous multi-beam optimization for mm-wave 5G base station applications in multi-user scenarios is presented. The inter-user interferences are suppressed by minimizing the maximum sidelobe level (SLL) for a beam scanned freely inside a given sector. The aperture size is restricted to the size of the heatsink baseplate dimensions. A minimum guaranteed inter-element spacing in the final layout is pre-defined, which prevents element overlapping, eases the thermal problem and helps reduce the effects of high mutual coupling (MC). The algorithm performance is tested via the synthesis of a 64-element integrated array with at least half a wavelength inter-element spacing. The optimized array results show that, compared to their regular counterparts, significant reduction in the SLLs is achieved for a beam scanned inside the defined sector, while keeping the maximum temperature of the array at a reliable level. The effect of MC on the results is also investigated via full-wave simulations and it is explained how embedded element patterns can potentially be included in the optimization. Superior capabilities of the proposed method are illustrated by comparing the algorithm output to those reported in the state-of-the-art literature.@en

The thermal and electromagnetic effects of varying the ground plane thickness and aperture size of the 5G integrated base station antennas are investigated. A double-sided PCB structure is designed with antennas and digital beamforming chips on the opposite sides. Fully-passive cooling is achieved by using fanless CPU coolers attached to the chips. The simulation results indicate that as compared to the standard counterparts, much better cooling performance can be achieved using relatively thick ground planes with extended aperture sizes, with no significant effect on the electromagnetic properties.@en

The performance of space-tapered multi-beam arrays with minimized side lobe levels is statistically evaluated in a line-of-sight propagation environment within a cell sector in terms of the signal-to-interference-plus-noise ratio at the multiple user ends. Comparative analyses are performed to examine the advantages of space-tapered, irregular arrays over the conventional regular array layouts. The system model is formulated with a meaningful link-budget analysis. Two different precoding techniques, conjugate beamforming and zero-forcing, are applied to compute the excitation coefficients at the antenna elements. The effects of several practical factors such as approaches in user scheduling, errors in channel state information estimation and quantization in excitation amplitudes and phases are studied. The simulation results indicate that space-tapered arrays with conjugate beamforming statistically perform better than the regular counterparts and can achieve similar performance to zero-forcing precoding when the impact of non-ideal system conditions is considered.@en

Minimization of the maximum sidelobe level for a given array geometry, amplitude distribution, and nulling sectors by phase-only adjustment of the element coefficients is studied. Nonlinear optimization problem for phase distribution is solved using a novel iterative convex optimization algorithm, which includes mutual coupling effects and exploits small phase perturbations at each step. Superiority of the algorithm in terms of the peak sidelobe level and nulling depth achieved over several optimization methods reported in the most relevant literature is demonstrated in several case studies. Finally, a case study is performed to demonstrate added value of the algorithm for millimeter-wave fifth generation application with phase-only radiation pattern forming.

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A novel hybrid beamforming architecture based on aphased array of active multiport subarrays is proposed for multi-user 5G applications. The subarrays have multiple simultaneous fixed beams which are smartly combined at the user locations withrelatively large gains towards the intended co-frequency users and sufficiently low inter-user interference levels. The presented architecture has a wider angular coverage than the existing subarray-based hybrid beamforming schemes and reduces the signal processing complexity significantly as compared to the fully digital beamforming.@en

Heat removal capabilities and radiation performances of several sparse antenna array topologies are studied for cooling enhancement in 5G millimeter-wave base station antennas. Both electromagnetic and thermal aspects are jointly considered for the first time in array layout optimization and a novel connection between layout sparsity and thermal management is presented. Two types of active electronically scanned arrays (AESA’s), based on the traditional and planar approaches, are examined. Thermal management in AESA’s is discussed, with a focus on cooling challenges at millimeter waves. Being relatively low-cost and low-profile while supporting flexible beamforming, passively cooled planar AESA’s with fanless CPU coolers are proposed, for the first time, to be used in 5G base stations. Additional cooling for such arrays is achieved by increasing the inter-element distances in the layout. Linear irregular arrays, spiral arrays, thinned arrays, circular ring arrays and heat sink antenna arrays are revisited with a critical discussion on their electromagnetic and thermal performance. The results are compared with regular and square layouts that are used as benchmarks throughout the paper.@en

Optimization of heat source distribution in two dimensional heat conduction for electronic cooling problem is considered. Convex optimization is applied to this problem for the first time by reformulating the objective function and the non-convex constraints. Mathematical analysis is performed to describe the heat source equation and the combinatorial optimization problem. A sparsity based convex optimization technique is used to solve the problem approximately. The performance of the algorithm is tested by several cases with various boundary conditions and the results are compared with a uniformly distributed layout. These results indicate that through proper selection of the number of grid cells for placing the heat sources and a minimum inter-source spacing, the maximum temperature and temperature non-uniformity in the domain can be significantly reduced. To further assess the capabilities of the method, comparisons to the results available in the literature are also performed. Compared to the existing heat source layout optimization methods, the proposed algorithm can be implemented more easily using available convex programming tools and reduces the number of input control parameters and thus computation time and resources while achieving a similar or better cooling performance.@en

In this paper, we present a 5G base station phased antenna array concept based on the power equalization in the elevation cut. We designed aperture coupling microstrip patch array exploiting a substrate integrated waveguide structure as feeding line for realization of the cosecant radiation pattern in elevation cut. The antenna is designed to be operational at frequency about 28.5GHz targeting a candidate 5G mm-wave frequency band. The dimensions of the cosecant antenna array support wide-angle scanning in horizontal plane in the final phased antenna arrays. The antenna exhibits good impedance and radiation properties in the scanning range +/- 45deg.@en

A convex iterative algorithm for the synthesis of uniform amplitude, space-tapered linear phased arrays with simultaneous multiple beam optimization for 5G applications is presented. The performance of the algorithm is demonstrated by the synthesis of two arrays having 16 and 24 elements with 60 and 90 degree scan range, respectively. The effect of phase shifter quantization is also addressed. The results indicate that the space-tapered arrays with multiple beam optimization have improved radiation performance in terms of the side lobe level when compared to both single, broadside, beam optimized space-tapered arrays and uniformly distributed arrays with half wavelength spacing.@en

A tapered slot antenna element capable of reconfiguring its beam direction is presented. As the basic element, a Vivaldi antenna fed by a substrate integrated waveguide is chosen. The Vivaldi antenna is complemented by a parasitic planar array of small metallic patches placed in front of its aperture and by corrugated edges of the Vivaldi antenna's arms to provide reconfiguration capabilities. The proposed antenna's beam can be steered in five directions by configuring the interconnections of the parasitic patches and by activation/deactivation of the corrugated edges in the antenna arms. The antenna steers the radiation beam over ±30° in E plane and operates in the frequency band of 6.0–6.5 GHz. The measured gain at 6.25 GHz for 0°, ±15°, and ±30° beam direction of the antenna with ideal switches, is 8.4 dBi, 7.5 dBi, and 6.7 dBi, respectively.@en

A planar tri-band rectangle-rings microstrip antenna design is presented in this paper. The antenna has three equally tuned resonant bands and also maintains consistent radiation patterns in all the operational sub-bands. The antenna has a single port and its cavity-backed waveguide-like configuration results in minimum mutual coupling levels in antenna array configuration. The antenna element is tuned to operate over the L/S/C radar bands. The antenna is simple and compact structure and measures only 0.25lambda × 0.25lambda at the lowest frequency of operation. Due to its small dimensions, the element is well-suited for application to dense wide-scan phased arrays.

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Presents a reply to comments on the paper, ”Comments on Wideband Skin-Equivalent Phantom for V- and W-Band,”(Aminzaech, R., et al),IEEE Antennas Wirel. Propag. Letters.@en