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Pattern synthesis is a significant research focus in smart antennas due to its extensive use in several radar and communication systems. To improve the optimization performance of pattern synthesis of uniform and sparse linear antenna array, this paper presents an optimization method for solving the antenna array synthesis problem using the Mayfly Algorithm (MA). MA is a new heuristic algorithm inspired by the flight behavior as well as the mating process of mayflies, it has a unique velocity update system with great convergence. In this work, the MA was applied to linear antenna arrays (LAA) for optimal pattern synthesis in the following ways: by optimizing the antenna current amplitudes while maintaining uniform spacing and by optimizing the antenna positions while assuming a uniform excitation. Constraints of inter-element spacing and aperture length are imposed in the synthesis of sparse LAA. Sidelobe level (SLL) suppression with the placement of nulls in the specified directions is also implemented. The results gotten from this novel algorithm are validated by benchmarking with results obtained using other intelligent algorithms. In the synthesis of uniform 20-element LAA with nulls, MA achieved an SLL of −31.27 dB and the deepest null of −101.60 dB. Also, for sparse 20-element LAA, an SLL of −18.85 dB was attained alongside the deepest null of −87.37 dB. MA obtained an SLL of −35.73 dB and −23.68 dB for the synthesis of uniform and sparse 32-element LAA respectively. Finally, electromagnetism simulations are conducted using ANSYS Electromagnetics (HFSS) software, to evaluate the performance of MA for the beam pattern optimizations, taking into consideration the mutual coupling effects. The results prove that optimization of LAA using MA provides considerable enhancements in peak SLL suppression, null control, and convergence rate with respect to the uniform array and the synthesis obtained from other existing optimization techniques.

In this paper, a smart antenna array based on the image-aware technique that can automatically switch its beam to track users is proposed. Mobilenet, a deep neural network (DNN), is utilized to find the users' position information from images; it is trained using the collected dataset, and the parameters are optimized. The modified DNN is then implanted into a miniaturized embedded system RK3399. To obtain beam switchable radiation, a 2×2 microstrip patch antenna array with a 4×4 Butler feeding matrix is designed in the 2.4 GHz ISM band. Then, the RK3399 is compactly integrated with the patch antenna array, and a microcamera is used as the eye of the antenna to capture the environment information. A series of measurements of the received power and error vector magnitude (EVM) are performed in a real indoor scenario to verify the design. The results agree well with the expected results and show that the design is capable of guaranteeing communication quality and improving energy efficiency, making this technique a good candidate for indoor wireless applications.

Structure radio beams with diverse radiation patterns exhibit huge potentials in many applications. In this paper, we propose a plane spiral orbital angular momentum (PS-OAM) based structure radio beam construction scheme, in which several PS-OAM waves are superposed together to acquire the anticipated radiation pattern and phase distribution in azimuthal domain. Firstly, some typical shapes of the radiation patterns are demonstrated. Then, the properties of this kind of structure radio beam, for example diversity, periodicity, vorticity and directional gain are analysed in detail from mathematical analysis and simulation verification. Finally, a proof of principle experiment is carried out at 10 GHz using a multi PS-OAM antenna to further testify the feasibility of the structure radio beam construction. The interesting properties provided by structure radio beams would offer promising solutions to radar imaging, smart antenna, massive multiple input multiple output (MIMO) and spatial modulation multiple input multiple output (SM-MIMO).

Implementing an efficient frequency reuse (FR) plan is significantly important to meet the demand on high data rates and the required quality of service for 5G. In this paper, we use the direction of arrival algorithms and the correlator to determine the directions of the desired user and the interferers in the cell. Then, we use the beamformer to produce a beam towards the desired user and nulls in the direction of the interferers. Moreover, we implement the synthesizer to smartly form the desired beam shape and make the nulls deeper. We take the advantage of the smart antennas, beamforming capabilities, and the radiation pattern synthesizing techniques to build up an efficient FR plan for 5G. In addition, we develop a formula for calculating the signal to interference and noise ratio (SINR) in terms of the desired and the interferers directions. Our objective is to maintain the SINR at the minimum levels required for data calls with accepted quality while reducing the beam sizes, and hence increase the FR factor. Our simulation results show that with a uniform linear antenna of 11 elements, we can achieve the desirable SINR levels using beams of 10° width, which raises the FR factor from 1 to 18 and subsequently increases the number of mobile users by 18 times.

An accurate and reliable massive MIMO channel model is crucial for supporting design and performance evaluation of such systems in the future. However, massive MIMO channel sounding systems are cost prohibitive and complicated, where a large number of antenna elements and associated radio frequency transceiver chains are needed. Virtual large-scale arrays have been extensively utilized as an alternative for massive MIMO channel characterization. In this paper, we investigate virtual large-scale array systems formed by repositioning a real subarray system for channel characterization. With this scheme, we have the flexibility to scale between system cost and system channel sounding capability. Based on this scheme, general beampatterns of subarrays and subarray-based virtual large-scale arrays are derived, based on measured complex antenna patterns of antenna elements on the subarray. Three real subarray antenna systems, i.e., a 16-element uniform rectangular array (URA) at 3.5 GHz, an 8-element uniform circular array at 3.5 GHz, and an 8-element uniform linear array (ULA) at 10 GHz, were utilized to form the respective large-scale virtual arrays, i.e., a 128-element URA, a 48-element uniform cylinder array, and a 64 element ULA, respectively. Beamforming analysis based on the measured complex radiation patterns of the real arrays is provided to demonstrate that virtual large-scale arrays can significantly improve the capability of multipath parameter detection compared with the subarrays. Therefore, such cost-effective systems are promising for characterization massive MIMO propagation channels.

A reconfigurable loop antenna with two parasitic grounded strips for modern smartphone devices is presented in this paper. The most essential merit of this proposed reconfigurable antenna is that it can keep the intactness of the outer metal rim. In addition, it can generate multiantenna modes. The outer metal rim generates three loop modes and the inner parasite grounded strips can provide two monopole modes. By merging these two types of antenna modes, it can offer two wide bandwidths to cover GSM850/900, DCS/PCS/UMTS2100, and LTE2300/2500 operations with a compact antenna size of 945 mm2. The detailed operating principles and design considerations of this proposed reconfigurable antenna are described. In order to validate this proposed antenna, it was fabricated and tested. The measured antenna efficiencies and gains are satisfied with the requirements for the modern communication devices.

This paper presents system modelling and characterization of multiple-band notched ultra-wideband (UWB) antennas using the singularity expansion method (SEM). Multiple-band notches in a classical UWB coplanar disc monopole antenna are achieved by introducing systematic defection slots in the coplanar ground structure solely. The antenna uses two dual-band meander ground-defects to create quadruple band notches to avoid possible interference with pre-existing standard services. The SEM with an improved pole-residue extraction scheme is developed to precisely characterize the band-notched antenna in the time and frequency domains. The improved matrix pencil method is applied to the bore sight impulse response of the proposed notched-band UWB antenna to precisely recognize the band-notches and extract the complex poles and residues at the operating bands between the reject-bands. This procedure is validated by reconstructing the impulse response of the antenna from the extracted poles and residues. The obtained simulation and measurement results are in a very good agreement and demonstrate the reliability of the proposed antenna model and characterization method.

This paper introduces a multiple-input and multiple-output (MIMO) antenna system for deployment in the closed hinge slot region of notebook computers for long-term evolution (LTE)/wireless wide area network (WWAN)/wireless local area network (WLAN) applications. This antenna system was placed in the closed hinge slot region formed by the full metal cover, metal ground plate, and metal hinges. The MIMO antenna system, includes a main antenna (Ant 1), an auxiliary antenna (Ant 2), and an isolation element. The main and auxiliary antennas were integrated with the metal surrounding them and were used to excite several resonance modes of the closed hinge slot. Excellent antenna efficiency was achieved using the small antennas. Although Ant1 and Ant2 are only 25 mm $\times5$ mm in size, they could cover LTE/WWAN or WLAN operating bands by switching feed points in the same antenna pattern. The isolation element—a 10 mm $\times6$ mm metal sheet—was placed at the center of the closed hinge slot region, and enhanced isolation by more than 7 dB. The isolation levels exceeded 18 dB for LTE700/2300/2500 bands and 15 dB for 2.4/5.2/5.8 GHz WLAN bands.

An integrated radar and communication system can cooperatively form a radar-communication network with significantly enhanced efficiency and considerably less occupied hardware resources. Such a system exhibits great advantages compared with traditional individual radar and communication modes. Numerous papers have proposed achieving the integrated functions based on phased array radar, whereas the channel modeling and channel estimation problems concerning communications are seldom discussed in the literature. In this paper, we propose a ray-cluster-based spatial channel model and a sounding channel estimation scheme realized on the existing hardware of phased array radar. Considering the correlation, we model the channel by comparing the difference between adjacent antennas, and we present the response vector of the antenna array. We analyze the number of beams that are needed to cover the space, and we present the sequence of directional beamforming vectors when sounding the channel. Redundant dictionary matrices are utilized to present the channel as a sparse signal recovery problem, in which the spatial sparsity is leveraged for performance enhancement. A sparsity adaptive matching pursuit (SAMP)-based compressed sensing tool is exploited for the sparse recovery problem and compared with the conventional least squares (LS) algorithm. The experimental results demonstrate that our proposed scheme can effectively solve the channel estimation problem in the integrated radar and communication system with reduced complexity, and it outperforms LS by 25% when considering mean square error (MSE) performance in general.

Wireless power transfer (WPT) has long been one of the main goals of Nikola Tesla, the forefather of electromagnetic applications. In this paper, we investigate radio-frequency beamforming in the radiative far field for WPT. First, an analytical model of the channel fading is presented, and a blind adaptive beamforming algorithm is adapted to the WPT context. The algorithm is computationally light, because we need not explicitly estimate the channel state information. Then, a testbed with a multiple-antenna software-defined radio configuration on the transmitting side and a programmable energy harvester on the receiving side is developed in order to validate the algorithm in this specific power application. From the results, it can be seen that the implementation of this version of beamforming indeed improves the harvested power. Specifically, at various distances from 50 cm to 1.5 m, the algorithm converges with two, three, and four antennas with an increasing gain as we increase the number of antennas. These encouraging results could have far-reaching consequences in providing wireless power to Internet of Things devices, our target application.

Millimeter-wave (mm-Wave) MIMO systems have been proposed to achieve higher spectral efficiency via the hybrid beamforming structure, which consists of analog beamforming and digital beamforming. In analog beamforming, each antenna subarray generates a codebook-based directional beam, which determines the equivalent MIMO channel. Then, digital beamforming can be applied to fully exploit the spatial multiplexing gain of MIMO channels. In this paper, we propose a low-complexity analog beam selection scheme to achieve near-optimal spectral efficiency for the split hybrid beamforming system. The core of our scheme is the beam selection criterion, which is derived from capacity analysis. Furthermore, we propose a beam switching algorithm to ensure the robustness when blockage occurs. Through simulations under different channel conditions, the near-optimal performance of our scheme is demonstrated, and the beam switching algorithm is able to ensure robust network connectivity and achieve higher channel capacity when the blockage is relived.

A hybrid multi-mode narrow-frame antenna for WWAN/LTE metal-rimmed smartphone applications is proposed in this paper. The ground clearance is only 5 mm $\times45$ mm, which is promising for narrow-frame smartphones. The metal rim with a small gap is connected to the system ground by three grounded patches. This proposed antenna can excite three coupled-loop modes and one slot mode. By incorporating these four modes, the proposed antenna can provide coverage for GSM850/900, DCS/PCS/UMTS2100, and LTE2300/2500 operations. Detailed design considerations of the proposed antenna are described, and both experimental and simulated results are also presented.

In this paper, radio-frequency (RF) electromagnetic field (EMF) exposure evaluations are conducted in the frequency range 10–60 GHz for array antennas intended for user equipment (UE) and low-power radio base stations in 5G mobile communication systems. A systematic study based on numerical power density simulations considering effects of frequency, array size, array topology, distance to exposed part of human body, and beam steering range is presented whereby the maximum transmitted power to comply with RF EMF exposure limits specified by the International Commission on Non-Ionizing Radiation Protection, the US Federal Communications Commission, and the Institute of Electrical and Electronics Engineers is determined. The maximum transmitted power is related to the maximum equivalent isotropically radiated power to highlight the relevance of the output power restrictions for a communication channel. A comparison between the simulation and measurement data is provided for a canonical monopole antenna. For small distances, with the antennas transmitting directly toward the human body, it is found that the maximum transmitted power is significantly below the UE power levels used in existing third and fourth generation mobile communication systems. Results for other conceivable exposure scenarios based on technical solutions that could allow for larger output power levels are also discussed. The obtained results constitute valuable information for the design of future mobile communication systems and for the standardization of EMF compliance assessment procedures of 5G devices and equipment.

This paper investigates the downlink of a single-cell base station (BS) equipped with a large-scale antenna array system while considering a non-negligible transmit circuit power consumption. This consumption involves that activating all RF chains does not always necessarily achieve the maximum sum-rate when the total BS transmit power is limited. This paper formulates a sum-rate maximization problem when a low complexity linear precoder, such as conjugate beamforming or zero forcing beamforming, is used. The problem is first relaxed by assuming arbitrary antenna selection. In this case, we derive analytically the optimal number of activated RF chains that maximizes the sum-rate under either optimal power allocation or equal received power constraint for all users. Also, user scheduling algorithms are proposed when users require a minimum received signal-to-interference-plus-noise ratio. Two iterative user scheduling algorithms are designed. The first one is efficient in terms of fairness and the second one achieves the optimal performance. Next, the antenna selection is investigated and we propose iterative antenna selection algorithms that are efficient in terms of instantaneous sum-rate. Simulation results corroborate our analytical results and demonstrate the efficiency of the proposed algorithms compared with arbitrary and optimal brute force search antenna selection.

In the 5G system, we foresee the use of LOS-dominated mm-wave radio links to moving users being subject to slow fading resulting from the users’ random locations and orientations. We refer to this as a random-LOS channel. MIMO processing algorithms will be used in 5G to improve performance in slow fading, similar to how they are used in Rayleigh fading. To this end, we study the probability of detection in the random-LOS channel when there are dual-polarized antennas on both sides of the link. We introduce two polarization deficiencies: the polarization non-orthogonality and the amplitude imbalance between the ports of a two-port antenna. The MIMO efficiency is evaluated as a function of these deficiencies. In the analysis, we consider the MRC algorithm for one bitstream, and the ZF and SVD algorithms for two bitstreams. We also present two analytical formulas for the MIMO efficiency that can be used to determine performance. We use the formulas on two ideally orthogonal dipoles, and show by means of coverage plots how much the 1- and 2-bitstream performances degrade due to the polarization deficiencies in off-boresight directions.

In this paper, a channel measurement campaign is introduced, which utilizes direction-scan-sounding to capture the spatial characteristics of 28-GHz wave propagation channels with 500-MHz sounding bandwidth in office environments. Both line-of-sight and non-line-of-sight scenarios were considered. Measurements were performed by fixing a transmit pyramidal horn antenna, and rotating another one in the receiver site at 10° steps in azimuth. The antenna outputs are viewed as array signals, and a space-alternating generalized expectation-maximization (SAGE) algorithm is applied to estimate delay and angular parameters of multipath components. Benefiting from high resolution achieved by using the SAGE and deembedding of antenna radiation pattern and system responses, more multipath clusters with less spreads in delay and azimuth are found per channel compared with existing works on 28-GHz propagation. The statistics of channel parameters extracted here constitute a preliminary stochastic multipath-cluster spatial channel model.