Abstract: In this paper, we investigate and reveal the ergodic sum-rate gain (ESG) of non-orthogonal multiple access (NOMA) over orthogonal multiple access (OMA) in uplink cellular communication systems. A base station equipped with a single-antenna, with multiple antennas, and with massive antenna arrays is considered both in single-cell and multi-cell deployments. In particular, in single-antenna systems, we identify two types of gains brought about by NOMA: 1) a large-scale near-far gain arising from the distance discrepancy between the base station and users; 2) a small-scale fading gain originating from the multipath channel fading. Furthermore, we reveal that the large-scale near-far gain increases with the normalized cell size, while the small-scale fading gain is a constant, given by $\gamma = 0.57721$ nat/s/Hz, in Rayleigh fading channels. When extending single-antenna NOMA to M -antenna NOMA, we prove that both the large-scale near-far gain and small-scale fading gain achieved by single-antenna NOMA can be increased by a factor of M for a large number of users. Moreover, given a massive antenna array at the base station and considering a fixed ratio between the number of antennas, M , and the number of users, K , the ESG of NOMA over OMA increases linearly with both M and K . We then further extend the analysis to a multi-cell scenario. Compared to the single-cell case, the ESG in multi-cell systems degrades as NOMA faces more severe inter-cell interference due to the non-orthogonal transmissions. Besides, we unveil that a large cell size is always beneficial to the ergodic sum-rate performance of NOMA in both single-cell and multi-cell systems. Numerical results verify the accuracy of the analytical results derived and confirm the insights revealed about the ESG of NOMA over OMA in different scenarios.

Abstract: In this article, a novel slot-array defected ground structure (DGS) for decoupling microstrip antenna array is proposed. The slot-array DGS is etched surrounding each antenna element on the ground plane and parallel to the radiating edges of each antenna element. The decoupling mechanism is elucidated via an equivalent circuit model and the coupled current field analysis, which reveals slot-array DGS has the spatial band-stop characteristic and changes the direction of the partially coupled current, respectively. Both characteristics of the slot-array DGS contribute to mutual coupling reduction. Three practical design examples of applying slot-array DGS to single-linearly polarized (LP), dual-LP, and compact circularly polarized (CP) antenna array are given to illustrate the design process and considerations. The simulated and measured results show that about 50 dB isolation enhancement is obtained by using the slot-array DGS when the edge-to-edge spacing between CP antenna elements is 0.057 wavelength. Additionally, a wheel-shaped absorber based on the electromagnetic loss material is designed and fabricated to reduce the backward radiation caused by slot-array DGS. The absorber has an absorptivity of more than 95% in the frequency range of 1.2–1.35 GHz and suppresses the backward radiation over 12.5 dB in the plane phi = 0° and 16.1 dB in the plane phi = 90° without deteriorating other antenna performances.

Abstract: Metasurfaces, composed of 2-D planar arrays of sub-wavelength metallic or dielectric scatterers, have provided unprecedented freedoms in manipulating electromagnetic (EM) waves upon interfaces. The development of metasurface has always been closely related to antennas. On the one hand, metasurface was developed from reflect arrays/transmit arrays that are used as reflectors/lens of antennas, and most fundamental theories of metasurfaces are directly borrowed from antenna array theories; on the other hand, the development of antennas was flourished and expedited by progresses in metasurfaces. Many emerging antenna configurations have been constructed based on unique functional metasurfaces. In this article, we will review briefly the development roadmap of both metasurfaces and metasurface-based antennas, including antenna-inspired metasurfaces, metasurface-assisted antennas, and metasurface antennas. In particular, the recent fusion of metasurface and antenna as metantenna will bring significant impacts on methodologies of functional metasurface, antenna design, and radio-frequency device miniaturization.

Abstract: This paper presents a study of a planar antenna-array inspired by the metamaterial concept where the resonant elements have sub-wavelength dimensions for application in microwave medical imaging systems for detecting tumors in biological tissues. The proposed antenna consists of square-shaped concentric-rings which are connected to a central patch through a common feedline. The array structure comprises several antennas that are arranged to surround the sample breast model. One antenna at a time in the array is used in transmission-mode while others are in receive-mode. The antenna array operates over 2–12 GHz amply covering the frequency range of existing microwave imaging systems. Measured results show that compared to a standard patch antenna array the proposed array with identical dimensions exhibits an average radiation gain and efficiency improvement of 4.8 dBi and 18%, respectively. The average reflection-coefficient of the array over its operating range is better than S11 ≤ −20 dB making it highly receptive to weak signals and minimizing the distortion encountered with the transmission of short duration pulse-trains. Moreover, the proposed antenna-array exhibits high-isolation on average of 30dB between radiators. This means that antennas in the array (i) can be closely spaced to accommodate more radiators to achieve higher-resolution imaging scans, and (ii) the imagining scans can be done over a wider frequency range to ascertain better contrast in electrical parameters between malignant tumor-tissue and the surrounding normal breast-tissue to facilitate the detection of breast-tumor. It is found that short wavelength gives better resolution. In this experimental study a standard biomedical breast model that mimics a real-human breast in terms of dielectric and optical properties was used to demonstrate the viability of the proposed antenna over a standard patch antenna in the detection and the localization of tumor. These results are encouraging for clinical trials and further refinement of the antenna-array.

Abstract: A Ka -band wideband dual-polarized magnetoelectric (ME) dipole antenna with the feeding structure consisting of two orthogonal L-shaped probes with different heights is presented based on the low-temperature cofired ceramic (LTCC) technology. A simulated overlapped impedance bandwidth of 42.5% is achieved together with an isolation of higher than 24 dB between the two input ports and stable radiation characteristics over the operating band. By combining the radiating elements with a single-layered feed network composed of microstrip lines, a $4\times 4$ dual-polarized ME dipole antenna array is designed, fabricated, and measured. An overlapped impedance bandwidth of 45% that can cover the entire Ka -band, a gain up to 16.1 dBi, and stable symmetrical radiation patterns in the two orthogonal planes with cross polarization of less than −15 dB are experimentally confirmed. With advantages of the compact geometry, wide operating band, and promising radiation performance, the proposed antenna array with dual polarization would be attractive for millimeter-wave wireless applications in Ka -band.

Abstract: A multiple-input–multiple-output (MIMO) antenna array for broadband 5G new radio (5G NR) metal-frame smartphone applications is proposed. The MIMO antenna array is realized by loading eight identical antennas (Ant1–Ant8) into the metal frame of the smartphone to form an eight-antenna array for the sub-6 GHz 8 × 8 MIMO system. Each antenna element is a slot antenna type that is composed of an L-shaped open slot and a 50 Ω microstrip feedline, and good impedance matching in the upper frequency band can be achieved by loading a tuning stub to the feedline. The 10 dB impedance bandwidth of the proposed eight-antenna array can cover the 5G NR Bands n77/n78/n79 and wireless local area network (WLAN) 5 GHz band. Besides demonstrating desirable antenna efficiency of 50%–82% and envelope correlation coefficient of 12 dB. At 20 dB signal-to-noise ratio (SNR), the calculated peak channel capacity of the proposed eight-antenna array applied to an 8 × 8 MIMO system is 43.93 b/s/Hz.

Abstract: A metasurface lens antenna fed by a planar $8\times8$ dual polarized antenna array is proposed and characterized for full-dimensional massive multiple-input multiple-output (MIMO) and multibeam systems at sub-6 GHz bands. The lightweight multilayer metasurface structure consisting of Jerusalem cross elements is used for a planar lens design. The lens antenna with the size of $10\lambda _{0} \times 10\lambda _{0} \times 5\lambda _{0}$ is fed by an $8\times8$ dual-polarized stacked patch array to operate over the range from 5.17 to 6.10 GHz, where $\lambda _{0}$ is the free-space operating wavelength at the center frequency of 5.6 GHz. This article shows the scanning range of ±25° with a maximum gain of 22.4 dBi and the gain variation of 3.3 dB at 5.6 GHz. Beam coverage performance, pattern envelope correlation coefficient, and port isolation properties demonstrate its full-dimension access capability of the antenna. Besides, the multibeam antenna system with high-gain coverage is achieved by beams operating at the same frequencies, while the frequency division multiplexing can be realized for the isolated beams. The proposed metasurface lens antenna, featuring lightweight, compactness, and low cost compared to a 3-D dielectric lens and low-complexity compared to the array scenarios, can be an alternative for fifth-generation (5G) sub-6 GHz frequency bands.

Abstract: With the prevalence of breast cancer among women and the shortcomings of conventional techniques in detecting breast cancer at its early stages, microwave breast imaging has been an active area of research and has gained momentum over the past few years, mainly due to the advantages and improved detection rates it has to offer. To achieve this outcome, specifically designed antennas are needed to satisfy the needs of such systems where an antenna array is typically used. These antennas need to comply with several criteria to make them suitable for such applications, which most importantly include bandwidth, size, design complexity, and cost of manufacturing. Many works in the literature proposed antennas designed to meet these criteria, but no works have classified and evaluated these antennas for the use in microwave breast imaging. This paper presents a comprehensive study of the different array configurations proposed for microwave breast imaging, with a thorough investigation of the antenna elements proposed to be used with these systems, classified per antenna type, and per the improvements that concern the operational bandwidth, the size of the antenna, the radiation characteristics, and the techniques used to achieve the improvement. At the end of the investigation, a qualitative evaluation of the antenna designs is presented, providing a comparison between the investigated antennas, and determining whether a design is suitable or not to be used in antenna arrays for microwave breast imaging, based on the performance of each. An evaluation of the investigated arrays is also presented, where the advantages and limitations of each array configuration are discussed.

Abstract: The introduction of millimeter wave (mm-wave) frequency bands for cellular communications with significantly larger bandwidths compared to their sub-6 GHz counterparts, the resulting densification of network deployments and the introduction of antenna arrays with beamforming result in major increases in fronthaul capacity required for 5G networks As a result, a radical re-design of the radio access network is required since traditional fronthaul technologies are not scaleable In this article the use of analog radio-over-fiber (ARoF) is proposed and demonstrated as a viable alternative which, combined with space division multiplexing in the optical distribution network as well as photonic integration of the required transceivers, shows a path to a scaleable fronthaul solution for 5G The trade-off between digitized and analog fronthaul is discussed and the ARoF architecture proposed by blueSPACE is introduced Two options for the generation of ARoF two-tone signals for mm-wave generation via optical heterodyning are discussed in detail, including designs for the implementation in photonic integrated circuits as well as measurements of their phase noise performance The proposed photonic integrated circuit designs include the use of both InP and SiN platforms for ARoF signal generation and optical beamforming respectively, proposing a joint design that allows for true multi-beam transmission from a single antenna array Phase noise measurements based on laboratory implementations of ARoF generation based on a Mach–Zehnder modulator with suppressed carrier and with an optical phase-locked loop are presented and the suitability of these transmitters is evaluated though phase noise simulations Finally, the viability of the proposed ARoF fronthaul architecture for the transport of high-bandwidth mm-wave 5G signals is proven with the successful implementation of a real-time transmission link based on an ARoF baseband unit with full real-time processing of extended 5G new radio signals with 800 MHz bandwidth, achieving transmission over 10 km of 7-core single-mode multi-core fiber and 9 m mm-wave wireless at 255 GHz with bit error rates below the limit for a 7% overhead hard decision forward error correction

Abstract: In this communication, a circularly polarized (CP) reconfigurable 2 bit antenna array is proposed for beam-steering applications. The proposed antenna array utilizes a novel CP reconfigurable 2 bit patch antenna as radiation element. For a reconfigurable 2 bit element, there should be four phase states (i.e., 0°, 90°, 180°, and 270°). In the proposed radiation element, a corner truncated microstrip patch antenna is presented for CP radiation. Owing to the symmetry of the patch antenna, the 0° and 180° phase states are achieved by selecting feeding points of the patch instead of using complex feeding network. A 90° digital phase shifter is cascaded to realize the 90° and 270° phase states for the 2 bit reconfigurable element. Based on the novel 2 bit CP element, an eight-element CP reconfigurable 2 bit antenna array is fabricated and tested to verify the design strategy at 3.65 GHz. The measured results match well with simulation. By appropriately controlling the ON and OFF states of p-i-n diodes, the proposed CP array can be steered from −49° to +49°.

Abstract: substrate-integrated gap waveguide (SIGW)-fed metasurface antenna (metantenna) array with nonuniform excitation is proposed for wideband operation and sidelobe-level (SLL) reduction at millimeter-wave Ka -band. To achieve wideband and low profile, a $2 \times 2$ square patch-based metasurface is introduced based on characteristic mode analysis (CMA). The ridged microstrip-fed slot is employed to excite the metasurface, while the mushroom-like patches are positioned around feeding lines to operate as the SIGW for suppressing the undesired modes. Due to the compactness of the proposed SIGW, the amplitude of each element is controllable using unbalanced T-junctions. A nonuniformly excited $4 \times 4$ antenna array is designed and fabricated for validation. The measured results show an impedance bandwidth ( $\vert \text{S}_{11}\vert dB) of full Ka -band with a 3 dB gain bandwidth of 28–40 GHz (35.3%) and SLLs less than −12.1 and −15.6 dB in the E- and H-planes, respectively.

Abstract: We propose a low-profile and high-gain pattern-reconfigurable planar array antenna (PRPAA) based on digital coding characterization. The radiating elements in the PRPAA are designed ingeniously to realize digital “0” and “1” elements. By dynamically encoding the digital radiating elements with different coding patterns, various radiation beams can be achieved and switched in real time based on one antenna aperture. More importantly, for different coding patterns, the number and direction of the radiation beams of the digital PRPAA can be well predicted. We fabricate such a PRPAA and validate its digital-controllable radiation patterns experimentally. This communication provides many opportunities to realize low-cost, lightweight, high-gain, and multi-unit PRPAA, which offers promising applications in massive multi-in multi-out (MIMO) antenna array system, smart antenna, radar system, and dynamic microwave imaging.

Abstract: A dual-wideband dual-polarized antenna using metasurface for the fifth generation (5G) millimeter wave (mm-wave) communications is proposed. It is designed and analyzed based on characteristic mode theory (CMT). The proposed metasurface is mainly composed of a $3\times 3$ square-patch, in which its four corner patches are further sub-divided into a $4\times 4$ sub-patch array, while the size of the other four edge patches is reduced and the center patch is etched with a pair of orthogonal slots. By doing so, the side lobe level can be effectively reduced and the main beam radiation can be enhanced. The metasurface is excited by a pair of orthogonally arranged substrate-integrated-waveguide (SIW) to grounded-coplanar-waveguide (GCPW) dual-polarized feeding networks that help to reduce the insertion loss and expand the frequency bandwidth of the feeding ports. In order to yield higher gain, four proposed metasurfaces are fed by a pair of 1-to-8-way power divider feeding networks including a pair of low-transmission-loss E-plane phase shifter. Measured results show desirable impedance bandwidths of 13.85% (24.2-27.8 GHz) and 14.81% (36.9-42.8 GHz) in the lower and upper frequency bands, respectively, and their corresponding average gains are 13.96 and 15.46 dBi.

Abstract: Loading effects of radiating discontinuities have been explored to increase the phase constant’ frequency sensitivity of leaky-wave antennas (LWAs), based on which a quasi-uniform transversely slotted substrate integrated waveguide LWA featuring rapid beam-scanning and its hexagonal array have been proposed and investigated for millimeter-wave applications. The design concept is simply based on the use of a short period of unit cells and a long transverse slot with a sharp inductive reactance, and it has been theoretically elaborated and effectively validated by both full-wave and circuit-based simulations. A taper design with −25 dB Taylor amplitude distribution is implemented for the proposed LWA to have a low sidelobe radiation. For practical system applications, a hexagonal array consisting of six proposed LWAs is developed to provide an omnidirectional coverage in the azimuth plane while remaining the rapid frequency-driven beam-scanning in the elevation plane. Both the measured and simulated results are in an acceptable agreement with respect to the LWA block and the associated hexagonal array in terms of circuit and radiation performances. The proposed antenna will be a good candidate to be applied for prospective millimeter-wave systems such as autonomous driving and flying.

Abstract: A hybrid metasurface (HMS) is proposed to form a low-profile wideband antenna array. The antenna element is an array of $4\,\,\times4$ square metal patches and fed by a $50~\Omega $ microstrip line through an H-shaped coupling slot on the ground plane. Only are the edge patches of HMS antenna element grounded by shorting pins for the suppression of surface waves and cross-polarization levels as well as the enhancement of the gain. With the HMS antenna element, a compact $2\times 2$ array with an overall size of $1.58\lambda _{0} \times 1.58\lambda _{0} \times 0.068\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at 5.0 GHz) is designed, where the adjacent elements share the edge patches of the elements. The measurement shows the impedance bandwidth of 28% (4.41–5.85 GHz) for $\vert \text{S}_{11}\vert \le -10$ dB is obtained, and the boresight gain is greater than 8.4 dBi across the operating band, covering both fifth-generation (5G) sub 6 GHz and WiFi bands.

Abstract: An extremely wideband (EWB) antenna array is presented that covers the UHF to $C$ -bands (0.13–6 GHz). The array has dual-linear polarization and is capable of wide-angle scanning. Notably, this array achieves a 46:1 contiguous impedance bandwidth at broadside with VSWR $12\times12$ array prototype was fabricated and tested to verify the bandwidth and gain performance of a finite array. The simulated radiation efficiency was demonstrated to be 72% on average across the band.

Abstract: For many object tracking systems, how to quickly and efficiently estimate the direction of arrival (DOA) of radio waves impinging on the antenna array is an urgent task. In this paper, a new efficient DOA estimation approach based on the deep neural networks (DNN) is proposed, in which a nonlinear mapping that relates the outputs of the receiving antennas with its associated DOAs is learned by using the DNN-based network. The novel network architecture is divided into two phases, the detection phase and the DOA estimation phase. Additional detection network dramatically reduces the size of the training set and the process of the training data preparation is discussed in detail. After finishing the training phase, the corresponding DOAs can be identified based on current input data during testing phase. It has been shown that the proposed method can not only achieve reasonably high DOA estimation accuracy, but also reduce the computational complexity required by traditional superresolution DOA estimation methods such as multiple signal classification (MUSIC) and estimation of signal parameters via rotation invariance (ESPRIT). The computer simulation results are performed to investigate the generalization and effectiveness of the proposed approach in different scenarios.

Abstract: In this paper, we have introduced a compact eight-element antenna array for triple-band MIMO (multi-input multi-output) operation in 5G (fifth generation) mobile terminals, which consists of two symmetric four-element sub-arrays disposed, respectively, along two long side-edges of the system ground plane of the mobile terminal. This antenna element can operate at two dual-wideband of 3250-3820 MHz and 4790-6200 MHz with three resonance frequencies which can fully cover 5G NR (New Radio) BandN78 (3300-3800 MHz), China 5G-Band of 4800-5000 MHz and LTE Band-46 (5150-5925 MHz). The main parameters that characterize the performance of the proposed MIMO antenna system, such as bandwidth, reflection coefficient, isolation (more than 10.5 dB), total radiation efficiency (more than 43%), ECC (envelope correlation coefficient, less than 0.12) and CC (channel capacity, 34.9-37.6 bps/Hz), are analyzed and presented in this paper. Besides, the effects of single-hand and dual-hand on performance of the MIMO antenna system are also discussed. The structure of antenna element is only 15 mm × 3 mm (0.175 λ 0 × 0.035 λ 0 , λ 0 is the free-space wavelength at the frequency of 3.5 GHz) with a very small ground clearance of 13 mm × 2 mm on the main board of the proposed mobile terminal. The antenna system has the possibility to be used in 5G mobile terminals with triple-band operation, narrow frame and large display. The corresponding antennas prototype is fabricated and measured; and a quite good agreement between simulation and measurement is obtained.

Abstract: New electromagnetic (EM) structures are demonstrated to realize low-radar-cross section (RCS) antennas by making effective use of frequency-selective absorber (FSA). According to the well-known reciprocity principle, the two-layered FSA can be considered as an actual receiving antenna and then transformed to a circularly polarized (CP) antenna. At the radiation state, a truncated patch resonator on the bottom layer is fed by a coaxial probe so as to produce CP wave, and it further excites the slots on the upper layer, resulting in its radiation toward free space, and when the antenna at the stealth state, the detective incident wave can be effectively absorbed outside the radiation band, thus achieving RCS reduction. The design strategies are then explained and verified with the aid of the corresponding equivalent circuit models. Two examples of $2 \times 2$ and $4 \times 4$ antenna arrays were designed to validate the flexibilities of the proposed design method. Finally, the $4 \times 4$ antenna array was fabricated and measured, and reasonable agreement is achieved.

Abstract: In this letter, fully convolutional denoising approximate message passing (FCDAMP) algorithm is proposed by combining fully convolutional denoising networks with learned approximate message passing networks in millimeter-wave massive MIMO system. In particular, an asymmetric neural network architecture is considered that can learn channel structure and extract noise characteristics. Simulation and analysis show that the proposed FCDAMP algorithm satisfies the lower estimation error and the higher achievable sum rate especially in the low SNR. Moreover, the performance can be further improved by increasing the antenna array in massive MIMO system.

Abstract: Due to its high speed and low latency, D2D communication plays an important role in providing proximity data services in 5G systems, which may contain privacy sensitive data. Covert communication is useful to protect the privacy of user data against adversaries. In a D2D underlaying cellular network, an antenna array can be used at a base station (BS) to transmit artificial noise to confuse adversaries that try to detect D2D covert signals. Based on the numbers of antennas at BS, two covert schemes are presented in this work and their performances are evaluated in terms of D2D covert throughput, i.e., maximum achievable D2D data rate with the given covertness requirements. As only channel distribution information (CDI) of adversary links is known to the BS, the average minimum error probability (AMEP) is used as a metric to measure the covertness performance. In the proposed schemes, closed-form expressions of the minimum AMEP and achievable D2D data rate are derived. It is shown that the derivation of minimum AMEP can be simplified if either one or massive antennas are allocated for sending artificial noise. The analytical results are compared to Monte-Carlo simulation results to verify the feasibility of the proposed schemes. It is also revealed that covert throughput can be further improved by setting system parameters properly, e.g., the number of antennas at BS and artificial noise transmit power.

Abstract: The concept of a self-decoupled antenna array using the cancellation of two opposite couplings is proposed in this article. A pair of such antennas can be closely placed with inherent high isolation without using an extra decoupling structure between the antennas. A pertinent equivalent circuit model is presented to illustrate the physical mechanism of this new concept. It is found that the inductive and capacitive couplings between the antennas can be well canceled out with each other by properly adjusting the antenna dimensions. A demonstrating antenna array with a spacing of $0.024\lambda _{0}$ at the working frequency of 3.5 GHz and its counterpart array are first studied. The measured results show that although the proposed antenna array occupies a slightly larger size than its counterpart array, it presents better performance compared with its counterpart antenna array in port isolation (from 10 to 20 dB), total efficiency (from 68% to 80%), and envelope correlation coefficient (ECC) (from 0.14 to 0.04) throughout the desired frequency band of 3.3–3.8 GHz. A 3-D self-decoupled antenna array is designed to show that the proposed antenna can be in a compact form factor. Another self-decoupled array and its counterpart working at 2.14 GHz (long-term evolution (LTE) band 1) are studied through multi-input multi-output (MIMO) over-the-air (OTA) test when the arrays are integrated with an LTE module, showing significant improvement on the data throughput.

Abstract: A compact wideband wide-angle polarization-free metasurface lens (MSL) antenna array is proposed for a multibeam base station operating over the band of 1.71–2.2 GHz. The MSL element comprises of a planar wideband wide-angle polarization-free reflectionless MSL and three feeding sources of ±45° polarized cross-dipole antennas. With the shared lens aperture, the antenna achieves the three beams in the directions of 0° and ±30° in a horizontal plane. A five-layer patch-based metasurface loaded with metal poles are introduced to achieve consistent performance for wide-angle response. To reduce spillover loss, the feeding antennas are loaded with a metasurface and four directors for narrow beamwidth and low profile. With the optimized feeding antennas and MSL, a section of array with $1\,\,\times \,\,4$ MSL elements is prototyped for validation. The measured results show that an impedance bandwidth for return loss ≥ 10 dB is 1.63–2.24 GHz with the isolation larger than 22.3 dB. The measured gain ranges for 0° and 30° beams are 11.8–13.5 and 10–12.2 dBi with the sidelobe levels less than −22.6 and −13.6 dB, respectively.

Abstract: In this study, a dual-functional radar and communication (RadCom) system architecture is proposed for application at base-stations (BSs), or access points (APs), for simultaneously communicating with multiple user equipments (UEs) and sensing the environment. Specifically, massive multiple-input multiple-output (mMIMO) communication and orthogonal frequency-division multiplexing (OFDM)-based MIMO radar are considered with the objective to jointly utilize channel diversity and interference. The BS consists of a mMIMO antenna array, and radar transmit and receive antennas. Employing OFDM waveforms for the radar allows the BS to perform channel state information (CSI) estimation for the mMIMO and radar antennas simultaneously. The acquired CSI is then exploited to predict the radar signals received by the UEs. While the radar transmits an OFDM waveform for detecting possible targets in range, the communication system beamforms to the UEs by taking into account the predicted radar interference. To further enhance the capacity of the communication system, an optimum radar waveform is designed. Moreover, the network capacity is mathematically analyzed and verified by simulations. The results show that the proposed RadCom can achieve higher capacity than conventional mMIMO systems by utilizing the radar interference while simultaneously detecting targets.

Abstract: A compact multibeam endfire dual-polarized antenna array for low-cost millimeter-wave (mmWave) applications is proposed in this letter. Multimode substrate-integrated waveguide (SIW) section with interactions is applied as the basic beamformer. The dual-mode SIW is used in the beamforming network to support dual-polarization application without occupying an extra area. The printed dipole antenna with integrated balun and the open-ended SIW antenna with metallic strips are integrated to realize an endfire dual-polarized antenna element. Based on this endfire antenna element, a multibeam dual-polarized antenna array is developed. The proposed antenna array includes a four-element antenna array, an SIW beamforming network, and transitions. Additional air gaps between antenna elements are designed for mutual coupling reduction. The fabricated multibeam endfire dual-polarized antenna array achieves an impedance bandwidth of 11.3%, and the overlapped 3 dB beamwidth of the four generated beams in two polarizations are able to cover a wide range between ± 41°. The proposed low-cost multibeam antenna array can be a good candidate for 5G mmWave wireless applications.

Abstract: Millimeter wave antennas have applications in several sensing and communication systems. Such antennas, designed for modern miniaturized devices and systems, must be low profile, flexible, and low cost. Some applications also require beam steering for detection purposes. Combining all these features into an antenna system and delivering decent antenna performance is challenging. In this study, we combined a partially reflective surface with a parasitic patch array to create a simple beam-switching, low-profile, and flexible wearable detection system. To ensure lower costs as well as compatibility with wearable systems, screen printing was utilized on a flexible substrate. The antenna array was optimized for the 77 GHz band and had a high gain of 11.2 dBi. The designed system has three independent beams, which can be oriented from bore-sight to ±32° through a simple switching mechanism. The antenna array maintains its performance in both flat and flexed conditions. Finally, the antenna array was tested in the field to successfully detect objects moving in three different directions.

Abstract: In this article, a novel millimeter-wave dual-polarized 2-D multibeam antenna array incorporating differentially fed antenna elements is proposed to achieve high cross-polarization discrimination (XPD) when the beams scan to the maximal pointing angles. The antenna element is composed of an SIW cavity with four shorted patches placed inside, and it is differentially excited for dual-polarization by a pair of feeding strips and transverse slots beneath the patches. Differential excitation is realized by a power divider designed on two laminate layers. Two Butler matrices placed perpendicularly with each other in different laminates are employed to generate four tilted beams with dual-polarization. A $2\times 2$ dual-polarized 2-D multibeam antenna array working at 28 GHz is designed, fabricated, and measured. The operation bandwidth of the antenna is 26.8–29.2 GHz. The improvement in the XPD is experimentally demonstrated by far-field measurement. When the beams scan to 30° off the boresight, the measured XPDs are 28 dB at the center frequency and higher than 25 dB over the operation bandwidth, which confirms that the cross-polarized radiation in the 2-D multibeam antenna array is suppressed by using the differential-feeding technique. The measured gain is in the range from 7.6 to 10.5 dBi.

Abstract: Hybrid analog-digital (A/D) transceivers are an appealing solution to reduce the transceiver hardware complexity and power consumption for the millimeter wave (mmWave) communication and more general large-scale antenna array (LSAA) systems. In contrast to fully digital conventional multiple-input-multiple-output (MIMO) systems, the baseband precoding operation splits into a lower-dimensional digital precoder followed by a network of analog phase shifters. In this paper, we consider the hybrid precoder design as a constant modulus constrained matrix factorization (CMCMF) problem for the most common types of hybrid architectures namely, the fully and the partially connected ones. Two lines of algorithms based on the majorization-minimization (MM) and the minorization-maximization framework, respectively are proposed for these architectures. In particular, we present efficient algorithms scalable for LSAA systems with provable convergence guarantees to a stationary point. We also consider the hybrid postcoder design at the receiver end. Simulation results demonstrate that the proposed algorithms converge faster to a stationary point as compared to the state-of-the-art solutions that exist in literature. Furthermore, the solution tailored for the partially connected case achieves significantly improved performance in terms of the system spectral efficiency when compared to the existing solutions.

Abstract: The millimeter-wave (mmWave) antennas for smartphones are one of the key components to complete the transition to 5G mobile networks. Although research and development of mmWave 5G antennas for cellular handsets are currently at the center of a significant research effort in both academia and telecommunication industry, a systematic antenna design approved by wireless community has not been proposed yet. With this communication, we propose a novel, high gain, wide band and compact mmWave 5G antenna, namely clover antenna for cellular handsets. The presented antenna has clover like conductor profile whose parameters can be adjusted to obtain high gain or wide band. The designed antennas are simulated with a widely used full-wave analysis tool. Numerical results of the mmWave antenna are confirmed successfully by the experimental results in ${{\text{24}}}$ – ${\text{28}}$ GHz band. The antenna achieves measured peak gain of ${\text{ 7.8}}$ – ${\text{9}}$ dBi in the band. Besides, with a ${\text{16}}$ -element clover antenna array, the beam steering capability of the antenna is demonstrated. Beam steering between ${{ \pm \text{45}^\circ }}$ is achieved with low side lobe levels. Practical design considerations for the integration of the arrays in handset to obtain full-coverage in horizontal plane are investigated. The calculated spatial peak power density values of the proposed array on the outer surface of a head phantom are demonstrated for different scan angles.