Mm-wave Frequencies Research Articles

H-plane SIW horn antenna with enhanced front-to-back ratio for 5G applications

Millimeter-wave (mmWave) antennas are indispensable components in the fifth-generation (5G) wireless communication systems. With the inherent advantages of integration capability, substrate integrated waveguide (SIW) antenna is an excellent choice for applications in the mmWave frequency bands. However, reflection losses occur at dielectric-filled thin apertures of SIW antennas. These reflections can be overcome by impedance matching between the aperture and the free space. In this study, we introduce an mmWave SIW horn antenna having impedance matching transitions (IMTs) across the horn's aperture width. The designed antenna, operating in the 24-28 GHz band, is simulated with a full-wave analysis tool. The simulation results of the modified SIW horn have been confirmed by the experimental results and shown to be satisfactory. The IMTs result in an enhancement of the front-to-back ratio (FTBR). The modified SIW horn antenna with a novel printed transition achieves sidelobe levels (SLLs) of better than ?9 dB at 27 GHz, with an enhanced FTBR above 15 dB. In the 24?28 GHz band, the antenna has a reflection coefficient variation of better than ?10 dB.

MmWave Physical Layer Network Modeling and Planning for Fixed Wireless Access Applications.

The large bandwidths that are available at millimeter-wave frequencies enable fixed wireless access (FWA) applications, in which fixed point-to-point wireless links are used to provide internet connectivity. In FWA networks, a wireless mesh is created and data are routed from the customer premises equipment (CPE) towards the point of presence (POP), which is the interface with the wired internet infrastructure. The performance of the wireless links depends on the radio propagation characteristics, as well as the wireless technology that is used. The radio propagation characteristics depend on the environment and on the considered frequency. In this work, we analyzed the network characteristics of FWA networks using radio propagation models for different wireless technologies using millimeter-wave (mmWave) frequencies of 28 GHz, 60 GHz, and 140 GHz. Different scenarios and environments were considered, and the influence of rain, vegetation, and the number of subscribers was investigated. A network planning algorithm is presented that defines a route for each CPE towards the POP based on a predefined location of customer devices and considering the available capacity of the wireless links. Rain does not have a considerable effect on the system capacity. Even though the higher frequencies exhibit a larger path loss, resulting in a lower power of the received signal, the larger bandwidths enable a higher channel capacity.

Millimeter-Wave Channel Measurements and Path Loss Characterization in a Typical Indoor Office Environment

In this paper, a path loss characterization at millimeter-wave (mmWave) frequencies is performed in a typical indoor office environment. Path loss results were derived from propagation channel measurements collected in the 25–40 GHz frequency band, in both line-of-sight (LOS) and obstructed-LOS (OLOS) propagation conditions. The channel measurements were performed using a frequency-domain channel sounder, which integrates an amplified radio over fiber (RoF) link to avoid the high losses at mmWave. The path loss was analyzed in the 26 GHz, 28 GHz, 33 GHz and 38 GHz frequency bands through the close-in free space reference distance (CI) and the floating-intercept (FI) models. These models take into account the distance dependence of the path loss for a single frequency. Nevertheless, to jointly study the distance and frequency dependence of the path loss, multi-frequency models were considered. The parameters of the ABG (A-alpha, B-beta and G-gamma) and the close-in free space reference distance with frequency path loss exponent (CIF) models were derived from the channel measurements in the whole 25–40 GHz band under the minimum mean square error (MMSE) approach. The results show that, in general, there is some relationship between the model parameters and the frequency. Path loss exponent (PLE) values smaller than the theoretical free space propagation were obtained, showing that there are a waveguide effect and a constructive interference of multipath components (MPCs). Since the measurements were obtained in the same environment and with the same configuration and measurement setup, it is possible to establish realistic comparisons between the model parameters and the propagation behavior at the different frequencies considered. The results provided here allow us to have a better knowledge of the propagation at mmWave frequencies and may be of interest to other researchers in the simulation and performance evaluation of future wireless communication systems in indoor hotspot environments.

A Circularly Polarized mmWave Dielectric-Resonator-Antenna Array for Off-Body Communications

This paper presents a novel 28 GHz circularly polarized rectangular dielectric-resonator antenna (DRA) array for millimeter-wave (mmWave) off-body applications. A feed network incorporating cross slots was utilized in the rectangular DRA design to realize circular polarization (CP). In terms of the free-space wavelength, λo, the DRA dimensions were (0.48λo × 0.48λo × 0.27λo) at 28 GHz. The antenna array was simulated by incorporating dielectric layers with parameters that are equivalent to those of the human body at the desired frequency of 28 GHz for off-body communications. Moreover, the precise alignment and assembly of the DRA, which pose major difficulties at mmWave frequencies, were achieved by outlining the DRA positions on the ground plane using a three-dimensional (3D) printer. The array configuration was fabricated and measured with excellent performance, realizing a measured impedance bandwidth of 29% in conjunction with an axial-ration (AR) bandwidth of 13% and a broadside gain of 13.7 dBic at 28 GHz.

A 39-GHz High Image-Rejection Up-Conversion Mixer in 65-nm CMOS for 5G Communication

This brief presents an up-conversion mixer with high image rejection ratio (IRR) for 5G mmWave communication. To achieve broadband IRR at mmWave frequency with high area efficiency, a current-mode second-order tunable notch filter embedded in a cascode radio frequency (RF) buffer is proposed to realize tracking of the pole and zero frequencies with the switch capacitor array. To address the local oscillator (LO) leakage and even-harmonic distortion, a double-balanced passive mixer is adopted. For better isolation and lower insertion loss, a capacitor-inductor-capacitor (C-L-C) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\pi }$ </tex-math></inline-formula> -type impedance network is introduced in the mmWave T/R switch, realizing the equivalent lumped quarter wave transmission line with high area efficiency. Fabricated in a 65-nm CMOS process, the up-conversion mixer consumes 48.6 mW from a 1.2-V supply. Within the 3-dB bandwidth from 36 to 40.6 GHz, the mixer has a peak conversion gain of 0 dB, and its measured output 1-dB gain compression point (OP1dB) varies from −3 to −1.8 dBm. With the proposed tunable notch filter, the up-conversion mixer achieves a measured IRR of more than 53 dBc from 36 to 40.6 GHz, with a peak value of 58 dBc at 38.2 GHz.

A Low-Phase-Noise Quad-Core Millimeter-Wave Fundamental VCO Using Circular Triple-Coupled Transformer in 65-nm CMOS

The minimal achievable phase noise (PN) of millimeter-wave (mm-wave) voltage-controlled oscillators (VCOs) is bounded by the smallest realizable inductor with a reasonable high quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> ). A multi-core VCO reduces the total equivalent inductance of the tank by synchronizing multiple VCO cores, therefore improving the PN performance. This article presents a 60-GHz fundamental VCO based on a mode-rejection circular triple-coupled-transformer tank, which improves the PN performance of the VCO from three aspects. 1) the circular topology improves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> of small inductors in the mm-wave frequency range by alleviating the inner edge deconstructive coupling; 2) compared with the circular inductor topology, the triple-coupled transformer provides the flexibility to suppress the unwanted oscillation mode at the center taps of the gate coils, which enables the NMOS-only VCO configuration to avoid PN degradation due to limited PMOS performance in the mm-wave frequency range; and 3) the triple-coupled transformer boosts the gate-to-source voltage swing of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}_{m}$ </tex-math></inline-formula> transistors. The quad-core VCO prototype is designed and fabricated in a 65-nm CMOS process. It achieves a measured PN of –104.7 dBc/Hz at 1-MHz offset and a corresponding figure of merit (FoM) of 186.5 dBc/Hz at 59.1-GHz carrier frequency.

On the Efficiency of the Advanced TWA Approach to the 60-GHz Microstrip Antenna Analysis for 5G Wireless Communication Systems

The bandwidth demand in mobile wireless applications has grown at an astounding rate due to the fast evolution of technology, spurring the antenna design fields. The approaches associated with realizing antenna structure at mm-Wave frequency bands for future 5G cellular devices present advantages and disadvantages. This paper exhibits a fast and original approach based on the transverse wave formulation called-up Advanced Transverse Wave Approach (ATWA). A compact 5G patch antenna is designed, measured, simulated, and analyzed in the context of unlicensed mm-wave ISM-band applications. Compared to recently published works, the obtained result analysis proves the efficiency of the proposed method in terms of calculation accuracy, computational efficiency, and peak memory usage and the overall good performance of the proposed antenna.

Performance Assessment and Comparison of Deployment Options for 5G Millimeter Wave Systems

The roll-outs of fifth-generation (5G) New Radio (NR) systems operating in the millimeter-wave (mmWave) frequency band are essential for satisfying IMT-2020 requirements set forth by ITU-R in terms of the data rate at the access interface. To overcome mmWave-specific propagation phenomena, a number of radio access network densification options have been proposed, including a conventional base station (BS) as well as integrated access and backhaul (IAB) with terrestrial and aerial IAB nodes. The aim of this paper is to qualitatively and quantitatively compare the proposed deployments using coverage, spectral efficiency and BS density as the main metrics of interest. To this end, we develop a model capturing the specifics of various deployment options. Our numerical results demonstrate that, while the implementation of terrestrial relaying nodes potentially improves coverage and spectral efficiency, aerial relays provide the highest coverage, three times that of a direct link connection, and also significantly reduce the required BS density. The main benefit is provided by the link between the BS and the aerial relay. However, gains are highly dependent on a number of elements in antenna arrays and targeted outage probability. The use of terrestrial relays can be considered a natural trade-off between coverage and the aggregate rate.

Predicting Path Loss of an Indoor Environment Using Artificial Intelligence in the 28-GHz Band

The propagation of signal and its strength in an indoor area have become crucial in the era of fifth-generation (5G) and beyond-5G communication systems, which use high bandwidth. High millimeter wave (mmWave) frequencies present a high signal loss and low signal strength, particularly during signal propagation in indoor areas. It is considerably difficult to design indoor wireless communication systems through deterministic modeling owing to the complex nature of the construction materials and environmental changes caused by human interactions. This study presents a methodology of data-driven techniques that will be applied to predict path loss using artificial intelligence. The proposed methodology enables the prediction of signal loss in an indoor environment with an accuracy of 97.4%.

Synthesis of Quadband mm-Wave Microstrip Antenna Using Genetic Algorithm for Wireless Application

Antennas with multifunctional capabilities integrated into a single device that demonstrates a high performance are in demand, and microstrip antennas with quadband coverage are very useful for a wide range of mm-wave applications. Antennas and propagation at mm-wave frequencies, on the other hand, poses several challenges which can be overcome by applying performance enhancement techniques to meet design objectives. This article presents the use of a binary-coded genetic algorithm for developing an improved quadband mm-wave microstrip patch antenna. The patch shape was optimized by dividing a conducting surface into 6 × 6 tiny rectangular blocks. The algorithm generated the solution space by introducing conducting and nonconducting features for each radiating cell on the patch surface and then greedily searched for the best-fitted individual based on the cost function. With the combination of High-Frequency Structure Simulator (HFSS) and MATLAB, candidate antennas were iteratively modeled by applying the suggested algorithm. The optimized antenna resonated at four frequencies centered at 28.3 GHz, 38.1 GHz, 46.6 GHz, and 60.0 GHz. The antenna realized a peak broadside directivity of 7.8 dB, 8.8 dB, 7.3 dB, and 7.1 dB, respectively, with a total operating bandwidth of 11.5 GHz. The research findings were compared with related works presented in the literature and found that the optimized antenna outperformed them in terms of bandwidth, directivity, and efficiency.

A Broadband Meta surface Based MIMO Antenna with High Gain and Isolation For 5G Millimeter Wave Applications

This paper proposes a Broadband Meta surface-based MIMO Antenna with High Gain and Isolation For 5G Millimeter applications. A single antenna is transformed into an array configuration to improve gain. As a result, each MIMO antenna is made up of a 1x2 element array supplied by a concurrent feedline. A 9x6 Split Ring Resonator (SRR) elongated cell is stacked above the antenna to improve gain and eliminate the coupling effects between the MIMO components. The substrate Rogers 5880 with a thickness of 0.787mm and 1.6mm is used for the antenna and meta surface. Furthermore, antenna performance is assessed using S-parameters, MIMO characteristics, and radiation patterns. The final designed antenna supports 5G applications by embracing the mm-wave frequency spectrum at Ka-band, there is a noticeable increase in gain. In addition, once the meta surface is introduced, there is an improvement in isolation.

Characterization of Resistance and Inductance of PIN Diode at mmWave Frequency Using 7-Layer Deep Neural Network

Characterization of Resistance and Inductance of PIN Diode at mmWave Frequency Using 7-Layer Deep Neural Network

Integrated Beam Tracking and Communication for (Sub-)mmWave Links With Stochastic Mobility

We consider the problem of active sensing and sequential beam tracking at mmWave frequencies and above. We focus on the setting of aerial communications between a quasi-stationary receiver and mobile transmitter, for example, a gateway array tracking a small agile drone, where we formulate the problem to be equivalent to actively sensing and tracking an optimal beamforming vector along the single dominant (often line-of-sight) path. In this setting, an ideal beam points in the direction of the angle of arrival (AoA) with sufficiently high resolution to ensure high beamforming gain. However, narrow beams are inherently sensitive to stochastic mobility. Without active sensing, narrow beam alignment can only be maintained in the case of highly predictive mobility with low prediction error. We pose the problem of active beam tracking and communication as a partially observed Markov decision problem (POMDP) with an expected average cost constraint. We establish the existence of a solution to the dynamic programming equation under reasonable technical assumptions. Drawing on the insight obtained from this solution, we propose an active joint sensing and communication algorithm for tracking the AoA through evolving a Bayesian posterior probability belief which is utilized for a sequential beamforming selection. Our algorithm relies on an integrated strategy of adaptive allocation of pilot versus data symbols as well as an active selection of beamforming vectors that trades off mutual information between the AoA and measurements (sensing) against spectral efficiency (communication). Through extensive numerical simulations, we analyze the performance of our proposed algorithm under various stochastic mobility models and demonstrate significant improvements over existing strategies. We also consider the impact of model mismatch on the performance of our algorithm which shows a good degree of robustness to model mismatch.

MmWave Yagi-Uda Element and Array on Liquid Crystal Polymer for 5G

Arrays on personal terminals are feasible using mmWave frequencies, but are limited by mutual coupling. A standard specification for MIMO is −15 dB coupling which can be readily attained over a modest bandwidth, and decoupling modifications can reduce this to less than −20 dB. Such a change has relatively little impact on narrowband MIMO performance but is significant for wideband phased arrays, demonstrated here using simulation and measurement of a new design. For the element, we present a Yagi-Uda structure on PCB with a bandwidth from 22 to 44 GHz to cover a set of standard mmWave bands for 5G. Our prototype uses the RFIC packaging material Liquid Crystal Polymer which is suitable for Antenna-in-Package technology. For the array, the element spacing is set small enough to suppress grating lobes at the highest frequency. At the lowest frequencies, the lowest electrical spacing means the highest mutual coupling, and we apply a decoupling modification for this. The associated improvements in the impedance bandwidth, scan range, gain and radiation efficiency are presented for edge- and corner-mounted arrays designed for a mobile terminal such as a cellphone. Our array combining comprises simulation-based signal phasing and the simpler beam switching using element selection. The edge-mounted array has a 59% TARC bandwidth (24–44 GHz) over which the scan range is between ±60° and ±35°, the gain is 9.5 to 13 dBi with a radiation efficiency better than −0.2 dB. The corner-mounted switched array has peak gains of 6 to 9 dBi, showing the gain penalty associated with the simpler switched beam architecture. Finally, the impact of a cellphone chassis on the antenna performance is assessed by simulation.

Wideband Digital Predistortion for Frequency Multipliers Driven by Nonideal Upconverters

This letter proposes a new technique to calibrate the frequency response of the upconverter in frequency-multiplier-based transmitters. The proposed technique only requires capturing the multiplier output, using the same feedback path needed to train the digital predistortion (DPD) module. In addition, this letter proposes a low-complexity piecewise-based DPD model to compensate for the multiplier nonlinearity. Experiments carried out on a millimeter-wave (mm-wave) frequency doubler showed excellent output signal quality with a 400-MHz modulation bandwidth.

Multifunctional Frequency Selective Absorber Enabling FR1 and FR2 5G OTA Tests in a Hybrid Reverberation Chamber

Due to the special advantages of the reverberation chamber (RC), it has been recognized as a standardized over-the-air (OTA) testing methodology by the cellular telecommunications industry association (CTIA). Currently, OTA tests of the fifth-generation (5G) wireless terminals are usually performed in different testing environments, e.g., in a reverberation chamber for fast isotropic tests in the sub-6 GHz frequency band, and in an anechoic chamber for directional tests in the millimeter-wave (mm-wave) frequency band, which are inconvenient and costly. In this work, two multi-functional frequency selective absorbers (FSAs) are designed to realize absorption in the 5G mm-wave band and reflection/transmission in the sub-6 GHz band. By loading the FSAs to the RC, an integrated testing environment for 5G terminals can be established. Namely, a quasi-anechoic environment in the mm-wave band and a reverberation environment in the sub-6 GHz band can be simultaneously achieved in the RC loaded with the proposed FSAs. Experimental and simulated results are presented to demonstrate the effectiveness of the proposed scheme.

New Self-Isolated Wideband MIMO Antenna System for 5G mm-Wave Applications Using Slot Characteristics

This paper proposes a simple novel technique for self-isolating a MIMO antenna for mm-wave applications. MIMO antenna elements with inter-element separation of 0.2 mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.023\lambda $ </tex-math></inline-formula> at 35 GHz) and measured high isolation (>50 dB) are presented. By observing the concentration of surface waves on the radiating patch, several rigorously optimized slots of different shapes, positions, and dimensions are etched on the patch to enhance the inter-element isolation and increase the bandwidth within 28-37.5 GHz. The circuit models of the reference and proposed antennas have been presented. The coupling is measured by the level of the differences in the output voltage in both antennas. The novel mm-wave antenna exhibits high impedance bandwidth (>29%), high isolation (>50 dB), high efficiency (>90%), and low envelope correlation coefficient (< 0.005). Two configurations of MIMO antenna (i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 2$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> ) are fabricated and measured to validate the simulation outcomes. The single reference antenna has dimensions of 10x12 mm 2 while the 1x2 array has dimensions of 19x12 mm 2. The presented design is the first to exhibit such wideband isolation improvement without any external decoupling structure at the mm-wave frequency range, to the best of the authors’ knowledge.

Radio SLAM: A Review on Radio-Based Simultaneous Localization and Mapping

Simultaneous localization and mapping (SLAM) algorithm has enabled the automation of mobile robots in unknown environments. It enables the robot to navigate through an unknown trajectory by employing sensors that provide measurements to infer the surrounding environment and use this information to localize the robot. Sensor technology plays a key role in defining the quality of measurements as it affects the overall performance of SLAM. While visual sensors, like cameras, can capture rich features of the environment, they, however, fail to work in low-light conditions. On the other hand, radio frequency sensors are invariant to light conditions, however, high-frequency signals such as millimeter wave (mm-wave) are prone to severe channel attenuation, therefore, they are suitable for short-range indoor applications. Despite the high localization accuracy that the mm-wave frequency band has to offer, its shortcomings have limited the amount of research work carried out to enhance the performance of SLAM. Therefore, this paper aims to provide an overview of the recent developments in radio SLAM, with a specific focus on mm-wave enabled localization and SLAM methods. However, some notable research work based on other radio frequency sensors has also been discussed. In addition, we highlight the role of deep learning-based methods for localization and identify some of the key challenges in data-driven implementation.

Highly Efficient Calibration of Antenna Arrays by Active Targets in the Near-Field

To enhance the capabilities of high-resolution imaging or beamforming, the trend goes towards arrays with high-channel count and large aperture sizes. The operation at increasing mm-wave frequencies exacerbates the consequences of manufacturing tolerances on the array performance, further necessitating the development of high-quality calibrations. Thereby, a large number of array response vectors, addressed in the following as data points, is stored. Typically, one data point is measured at a time for each angle. To reduce the calibration effort, hereby defined as the number of required measurements, a calibration setup employing active calibration targets (ACT) is proposed. This setup allows the storage of a multitude of data points within a single measurement. In addition, this measurement setup is placed in the near-field of the array to relax the requirements on the size of the anechoic chamber. Employing multiple targets makes it challenging to compensate the near-field effects. Therefore, methods are discussed to ensure a consistent quality of the calibration considering the near-field influences from the ACTs. Exemplary measurements deploying an antenna array operating at 78.5demonstrate that this calibration measurement setup employing three ACTs placed in the near-field of the array reduces the calibration effort by a factor of 3 compared to state-of-the-art setups. The average deviation of the antenna phase relations amounts to 4.1 degree, proving that the presented setup achieves the same calibration quality as state-of-the-art setups.

Broadband Characterization of Silicate Materials for Potential 5G/6G Applications

This paper provides a broadband dielectric characterization of different silicate substrates up to 115 GHz, to fill the gap of the properties of different kinds of glasses in a broad part of the mm-wave spectrum. Both the internal structure (crystalline or amorphous) and the chemistry of the substrates has an influence in the permittivity and loss tangent of the material. Quartz and sapphire are crystalline materials that exhibit low loss in the mm-wave frequency range. Amorphous silicates generally have higher loss values than crystalline materials, and within the glasses, the level of impurities added also affects the dielectric loss. Several characterization techniques have been employed to cover a broad frequency band. The limitations of the different characterization techniques are also included. Once the dielectric properties of substrates are characterized, a metasurface has been designed and fabricated at 100 GHz to increase the reflection in window glass and provide coverage on areas that would otherwise be shadowed. The measurement results are in good agreement with the simulations.