Microwave Frequency Band Research Articles

Ultrathin hybrid absorber based on high-order metamaterial

In this work, we utilized a hybrid resonator to achieve near-perfect and dual-band absorption in the VHF and the LTE/Bluetooth/WiMAX bands. An electromagnetic (EM) wave at an oblique incidence was captured efficiently by exciting the fundamental magnetic resonances at 106 and 123.4 MHz. In particular, the effective thickness of the metamaterial perfect absorber (in comparison with the working wavelength ) is miniaturized to be at the high-order resonances (induced in the 2.0–4.0 GHz range) at a specific incident angle of EM wave, = 45°, 30°, 15° and = 5°. Our results contribute to the realization of meta-devices, such as sensors, optical filters/switchers, photodetectors, and energy converters, for future applications in the radio to the microwave frequency bands.

Comparison of 1800MHz Frequency Bands Path Loss Measurements with Conventional Models in Osun State, Nigeria

The role of propagation models in the planning of wireless network, evaluation of cell parameters and frequency assignment cannot be overemphasized. One of the major difficulties with the application of path loss predicting models for any environment is that no two environments are the same in building patterns, terrain, atmospheric conditions, etc. It is therefore impracticable to formulate a single path loss model for all environments. In this study, an assessment of microwave frequency band measurement results based on received signal strength (RSS) values from four base stations in four urban environments in Osun State, Nigeria, are presented. The measured path loss values of each base station were extracted from the RSS values and compared with the results estimated from five conventional path loss models. Model comparison results based on three metric measures and fitting accuracy showed that a log-normal shadowing model exhibited a better agreement with the measured path loss with RMSE of less than 8 dB, the lowest RE, and R2 closer to one, in all the environments monitored. The best probable probability distribution for modelling the path loss at the investigated urban environments was also determined. The result of the various distribution functions tested using three goodness of fits showed that the normal distribution function offered the best match with the path loss values based on RMSE, RE, and R2 values calculated and fitting accuracy for both environments. Practical path loss parameters were also estimated for each of the base stations considered. The overall results should be useful for planning future mobile network channels.

Popularity and Size-Aware Caching With Cooperative Transmission in Hybrid Microwave/ Millimeter Wave Heterogeneous Networks

In this paper, a file popularity and size-aware (PSA) caching scheme is proposed for a hybrid heterogeneous network (HetNet) comprising a file server, macro base stations (BSs) operating in the microwave frequency bands, and pico BSs operating in the millimeter wave frequency wave bands. Different than the state-of-the-art size-weighted popularity (SWP) and popularity-based caching schemes that assume equal file size, the file PSA caching scheme utilizes knowledge of the file popularity and size distributions to maximize the network average cache hit probability and the network average success probability subject to the available cache capacity. Moreover, the maximization of the network average success probability is shown to be non-convex and dynamic programming and branch and bound algorithms are employed to circumvent its convexity. New expressions for the optimal file caching probabilities that maximize the network average success probability in noise-limited and interference-limited HetNet scenarios are provided which are evaluated using numerical techniques. The results demonstrate that the proposed file PSA caching scheme provides up to 7% gain in the network average success probability compared to the SWP-based scheme. Lastly, the combination of coded caching with cooperative transmission achieves up to 40% gain compared to a non-cooperative transmission scheme without coded caching.

A RFID Tag Antenna for Wearable Application System in Microwave Frequency Band

A RFID tag antenna for wearable application system in microwave frequency band is proposed and presented. The proposed RFID tag antenna is operated in the microwave frequency band of 1 to 12 GHz. Several numbers of the slot resonator are introduced that attached on jeans fabric as substrate material. The presence of the slot resonator also will be used to generate the unique identification or spectral signature of the RFID tag antenna. In real life, the monostatic radar system, which consists of the Vector Network Analyzer and a horn antenna is configured to test the RFID tag antenna. The performances of the proposed RFID tag antenna are evaluated based on their reflection coefficient, operating frequency, and surface current. The obtained results give a good agreement between the measurements and simulation.

Wearable metamaterial for electromagnetic radiation shielding

A novel wearable Frequency Selective Surface (FSS) created using fabric materials capable of blocking electromagnetic radiation around the frequency of 10.64 GHz (X Microwave frequency band) is presented in this paper. Two different unit cell shapes are tested: embroidered metal yarn squares and hexagons. A cotton fabric with permittivity 1.9 and thickness 0.4 mm is used as a substrate. The proposed design is validated by comparison of 3 D electromagnetic simulations and measurements. The obtained results correspond to a maximum absorptivity of 99.23% at 10.63 GHz for the simulation using a square as unit cell, whereas the simulations using hexagons led to a maximum in absorptivity of 99.94% at 10.68 GHz. Experimental results, at their turn, showed maximums of 98.39% for the squares and 98.00% for the hexagons, both at 10.46 GHz. So, results showed that the textile was actually offering a high degree of electromagnetic shielding, increasing the safety for civil and occupational exposures to electromagnetic radiation. In this case, this protection is offered at the microwave frequencies, used especially for telecommunications Earth-satellite which is in the range considered as a potential risk by the WHO (World Health Organization).

Compact dual and triple band antennas for 5G-IOT applications

AbstractDesigning miniaturized multiband antennas to cover both the 5G new radio frequencies (FR1 and FR2) simultaneously is a challenge for wireless communication researchers. This paper presents two antenna designs : a dual-band printed antenna of size 18 × 16 × 0.285 mm3 operating at FR1–5.8 GHz and FR2–28 GHz and a triple-band printed antenna with dimensions 30 × 25 × 0.543 mm3 operating at FR1–3.5 GHz and 5.8 GHz (sub-6 GHz microwave frequency bands) and FR2–28 GHz (mm-wave frequency band). The final projected triple-band antenna has a compact size with an impedance bandwidth of 12.71%, 11.32%, and 18.3% at 3.5 GHz, 5.8 GHz, and 28 GHz, respectively with the corresponding gain of 1.86 dB, 2.55 dB, and 4.41 dB. The measured radiation characteristics of the fabricated prototypes show that the proposed designs are suitable for trendy 5G-RFID and mobile Internet of things (IoT) applications.

A High-Power Sheet Beam Slow-Wave Structure of Traveling Wave Tubes

In future electronic devices, the trade-off between power capacity and thermal management will be a severe challenge. In this letter, a sheet beam slow-wave structure (SB-SWS) has been proposed to realize high-power output while taking into account cooling design inside the traveling-wave tubes (TWT). The design of the modified structure ensures a sufficient axial electric field component to realize efficient interaction, meanwhile expands the width of the metal vanes by 327% to design micro-channel cooling. The power load capacity for electronic interception increased by 25%. Utilizing all-period optimization technology, the maximum output power can reach 4 kW, corresponding 18.8% electronic extraction efficiency. Also presented further is a proof-of-concept design model of Ka-band for practical test. The consistency between experiment and theory shows that this SWS is not only suitable for microwave frequency band, but more suitable for future miniaturized devices in sub-millimeter wave and terahertz bands.

Single‐fed dual wideband filtenna for 4G / 5G mobile applications

This article presents a single-fed single-layer dual-band slotted antenna which has the ability to simultaneously operate at microwave and millimeter-wave (MMW) frequency bands. It consists of a rectangular slotted ground plane, double cascaded tuning stubs, and embedded MMW element of L-shape inside the slotted ground. Ultra-wideband bandstop filter (BSF) is inserted at the feeding for isolating the two operational bands. The BSF consists of 3-open circuited stubs and in-line coupled line section. For demonstration, a design prototype of the complete integrated filtenna is fabricated and measured. Good agreements between simulated and measured results are observed. The proposed filtenna operates at 5.2 and 28 GHz with impedance bandwidth (15.23% and 17.03%) and the gain reaches (4.09 and 6.18 dBi).

Mechanically toughened EMI shielding natural rubber composite in microwave frequency bands

ABSTRACT Mechanically toughened high electromagnetic interference (EMI) shielding natural rubber composite material was prepared and characterised. The aim of this investigation was to reveal the role of adding cobalt nanowire and conductive graphene nanoplatelet in toughening and EMI shielding effectiveness of rubber composite in microwave bands (E, F, I and J). The composites were prepared using two roll-mill and cured at 150οC. The mechanical and EMI shielding behaviour was measured following ASTM standards. The addition of graphene nanoplatelet improved the toughness and skin effect of rubber, whereas cobalt nanowire improved the magnetic permeability. A highest EMI shielding of −17.6 dB in absorption and −20 dB in reflection at 18 GHz was observed for the composite made of graphene nanoplatelet and cobalt nanowire of 3 and 8phr. These mechanically toughened promising EMI shielding composite materials could be used as EMI filters and electromagnetic wave absorbers in antennae application with good toughness.

Terahertz measurement based on Rydberg atomic antenna

Rydberg atoms have large electric dipole moments in the microwave and terahertz frequency band. The detection of electromagnetic field intensity in this frequency band can be achieved by using quantum interference effects. Theoretically, this detection method can have a sensitivity much higher than the traditional detection methods. Therefore, electromagnetic field detection and precision measurement technology based on Rydberg atomic quantum effects has great application prospects in terahertz field strength and power measurement, terahertz communication and imaging. In this paper, we review the basic theory and experimental methods to realize the self-calibration and traceability measurement of electromagnetic field based on Rydberg atomic quantum effects. The principle and technical scheme of high-sensitivity terahertz field strength measurement, terahertz near-field high-speed imaging and terahertz digital communication based on Rydberg atom are introduced in detail. Finally, the processing terahertz detection work based on Rydberg atom by our research team is also mentioned briefly.

Design and Experimental Analysis of Multiband Frequency Reconfigurable Antenna for 5G and Sub-6 GHz Wireless Communication.

A low-profile frequency reconfigurable monopole antenna operating in the microwave frequency band is presented in this paper. The proposed structure is printed on Flame Retardant-4 (FR-4) substrate having relative permittivity of 4.3 and tangent loss of 0.025. Four pin diode switches are inserted between radiating patches for switching the various operating modes of an antenna. The proposed antenna operates in five modes, covering nine different bands by operating at single bands of 5 and 3.5 GHz in Mode 1 and Mode 2, dual bands (i.e., 2.6 and 6.5 GHz, 2.1 and 5.6 GHz) in Mode 3 and 4 and triple bands in Mode 5 (i.e., 1.8, 4.8, and 6.4 GHz). The Voltage Standing Waves Ratio (VSWR) of the presented antenna is less than 1.5 for all the operating bands. The efficiency of the designed antenna is 84 % and gain ranges from 1.2 to 3.6 dBi, respectively, at corresponding resonant frequencies. The achieve bandwidths at respective frequencies ranges from 10.5 to 28%. The proposed structure is modeled in Computer Simulation Technology microwave studio (CST MWS) and the simulated results are experimentally validated. Due to its reasonably small size and support for multiple wireless standards, the proposed antenna can be used in modern handheld fifth generation (5G) devices as well as Internet of Things (IoT) enabled systems in smart cities.

Butler Matrix Based Beamforming Networks for Phased Array Antenna Systems: A Comprehensive Review and Future Directions for 5G Applications

Due to the rapid development of wireless communication technologies, the number of wireless users are radically increasing. Currently, ~23 billion wireless devices are connected to the internet, and these numbers are expected to increase manifolds in the years to come. The technology growth of the fifth-generation (5G) wireless systems will be needed to meet this high demand of the network. 5G wireless systems offer data-rates of up to 10Gbps, 1-ms latency, and reduced power consumption. It is a known fact that 5G wireless systems will be exploiting beyond the presently used 3 GHz microwave and millimetre-wave (mm-wave) frequency bands. This is the primary driver in the development of the 5G wireless system. Multi-beam Phased array antenna (PAA) systems are typically used in the deployment of 5G systems for high-gain and directionality. In current 5G and future Beyond 5G (B5G) antenna array systems, beamforming networks (BFNs) such as the Butler Matrix (BM) will play a key role in achieving multi-beam characteristics. So, this paper presents an extensive review of the BM based BFNs, and discusses which type of BM will be suitable for the phased array antenna (PAA) systems in the upcoming 5G and next-generation of B5G wireless systems. Moreover, this paper also summarizes the different types of BM designs based on the number of layers. The BMs are classified into the bi-layer, tri-layer, and four-layer structures. It includes different techniques that have been used to solve the problem of crossing, narrow bandwidth, and size reduction of the BM. From the previous studies, it is found that most of the past research work was performed using the bi-layer BM system, whereas the difficult geometries like tri- and four-layer BM are avoided due to their complex fabrication process. It is also found in this paper that the metamaterial (MTM) based bi-layer BM achieves low insertion-loss and phase-error, excellent bandwidth and compact size, and good S-parameter performance, which makes them an ideal BFN candidate for the upcoming 5G and next-generation B5G systems.

Reference Breast Phantoms for Low-Cost Microwave Imaging

Microwave imaging provides an alternative method for breast cancer screening and the diagnosis of cerebrovascular accidents. Before a surgical operation, the performance of microwave imaging systems should be evaluated on anatomically detailed anthropomorphic phantoms. This paper puts forward the advances in the development of breast phantoms based on 3D printing structures filled with liquid solutions that mimic biological tissues in terms of complex permittivity in a wide microwave frequency band. In this paper; four different experimental scenarios were created, and measurements were performed, and although there are many vector network analyzers on the market, the miniVNA used in this study has been shown to have potential in many biomedical applications such as portable computer-based breast cancer detection studies. We especially investigated the reproducibility of a particular mixture and the ability of some mixes to mimic various breast tissues. Afterwards, the images similar to the experimentally created scenarios were obtained by implementing the inverse radon transform to the obtained data.

RFI Suppression for SAR Systems Based on Removed Spectrum Iterative Adaptive Approach

A synthetic aperture radar (SAR) system can be seriously contaminated by radio frequency systems because of working in the same microwave frequency bands, which would degrade the SAR image quality and affect the accuracy of image interpretation. In this paper, a novel radio frequency interference (RFI) suppression approach including RFI identification, band-stop filtering and a removed spectrum iterative adaptive approach (RSIAA) is proposed. First, the smoothing process is added before RFI signal detection to improve the RFI detection capacity. Afterwards, the band-stop filtering with a broaden factor is proposed to mitigate the residual RFI, and it ensures the accuracy of the following removed spectrum recovery by the RSIAA. Finally, the removed spectrum components are estimated from available adjacent spectrum data by the RSIAA in turn to obtain the desired range spectra. Compared with the conventional range frequency filtering method for RFI suppression, the capacity of the weak RFI signal detection is improved, and the increased sidelobes due to the discontinuous spectra are well suppressed. Simulation experiments on both simulated SAR raw data, Gaofen-3 and Sentinel-1 SAR raw data validate the proposed RFI suppression approach.

100 GHz zinc oxide Schottky diodes processed from solution on a wafer scale

Inexpensive radio-frequency devices that can meet the ultrahigh-frequency needs of fifth- and sixth-generation wireless telecommunication networks are required. However, combining high performance with cost-effective scalable manufacturing has proved challenging. Here, we report the fabrication of solution-processed zinc oxide Schottky diodes that can operate in microwave and millimetre-wave frequency bands. The fully coplanar diodes are prepared using wafer-scale adhesion lithography to pattern two asymmetric metal electrodes separated by a gap of around 15 nm, and are completed with the deposition of a zinc oxide or aluminium-doped ZnO layer from solution. The Schottky diodes exhibit a maximum intrinsic cutoff frequency in excess of 100 GHz, and when integrated with other passive components yield radio-frequency energy-harvesting circuits that are capable of delivering output voltages of 600 mV and 260 mV at 2.45 GHz and 10 GHz, respectively. Nanoscale electrodes fabricated using adhesion lithography can be combined with solution-processed metal oxide semiconductors to create Schottky diodes with performance suitable for 5G communications and beyond.

Detection of Hazardous Liquids Using Microwave Data and Well-Known Classification Algorithms

The recent increase in terrorist attacks realized using liquid explosives has made it important to develop quick and reliable methods that can distinguish between nonhazardous liquids and other liquids that can be used in these explosives. Since the stability and sensitivity properties of microwave systems are high, microwave frequency band is preferred to differentiate hazardous liquids from non-hazardous liquids. In this study, a noncontact system based on electromagnetic response measurements of liquids in microwave frequency band is proposed to develop a classification approach that can be used in liquid scanners. Naive Bayes, linear discriminant analysis, qualitative data analysis, support vector machine, sequential minimal optimization, K-nearest neighbors classification algorithms are used to classify liquids and their classification performances are analyzed. The results of the set of classification experiments prove the success of the proposed measurement method. As the results prove, K-nearest neighbors is the most appropriate classification algorithm for hazardous liquid detection. Since it can be easily implemented and its detection process is fast, a classification system based on the proposed approach can be very useful in airports and shopping malls.

Distributed Beamforming in the Presence of Adversaries

In this article, we investigate the problem of distributed coherent beamforming in wireless networks where multiple distributed transmitters adjust the phases of their signals to form a directional and targeted communication link to a client receiver. The quality-of-service (QoS) and security are key components of robust and secure wireless networks. Although the security can be improved by exploiting information about potential adversaries, such information may not be available in practical networks since the adversaries are often passive. Therefore, we introduce transmission strategies which not only send a confidential message by forming a beam towards the client but also broadcast interference with the aim of obfuscating adversaries without having any information about them. Since the interference may degrade the QoS of the client, the transmitters radiating the interference steer a null to the client to alleviate the interference. We develop two algorithms. The first assumes that a subset of the transmitters send the confidential message in the direction of the client via coherent beamforming. Then, the others transmit interference while creating a null towards the client. In the second, each node transmits both the confidential message and interference simultaneously. Two different client feedback scenarios are considered, two-bit and rich feedback. Both of the proposed algorithms can be performed in a fully distributed manner without any knowledge about potential adversaries. Numerical simulations in both microwave and low-very high frequency (low-VHF) bands validate the effectiveness of the proposed schemes.

Crystal structure and microwave dielectric properties of a novel rock-salt type Li3MgNbO5 ceramic

A new rock-salt type compound, namely Li3MgNbO5, was synthesized using traditional two-step sintering process for the first time. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermal dilatometer and network analyzer. The Li3MgNbO5 ceramic sintered at 1260 °C adopted a cubic structure with Fm-3 m space group and exhibited excellent microwave dielectric properties (MDPs) of er = 16.2, Q × f = 96796 GHz, and TCF = − 24.8 ppm/°C. The fitting results of the infrared spectrum indicated that the dielectric polarization of Li3MgNbO5 in microwave frequency band was contributed by phonon absorption in infrared band. Furthermore, the negative TCF value of Li3MgNbO5 ceramic was compensated with a traditional TCF compensator ~ CaTiO3. A near-zero TCF value of + 1.2 ppm/°C was achieved in the composite 0.96Li3MgNbO5–0.04CaTiO3 ceramics with er = 18.4 and high Q × f = 86625 GHz, exhibiting a great potential to be applied in microelectronics systems.

The Use of Microwave and K* Algorithm in Determination of Alcohol Concentration in Liquids

Alcohol is widely used in various fields today. Alcohol overdose and its improper use can cause many health problems. Drinking liquids with high alcohol concentration, especially methanol, causes poisoning, and the use of colognes with high alcohol concentration causes various skin conditions and respiratory diseases. Therefore, for public health it is important to determine the type and concentration of alcohol in beverages and liquid products. In this paper, K* algorithm is used to detect and classify liquids containing high concentration of alcohol by measuring the scattering parameter of the liquids in the microwave frequency band. For this purpose, scatter parameter values of aqueous solutions of ethanol, methanol, 1-propanol and 2-propanol at different concentrations have been used as training sets. Commercial liquids with known ethanol concentrations and liquids with other known alcohol concentrations have been tested to prove the accuracy of the proposed approach. As the results show the proposed approach can classify liquids containing alcohol and their alcohol concentrations successfully and with high accuracy.

A theoretical investigation on reciprocity-inspired wide-angle spectrally-selective THz absorbers augmented by anisotropic metamaterials

In this paper, a theoretical framework relying on the reciprocity theorem is proposed to accurately design a spectrally-selective THz superstrate-loaded metamaterial absorber (SLMA) exhibiting wide-angle feature. By leveraging high-order Floquet harmonics in a generalized transmission line model characterizing the conventional metamaterial absorbers (MAs), it is demonstrated that MAs suffer from impedance mismatch, especially at near grazing angles. From an impedance matching viewpoint, this major challenge is tackled in this paper via two different designs, exploiting a magneto-electric anisotropic Huygens' metamaterial and a multilayer dielectric structure at a certain distance over the MA plane. The numerical results corroborate well the theoretical predictions, elucidating that the proposed SLMA significantly broadens the angular performance of the MA up to near grazing angles (about 80°), where high absorptivity is still achieved in both principal planes. The deteriorating effect of diffraction modes has been comprehensively analyzed. In comparison to the previous wide-angle MA reports based on intricate particle geometries and brute-force optimizations, the proposed design features a straightforward semi-analytical algorithm, which can also be re-developed for microwave, mid-infrared, and optical frequency bands and for any type of MA element. The proposed SLMA would be very promising for various wavelength-selective applications such as sensors and imaging.