Vol. 116

This paper proposes a Yagi-Uda antenna array realized on a Silicon substrate and supported by a substrate integrated waveguide for multi-band operation in the K and Ka bands. The structure of the dipole and the first director of the Yagi-Uda antenna were modified and tuned for multi-band response, making it completely novel in comparison to the existing Yagi-Uda structures supporting multi-band operation. As the feed, a substrate integrated waveguide was designed to assist with multi-band operation and to overcome the challenges presented by the Silicon substrate. An array is implemented to improve the gain. The antenna array's prototype was constructed and tested to back up the claims. The proposed array operates at frequencies of 23.7, 26.3, 27.5-28.3, and 29.4 GHz. The array exhibits good end-fire radiation patterns for the resonant frequencies, with a peak gain of 19.65 dBi and an efficiency of 89.8% at 23.7 GHz. This is the first report of an antenna fed by a substrate integrated waveguide and realized on Silicon with a high gain and applications in the K and Ka bands.

This proposal presents a novel design of a reconfigurable antenna with frequency, polarization, and pattern diversities for wireless body area networks. The design makes use of a 3.2 mm thick FR4 substrate of 39X36 mm² dimensions with a square patch and partial ground structure. The antenna operates in sixteen different modes and resonates at various frequencies ranging from 2.456 to 14.384 GHz. The proposed model has the capability to exhibit elliptical as well as linear polarization with different radiation patterns. For suitability of the proposed design in healthcare applications its SAR analysis has been performed along with other antenna characteristics like reflection coefficient, gain, radiation pattern, and axial ratio. Four PIN diodes have been used to switch the antenna operational modes.

Due to recent developments in wireless communications, frequency reconfigurable antennas have increased in popularity. This paper presents an integrated design for MIMO antennas that uses octagonal ring-shaped with a frequency-tunable dual-band reconfigurable for wireless communication applications. On the ground plane, the designed antenna has four octagonal ring-shaped radiators with a total size 50 x 50 x 1.6 mm³. In the center of each radiator, a varactor diode is employed to control the capacitive reactance of the slot to provide frequency reconfigurability. Between orthogonally positioned antennas, rectangular defective ground gaps are used for isolation purposes as well. Dual-band operation is achieved by linking the varactor to a slot line of radiating rings. The antenna's lower-frequency band resonates at 4.2 GHz, and its upper-frequency band can be tuned from 4.55 to 5.56 GHz (with isolation > 25 dB in the operating bands). The simulated results are found to be highly consistent with the experimental data. As a result, frequency agility, large tuning range, compactness, and planar structure make it appropriate for a wide range of existing and future wireless communication applications.

Magnetoacoustic concentration tomography with magnetic induction (MACT-MI) is a noninvasive imaging method that reconstructs the concentration image of magnetic nanoparticles (MNPs) based on the acoustic pressure signal generated by the magnetic properties of MNPs. The performance of MNPs is of great significance in MACT-MI. To study influences of the uniaxial anisotropy of MNPs on MACT-MI, firstly, based on the static magnetization curve, the force characteristic that the MNPs with uniaxial anisotropy experienced was analyzed. The magnetic force equation with the space component separated from the time term was deduced. The acoustic pressure equation containing the concentration of the MNPs with uniaxial anisotropy was derived. Then, a two-dimensional axisymmetric simulation model was constructed to compare magnetic force, acoustic source, and acoustic pressure before and after considering the uniaxial anisotropy of MNPs. The effect of scanning angle and detection radius of ultrasonic transducer on the acoustic pressure was studied. Finally, the concentration image of the MNPs with uniaxial anisotropy was reconstructed by the time reversal method and the method of moments (MoM). Theoretical considerations and simulation results have shown that the magnetic force has a triple increase after taking into account the uniaxial anisotropy of MNPs. The take-off time of acoustic pressure waves is only related to the position of the uniaxial anisotropy MNPs region. From the reconstructed image, concentration distribution and spatial location and size information of the uniaxial anisotropy MNPs region can be distinguished. The research results may lay the foundation for MACT-MI in subsequent experiments and even clinical applications.

This paper analyzes and solves the complexity to determine the optimum positions of the Fishnet & Complementary Circular Ring Resonator (CCRR) based Defected Ground Structures (DGS) for Substrate Integrated Waveguide (SIW) based antennas. A new state-of-art technique based on Artificial Neural Network (ANN)-Machine Learning (ML) is proposed for overcoming the lack of solid and standard formulations for the computation of this parameter related to a targeted frequency. As a proof of concept and to test the performance of our approach, the algorithm is applied for the determination of the CCRR and Fishnet-DGS's optimal positions for a SIW based antenna. The SIW technique provides the advantages of low cost, small size and convenient integration with planar circuits. The ANN-ML based technique is optimized to attain dual-band resonances with optimal gain and radiation efficiency. The simulation results of the first Fishnet-DGS based antenna show good minimum return losses at two center frequencies, namely, 16.6 GHz (with gain of 6 dB and radiation efficiency of 95%) and 17.7 GHz (with gain and radiation efficiency of 9 dB and 96%, respectively). The second CCRR-DGS based antenna shows about 8\,dB gain and a radiation efficiency of 87% at 17.3 GHz, and gain and efficiency of about 8.5 dB and 85% are observed at 17.8 GHz. The proposed CCRR and Fishnet-DGS based antenna are low profiles, low costs, with good gains and radiation efficiencies, making both designs very suitable for Ku-band applications. There is a fair agreement between the measured and simulated results. The achieved dual-band resonances act as a proof of concept that the proposed ANN-ML techniques can be employed for the determination of the optimal positions for CCRR and Fishnet thereby attaining any target dual-bands in the Ku-band with good accuracy of about 98% and a save of 99% in the overall the computational time.

In this paper, an intracranial hemorrhage stroke detection and classification method using microwave imaging system (MIS) based on machine learning approaches is presented. To create a circular array-based MIS, sixteen elements of modified bowtie antennas around a multilayer head phantom with a spherical target with radius of 1 cm as an intracranial hemorrhage target are simulated in CST simulator. To obtain satisfied radiation characteristics in the desired frequency band of 0.5-5 GHz a suitable matching medium is designed. Initially, in the processing section, a confocal image-reconstructing method based on delay-and-sum (DAS) and delay-multiply-and-sum (DMAS) beam-forming algorithms is used. Then, reconstructed images are generated, which shows the applicability of the confocal method in detecting a spherical target in the range of 1 cm. Separating and categorizing targets is a challenging task due to the ambiguity in the extracted target from MIS. Thus, to distinguish between healthy and unhealthy brain tissues, a new compound machine learning technique, including filtering, edge-detection based segmentation, and applying K Means and fuzzy clustering techniques, which reveal intracranial hemorrhage area from reconstructed images is adopted. Simulated results are presented to validate the proposed method effectiveness for precisely localizing and classifying bleeding targets.

This paper proposes a dual-beam switchable self-oscillating active integrated array antenna for Ku-band wireless power transfer systems. The oscillation is sourced by a positive feedback type Push-Push oscillator, which shows an excellent measured output power of +9.3 dBm obtained at the second harmonic frequency as well as good suppression of the undesired harmonics. The generated RF power from the oscillator excites four patch antenna elements. Moreover, a PSK modulator is adopted for binary phase switching between 0˚ and 180˚. Using in/anti-phase RF signal combination of the antenna elements, it is possible to switch between two beams, sum and difference radiation patterns. The proposed structure is fabricated and tested; the measured results verify the dual-beam switching concept with an effective isotropic radiated power (EIRP) of +17.77 dBm, DC-to-RF efficiency of 0.43%, and an oscillator figure of merit (FOM) of -158.05 dBc/Hz at the second harmonic frequency of 14.7 GHz.

In this paper, a highly efficient microstrip diplexer with low insertion loss, high selectivity, and high isolation is introduced. The proposed diplexer employed two compact size coupled squared open-loop resonator (SOLR) based band pass filters (BPFs). Firstly, a matching network is utilized to ensure that the two BPFs and the antenna load are properly matched. This is accomplished by connecting the two BPFs and the antenna with a conventional T-junction that acts as a combining circuit, resulting in good isolation between the up-link and down-link BPFs. As a second step, a defected ground structure (DGS) is used to improve the overall filter response in terms of insertion loss and isolation without affecting the diplexer selectivity. Based on this structure, the proposed diplexer has two resonance frequencies of 2.5 GHz and 2.8 GHz. The structure provides good insertion losses of about 1.6 and 1.3 dB for the two channels, respectively with fractional bandwidth of 2.8% at 2.5 GHz and 3.2% at 2.8 GHz. The measured isolation levels are 70 dB and 50 dB for 2.5 GHz and 2.8 GHz, respectively. The proposed diplexer is useful for several wireless communication applications such as WiMAX. The good agreements between simulated and measured results verified the practical validation of the proposed diplexer.

In this work, a radio frequency (RF) micro-electromechanical system (MEMS) based analog phase shifter is presented over 17-30 GHz. The proposed phase shifter is made using two back-to-back single-pole-seven-throw (SP7T) switches and connected through seven distributed MEMS transmission lines (DMTL). The SP7T switch is designed with lateral electrostatic actuation and demonstrates measured average return loss of > 11.3 dB, insertion loss of < 5.94 dB, and isolation of > 22 dB up to 30 GHz. Total area of the SP7T switch is only 0.89 mm² including bias lines and pads. The proposed wide-band phase shifter can be tuned at all the frequencies between 17 and 30 GHz. Phase shifter gives measured average insertion loss of < 6.94 dB, return loss of > 10 dB, and phase error of ~10 at 17 GHz to 30 GHz over 500 MHz bandwidth. All phase shifts can be tracked with a resolution of 22.50 based on predefined actuation voltages. Total area of the fabricated device is ~11.72 mm². In addition, switches and phase shifter work satisfactorily > 1 billion cycles with 0.1-1 W of RF power. The proposed phase shifter bank gives phase shifting performances at each frequency over 17-30 GHz with a constant resolution utilizing analog tuning, and it operates > 1 billion cycles of reliability with 1 W of RF power.

A novel 4-element UWB MIMO (multiple-input multiple-output) slot antenna with triple band-notched characteristics is designed and fabricated. It is composed of four rectangular slot antennas with two C-slots and a T-slot. To improve the isolation, cross-shaped branches are added. The measured results demonstrate that the antenna can operate ranging 2.51-11.07 GHz with the impedance bandwidth (S₁₁ < -10 dB) of 856 MHz except three rejected bands, including 3.02-4.07 GHz, 4.54-5.83 GHz and 7.88-9.38 GHz, and the inter-element isolation of antenna in the range of UWB band is higher than 21 dB. The presented antenna can filter the interference of WiMAX (3.3-3.7 GHz), WLAN (5.15-5.825 GHz) and X-band (7.9-8.4 GHz). What's more, the parameters of diversity performance like envelope correlation coefficient (ECC), diversity gain (DG), efficiency, gain, channel capacity loss (CCL), mean effective gain (MEG) and total active reflection coefficient (TARC) have been analyzed. Based on the analysis on simulated and measured results, the proposed MIMO antenna is competent for UWB applications with notched bands for WiMAX, WLAN and X-band.

Low power, near-field (NF) radar imaging techniques have been proposed for breast cancer detection and long-term monitoring. It is important to optimize the data processing paths required for NF image reconstruction given the inherent resolution limitations of microwave compared to MRI or X-ray imaging. A key limitation in obtaining internal tumour and breast feature information is the reflection from the skin surface physically close to the antenna. Typically, algorithms to remove this dominant reflection involve subtracting an estimate of the time domain signal for the skin reflection from one antenna location using information from other locations. A key challenge in these approaches is determining the portion of the signal, the skin dominant window (SDW), to use to determinethe weights applied to nearby antenna signals when calculating the skin reflection estimate. Equipment limitations and breast characteristics impact the amount of data that can be captured, leading to the well-known Gibbs' ringing distortionsin the time domain signals. We suggestthat the Gibbs' ringing from the magnitude larger skin reflection has caused the length of the SDW to be over-estimated in previous determinations. Since this distorted signal now overlaps the time signals from the tumour and breast responses, removing the skin reflection estimatemay result in attenuation of tumour responses. In this contribution, two alternative strategies for designing the SDW are proposed. One minimized the first skin peak in the SDW, i.e., the furthest from the breast feature signals, and the other minimized the main, i.e., largest, skin peak within the SDW. Both new approaches were shown to effectively suppress the skin signal on simulated and patient data while allowing recovery of the missing portions of the desired internal breast feature signals leading to an increase in the overall intensity of the images and preserving the tumour response. However, we provided reasons why we considered that basing the suppression on the largest skin signal peak would provide a more consistent improvement in the breast feature signals.

In recent years, additive manufacturing has found increasing interest in fabrication of dielectric antennas. Using additive manufacturing brings significant advantages such as design flexibility, compactness, fast and low-cost manufacturing compared to traditional fabrication methods. Dielectric antennas having dense material allow high power transfer efficiency through the lens. However, a successful 3D printing process with dense dielectric materials is a great challenge. In this paper, impact of main process parameters during 3D printing; namely printing speed, process temperature and layer height on the resulted relative electrical permittivity values of a dense dielectric material is investigated. Test samples are printed with a dielectric material having ε_r = 10, and relative permittivity variations of these samples are measured with a vector network analyzer in X-band (8.2-12.4 GHz). In this way, optimum printing parameters are determined. Influence of dielectric constants of printed materials on the antenna radiation characteristics are inspected for an extended hemispherical lens antenna by a full-wave computer-aided design tool. Results demonstrate that an additively manufactured dense dielectric antenna will act as a traditionally manufactured dielectric antenna if and only if it is manufactured with optimum printing parameters.

As the advanced technology in the Internet of Things (IoT), ultra-high frequency radio frequency identification (UHF RFID) tag has broad application prospects and significant research value. However, the transmission performance of UHF RFID on the metal surface and embedded in metal is severely impaired, bringing new challenges to its application for long-distance reading and writing. On this basis, an embedded metal UHF RFID tag design method is proposed in this paper. A planar inverted F antenna (PIFA) structure is optimized to enhance the anti-metal performance of the tag. The embedded feed design is adopted to achieve preferable impedance matching between antenna and chip. Besides, a series of electromagnetic simulations were investigated to optimize the performance of the tag, which can ultimately achieve the maximum gain of -9.7 dB in the metal groove, with the reduced volume of 19.8 mm×25.8 mm×2 mm by employing the meandering technology and the method of adding metal via holes. Finally, when the self-made tag is embedded in the metal groove, the experimental results demonstrate that the maximum reading distance can reach 1.26 m, indicating that the tag developed in this paper has significant practical value in the case of embedded metal.

A MIMO antenna for smartphones with radiation diversity is presented in this article. The proposed design consists of dual-fed Complementary Split Ring Resonator metamaterial antenna components design, which is located at the edges of an FR-4 substrate. The total dimension is 75 mm x 150 mm x 1.6 mm. 50-ohm dual microstrip feed lines placed orthogonal to each other are used to feed the SRR. Due to this orthogonality, radiation diversity is easily achieved. The proposed structure is operated in dual bands from 3.43 GHz to 3.62 GHz and 4.78 GHz to 5.04 GHz. In both, the band's good impedance bandwidth with a reasonable gain is achieved. The entire structure is simulated using CST EM software. All the simulated results are presented, which clearly show that the proposed structure is a good candidate for the future smartphone massive MIMO application.

A multiband circularly polarized microstrip patch antenna including a Minkowski fractal slot for wireless communication applications in the frequency bands 1.39 GHz, 2.45 GHz (WLAN band), 3.48 GHz (Mobile Wi-Max), 5.8 GHz (U-NII high-band) and 6.29 GHz has been proposed. The proposed antenna consists of two substrates mounted on top of the ground plane. The antenna has been fed with a 50 Ω microstripline which is etched on top of the lower substrate. The second iteration Minkowski fractal slot is etched on the truncated square patch which is on top of the upper substrate. The substrate has a size of 80 mm x 82 mm x 1.6 mm. The measured results show that the proposed antenna could excite for five resonant bands of 1.35 GHz, 2.45 GHz, 3.5 GHz, 5.8 GHz and 6.25 GHz and has reflection coefficients of -15 dB for 1.35 GHz, -16 dB for 2.45 GHz, -22 dB for 3.5 GHz, -23 dB for 5.8 GHz and -13 dB for 6.25 GHz as well as an axial ratio bandwidth of 3.42 GHz-3.47 GHz. The maximum gains of the antenna are 5.92 dBi for 1.39 GHz, 6.15 dBi for 2.45 GHz, 8.36 dBi for 3.48 GHz, 9.64 dBi for 5.8 GHz and 6.69 dBi for 6. 29 GHz. The simulations and optimizations have been carried through Computer Simulation Technology Microwave Studio (CST-MWS) software.

A compact pot-shaped Multiple Input Multiple Output (MIMO) Antenna with Triple notched band characteristics is presented for Ultra Wide Band (UWB) Applications. The comprehensive dimension of the presented antenna is 17×32 mm². The presented antenna has two identical pot-shaped radiators, 7-shaped stubs, T-shaped strips, M and C-shaped slots. Two novel 7-shaped stubs are connected to the antenna ground plane to obtain -22 dB enhanced isolation. The presented antenna works from 2.95 to 12.1 GHz with triple stopped WiMAX, WLAN, and X bands. A novel T-shaped strip is connected to the antenna ground plane to stop the WiMAX band (3.3-4.4) GHz. C and M-shaped slots are etched in the antenna radiators to stop WLAN (5.20-6.12) GHz and X (7.6-8.15) GHz bands respectively. The peak gain of the proposed antenna is from 1.5 to 5 dB with a radiation efficiency of 80-90%. The Envelope Correlation Coefficient (ECC) of the proposed antenna is less than 0.01 with a Diversity Gain greater than 9.99 except for the notched bands.

In this paper, a rectangular eight shaped Electromagnetic Band Gap (EBG) structure at 5.8 GHz Industrial, Scientific and Medical (ISM) band for wearable application is proposed with intent to improve impedance bandwidth of antenna. The unit cell of an EBG structure is formed using eight shape on outer ring with inner square patches. The simulation of the eight shape EBG unit cell is carried out using eigen mode solution of Ansys High Frequency Structure Simulator (HFSS). Simulated results are validated by experimental results. The application of proposed EBG for an inverse E-shape monopole antenna at 5.8 GHz is also demonstrated. Band stop property of EBG structure reduces surface waves, and therefore, the back lobe of a wearable antenna is reduced. The frequency detuning of antenna takes place due to high losses in human body. Suitably designed EBG structure reduces this undesirable effect and also improves front to back ratio. The proposed compact antenna with designed EBG has observed the impedance bandwidth of 5.60 GHz to 6.15 GHz which covers 5.8 GHz ISM band. Evaluation of antenna performance under bending condition and on-body condition is carried out. Effectiveness of EBG array structure for Specific Absorption Rate (SAR) reduction on three layer body model is demonstrated by simulations. Calculated values of SAR for tissue in 1 g and 10 g are both less than the limitations. In conclusion, it is appropriate to use the proposed antenna in wearable applications.

Cross polarization (X-pol) effect is the undesired radiation of an antenna which wastes bandwidth (BW) and power of the communication system. Especially in the miniaturized microstrip antenna (MSA) the X-pol level is more. The observed X-pol level of the classical MSA at the direction of maximum radiation (φ =0˚) is -49.72 dB, whereas X-pol level of miniaturized H shaped MSA (MHMSA) is -39.96 dB. This paper presents miniaturized complementary split ring resonators loaded H shaped microstrip antenna (CSRR-MHMSA) and slots and CSRRs loaded MHMSA (S-CSRR-MHMSA) with reduced X-pol level. An array of CSRRs and slots are placed at the ground of the proposed antenna. Due to slots, the antenna is miniaturized and the polarizability of the electric field along the desired direction is increased by CSRRs. The CP-XP (Co-pol X-pol) isolation of CSRR-MHMSA and S-CSRR-MHMSA at φ =0˚ are measured. The measured E plane CP-XP isolation for CSRR-MHMSA and S-CSRR-MHMSA is 29.00 dB and 26.73 dB respectively. The measured CP-XP H plane isolation for CSRR-MHMSA and S-CSRR-MHMSA is 27.00 dB and 24.5 dB, respectively. While bandwidth (BW), gain G and radiation efficiency η are improved.

This work presents high isolation UWB-MIMO antenna with a bandwidth of up to 8.6 GHz based on a Minkowski fractal structure. The proposed antenna is fed by microstrip and be comprises two orthogonal monopole antennas, which delivers a decent isolation effect. Moreover, the ground is designed as two separated blocks with an I-shaped branch for improving the isolation degree between the units. The resultant isolation degree of this antenna is greater than 25 dB. Besides, the electromagnetic interference in the partial frequency band (such as Wi-Max band (3.45-4.45 GHz), WLAN band (5.1-5.8 GHz) and X-band (7.25-7.75 GHz)) is further prevented through etching a split-ring resonator (SRR) and C-slot on the unit. The antenna reflection coefficient of the UWB-MIMO antenna at the notch is 3.5 dB, which indicates that the antenna has a conspicuousness anti-interference effect. Through the above judicious design, the proposed UWB-MIMO antenna possesses a relative bandwidth of 113% (up to 8.6 GHz), and the envelope correlation coefficient between antenna units is less than 0.005, and the antenna radiation efficiency is up to 80%. The results indicate that the proposed MIMO antenna meets UWB applications.

In this paper, a novel design of a small printed Ultra-Wideband (UWB) Multi-Input Multi-Output (MIMO) antenna with a wide impedance bandwidth from 3.05 GHz to 11.65 GHz is introduced. The newly designed UWB MIMO antenna has an isolation enhancement of more than -15 dB between the two elements. This isolation is achieved by inserting a three-line stub on the ground plane between the two radiating elements. In addition, these parallel lines improve the impedance matching and the bandwidth of this structure. Dual band notched characteristics are achieved for the 5G band (3.6 GHz) and the Wi-fi 6E application (6 GHz), by loading the split ring resonator (SRR) on the ground plane at the back of antenna and etching a complementary split ring resonator (CSRR) in both the truncated square patch elements, respectively. The SRR and its complement are metamaterials structures, showing the behavior of an LC resonator circuit. The hybrid technique improves impedance matching, bandwidth, minimizes the mutual coupling in UWB frequency range, and delivers dual-notch characteristics. The simulation and measurement results of the proposed antenna with a good agreement are presented. The proposed structure exhibits high performances in terms of envelope correlation coefficient (ECC), diversity gain (DG), efficiency, total active reflection coefficient (TARC), and channel capacity loss (CCL) except the notched band.