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The potential of higher band millimeter waves for characterization of different types of breast tissues based on the dielectric contrast between normal and malignant tissues has been reported. Lowcost phantom samples of normal and malignant tissues have been prepared using naturally occuring components, i.e., agar, water, olive oil and pectin. Waveguide probe based calibration technique was used to extract the complex permittivities of the twocomponent (wateragar) and threecomponent (wateroilagar) phantoms. The twocomponent phantoms were used to study the change in the dielectric properties of phantom with change in agar concentration. Water, agar and varying proportions of oil were used to develop threecomponent phantom mixtures to mimic the dielectric properties of fat, fibrous and malignant breast tissues. Finally, the reflection and transmission properties of tissue mimicking phantoms were tested using the waveguide probe calibration based measurement setup. The difference in the S parameters between the three types of phantoms demonstrate the potential utility of D band based data acquisition setups for tumor margin assessment applications.

A simple and effective body-centric localization algorithm has been proposed in this paper using UWB wearable technology. The algorithm has been validated through measurement campaigns with a human subject volunteer in an indoor environment. The algorithm takes into account statistical channel parameter analysis, machine learning (ML) algorithms and time-of-arrival (TOA) based range estimation/data fusion techniques. Two channel parameters namely path loss magnitude and rms delay spread are proposed as classification features to be applied to the ML algorithm to accurately classify the off-body channel links into LOS, PNLOS and NLOS scenarios. Multi-class support vector machine (MC-SVM) classifier along with SMOTE algorithm to take into account class imbalance is applied with the channel classification accuracy of 98.63 %. Threshold based range estimation algorithms are applied in order to mitigate NLOS scenarios caused mainly due to the presence of the human subject. Results report human localization accuracy in 0.5-3 cm range using TDOA data fusion technique for target estimation. Further validation is presented considering wide range of Tx-Rx distance, presence of another obstruction between the Tx-Rx links and performance in different environment which shows the suitability of the proposed methodology.

This paper presents a very thin metasurface (MS) planar lens for millimeter wave MIMO applications. The MS planar lens consists of array of mm-wave resonators providing varying phase response to transform the phase profile of the electromagnetic wave propagating through this array. Each resonator consists of two identical layers having substrate separated by an air gap of h=0.8mm and are 4mm × 4mm in size. The MS lens having a focal length of f=12mm is loaded to a three-port proximity fed antenna array to operate at 27.5 GHz to 32 GHz. the designed lens is polarization insensitive and can be used with any polarization. The three-port antennas with the MS lens is fabricated and tested, measured results have confirmed a beam scanning of ± 15° with a peak gain of 20.2dBi for port-2.

In this work, a wide‐angle forward to backward scanning wideband leaky‐wave antenna (LWA) based on the microstrip spoof surface plasmon polaritons (SSPPs) transmission line (TL) is proposed. The proposed microstrip SSPP TL has tapered corrugations on both sides of the metallic strip conductor. After designing an efficient transition with a good transition occupation ratio and excellent transmission efficiency, a wide‐angle scanning LWA is realised. A methodology of achieving high gain and wide‐angle scanning by adjusting a large number of radiating elements in a compact area is proposed. The proposed antenna operates in the frequency range of 8.9–12.7 GHz having fractional bandwidth of 35.18% with a continuous scanning range from −35° to +51°. The maximum gain of 19.03 dBi with a maximum radiation efficiency of 90% is achieved from the structure. The proposed antenna can easily be integrated with planar wireless communication systems due to the presence of an unbroken ground plane.

In this article, a wideband transition from a microstrip transmission line to a microstrip spoof surface plasmon polariton (SSPP) transmission line is reported. The proposed transition is realized to achieve better performance starting from low frequencies up to 40 GHz. The proposed shape of the unit cell is taken in such a manner that the momentum, impedance, and polarization of the microstrip line can be matched with that of the SSPP transmission line. The wide operating band of the transition can be achieved by perturbing only the shape of the unit cell. Extra care is taken in choosing the shape of the unit cell so that the fabrication of the circuit becomes easier, especially at millimeter-wave frequencies. The proposed transition has a good transition-occupation ratio and transmission efficiency. The achieved transition-occupation ratio and transition efficiency for all three designed cases are excellent, and it is 34.18%, 44%, and 39% for p = 1 mm, 2 mm, and 3 mm, respectively. It is a potential candidate for realizing millimeter-wave antennas and devices due to its attractive properties, such as compact layout, low fabrication cost, ease of fabrication even at millimeter-wave frequencies, and good operational characteristics.

Wireless communication has witnessed rapid developments in the last few decades. To further improve the performance of wireless radio-frequency (RF) systems, emphasis has been given to designing multifunctional modules. The front end of RF systems includes transmitting/receiving antennas integrated with bandpass filters (BPFs). These integrated units are commonly known as filtering antennas or filtennas . The techniques related to designing filtennas have been continuously upgraded in the last couple of years. However, different design constraints are encountered during filtenna implementation, which can be better described in terms of frequency selectivity, bandwidth, high gain, radiation efficiency, polarization, and so on. Therefore, an extensive review has been carried out on integrated filtering antenna structures that were introduced during the last decade. The objective of the article is to present an overview of various approaches adopted to deal with different design challenges. The authors hope that this review exercise will be helpful for RF engineers to get a better understanding on filtenna designs and will encourage young researchers who would like to work in this domain.

This paper reports a non-invasive sub-Terahertz glucose concentration measurement system consisting of Sensor Unit (SU) and Processing Unit (PU). The SU. uses waveguide probe sensors to obtain the ${S}$ parameters of glucose samples of different concentrations. These ${S}$ parameters depend on the dielectric properties of glucose samples. The frequency-dependent permittivity values of various glucose samples are theoretically estimated using the double–Debye model for sensitivity and uncertainty investigations. The glucose sample concentration is used in the range 70–145 mg/dl to mimic healthy human bodies’ blood glucose levels, ranging from 70 to 140 mg/dl. The ${S}$ parameters obtained through SU are converted to the time domain to obtain real-valued impulse responses, which are normalized in PU, making the input data suitable for analysis using Levenberg–Marquardt (LM) algorithm-based Back Propagation Neural Network. The proposed SU. provides a sensitivity of 2 dB for 15 mg/dl change in glucose concentration, and PU exhibits an accuracy of ±5%, which falls within the clinical range specified for non-invasive based monitoring systems for diabetes. Overall, SU provides high sensitivity towards blood glucose measurement, and PU enhances the measurement system’s readability by forming a non–linear relationship between ${S}$ parameters and glucose concentration values

This paper presents an in depth analysis on the variation of the ultra-wideband (UWB) path loss (PL) statistics in the x–y plane and z-axis for the off-body links in relation to the position of the base stations (BSs) keeping the focus on the indoor body centric localization and sensing applications. In real life scenarios, apart from variation in linear distance between the BS and wearable antenna, and the BS/wearable antenna orientation varies over a coverage area leading to different types of links in the localization region such as LOS, NLOS and partial LOS/NLOS, which needs to be considered. The variation in PL statistics is dependent on various factors such as the orientation/placement of the wearable nodes, location of the human subject and the position of the BSs which has been evaluated in this work. For the mobile station (MS)-BS pair in which both line of sight (LOS)/non-(N)LOS links are present in the x–y plane due to change in position of the human subject over the localization region, are analyzed separately and show different PL statistics in comparison to total LOS/NLOS region. The change in PL magnitude in relation to the distance in the x–y plane or z-axis is more notable for LOS in comparison to NLOS scenarios. PL values in the range of 45–60/65–75 dB are observed for total LOS/NLOS links. The percentage of occurrence of LOS/NLOS links in the localization region is maximum for elbow/torso region and BS1/BS4 respectively. High accuracy localization results have also been presented which take into account channel information (such as PL analysis) and time of arrival (TOA) based range estimation/localization techniques. Hence, the influence of the spatial arrangement of the base stations and the wearable nodes is an important factor in WBANs channel modeling and classification.

This article proposes a single band circularly polarized (CP) rectenna operate at a 2.45 GHz Wi-Fi band, using a hexagonal shape of a microstrip radiator and a voltage doubler rectifier for smart c...

This paper presents two compact textile-based planar dipole and loop antennas for wearable communication applications operating in the 2.4 GHz industrial, scientific, and medical radio (ISM) bands. The antennas were fabricated on a 0.44 mm thin camouflaged-military print, cotton jean cloth using conductive copper threads, and sewing embroidery technique to create the radiating structure. Design and performance analyses of the antennas were carried out using simulations; further experiments were performed in anechoic chamber and indoor environment to validate the designs. The experiments were carried out in a free space scenario and on the various locations of the human subject such as the torso and limb joints. The performance of the antennas was investigated based on the reflection coefficient in normal and bent conditions corresponding to the different radii of the locations of the human limbs. The antennas perform well in free space and on-body scenarios in flat and bend conditions providing return loss below −10 dB in all cases with an acceptable resonant frequency close to 2.4 GHz due to the antenna bending and body effects. The radiation pattern measurements are also reported in this work for free space and on-body scenarios. It is observed that the presence of the human body significantly influences the antenna radiation pattern which leads to an increase in the front-to-back ratio and also makes the antenna more directive. Overall, the performance of the fabricated embroidered textile antennas was found suitable for various wearable body-centric applications in indoor environments.

In this article, a closed ring resonator-based absorber with eleven consecutive absorption peaks is proposed over X and K bands with an average absorption rate of 96.29%. The proposed design consists of circular ring resonators embedded in the circularly slotted square patch printed on the top of the grounded FR-4 substrate. The surface current distributions well illustrates the reason behind the electromagnetic (EM) wave absorption. The design is polarization insensitive for normal incidence and wide angular stable up to 45° for TE (60° for TM) polarization. The structure is fabricated on a single-layered FR-4 dielectric substrate with a periodicity of ${{\boldsymbol{\lambda }}_{\boldsymbol{o}}}$ /2.32 and thickness of ${{\boldsymbol{\lambda }}_{\boldsymbol{o}}}$ /16.74, where ${{\boldsymbol{\lambda }}_{\boldsymbol{o}}}$ is the free-space wavelength at the lowest resonant frequency. A transmission line-based equivalent circuit model has been illustrated and good agreement is observed with full-wave simulations. This article's novelty lies in the absorption mechanism of eleven consecutive absorption peaks, demonstrating the controllability of the absorptivity peaks and resonant frequency. To the best of the authors’ knowledge, the proposed absorber demonstrates the highest number of near-unity successive absorption bands with better angular stability. The proposed structure was checked for radar cross section reduction application with an X -band antenna and results show 19.7-dBsm reduction at normal incidence.

The past two decades have witnessed an unprecedented growth in the study and implementation of different short-range wireless services. However, the deployment of multiple short-range communication techniques has led to an overpopulation of the radio spectrum. Ultrawide-band (UWB) technology aims to offer an alternative to this spectrum scarcity as it can coexist with other radio technologies [Bluetooth, Worldwide Interoperability for Microwave Access (WiMAX), and Wireless Local Area Network (WLAN)] while causing minimal interference. The prospects of UWB technology allowing high data rate (up to 500 Mb/s) with low power consumption (l0.5 mW) up to a typical range of 10 m have escalated their demands over other short-range communication systems.

In this article, the authors have made an attempt to capture the recent developments taking place in the design of band pass filters (BPF) as a tutorial article. The article deals with the design o...

This article presents ultra-wideband (UWB) body-centric channel parameters for assessing the performance of the physical activities suitable for rehabilitation and physiotherapy purposes in the healthcare domain. Two channel parameters, path loss magnitude and rms delay spread, have been proposed to study the patterns/trends of various upper and lower limb activities for different positions. The channel for various activities has been distinguished into line of sight (LOS) and non-line of sight (NLOS) links. Three orientations of the wearable antenna have been considered for the placement on the wrist/ankle which are outer, inner, and front region, leading to significant differences in the channel parameters while performing physical exercises. The channel parameter values obtained are based on the orientation/placement of the wearable antenna, the distance between the two wearable nodes and the amount of obstruction caused by the human body, e.g., thigh/torso region. The proposed method enables effective monitoring capabilities and computes patterns of different exercises for all the limb positions measured, which in turn will aid in accurate human activity monitoring.

This article presents a design strategy to improve the bandwidth of the three-stage Doherty Power Amplifier (DPA) by controlling the phase difference between the dual RF inputs digitally. The theory also proposes multiple back-off reconfigurability without using tuning elements and extra circuitry. The proposed theory is validated by demonstration of a dual-input three-stage DPA which is designed and implemented using Wolfspeed’s GaN HEMT transistors. The measured results show a drain efficiency of 50.4 – 58% and 46.1 – 65.4% at 12 dB and 6 dB back-off respectively, over the frequency range of 550-900 MHz. Over this 350 MHz band, the drain efficiency is between 53.97% and 71.5% at saturation, corresponding to 48.3% fractional bandwidth. The measurement results also show that both the back-offs are reconfigurable by changing the drain bias of main and first auxiliary power amplifier. The modulated measurements are carried with a 10 MHz LTE signal with a PAPR of 11.75 dB. The high average efficiency of 51.6%, 54.9%, and 52.6% is reported at 600, 700, and 800 MHz, respectively, at an average power of around 30 dBm. The measurement results validate the theory proposed making the presented DPA as a potential candidate for future wireless transmitters.

In this letter, we present an innovative filter configuration employing transversal coupled triple-mode spherical resonators while capable of realizing transmission zeros (TZs). Transversal coupling involves simultaneous source and load-controlled couplings to all the three modes of the spherical resonator. Spherical resonators inherently have very large quality factor (Qu) and exhibit a farther spurious response thus yielding bandpass filters (BPFs) with lower insertion loss and wider spurious-free window. The design methodology for transversal coupling is explained and is employed for designing a third-order bandpass filter with TZs. In addition, a sixth-order bandpass filter using cascaded trisection is also presented. A third-order BPF with symmetric TZs is fabricated for verifying proof of the concept. The filter designed at 6.545 GHz with a bandwidth of 120 MHz has an insertion loss better than 0.1 dB and a spurious-free window better than 1.7 GHz. The proposed filter promises to be useful in aerospace applications that demand high Qu, low volume, and wider spurious-free window.