GHz ISM Band Research Articles

Compact Amplitude-Monopulse Antenna for Joint Two-Dimensional Direction Finding and Sectorized Communications in the 2.4 GHz ISM Band

Compact Amplitude-Monopulse Antenna for Joint Two-Dimensional Direction Finding and Sectorized Communications in the 2.4 GHz ISM Band

Optically control tissue-independent reconfigurable antenna for body-centric communications at 2.4 GHz ISM band

The objective of this article is to design a tissue-independent reconfigurable antenna that operates at the Industrial, Scientific, and Medical band (ISM band: 2.4 − 2.485 GHz) for body-centric wireless communications. The primary radiator of the proposed antenna consists of three concentric split-ring resonators (SRRs) and a photodiode appropriately placed between the rings. In addition, a hook-shaped slot in the ground plane, and a shorting pin between the radiator and the ground plane are employed to improve the impedance matching and adjust the resonance frequency, respectively. The optically controlled implantable antenna (OCIA) with the novel configuration operates in the respective frequency band in the skin and muscle tissue in the OFF state and the fat tissue in the ON state of the diode. The numerical design and analysis of the OCIA were carried out using CST Microwave Studio and the obtained results were verified by the in-vivo, ex-vivo, and in-vitro measurements of the fabricated antenna. To the best of the authors' knowledge, this is the first optically reconfigurable antenna capable of covering the 2.4 GHz ISM band within three different body tissues.

Circularly polarized implantable MIMO antenna for skin, brain and heart implantation with wide axial ratio bandwidth

SummaryA unique MIMO antenna with circular polarization characteristics that works similarly for skin, brain and heart phantoms has been proposed in this paper. The twin rectangular X‐shaped slot that serves as the basic structure of the proposed antenna is entirely planar and low‐profile but has a defective ground plane. For three different phantoms, the proposed antenna resonates at 2.4–2.45 GHz ISM band. With a dimension of , the antenna exhibits compactness. Rogers RT/duroid 6010 substrate material has been used to fabricate the antenna in order to validate the designed antenna structure. Utilizing the high dielectric material for both substrate and superstrate, both skin‐mimicking gel and minced hog meat were employed in the experiment setup at 2.45 GHz ISM band. At ISM band, −28.3 dBi has been observed has realized peak gain. The obtained fractional bandwidth (FBW) and Axial Ratio Bandwidth (ARBW) values are 30.67% and 45%, respectively. Also, the maximum specific absorption rate (SAR) values are found to be in the acceptable limit regulated by IEEE.

Design of highly selective balanced bandpass filter with wide differential-mode stopband and high common-mode suppression

A highly selective and wide stopband bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) has been proposed. The BPF employs a box-like coupling structure consisting of two half-wavelength resonators and a dual-mode open stub loaded resonator, enabling the generation of two TZs and four TPs. Three controllable TZs are obtained by adding an annular spiral open stub to the terminal of the input and output coupling lines, which significantly improves the selectivity of the BPF. To achieve a wide stopband characteristic, a wide stopband unit with three additional TZs is cascaded within the structure. A balanced BPF is realized by introducing a microstrip-slotline-microstrip balun structure to the input and output ports of the proposed BPF. Experimental results validate the feasibility of the proposed BPF and balanced BPF applied in 2.45 GHz ISM band. The introduction of eight TZs gives the BPF a 20 dB rectangular coefficient of 1.3 with an upper stopband exceeding than 12 GHz. The balanced BPF can achieve 40 dB of high common-mode(CM) suppression in the passband, while differential-mode (DM) transmission is close to the performance of the proposed BPF. The minimum insertion loss for BPF and balanced BPF is 0.8 dB and 1.3 dB, respectively.

A Dual-Band Low SAR Microstrip Patch Antenna with Jean Substrate for WBAN Applications

This paper presents a low-profile dual-band microstrip patch antenna operated at the 2.45/5.8 GHz ISM bands, targeting wireless body area network (WBAN) applications. The proposed antenna is fabricated on a jean substrate measuring 74×82 mm2. The four corners of the conventional rectangular patch are cut to activate an additional operating frequency and to enhance the radiation pattern. The circular slot is added to the radiating patch to fine-tune the desired frequencies. The measured impedance bandwidth of the proposed antenna at 2.45 GHz and 5.8 GHz bands is 3.68% (2.40 GHz–2.49 GHz) and 3.81% (5.67 GHz–5.89 GHz), respectively. The measured maximum gains are 3.08 dBi at 2.45 GHz and 2.15 dBi at 5.8 GHz. Moreover, the antenna’s performance when placed on flat and rounded body surfaces is also investigated. The proposed antenna achieves stable radiation pattern and low specific absorption rate (SAR) value with low complexity in design. The results indicate that the proposed antenna can be a promising candidate for WBAN applications.

Polarization Agile Reconfigurable Rectangular Patch Antenna for Biomedical Applications

A polarization agile patch antenna resonating at 2.4 GHz ISM band is presented. The antenna is based on a rectangular radiating element along with reconfigurable parasitic patches located at its periphery of the radiating element. Two switching diodes are used to reconfigure the geometry of the radiating element. Upon proper biasing of the switching diodes the antenna attains linear or circular (LHCP/RHCP) polarization states. The entire antenna is modelled using a high-frequency structure simulator and is validated using an Agilent network analyser (N9925A) and antenna test systems for measuring impedance and radiation characteristics. Over the entire operating band, the antenna shows better impedance matching and achieves −10 dB impedance bandwidth of 100 MHz (2.40-2.5 GHz) in linear state and 85 MHz (2.41-2.495 GHz) in the circularly polarization states along with peak gain of 5.61 dBi for LP state and 4.98 dBi for CP state in the operatingrange.

Development of a microwave chemical cell coupled with post-wall waveguide for in situ/operando soft x-ray absorbance spectroscopy under microwave irradiation

In this study, we developed a microwave chemical cell for total electron yield soft x-ray absorption spectroscopy (XAS) using synchrotron radiation under microwave irradiation. In addition, in situ XAS measurements of ammonia borane were performed using the device developed. The device comprises a post-wall waveguide housing a sample holder formed within it. Electrons emitted from the sample during soft x-ray irradiation pass through the metal plates of the waveguide and are measured using a picoammeter. Integration of the microwave irradiation structure into a synchrotron radiation beamline, which is a challenge in soft x-ray analysis requiring measurements in a high-vacuum atmosphere, was achieved by miniaturizing the device using 24.125 GHz ISM band microwaves, instead of the typical 2.45 GHz microwaves. Performance of the device was thoroughly assessed through temperature distribution simulation, temperature measurement of water, and evaluation of frequency characteristics. When the sample holder was filled with water and irradiated with 3 W microwaves, the temperature increased to 97 °C, which is close to the boiling point. The in situ XAS measurements performed using this device with ammonia borane/graphite (2:1) powder at the B-K edge during microwave irradiation showed that peaks associated with hydrogen desorption intensified with prolonged microwave exposure. This result indicates that microwave heating in a vacuum and soft x-ray analysis during microwave heating were achieved. The developed microwave chemical cell emerges as a powerful tool, facilitating advancements in our understanding of elementary chemical processes and elucidating microwave-specific effects such as local heating during microwave irradiation.

Design and Optimization of Double-Layered Wearable Antenna at 5.7GHz ISM Band

Design and Optimization of Double-Layered Wearable Antenna at 5.7GHz ISM Band

Permittivity-customizable Low-cost Laminated PET Sheet Multilayer Substrate to Design Flexible and Conformal Planar Inverted F Antenna

Abstract: In this article, a Planar Inverted F Antenna (PIFA) has been designed using low-cost commercially available transparent laminated sheets. Energy Dispersive X-ray (EDX) analysis is used to acquire the element composition of the transparent laminated sheet. Methods: The flexibility is attained using a market-available low-cost Polyethylene Terephthalate (PET) sheet as a substrate. The dielectric properties of this non-conventional laminated sheet need to be identified for antenna design and the microstrip ring resonator test method is used to determine the dielectric properties of the multilayer PET sheets. Results: The linear match has been observed on multilayer laminated PET sheets for dielectric properties and radiation characteristics. Adhesive copper foil of a thickness of 0.08 mm has been used as for conducting layer on the PET lamination sheet. As per the literature survey, it is evident that this is the first attempt to use the reported methodology for PIFA design application. The gain of proposed antenna is 5.2dB. Conclusion: The designed flexible antenna has been developed for wearable and IoT applications in 2.45 GHz ISM band. A good match has been observed between the simulated and measured characteristics.

Opportunities and Challenges of LoRa 2.4 GHz

Internet of Things (IoT) technologies are increasingly used in our daily life. Among these technologies, LoRa is widely used for low power IoT data collection in wide areas. LoRa typically operates in sub-GHz bands which are region-specific, and thus has limited world-wide applications. The version of LoRa developed for the 2.4 GHz ISM band has spurred recent interest in the scientific community, as it enables the use of worldwide frequency channels. However, it requires the coexistence with numerous concurrent technologies within this 2.4 GHz band, and an evolution of the MAC and networking protocols for utilizing LoRaWAN connectivity. In this paper, we make the first experimental comparison between LoRa sub-GHz and LoRa 2.4 GHz in both indoor and outdoor scenarios. We show that LoRa 2.4 GHz can have a communication range of more than 2 km outdoor, and it can achieve a packet delivery rate of at least 0.98 for a distance of up to 39 meters indoor with the presence of obstacles. We also make an extensive discussion on the researches challenges that need to be addressed in order to fully take advantage of this new technology.

A High-Performance Circularly Polarized and Harmonic Rejection Rectenna for Electromagnetic Energy Harvesting.

This paper presents a novel circularly polarized rectenna designed for efficient electromagnetic energy harvesting at the 2.45 GHz ISM band. A compact antenna structure is designed to achieve high performance in terms of radiation efficiency, axial ratio, directivity, effective area, and harmonic rejection over the entire bandwidth of the ISM frequency band. The optimized rectifier circuit enhances the RF harvested energy efficiency, with an AC-to-DC conversion efficiency ranging from 36% to 70% for low-level input power ranging from -10 dBm to 0 dBm. The stable output of DC power confirms the suitability of this design for various practical applications, including wireless sensor networks, energy harvesting power supplies, medical implants, and environmental monitoring systems. Experimental validation, which includes both the reflection coefficient and radiation patterns of the designed antenna, confirms the accuracy of the simulation. The study found that the proposed energy harvesting system has a high total efficiency ranging from 53% to 63% and is well-suited for low-power energy harvesting (0 dBm) from ambient electromagnetic radiation. The proposed circularly polarized rectenna is a competitive option for efficient electromagnetic energy harvesting, both as a standalone unit and in an array, due to its high performance, feasibility, and versatility in meeting various energy harvesting requirements. This makes it a promising and cost-effective solution for various wireless communication applications, offering great potential for efficient energy harvesting from ambient electromagnetic radiation.

Design and Realization of Wearable Textile Slotted Waveguide Antennas.

The design of wearable antennas presents a challenge from multiple perspectives, as they must meet technical requirements and satisfy safety standards while also being suitable for integration into clothing and aesthetically pleasing. In recent years, the development of conductive fabrics has, in many ways, allowed for significant progress in the manufacturing of wearable antennas, and in previous work, we developed textile slotted waveguide antennas using conductive textiles and traditional sewing processes. However, various aspects of the design and realization of such antennas remain challenging. In particular, this work investigates the issue of using foam-based molds, which enables the realization of thin, flexible, wearable antennas, as well as the issue of antenna feed, specifically the transition from a classic coaxial transmission line to a waveguide. The design of the transition was focused on simplicity and robustness, due to which we limited the number of degrees of freedom in the design process in order to achieve a structure suitable for mounting on textile waveguide antennas. In addition, the antenna design procedure and the body-channel model were considered in order to optimize the performance of the antennas and the wireless body-centric system itself. Several prototypes of different kinds were developed in the 5.8 GHz ISM band, confirming the feasibility of the proposed concepts through experimental results.

Performance evaluation of planar dipole antenna for smart home applications

In a Smart Home wireless module, the antenna generally occupies one-third of the total circuit advances in the Internet of Things (IoTs). Dipole antenna comes in various shapes, but the planar antenna is the most suitable and attractive design for the IoTs application in Smart Homes because it is smaller in size and has a thin profile, making it suitable for mounting on portable equipment. In this research, two antennae, Meandered Dipole and Wideband Planar Antenna, were designed using Advance Design System (ADS) software on a PCB size of 18.8 mm × 43.2 mm, FR4 substrate with 4.6 dielectric constant and 0.8 mm thickness using copper metal as the conducting element. The transmission line has designed width of 1.25 mm, resulting in a typical line impedance of 50 Ω. A comparison of the analysis of simulation and measurement results from feeding port 1 of the Meandered PIFA Antenna shows a better performance of 95.43% efficiency with a gain of 2.54391dBi and a return loss of −24.49 dB at resonant frequency of 2.4 GHz than that from feeding port 2 whose efficiency was only 73.99%. Whereas, the wideband planar antenna shows an average bandwidth of 93.91% from 1.3 to 2.4 GHz. This range covers the GPS applications, the 2.4 GHz ISM band, and the general WCDMA and the LTE 3GPP bands useable for smart home and IoT applications. The proposed antenna provides low power operation, extended range and compact, cost-effective designs to support vendor's customers, and make quality of life smarter and more economical with the use of the smart home device.

Microwave Grooved SRR Sensor for Detecting Low Concentration Ethanol-Blended Petrol

The rise in global energy demand due to economic development and an increase in population, have posed major concerns regarding energy security and environmental impact. Ethanol-blended petrol is an emerging alternative fuel that is considered cost-effective and environmentally friendly. However, the detection of low concentrations of ethanol in petrol is a significant challenge, especially as most nations mandate the blending of petrol with 5%-25% ethanol. This paper proposes a microwave sensor operating at 2.4GHz ISM band frequency to detect low concentrations of ethanol in petrol. The change in the magnitude of the reflection coefficient is adopted as the main sensing parameter. A single-frequency sensor composed of a square-shaped monopole loop antenna embedded with an SRR is proposed, which avoids the need for a wideband interrogation signal. The proposed design utilizes a filter paper wetted with the ethanol-petrol solution, placed along the split edge of the SRR, thus the use of complex and costly fluidic channels and space-consuming sample holders is avoided, bringing down the cost and complexity. The device dimensions are small, 4.2cm x 4.5cm. The sensitivity achieved in terms of amplitude change of the reflection coefficient is 2.83dB/5 % change of ethanol concentration in petrol, at a fixed frequency. In terms of the received power at 2.4GHz, the sensitivity is 2dBm/5 % change of ethanol concentration. Overall, this proposed sensor offers a simple, cost-effective, and efficient solution for detecting low concentrations of ethanol in petrol, which can aid in the adoption of ethanol-blended petrol as a viable alternative fuel.

Energy-Efficient Long-Range Sectored Antenna for Directional Sensor Network Applications

The popularity of Directional Sensor Network (DSN) is increasing due to their improved transmission range, spectral reusability, interference mitigation, and energy efficiency. In this paper, the radio module of the DSN is implemented using an eight-sector antenna array. Two types of sectored antennas, namely the Rectangular Patch Sectored Antenna (RPSA) and the Triangular Patch Sectored Antenna (TPSA), are proposed to operate at frequency of 2.4 GHz ISM band. The RPSA has a half-power beamwidth (HPBW) of 45° and a peak gain of 5.2 dBi, while the TPSA has an HPBW of 48° and a peak gain of 4.16 dBi. The design and performance evaluation of RPSA and TPSA in terms of gain, reflection characteristics (|S11|), and HPBW are conducted using Ansys High Frequency Structure Simulator (HFSS) and Vector Network Analyzer (VNA). To demonstrate the concept, the fabricated sectored antennas are connected to MicaZ Wireless Sensor Network (WSN) nodes using an indigenously designed Single Pole 8 Throw (SP8T) Radio Frequency (RF) switchboard. The performance of the DSNs based on RPSA and TPSA is evaluated using the Cooja simulator and a testbed consisting of MicaZ nodes. The results show that RPSA outperforms TPSA and omnidirectional-based WSNs in terms of power consumption, received signal strength, and packet delivery ratio.

Wideband TDoA Positioning Exploiting RSS-Based Clustering.

The accuracy of radio-based positioning is heavily influenced by a dense multipath (DM) channel, leading to poor position accuracy. The DM affects both time of flight (ToF) measurements extracted from wideband (WB) signals-specifically, if the bandwidth is below 100 MHz-as well as received signal strength (RSS) measurements, due to the interference of multipath signal components onto the information-bearing line-of-sight (LoS) component. This work proposes an approach for combining these two different measurement technologies, leading to a robust position estimation in the presence of DM. We assume that a large ensemble of densely-spaced devices is to be positioned. We use RSS measurements to determine "clusters" of devices in the vicinity of each other. Joint processing of the WB measurements from all devices in a cluster efficiently suppresses the influence of the DM. We formulate an algorithmic approach for the information fusion of the two technologies and derive the corresponding Cramér-Rao lower bound (CRLB) to gain insight into the performance trade-offs at hand. We evaluate our results by simulations and validate the approach with real-world measurement data. The results show that the clustering approach can halve the root-mean-square error (RMSE) from about 2 m to below 1 m, using WB signal transmissions in the 2.4 GHz ISM band at a bandwidth of about 80 MHz.

Dielectric Characterization of Fabric Aggregates around the 2.45 GHz ISM Band under Various Humidity, Density, and Temperature Conditions.

Fabric permittivity is critical for the manufacturing of wearable sensors and antennas as well as predicting how fabrics interact with electromagnetic fields. Engineers should also understand how permittivity changes under different temperatures, densities, and moisture content values, or when several fabrics are mixed in aggregates, when designing future applications such as microwave dryers. The permittivity of cotton, polyester, and polyamide fabric aggregates is investigated in this paper for a wide range of compositions, moisture content levels, density values, and temperature conditions around the 2.45 GHz ISM band using a bi-reentrant resonant cavity. The obtained results show extremely comparable responses for all characteristics investigated for single and binary fabric aggregates. Permittivity always increases as temperature, density, or moisture content levels rise. Moisture content is the most influential characteristic, causing enormous variations in the permittivity of aggregates. Fitting equations are supplied for all data, with exponential functions used to accurately model variation in temperature and polynomial functions employed to precisely model density and moisture content variations with low error levels. The temperature permittivity dependence of single fabrics without the influence of air gaps is also extracted from fabric and air aggregates by using complex refractive index equations for two-phase mixtures.

A Wearable Localized Surface Plasmons Antenna Sensor for Communication and Sweat Sensing

This paper presents a novel wearable antenna sensor based on localized surface plasmons (LSPs) for communication and non-invasive sweat monitoring. The sensor is made up of corrugated plasmonic structures based on the conventional printed monopole antenna, which achieves multi-band and miniaturization. The physical dimensions of the antenna sensor are 35 × 34 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with a thickness of only 0.13 mm. Simulated and measured results demonstrate that the proposed antenna sensor covers triple operating bands, including 2.4 GHz and 5.8 GHz ISM bands, as well as high frequency ultra-wideband ranging from 7.89 GHz to 9.56 GHz. The antenna sensor exhibits a good radiation pattern with a peak gain of 3.02 dBi and a high quality factor (Q) up to 35. The use of polyimide as a dielectric substrate enables the antenna sensor to achieve flexibility and conformality, maintaining stable operating states even when bent and deformed. The specific absorption rate (SAR) values in three frequency bands are simulated and evaluated to ensure its safety for human health. Moreover, the resonant frequency of antenna sensor significantly shifts with the volume and concentration of sweat, indicating that the proposed sensor is highly sensitive to sweat volume and concentration with a sensitivity of 120 MHz/1mm and 4.57 MHz/1, respectively. The proposed wearable antenna sensor is a promising candidate for a sweat monitoring system for athletes or patients, allowing for health monitoring at any time and place.

Improved Spectrum Coexistence in 2.4 GHz ISM Band Using Optimized Chaotic Frequency Hopping for Wi-Fi and Bluetooth Signals.

Efficiently managing coexistence is crucial for achieving high-quality wireless communication in the Industrial, Scientific, and Medical (ISM) band where multiple wireless communication systems operate. Coexistence problems between Wi-Fi and Bluetooth Low Energy (BLE) signals are especially significant due to their shared frequency band, which often leads to interference and a reduced performance for both systems. Therefore, effective coexistence management strategies are essential for ensuring the optimal performance of Wi-Fi and Bluetooth signals in the ISM band. In this paper, the authors conducted a study to investigate coexistence management in the ISM band by evaluating four frequency hopping techniques: random, chaotic, adaptive, and an optimized chaotic technique proposed by the authors. The optimized chaotic technique aimed to minimize interference and ensure zero self-interference among hopping BLE nodes by optimizing the update coefficient. Simulations were conducted in an environment with existing Wi-Fi signal interference and interfering Bluetooth nodes. The authors compared several performance metrics, including the total interference rate, total successful connection rate, and trial execution time for channel selection processing time. The results indicated that the proposed optimized chaotic frequency hopping technique achieved a better balance between reducing interference with Wi-Fi signals, achieving a high success rate for connecting BLE nodes, and requiring minimal trial execution time. This makes it a suitable technique for managing interference in wireless communication systems. While the proposed technique had a higher interference than the adaptive technique for small numbers of BLE nodes, for larger numbers of nodes it had a much lower interference than the adaptive technique. The proposed optimized chaotic frequency hopping technique provides a promising solution for effectively managing coexistence in the ISM band, particularly between Wi-Fi and BLE signals. It has the potential to improve the performance and quality of wireless communication systems.

Design and analysis of compact flower-shaped wideband slotted monopole antenna for RFID reader applications

This article introduces the design and analysis of a compact, high gain, and wide bandwidth flower-shaped slotted monopole antenna for RFID reader antenna applications. The proposed antenna comprises a flower-shaped radiator with six arc-shaped slots and a partial ground plane. The measurement results indicate a wide operating band in the frequency range of 2.4 GHz–7.6 GHz. The proposed antenna is designed to operate at 5.8 GHz ISM band for RFID reader applications with a peak measured gain of 3.9 dBi. The structure has an overall dimension of 0.78λ× 0.58λ× 0.03λ at an operating frequency of 5.8 GHz and is found compact in comparison to some related designs. The monopole antenna shows an omnidirectional radiation pattern in the operating band and indicates a maximum realized gain value of 4.2 dBi. The study provides a detailed mathematical analysis of the operating principle with surface current distribution plots. The design indicates a reading range of 2.56 cm at 5.8 GHz and the satisfaction of the propagation-test makes the compact, wideband, and high-performance design suitable for different short-range RFID reader applications.