In this article, a single-layer frequency selective surface (FSS)-loaded compact coplanar waveguide (CPW)-fed antenna is proposed for very high-gain and ultra-wideband applications. At the initial stage, a geometrically simple ultra-wideband (UWB) antenna is designed which contains CPW feed lines and a multi-stub-loaded hexagonal patch. The various stubs are inserted to improve the bandwidth of the radiator. The antenna operates at 5–17 GHz and offers 6.5 dBi peak gain. Subsequently, the proposed FSS structure is designed and loaded beneath the proposed UWB antenna to improve bandwidth and enhance gain. The antenna loaded with FSS operates at an ultra-wideband of 3–18 GHz and offers a peak gain of 10.5 dBi. The FSS layer contains 5 × 5 unit cells with a total dimension of 50 mm × 50 mm. The gap between the FSS layer and UWB antenna is 9 mm, which is fixed to obtain maximum gain. The proposed UWB antenna and its results are compared with the fabricated prototype to verify the results. Moreover, the performance parameters such as bandwidth, gain, operational frequency, and the number of FSS layers used in the proposed antenna are compared with existing literature to show the significance of the proposed work. Overall, the proposed antenna is easy to fabricate and has a low profile and simple geometry with a compact size while offering a very wide bandwidth and high gain. Due to all of its performance properties, the proposed antenna system is a strong candidate for upcoming wideband and high-gain applications. With the rapid advancements in wireless communication technology, the current and impending communication systems necessitate electrically small, geometrically simple, and low-profile antennas with high gain and wideband characteristics ,2. Due tIn addition to the aforementioned techniques, frequency selective surfaces (FSSs) have been investigated recently for gain improvement. FSSs based on artificial intelligence are used for gain enhancement, however, these types of FSS require a lot of knowledge and coding skill which are time-consuming . Thus, aOn the other hand, various single-layered FSS-loaded antennas are reported in the literature ,36,37,38Considering the limitations and discrepancies observed in previously reported works, this work proposes a simply shaped, compact, ultra-wideband, low-profile, and high-gain FSS-loaded patch antenna for WiMAX, 5G sub-6 GHz, C-band, S-band, and X-band applications used for 5G and future 6G communicating devices. The rest of the article is split into three sections. In In this section, the design of the proposed ultra-wideband antenna as well as proposed FSS, along with design stages and optimization algorithm, is discussed. The performance of the antenna, as well as parametric analysis of key parameters, is also explained in this section.1 × L1 × H = 32 mm × 25 mm × 1.52 mm. Moreover, the results were verified by using the electromagnetic (EM) software High Frequency Structural Simulator (HFSSv9). The optimized parameters of the proposed ultra-wideband antenna are given below:1 = 32, W2 = 11, W3 = 1.5, W4 = 5, W5 = 8, L1 = 25, L2 = 5, L3 = 8, L4 = 4, L5 = 2, L6 = 9.5, R = 8.5, H = 1.52; all units are in millimeters (mm).WIn order to obtain the required antenna characteristics, various design steps were carried out to obtain the final proposed antenna geometry operating at ultra-wideband. In the first step, the hexagonal patch antenna with CPW feedline was designed for the central frequency of 12 GHz. The antenna has operational bandwidth of 2 GHz covering 11–13 GHz. In the second step, the rectangular stub was added between the radiating patch and the feedline. The addition of this stub increases the electrical length of the antenna, which results in an improvement in return loss and bandwidth. The antenna starts operating at 11 GHz and 15 GHz with a return loss of less than 15 dB. In the third step, another rectangular stub was added below the existing stub, as shown in 11| and identifying the antenna parameters R, W2, W4, W5, and L3. Refs. [A genetic algorithm (GA) was used in collaboration with the full-wave modeling tool (CST MWS) to improve the characteristics of the UWB antenna. Genetic algorithm optimizers, as is well known, are robust stochastic search techniques based on the ideas and concepts of natural selection and evolution. The optimization was completed quickly and efficiently by identifying design goals for a UWB impedance bandwidth with a low |S3. Refs. ,40,41 ha4 and W5 is discussed in this section. The length of the lower rectangular stub (W4) was analyzed to observe the impact on the |S11| characteristic. At its optimal value of W4 = 5 mm, the proposed antenna offers a wideband of 5–17 GHz with resonant frequencies of 8 GHz and 13 GHz. When the value of W4 is fixed at 4 mm, the proposed antenna’s bandwidth is reduced to a dual band of 7.5–9.5 GHz and 12–17 GHz. Similarly, when the value is increased to 6 mm, again in the dual band, a slight shift towards the left side is noticed, as given in To obtain the final geometry of the proposed UWB antenna, various design steps (as discussed above) as well as parametric analysis of important and key parameters were performed. The parametric analysis of rectangular stubs W5 = 8 mm, ranging from 5–17 GHz. If the value is reduced to 7 mm, the wide bandwidth and return loss are compromised and generate dual frequency bands at 8 GHz and 14 GHz with bandwidth ranging from 7.5–9 GHz and 12.5–15.5 GHz, respectively. If W5 is increased to 9 mm, the suggested UWB antenna operates over 7–15 GHz, which implies a reduction of bandwidth, as shown in In X × MYM = 50 mm × 50 mm. The proposed FSS offers a wide stopband, ranging from 4–18 GHz, as given in X = 10, CY = 10, C1 = 9, C2 = 9, C3 = 0.5, C4 = 1.25, R1 = 2, R2 = 2.75; all units are in millimeters (mm).To obtain the final geometry of the proposed UWB antenna, various design steps (as discussed above) were carried out. In this portion, the working mechanism of the proposed FSS-loaded UWB antenna is explained. The suggested antenna design is planted above the FSS sheet to reflect the radiation of the antenna coming from the back direction. The reflected wave by the FSS placed behind the antenna is in-phase with the antenna radiation, which results in an improvement in gain. The most important parameter is the distance or gap (G) between the antenna and FSS, which establishes the constructive interface of wave reflecting back from the FSS with the waves radiating from the proposed UWB antenna. The equation given below is used to adjust the gap between the antenna and FSS .𝜑 − 2𝛽G11| behavior of the suggested compact and UWB antenna in the presence and absence FSS is given in Equation (1) is composed of three parts: the reflection phase (𝜑), the free space propagation constant (𝛽), and the gap between the antenna and FSS (G), while π = 3.1415. The space in the middle of the antenna and FSS structure is optimized in order to obtain higher gain as well as wideband. In the case of the proposed work, the gap G = 9 mm. The placement of the antenna over the FSS structure is given in In The recommended UWB antenna’s gain versus frequency plot, either with or without FSS, is displayed in The radiation efficiency of the suggested UWB antenna is given in The suggested UWB antenna’s radiation pattern at resonance frequencies of 8 GHz and 13 GHz is illustrated in In This article presents a geometrically simple, compact, ultra-wideband (UWB) antenna with a frequency selective surface (FSS) that provides high gain. The antenna contains a simple hexagonal patch with multiple stubs inserted to obtain an ultra-wideband of 5–17 GHz. Afterwards, to reflect radiation directed backward, the FSS layer is positioned beneath the antenna to slightly improve bandwidth and enhance gain from 6.5 dB to 10.5 dB. The resultant FSS-loaded antenna offers an ultra-wideband of 15 GHz, ranging from 3–18 GHz. The FSS array contains 5 × 5 unit cells, which have an overall size of 50 mm × 50 mm. The proposed UWB antenna and FSS layer are engineered on top of Rogers RT/Duroid 6002 with a thickness of 1.52 mm. The proposed FSS-loaded UWB antenna is designed using the electromagnetic (EM) software tool High Frequency Structure Simulator (HFSS v9). The software-predicted outcomes of the suggested antenna loaded with FSS were verified with a fabricated hardware prototype. The suggested FSS-loaded UWB antenna was also contrasted with published research, demonstrating that it is a strong contender for future wireless high-gain and wideband devices.


In this paper, a stereoscopic ultra-wideband (UWB) Yagi–Uda (SUY) antenna with stable gain by near-zero-index metamaterial (NZIM) has been proposed for vehicular 5G communication. The proposed antenna consists of magneto-electric (ME) dipole structure and coaxial feed patch antenna. The combination of patch antenna and ME structure allows the proposed antenna can work as a Yagi–Uda antenna, which enhances its gain and bandwidth. NZIM removes a pair of C-notches on the surface of the ME structure to make it absorb energy, which results in two radiation nulls on both sides of the gain passband. At the same time, the bandwidth can be enhanced effectively. In order to further improve the stable gain, impedance matching is achieved by removing the patch diagonally; thus, it is able to tune the antenna gain of the suppression boundary and open the possibility to reach the most important characteristic: a very stable gain in a wide frequency range. The SUY antenna is fabricated and measured, which has a measured −10 dBi impedance bandwidth of approximately 40% (3.5–5.5 GHz). Within it, the peak gain of the antenna reaches 8.5 dBi, and the flat in-band gain has a ripple lower than 0.5 dBi. The 5G is the current generation of mobile communications expected to provide higher data rates and high-speed connectivity for multimedia applications ,2,3,4,5.In this paper, the magneto-electric dipole (ME) structure is used to improve the bandwidth of the antenna by impedance matching and to enhance the antenna gain by electromagnetic superposition. In order to further improve the gain of the Yagi antenna, metamaterials are proposed below to improve the Yagi antenna gain. In , enhanceIn this paper, we propose the SUY antenna which has ultra-wideband and stable gain for the RF energy harvesting to obtain a stable output voltage and conversion efficiency. The following three steps are used to achieve the characteristics of the ultra-wideband and stable gain: First, the ME structure is used to achieve the reinforcement of broadband and gain. Second, a pair of C-notches is cut out of the surface of the ME structure to make a near-zero-index metamaterial (NZIM). This metamaterial structure not only produces out-of-band radiation suppression by energy absorption but also increases the bandwidth of the antenna. Finally, in order to further improve the stable gain, the director and driven element achieve impedance matching for enhancement of the gain of the suppression boundary. To show the advantages of the SUY antenna stable gain, as shown in  antenna .To analyze the SUY antenna more clearly, the SUY antenna is divided into the A-type antenna, B-type antenna, C-type antenna, and D-type antenna in The C-type antenna realizes the filtering of out of band suppression by NZIM, which also increases the antenna bandwidth. The D-type antenna increases and flattens the gain of the upper suppression boundary at 4.9–5.5 GHz by adding director layer. The SUY antenna achieves stable the gain of lower suppression boundary from 3.5 to 4 GHz by cutting out the diagonal of patch 1 and patch 2. The four kinds of antennas are analyzed in the following sections.The ME structure has two characteristics: one is to improve the antenna gain by the electromagnetic superposition principle and the other is its impedance matching to improve the bandwidth as shown in Equations (1) and (2). As shown in First, the reason for the electromagnetic superposition at 4.7 GHz is illustrated to explain that the gain of the B-type antenna can reach more than 9 dBi. As shown in Equation . Finally factors .(2)1Q=Zmpedance .In this section, the dual-C-notch NZIM structure is designed to achieve two targets: one is to improve the out-of-band suppression by introducing the radiation nulls of the lower and upper gain stopbands by energy absorption and other is to enhance the bandwidth by impedance matching. This design idea of dual-C-notch NZIM is derived from absorptive-branch-loaded structure and dual-notch NZIM structure ,31. For The absorption function of NZIM is verified from two aspects: first, it is proved that the dual-C-notch belongs to NZIM at 2.6 GHz and 5.5 GHz; second, it has absorption function at 2.6 GHz and 5.5 GHz by electric field simulation. First, as shown in nit cell .In order to further improve the stable gain, the gain of the suppression boundary is enhanced to achieve two targets: one is to enhance the gain of upper suppression boundary by addition of the director layer from 4.9 to 5.5 GHz and the other is to improve the gain of lower suppression boundary by the diagonal cut of the patch from 3.5 to 4 GHz.Firstly, according to the Yagi antenna principle, the director layer is added to the C-type antenna to improve antenna gain. The antenna is defined as a D-type antenna. As shown in Secondly, there are three ways to improve the gain of upper suppression boundary: one is to add another director layer, another is to change the length of patch 1 and 2, and the last is to change the shape of patch 1 and 2. The first method reduces the overall gain of the antenna, so it is not used. The second and third methods are verified in terms of which method is suitable to improve the gain of upper suppression boundary by the quality factor (ion loss .(5)Qr=3hickness .(6)D=2xTo verify the validity of our design concept, a prototype of the proposed SUY antenna is fabricated and measured. The experimental setup in the anechoic chamber and the SUY antenna fabricated prototype are shown in In this paper, stereoscopic ultra-wideband (UWB) Yagi–Uda (SUY) antenna with stable gain by NZIM has been discussed and analyzed in detail. Its advantages are high gain, wide bandwidth, and stable gain. The disadvantage is that the three-dimensional size is larger. The combination of coaxial feed and ME structure using electromagnetic superposition and the impedance matching principle achieve high gain and excellent broadband performance. The NZIM with two radiation nulls as well as flat in-band radiation gain is realized in a poof-of-concept prototype of SUY antenna. In order to further improve the stable gain, adjusting the director and driven element impedance enhance the gain of the suppression boundary. The demonstration antenna has been designed and implemented, and the simulated and measured results with good accordance have been presented.


To meet the real demand for broadband full-band high-gain antenna sensors in the process of partial discharge (PD) Ultra-High frequency (UHF) detection test and online monitoring of power equipment, this paper builds a resonant cavity monopole UHF antenna sensor based on Fabry–Perot resonant cavity antenna technology, conducts the sensor Voltage Standing Wave Ratio (VSWR) optimization study using curved flow technology, conducts the sensor gain optimization study using slot dual resonant structure, and, finally, tests the sensor performance using the built PD detection test platform. The resonant cavity monopole antenna exhibits outstanding VSWR performance in the frequency range of 0.37 GHz–3 GHz, according to simulation and test data: the average gain in the frequency range of 0.3 GHz–3 GHz is 4.92 dBi, and the highest gain at the primary resonant frequency of 1.0 GHz is 7.16 dBi, with good radiation performance over the whole frequency spectrum. The electromagnetic pulse signal sensed by the UHF sensor developed in this paper can demonstrate the energy spectrum distribution characteristics of PD radiation electromagnetic wave signal more comprehensively, laying a firm technical foundation for thoroughly understanding the electromagnetic wave radiation characteristics of various types of PD insulation defects of various power equipment and the selection of a specific direction for its supporting optimization. Partial Discharge (PD) is one of the main causes of electrical power failures, which can lead to insulation deterioration, electrical faults, and equipment failures, and can even trigger safety risks such as fire and explosion ,2,3,4.The Ultra High Frequency (UHF) method is a method to determine the location, nature, and intensity of PD by using UHF sensors to receive high-frequency electromagnetic waves (300 MHz~3 GHz) generated by the PD inside the power equipment. By transmitting the received signals to the detection system they can be analyzed and processed, which has the advantages of high sensitivity and strong anti-jamming ability, and has been widely used in the power field and laboratory PD detection test has been widely used ,6,7,8.However, the area where PD is generated by power equipment is not fixed, resulting in the energy spectrum distribution of the electromagnetic wave signals radiated by PD in different types and different insulation environments also not being fixed. Although the International Electrotechnical Commission standard IEC 60270-2015 and China’s national standard GB/T 7354-2018 both put forward explicit requirements for the sensitivity of UHF sensors in the 300 MHz–3 GHz band range ,10, fromMore importantly, although a large number of currently developed UHF sensors meet the requirements of the relevant standards, the volatility between the corresponding sensor performance parameters  at different frequency points or different frequency bands means that the PD high-frequency electromagnetic wave signals obtained from power field PD monitoring or laboratory PD detection cannot fully respond to the PD radiation electromagnetic wave energy spectrum characteristics, and cannot guide the subsequent optimization of UHF sensors for different types of PD detection in diverse power equipment  ; therefoTo address the above problems, this paper carries out research on the design of broadband high-gain monopole UHF antenna based on the Fabry–Perot resonant cavity antenna design idea, carries out sensor VSWR optimization using curvilinear flow technique and sensor gain optimization using slot dual resonant structure, and uses High Frequency Structure Simulator (HFSS) to optimize and simulate the antenna structure, in the end, the designed antenna is prototyped and the performance of the antenna is tested and analyzed using a vector network analyzer and PD simulation experimental platform.A monopole patch antenna is a very common antenna, which usually consists of a radiating patch on a thin dielectric substrate and a relatively grounded metal floor for receiving electromagnetic signals propagating in space and feeding through coaxial probes, microstrip, or coplanar waveguides, with the advantages of a low profile, small size, and simple fabrication .R is the base radius of the equivalent cylinder, L is the height of the equivalent cylinder, a is the width of the radiating patch of the monopole antenna, and b is the length of the radiating patch.The planar monopole patch antenna can be approximated with an equal height cylindrical structure , as showg between the metal floor and the radiation patch, the lowest working frequency Lf of the antenna is obtained as follows:c is the speed of light and λ is the wavelength corresponding to the lowest operating frequency. After considering the effect of the dielectric substrate on the resonant frequency of the antenna, Equation (2) is corrected, that iseffε is the equivalent dielectric constant. It can be estimated asrε is the relative permittivity of the substrate.The real part of the input impedance of the monopole patch antenna is slightly less than 1/4 wavelength monopole length while considering the gap The above theory can be used to estimate the starting size of the monopole patch antenna. Subsequently, the design can be optimized on this basis to achieve the desired performance.w and the microstrip transmission line characteristic impedance z satisfies:h is the thickness of the dielectric substrate. The desired impedance, dielectric substrate thickness, and equivalent dielectric constant are brought into the equation to calculate the microstrip line width for good impedance matching.The microstrip feed line is a common way to feed antennas, its basic principle is to achieve the feed by laying metal strip lines on the dielectric substrate. When the electromagnetic wave propagates to the microstrip feed line, a surface wave is generated between the microstrip line and the ground plane, and this surface wave propagates along the microstrip line and eventually reaches the antenna radiation element. The microstrip transmission line width The Fabry–Perot resonant cavity is a multi-beam optical interferometer that can be used to accurately measure the wavelength and refractive index of light, invented by French physicists Charles Fabry and Alfred Perot in 1897 . The intLater, research scholars discovered that a similar principle could be applied to the field of antenna sensors, leading to the invention of the Fabry–Perot resonant cavity antenna. In the literature , Li Lu ll, between which multiple reflections of electromagnetic waves occur. The feed antenna and its floor are a fully reflective plate with a reflection coefficient of p, and the phase is The Fabry–Perot resonant cavity configuration is shown in n reflections, the superposition of the electric field intensity of all transmitted waves transmitted through the partially reflected layer gives:F(α) is the feed antenna radiation direction function, E0 is the maximum radiation field strength, nθ is the phase difference between the transmitted wave beam n, and the transmitted wave beam 0p < 1, we can obtain:α direction:α = 0°, and S is maximum when n = 0, 1, 2, … are satisfied, and its maximum value isp of the partially reflected surface [After The resonant cavity UHF antenna sensor designed in this paper is a Fabry–Perot resonant cavity monopole antenna sensor, which contains two parts: the feed antenna and the partial reflection cladding. The feed antenna is a microstrip monopole patch antenna with optimized VSWR using curved flow technique and optimized gain using slot dual resonant structure.rε= 4.4, the dielectric loss tangent angle tanδ = 0.03, and the thickness of the dielectric substrate h = 2.8 mm. The microstrip monopole antenna designed in this paper uses SMA coaxial feed with a characteristic impedance of 50 Ω.The dielectric substrate of the microstrip monopole antenna designed in this paper is rectangular rigid material FR-4 epoxy resin, the relative dielectric constant of the substrate Since the energy of the PD signal is concentrated in the range of 500 MHz–1.5 GHz, and the common monopole patch antenna is often used in the frequency band above 3 GHz in the communication field, if we want to make it detect partial discharge, we need to extend its working band.In this paper, the patch of monopole patch antenna in Curved flow technology is a technique to make the surface current flow along a specific structure on the metal patch of microstrip antenna by making slots or adding slits, introducing multi-step structure, etc. Such a design can free the equivalent length of the antenna from the physical length limitation, thus effectively increasing the equivalent length of the microstrip antenna and improving the bandwidth of the antenna without increasing its size ,22,23,24HFSS software is used to simulate and analyze the antenna with the above parameters and structure, and the data of VSWR is shown in The traditional slot double resonant structure is in the antenna surface of an artificially created rectangular groove: the groove will form a resonant cavity, so that the propagation of electromagnetic wave resonance thus increasing the antenna gain, but this practice will make the antenna bandwidth greatly reduced. Therefore, this paper uses the idea of slot dual resonant structure to form a slot dual resonant structure similar to the effect of a concave resonant cavity by adding a circle of peripheral patches around the microstrip monopole antenna as shown in The geometric parameters of the slotted dual resonant structure of the antenna in The VSWR and gain performance of the improved monopole antenna are simulated and analyzed. From the VSWR simulation plot in The general partial reflection cladding with the feed antenna has a narrow bandwidth, which is because the reflection coefficient of the partial reflection layer becomes smaller in phase as the frequency increases and is a negative reflection phase gradient . For thiThe partially reflective cladding unit designed in this paper adopts a single-layer double-sided asymmetric square structure, while empirically loading the perforations to make the gain performance smoother, and its structure is shown in a is 60 mm and the back square patch width b is 64 mm. The distance of the perforation with a diameter of 2 mm from both sides of the square patch is 20 mm in both x and y.To meet the desired direction of improvement, the front square patch width Wb = 20.6 mm and Lb = 2.6 mm.The front unit structure is expanded into a uniformly distributed 3 × 3 partial reflection cladding. The selection of dielectric substrate material is the same as the microstrip monopole antenna, i.e., FR-4 epoxy resin. The dimensions of the whole partial reflection cladding are also consistent with the microstrip monopole antenna, length × width × thickness = 205.2 mm × 241.2 mm × 2.8 mm, and the structure of the composed partial reflection cladding is shown in The feed antenna designed in Voltage Standing Wave Ratio (VSWR) is a parameter used to describe the ratio of reflected signal strength and forward signal strength at the input port of the antenna, measuring the impedance matching ability between the input and output circuits of the antenna. When the signal enters the transmission line and reaches the antenna sensor, part of the signal will be reflected back to the transmission line, while the other part will be transmitted into the air; these reflected waves will be superimposed with the original waveform, creating the so-called “standing wave”, which has a negative impact on the transmitted energy and signal. VSWR can be calculated by the following equation:In addition, since the UHF antenna sensor operates in a UHF environment, the signal attenuates quickly, so it is necessary to ensure that as much signal as possible is transmitted to the antenna to ensure the sensitivity and accuracy of the antenna. Therefore, a lower VSWR value is critical for the quality and stability of the transmission circuit in this case, so a lower VSWR is a fundamental requirement for the design and use of high-performance UHF antenna sensors. When VSWR ≤ 2 the antenna sensor receives the best electromagnetic energy, but in fact VSWR ≤ 5 can meet the engineering needs, so this paper will use VSWR ≤ 5 as the PD detection bandwidth of power equipment ,32,33,34The Fabry–Perot resonant cavity monopole antenna model in The VSWR of the physical antenna was measured using an E5063A vector network analyzer manufactured by Agilent with the same sweep range of 300 MHz–3 GHz. As shown in The gain directional map is a parameter used to describe the directionality of the antenna and the antenna efficiency, measuring the degree of concentration of the radiant energy of the antenna in free space and the degree of effectiveness of the antenna in converting wave energy into high-frequency current or energy ,35,36. TThe gain direction plots of the designed Fabry–Perot resonant cavity monopole antenna at six frequency points of 0.7 GHz, 1.0 GHz, 1.4 GHz, 2.0 GHz, 2.4 GHz, and 3.0 GHz are shown in The HFSS simulation shows that the average gain of the designed resonant cavity monopole antenna is 4.92 dBi in the frequency band of 0.3 GHz–3 GHz, and the maximum gain at each frequency point obtained from the simulation is given in 1, a regulator, a step-up transformer T2, a protection resistor Rr, voltage divider capacitors C1 and C2, and a cavity that simulates a GIS structure. The PD signal from the antenna sensor is fed through a coaxial cable to the signal acquisition device Tektronix*MSO44  Tektronix high-performance digital oscilloscope for acquisition. The GIS simulation chamber tank is filled with 0.5 MPa of SF6 gas with 99.999% purity. The experiment uses the air gap discharge model to simulate the insulation fault PD process inside the GIS equipment. The air gap defect is caused by the substandard process of GIS tub insulators, which produces air bubbles during the curing of epoxy resin and the air bubbles evolve into air gaps, and PD will occur in these air gaps during the operation of GIS. The air gap defect model used in this test is as follows: there are three pieces of epoxy resin sandwiched between the high-voltage electrode and the ground electrode, and the middle piece has an air gap defect with a volume of 10 mm × 10 mm × 5 mm, which is shown schematically in To verify the performance of the designed Fabry–Perot resonant cavity monopole antenna for detecting PD UHF signals, an industrial frequency, and high voltage testbed without local discharge was built in the laboratory, as shown in The experiment is based on the State Grid Corporation of China’s corporate standard: Q/GDW11304.8-2019 “Ultra-high frequency method of partial discharge Charged detection technical standards” .In this paper, a high-performance flexible monopole antenna designed in the literature  is used The results of the PD UHF signals detected by both sensors were recorded when the voltage was increased to 3.7 kV and the discharge was about 17.2 pC, as shown in The spectrum analysis of the detected PD signal and the background noise spectrum analysis are shown in Optimization of monopole patch antenna by using the idea of curved-flow technology and slot dual resonance structure, which greatly broadens the operating band of the antenna sensor and improves the antenna gain directionality. Based on the idea of Fabry–Perot resonant cavity antenna, partial reflection cladding was set up, so that the antenna sensor can obtain full-band high gain performance. The simulated and measured results show that the designed resonant cavity monopole antenna has VSWR ≤ 5 in the frequency band of 0.37 GHz–3 GHz, excellent VSWR performance, average gain of 4.92 dBi, peak gain of 7.16 dBi at the main resonant frequency, simple fabrication process, and meets the design requirements of PD UHF antenna sensors.Through the constructed partial discharge test platform, the designed resonant cavity monopole antenna is used to detect the typical air gap discharge defects, and compared with the mature flexible monopole UHF antenna, the results show that the resonant cavity monopole antenna can detect the PD signal more obviously, which proves the feasibility of resonant cavity monopole antenna for PD detection and reflecting the PD radiation electromagnetic wave energy spectrum characteristics.For the current demand for UHF antenna sensors for PD detection of power equipment with broadband full-band high-gain antenna sensors, this paper carries out the research of broadband high-gain resonant cavity monopole UHF antenna for PD detection of power equipment, using curved-flow technology and slot double resonant structure to optimize the monopole antenna. Based on the idea of Fabry–Perot resonant cavity antenna for high gain antenna, the designed antenna was analyzed and verified by experiments:


This paper proposes a flexible, frequency-reconfigurable monopole antenna design with frequency selective surface (FSS) for Internet of Things (IoT) applications. The proposed antenna operates at three of the IoT frequency bands. This antenna is a coplanar waveguide (CPW)-fed monopole with two balanced arms printed on a thin ROGERS 3003 flexible substrate. The length of the right-hand arm of the antenna is used to achieve frequency reconfiguration by using PIN diodes. Three frequency modes of operation have been obtained; the 2.4 GHz frequency band with the right-hand arm is fully truncated, the 3.5 GHz frequency band with the two arms is completely maintained, and the 4 GHz frequency band with the right-hand arm is partially truncated. To improve the gain of the antenna, a simple FSS surface is designed to be placed under the antenna at a distance of 15 mm. The FSS operates efficiently from 2 to 4.5 GHz and has improved the gain of the antenna. A maximum gain of 6.5 dBi, 7.52 dBi, and 7.91 dBi has been achieved at the three frequency bands respectively. The behavior of the flexible antenna has been evaluated in both the flat and bent states, and stable performance has been observed in both cases. The IoT technology put big challenges on the working communications systems as a huge amount of data is required to be transferred between the wireless nodes connected to the network5. By the way, the tremendous speed of progress in wireless communications techniques has led to an urgent necessity to design a high-speed system with efficient spectrum utilization. This in turn has led to the possibility of exploiting a single wireless device in more than one application, and then more than one frequency band has to be utilized. The antenna is characterized by its large size with respect to other components, and it will be impractical to design an antenna for each frequency band on the same platform. For these reasons, a careful design of an antenna that can satisfy the requirements of the next IoT technologies is a vital necessity4. One of the successful choices that satisfy the requirements of IoT applications is the reconfigurable antennas8. Reconfigurable antennas can change their behavior dynamically in a controlled fashion, i.e., they can change their characteristics such as operating frequency, radiation pattern, and polarization10. To achieve the required control on the antenna, a high-frequency switching device such as a varactor diode, PIN diode, field effect transistor (FET), or micro-electromechanical systems (MEMS) can be utilized12. With each switching process, the electrical equivalent circuit of the reconfigurable antenna changes, providing different behavior in each case.Recently, IoT has become an evolutional technology that aims to ease communication between human beings and their surrounding environment. The IoT merges the human and his surrounding wireless devices and sensors in a single network in real-timeDue to their interesting characteristics, reconfigurable antennas have attained more attention from researchers. The reconfigurability of the antenna can be applied to any of its performance parameters such as operating frequency band, radiation characteristics, or polarization.15. In7, a compact reconfigurable microstrip antenna has been designed to switch between different frequency bands which include many of the wireless standards such as ZigBee, WiMAX, Bluetooth, and GSM. Some research papers have reported reconfigurable multiband antenna while more than one frequency band can be switched simultaneously17. In18, a dual-band reconfigurable multiple input multiple outputs (MIMO) antenna has been proposed to cover the frequency band 1.3–2.6 GHz. Frequency reconfiguration has been realized by a varactor diode on the microstrip feed line. The antenna has achieved dual-band operation in each switching state. The reconfigurable antenna can be designed with radiation pattern reconfigurability, i.e., the radiated power distribution can be controlled spatially in the antenna's surrounding area21. In19, a reconfigurable radiation pattern MIMO antenna is designed as a rectangular monopole with two parasitic strips equipped with PIN diodes. According to the suitable operation switching between the two strips they act as a reflector or director and then the radiation pattern is switched between directional and bidirectional modes. Moreover, the reconfiguration of the antenna can be applied to the polarization of the radiated fields26. In this case, the antenna can be reconfigured to switch between more than one polarization pattern. For example, a reconfigurable polarization antenna has been proposed in27.Some reconfigurable antennas have been designed with frequency reconfigurability29. Design of the reconfigurable antenna on a flexible substrate is a challenging process due to the difficulties associated with the integration of the switches to a flexible surface in addition to the associated mechanical stability and electronic robustness issues. Despite the large number of reconfigurable antennas that appeared in the literature, a small ratio of them have been printed on flexible substrates.In the case of some IoT nodes that are related to health care and biomedical applications where the flexibility of the antenna is the main requirementIn this paper, a frequency reconfigurable antenna printed on a flexible substrate and equipped with FSS is presented. The antenna is a two arms planar monopole fed by a CPW feed line and matched to 50 Ω impedance. Two PIN diodes are used to split one of the two arms of the monopole into three parts, and accordingly, three frequency bands of operation are obtained. The antenna is printed on a ROGERS 3003 flexible substrate and its performance is tested under different degrees of bending. To improve the gain of the antenna, a wideband FSS is designed to be placed under the antenna. The designed FSS works as an upward reflector over the whole antenna's operating frequency. The following section of the paper discusses the reconfigurable antenna design process. The antenna description is studied in “r = 3, h = 0.13 mm, and tangent loss tan δ = 0.001 is utilized. The antenna dimensions are optimized as displayed in Fig. 3. The reconfigurability of the antenna is achieved by splitting the right-hand arm into three parts while two PIN diodes are used to interconnect these three parts. The state of each PIN diode ON or OFF decides the connection or disconnection of the split parts. The photograph of the fabricated antenna with the disconnecting slots of the right-hand arm is shown in Fig. The proposed antenna's radiator is constructed as a CPW-fed monopole with a width of 3.4 mm and two gaps of 0.2 mm to achieve the 50 Ω and with two balanced arms as illustrated in Fig. The reconfigurable antenna has been simulated using CST Microwave Studio Software. Fabrication and measurements have been conducted in the Electronics Research Institute (ERI) Labs. To be compromised with the requirements of IoT applications that require a changeable position of the antenna, the antenna has been added on a flexible substrate. The antenna has been fabricated using a chemical etching process (photo-lithographic technique). The schematic of the antenna is illustrated in Fig. 11 of the reconfigurable flat antenna in the three modes is illustrated in Fig. The antenna's performance is investigated in two different positions; flat and bent. The S11 has been simulated at different degrees of bending for each mode of operation. Simulation results are presented in Fig. To study the behavior of the antenna under bending, the antenna is bent around the y-axis as shown in Fig. 11 curves of the reconfigurable antenna at the different modes of operation are displayed in Fig. 11 of the antenna in the first mode of operation is shown in Fig. 11 with PIN#1 diode ON and PIN#2 OFF is illustrated in Fig. After the fabrication, reconfiguration of the proposed antenna is done by controlling the two PIN diodes (HPND-4005), i.e., PIN#1 and PIN#2, which are connected through the two slots. The two PIN diodes are used as switches and controlled by the biasing voltages applied through the connecting wires as displayed in Fig. The anechoic chamber is utilized to measure and extract the antenna's radiation pattern as displayed in Fig. 1 = 0.6587 pF and L1 = 4.328 nH. This behavior is utilized to enforce the reflection of the RF frequencies within the operating band of the reconfigurable antenna. The complete FSS structure is shown in Fig. It is highly required for the antenna to have a high gain. In this paper, an FSS is designed to improve the gain of the proposed antenna. The FSS is to be inserted under the antenna to force the radiated power in an upward direction. The FSS is a printed periodic structure with frequency filtering characteristics. The single unit of the proposed structure, as shown in Fig. 11 is too high (approximately 0 dB) in the frequency band 2–4.5 GHz and S21 is too small (less than −10 dB) in the same frequency band in both flat and bending configurations. These results demonstrate the high reflectivity and low transmission through the proposed FSS structure. The best behavior of the FSS is at 3 GHz.S2 as seen in Fig. The complete FSS is composed of 3 × 3 unit elements with 0.5 mm spacing between cells to achieve an overall dimension of 77 × 77 mm11 of the flat reconfigurable antenna with FSS are shown in Fig. 11 of −19 dB at the 2.4 GHz frequency. The return loss of the antenna with FSS in the second mode of operation while the two PIN diodes are ON is displayed in Fig. The simulation and tested S11 of the antenna is less than -10 dB in the frequency band 3 GHz to 4 GHz as shown in Fig. Looking at Fig. According to the measurements of the antenna with and without FSS, the antenna's gain in the presence of the FSS has been improved as follows: from 1.55 dBi (without FSS) to 6.5 dBi (with FSS) at 2.4 GHz, from 2.95 to 7.23 dBi at 3.5 GHz, and from 2.9 to 7.91 dBi at 4 GHz. The proposed antenna outcomes in comparison with other designs are summarized in Table A frequency-reconfigurable antenna with flexible characteristics equipped with an FSS structure is presented in this paper. The antenna is intended for IoT applications and switches between three frequency bands; 2.4 GHz, 3.5 GHz, and 4 GHz. The antenna has been simulated, fabricated, and measured to investigate its performance. Good electrical characteristics have been obtained at the three bands of operation. The performance of the antenna under bending has been tested while stable behavior has been obtained at different degrees of bending. In addition to the reconfigurability and flexibility, the antenna is equipped with FSS to improve its gain. The performance of the flexible reconfigurable antenna with FSS has been validated using simulations and measurements. The obtained results show that the FSS has contributed to a high improvement in the antenna's gain. All of the measurement results have good matching with the simulated outcomes which supports the suggested antenna to be utilized in IoT systems.


A textile bandwidth-enhanced polarization-reconfigurable half-mode substrate-integrated cavity antenna was designed for wearable applications. A slot was cut out from the patch of a basic textile HMSIC antenna to excite two close resonances to form a wide −10 dB impedance band. The simulated axial ratio curve indicates the linear and circular polarization of the antenna radiation at different frequencies. Based on that, two sets of snap buttons were added at the radiation aperture to shift the −10 dB band. Therefore, a larger frequency range can be flexibly covered, and the polarization can be reconfigured at a fixed frequency by switching the state of snap buttons. According to the measured results on a fabricated prototype, the −10 dB impedance band of the proposed antenna can be reconfigured to cover 2.29~2.63 GHz , and the circular/linear polarization radiation can be observed at 2.42 GHz with buttons OFF/ON. Additionally, simulations and measurements were carried out to validate the design and to study the effects of human body and bending conditions on the antenna performance. Additionally, our previous works [In the last decade, significant progresses were made in the applications of wearable antennas in medical monitoring , sports us works ,18, respus works  and 15.7On the other hand, the reconfigurable antenna became one of the hottest research topics for wearable antennas . The weaThis paper presents a textile HMSIC antenna with an enhanced bandwidth and reconfigurable polarization for wearable applications. Firstly, a textile HMSIC antenna is designed and simulated to investigate its bandwidth. Secondly, a slot is added to enhance its bandwidth to cover the medical body area network (MBAN) and 2.45 GHz industry science medical (ISM) bands, and the linear polarization (LP) and circular polarization (CP) radiations are predicted at different frequencies based on the simulated axial ratio (AR) curve. Thirdly, two sets of metallic snap buttons are installed along the edge of the patch as switches to shift the −10 dB band, and simulations with buttons OFF and ON are carried out to illustrate its band and polarization reconfiguration characteristics. The frequency and radiation characteristics of the proposed antenna on the human tissues are simulated and analyzed, and the specific absorption rate (SAR) in the human tissues are, respectively, simulated and analyzed. Lastly, a fabricated prototype of the proposed antenna is measured in an anechoic chamber to validate the design, and the influence of bending conditions is measured and analyzed.2). Other parameters of Antenna I were theoretically calculated based on our previous work [l = 2w = 88.4 mm, fx = 23 mm.As shown in ous work  and optisl, sw and sy. When sl increased, the lower resonance frequency did not change, while the higher resonance frequency increased. When sw increased, the higher resonance frequency stayed unchanged, but the lower resonance frequency increased. Additionally, when sy changed, the impedance matching could be changed. Based on parameter sweeps, the dimensions of Antenna II were optimized as: l = 2w = 88.4 mm, fx = 23 mm, fy = = 25 mm, sl = 28.5 mm, sw = 6.5 mm, sy = 1 mm.Inspired by our previous work , a strai11| parameter was below −10 dB in 2.29~2.50 GHz , and both the MBAN and 2.45 GHz ISM bands were covered. The lowest AR was observed at 2.42 GHz with its simulated value being 3.2 dB, which indicates the existence of CP radiation. When the frequency was within the range of 2.29~2.34 GHz, the simulated AR was over 10 dB, and Antenna II could be mainly predicted to be in the LP mode. To conclude, the polarization mode of Antenna II was circular at 2.42 GHz and linear at a lower frequency between 2.29 and 2.34 GHz.Reference  illustral, w, fx, fy, sl, sw, sy for Antenna III were of the same values of those for Antenna II. The reflection coefficient of Antenna III was simulated with different values of yv1 and yvd, and the simulated curves are presented in yv1 and yvd. For the button-ON scenario, however, the simulated curve shifted left when yv1 or yvd increased, and changing yv1 did not lead to the significant change of the impedance matching while changing yvd did. Through parameter sweeps, the values of yv1 and yvd were, respectively, optimized to be 38.4 mm and 1 mm to yield a maximum total frequency coverage with buttons OFF and ON and to keep the |S11| parameter below −10 dB at the frequency where the lowest AR was obtained.Parameters As shown in M (red solid lines with arrows), and, therefore, indicates the right-hand circular polarization (RHCP) radiation with buttons OFF. With buttons ON, the distribution of the E-field accords with the xz and yz planes were of a main beam towards the +z direction with a large beam width. The maximum coplanar LP gain was 6.6 dBi, and the maximum cross LP gain was 13.3 dBi lower than the former. Therefore, the pattern simulation results further indicate the RHCP and LP radiations of Antenna III at 2.42 GHz with buttons OFF and ON, respectively. In addition, the simulated radiation efficiency of Antenna III in free space was 95% with buttons OFF and 97% with buttons ON.The free-space gain patterns of Antenna III were simulated at 2.42 GHz and shown in 3 skin-fat-muscle phantom, as shown in A 300 × 300 × 60 mmThe simulated patterns of the CP and LP gains of Antenna III on the phantom at 2.42 GHz are shown in With an input power of 0.5 W applied into the feeding port, the SAR (1 g average) in the phantom at 2.42 GHz was simulated for Antenna III. The simulated SAR distributions with a 0.5 W input power are presented in A prototype of is fabricated for Antenna III using computerized embroidery. As shown in x-axis or y-axis with an 8 cm bending radius. In such bending scenarios, both resonance frequencies with buttons OFF slightly increased, but the measured −10 impedance band still well covered the target bands. The observed frequency shift can be due to the decrease in cavity width/length caused by physical deformations of the flexible fabric and foam substrate during bending.The reflection coefficient curves of Antenna III were measured by a vector network analyzer and presented in The 2.42 GHz gain patterns of Antenna III in free space were practically measured in an anechoic chamber and are presented in A novel textile bandwidth-enhanced polarization-reconfigurable HMSIC antenna was designed for wearable applications. Firstly, by applying a slot and two sets of metallic snap buttons in the geometry of a textile HMSIC antenna, not only the separate bandwidth with buttons OFF or ON was enhanced, but a larger frequency range can be covered by changing the state of the buttons to reconfigure the band. As shown in


An impedance BW of 110% (2.85–9.81 GHz) frequency boundaries was observed. Based on the measured results, a peak gain of 3.28 dBi was analyzed at 6 GHz. The SAR values were calculated to observe the radiation effects, and the SAR values obtained from the simulation at 4/6/8 GHz frequencies followed the FCC guideline. Compared to typical wearable miniaturized antennas, the antenna size is reduced by 62.5%. The proposed antenna has good performance and can be integrated on a peaked cap as a wearable antenna for indoor positioning systems.In this paper, a miniaturized textile microstrip antenna is proposed for wireless body area networks (WBAN). The ultra-wideband (UWB) antenna used a denim substrate to reduce the surface wave losses. The monopole antenna consists of a modified circular radiation patch and an asymmetric defected ground structure, which expands impedance bandwidth (BW) and improves the radiation patterns of the antenna with a small size of 20 × 30 × 1.4 mm Wireless body area networks (WBAN) devices have received increasing attention in recent years and this interest continues to grow . TherefoWearable systems require portable and miniaturized antennas for receiving and transmitting wireless signals ,9,10,11.In this paper, an improved miniaturized UWB antenna was fabricated using denim material by combining UWB electronics with textile technology. To ensure the electromagnetic parameters of the adopted material, the dielectric constant of the denim was measured using the transmission/reflection method in a coaxial line. The UWB tag antenna with an omnidirectional radiation pattern is integrated into a denim cap and can be used for indoor positioning. Since the peaked cap has a bending design, it is necessary to study the effect of bending on the antenna performance. The antenna was tested in a bending test and close to the human head. Tests have shown that the wearable antenna has stable performance regarding radiation patterns and BW. In addition, since the peaked cap was worn on the head, the head effect and the specific absorption rate (SAR) were investigated. It is suitable for communication at the human head. The antenna is miniaturized, bendable, inexpensive, and simple to make.The proposed antenna used denim fabric, as it is flexible, lightweight, and easy to integrate into clothing. The dielectric properties of denim should be known. Thus, the dielectric constant and loss tangent must be measured on the substrate. In this paper, the coaxial circular method was used to test the electromagnetic properties of denim fabrics. The electromagnetic performance test system of the cowboy substrate is shown in εr and z0. When a plane wave propagates in free space arriving on the surface of a medium of infinite thickness with electromagnetic parameters Using the Nicolson–Ross–Weir (NRW) method, periment ,27. As sElectromagnetic waves are reflected and transmitted multiple times at both ends of the medium. Using the sweep mode of Keysight N5222B Vector Network Analyzer (VNA), it is possible to measure in this case the multiple reflections  will interfere with the received signal of the antenna. To make the impedance BW just cover the frequency range of UWB, the value of l3 is chosen as 9 mm. The resonant frequency shifts to a higher frequency as the increase of l3 and the in-band matching will deteriorate.The proposed antenna generates two resonant frequency points so that a wide BW can be acquired. To study the effects of the patch size on the BW, HFSS 19.0 was used for simulation calculations with different values of the parameters The measurements were performed using Keysight’s 3672D VNA. Measured and simulated radiation patterns of the miniature antenna at 6 GHz in the xoz-plane and yoz-plane of free space are shown in −2 m−1.The structural deformation of the antenna must be studied to ensure the stability of the antenna. In addition, when an antenna is placed close to the head as a wearable device, bending tests should also be performed to determine whether the results of the reflection coefficient are disturbed. The specific absorption rate (SAR) is defined as the electromagnetic power absorbed or consumed by a unit mass of the biological body. The SAR limit set by the FCC is 1.6 W/kg for 1 g of tissue. For the antenna, this value should not exceed this value for the considered user safety. An ultra-wideband textile antenna for WBAN was designed. The electromagnetic parameters of denim fabrics were measured using the NRW method. The proposed antenna matches the impedance obtained in simulation over the entire UWB frequency range by improving the circular radiating patch with gaps and defected ground structure. However, the impedance BW of 110% (2.85–9.81 GHz) frequency bands is observed. Compared to typical wearable miniaturized antennas, the antenna size is reduced by 62.5%. The antenna was designed to be integrated into a peaked cap for indoor positioning. Therefore, the performance of this antenna bent and placed close to the human head was investigated. The measured performance of the antenna in bending and placed in front of the human head is consistent with the simulation. For the proposed antenna structure, it was found that the SAR level obtained from the model placed close to the human head was less than 1.8 W/kg, meeting the FCC guidelines. The antenna is a usable wearable antenna with small size, easy integration, and bendability. The antenna also has the advantage of low cost and simple manufacturing process.


Planar antennas have become an integral component in modern biomedical instruments owing to their compact structure, cost effectiveness, and light weight. These antennas are crucial in realizing medical systems such as body area networks, remote health monitoring, and microwave imaging systems. Antennas intended for the above applications should be conformal and fabricated using lightweight materials that are suitable for wear on the human body. Wearable antennas are intended to be placed on the human body to examine its health conditions. Hence, the performance of the antenna, such as its radiation characteristics across the operating frequency bands, should not be affected by human body proximity. This is achieved by selecting appropriate conformal materials whose characteristics remain stable under all environmental conditions. This paper aims to highlight the effects of human body proximity on wearable antenna performance. Additionally, this paper reviews the various types of flexible antennas proposed for biomedical applications. It describes the challenges in designing wearable antennas, the selection of a flexible material that is suitable for fabricating wearable antennas, and the relevant methods of fabrication. This paper also highlights the future directions in this rapidly growing field. Flexible antennas are the keystone for implementing next-generation wireless communication devices for health monitoring and health safety applications. Advancements in wearable electronics enables the realization of various body-worn applications. Wearable antennas that function as sensors have gained considerable research interest. These antennas can operate perfectly when worn on the human body. They are well suited for military applications, as they can provide soldiers with seamless and efficient communication capabilities while transmitting and receiving data. This can enhance the mobility and effectiveness of soldiers on the battlefield.However, wearable antennas suffer from the problem of signal fading, whereby the signal strength at the receiving end decreases when the path length difference, due to the movement of the mobile terminal, becomes comparable to the signal wavelength ,2. MultiBecause of their functionalities and abilities, body-worn wearable technologies have sparked significant research interest in the past decade . Figure The water absorption and physical changes in the human body will have a substantial impact on the overall effectiveness of the antenna . The desA high-performance antenna system worn on/off the body and communicating nearby can be made possible by conductive fabric materials. Conductive textile (e-textile) materials are created by combining polymer threads or conductive metals with regular fabrics. Flectron, Zelt, pure copper, taffeta, and Sheildith are examples of conductive fabrics ,17,18,19As previously stated, there are numerous ways to determine the dielectric characteristics of textile materials ,22. It mThe design factors considered for the implementation of wearable antennas are summarized below.Wearable antennas must operate perfectly when they are worn on the human body. Wearable antenna technology mostly employs the wireless body area network (WBAN). Hence, the selection of a suitable substrate material (conductive and non-conductive) is a crucial aspect in the design of these antennas. The selected substrate must allow for the placement of the developed antenna in close proximity to a human body. Numerous researchers have conducted in-depth studies to select the ideal substrate material .Human tissues can react with incident electromagnetic waves because of the complex permittivity and conductivity of the tissues. The performance of an antenna is altered when it is placed near to a human body. The resonant frequency of the antenna is reduced owing to the higher value of the human body . MoreoveWhen a wearable antenna is operated near the human body, the back radiation from the antenna is mostly absorbed by human tissues. Continuous exposure to the radiation might damage human tissues. All antenna sensors that are used in proximity to the human body must satisfy the specific absorption rate (SAR) standards defined by international organizations. The SAR value quantifies the amount of power absorbed per unit mass of human tissue. Therefore, while designing body-worn antennas, numerous factors such as the antenna’s radiation properties, the input impedance matching capabilities, and the power absorbed by the antenna should be considered ,28.An antenna that is worn on the human body undergoes bending, stretching, and twisting during the movement of the human body. Consequently, its radiation characteristics may degrade considerably, which affects the antenna’s radiation patterns, frequency tuning, and radiated energy ,30.Body-worn antennas that are fabricated from textile materials face certain operative challenges due to the presence of microscopic holes in the fabric. The microscopic holes can absorb moisture from the environment and increase the dielectric constant of the fibric material. This can significantly impact the antenna’s performance, thereby leading to effects such as frequency detuning, reduced radiation efficiency, and altered characteristics .As the substrate plays a major role in determining the antenna’s characteristics, this study aims to highlight the recent substrates proposed for wearable antennas, with an emphasis on flexible antennas suggested for biomedical purposes. Additionally, it sheds light on the prospective avenues of its applications.The primary difficulty with antennas worn on the body is ensuring that their characteristics remain constant under varying conditions like room humidity variations, body temperature and wet conditions .Similarly, when many wearable antennas/sensors are employed in a single application, the location and distance between the sensors are the most important elements in improving the system’s performance.A UWB health monitoring system tracks plenty of regular activities leading to a healthy lifestyle by employing several wearable sensors at varied locations and distances .Furthermore, most wearable antennas are linearly polarized, and polarization mismatches arise owing to human body movement.Wearable antennas work in close proximity to a lossy human body, which affects the antenna’s efficiency, driving point impedance, bandwidth, and gain. When electromagnetic waves are utilized for communication, part of the radiation is directed at the human body, penetrates through the skin, and is absorbed by the body, resulting in detrimental health consequences. Wearable antennas should comply with a high efficiency and a low specific absorption rate (SAR) in addition to bending and crumpling repercussions and flexibility. The amount of energy that is absorbed by the human body per unit mass is measured in W/kg as the SAR. This problem has been important for the past few years, and various regulating agencies have established a safe limit for the SAR for these antennas.Various solutions have been offered in the past to overcome the aforementioned issues . In 35]35], the To achieve a multiband response, the authors used the method of fractural slot loading. Furthermore, the increased bandwidth comes at the expense of structural complexity . To loweAdditionally, PEC reflectors are employed as an additional antenna component to improve the effective radiation efficiency and lower the SAR of wearable antennas .However, the low-profile property suffers when PEC reflectors are used. The SAR of antennas may also be reduced using ferrite sheets; however, this results in a greater integration cost and a bulkier volume, making the antenna unsuitable for body-worn applications .The purpose of this review study is to summarize the current advancements in the field of wearable antennas for body-centric communication as well as other crucial elements. Conventional antenna materials might be unpleasant and are not suitable for body-worn antennas. To overcome this issue, an appropriate textile material may be employed in their design. Conductive (e-textile) materials have the properties of an imperfect and anisotropic electric conductor. As a result, these conductive materials have different conduction characteristics than standard conductors that are employed in conventional antenna designs . The eleConductive (radiating element) and non-conductive (substrate) materials are the two most critical materials that influence the overall performance of wearable antennas. The dielectric characteristics, deformation , sensitivity to miniaturization, and endurance in the external environment are used to select the substrate materials, while electrical conductivity is used to select the conductive materials. Prior to selecting a conductive material for the radiating portions, such as the feed line, patch, and ground plane, it is required to pick the most appropriate substrate material to support the layers. Wearable antennas will address the demand for comfort while also protecting consumers from dangerous radiation by adopting these materials. Furthermore, the material is chosen based on the aforementioned qualities to provide acceptable gain, high efficiency, and a suitable bandwidth ,44Non-conductive (substrate) materials or smart textiles can play essential roles in the construction of wearable antennas. To achieve higher efficiency, durability, and enough bandwidth, these materials must have minimum dielectric loss, thermal expansion coefficient, and relative permittivity . The nonFurthermore, the substrate material is crucial in terms of functioning, wear resistance, and manufacture. When choosing a substrate material, the permittivity, thickness, loss tangent, and flexibility should all be taken into account. The antenna’s performance, influencing the bandwidth, depends highly on parameters like material thickness and permittivity . The los7 S/m. Conductive textile (e-textile) materials are employed for wearable antennas. As a result, materials with a higher electrical conductivity are preferred. As a result, the conductive materials that are utilized to construct wearable or flexible antennas must be very conductive. Therefore, the electrical characteristics of these materials must be characterized [Conducting materials are required for both the ground plane and the radiating element in all antennas. To maintain adequate antenna emission characteristics, wearable antennas must contain conductive radiating components and ground planes. Conductive materials (electro-textiles) are employed in the creation of wearable/textile antennas to serve as completely flexible and wearable antenna designs. The conductivity of the material determines the current that flows through the conductor, which is responsible for radiation. The conductivity of a substance is its capacity to allow for charges to flow freely through it. The material’s conductivity is measured in Siemens per meter (S/m). The perfect electric conductor (PEC) has unlimited electrical conductivity, making it excellent for antenna construction. In practice, however, all the materials have a limited conductivity. For example, the conductivity of an ordinary copper material is 5.8 × 10cterized .τ is the thickness of the material. As a result, a low-loss dielectric material will be required as a substrate, and a highly conductive material will be required as a radiating portion for wearable antennas in order to provide effective electromagnetic radiation and acceptable performance.The electrical conductivity of the chosen material can have a significant impact on the performance of the antennas. Zelt, Flectron, Shieldit, and Taffeta are four different forms of electro-textile materials that have been documented in the literature and are commonly utilized as radiating elements and as ground planes. The conductivity of conductive materials may be estimated using Equation (1) below.Advancements in wireless technology and on-body sensor design can revolutionize the traditional healthcare system by introducing wearable devices for healthcare monitoring . Figure The experimental analysis and design of body-worn antennas is integral to the implementation of body sensor networks (BSNs). Out of eighteen antenna designs, four designs were chosen, and their active and passive performances were assessed. The challenges encountered in this process, such as optimizing the antennas with impedance matching, transforming unbalanced signals to balanced signals, and characterizing antennas in different configurations (on-body and off-body), were investigated and resolved. This resulted in the development of a methodology for characterizing on-body antennas, considering the effects of the transceiver . The proIn this study, we discuss the major challenges faced during the design and testing of on-body antennas in an anechoic chamber. This study builds on prior research by introducing three additional antennas and providing a more comprehensive explanation of the requirements analysis, design, development, and testing procedures. It introduces a systematic approach for actively evaluating the performance of a BSN antenna integrated with battery-powered devices, thereby yielding more realistic results. Additionally, this study examines the influence of the human body on the performance of an antenna through on-body experiments conducted in an anechoic chamber. Finally, it proposes and validates the use of a phantom to simulate and facilitate human experimentation with antennas.3, and a 0.1 mm thick polyimide substrate was used as the dielectric material. The fabricated antenna had three resonant frequencies, 2.4, 5.2, and 5.8 GHz, with a bandwidth of 100–1300 MHz. The antenna exhibited relatively low gains of 1.65 and 4.37 dBi at the resonant frequencies of 2.4 and 5 GHz, respectively, despite its small size. This antenna showcases practicality and holds a wide range of potential applications.A sequential array structure consisting of systematically arranged Minkowski fractal array elements was proposed in . Figure 3 and exhibited multiple resonance is shown in A portable triple-band antenna was suggested for internet of things (IoT) devices in . The radVarious periodic structures of radiating surfaces were proposed for realizing WBANs. Three different types of metamaterials were developed, namely electromagnetic band gap (EBG), artificial magnetic conductor (AMC), and metamaterial compounds. A compact composite right/left-handed coaxially fed dual-band antenna was fabricated and tested for GSM and wireless applications . The AMCThe invention of multiple wireless communication techniques ushers in a new era of remote health monitoring systems that enhance the value of health services provided to patients is shown in Leaky wave antennas (LWAs) are a unique class of antennas that exhibit a highly directional radiation pattern is shown in With the smartphone market reaching saturation, a new trend is emerging in the field of personal mobile devices, known as wearable mobile devices or simply wearables . These d2. It had a rectangular slot with three parallel stubs optimized for the radiator patch, as well as a T-shaped structure inverted in the ground plane. The final prototype of the antenna had three resonance frequency bands, 2.4–2.9, 3.7–5.2, and 5.7–6 GHz, with a return loss of less than −10 dB. The paper discussed the antenna configuration and design and its simulation and experimental results. It highlighted the compactness, simple feeding technique, and uniplanar design of the antenna, which simplify the integration of the antenna into various wireless devices.A previous study  presenteA miniaturized button-shaped wearable antenna was designed for wireless signal transmission . This anThe small size of millimeter-wave antennas makes them challenging to fabricate. Many applications, such as WiGig, employ the unlicensed V band (57–64 GHz). However, research on wearable millimeter-wave antennas is lacking. Karthikeya et al. proposed a wearable V-band antenna  designed2 (0.0817 × 0.0817 λ02 at 2.45 GHz) and maintained a good performance in the ISM band.A wearable antenna with a small feeding network was discussed in . The antIn , a dumbbAntennas employed in short-range near-field ultra-high frequency (UHF) radio frequency identification (RFID) systems are typically positioned close to the human body . This imThe design considerations for a UHF band card-type tag, which was enclosed in a packet and placed near the chest for applications on our university campus, were discussed in . The FEKRecently, body-centric wireless communications have gained considerable interest. A small and efficient planar inverted-F antenna (PIFA) that operates at 2.45 GHz for on-body communications was introduced in . The ant2. It was fed using a co-planar waveguide (CPW) [A flexible antenna operating at two frequency bands was proposed for data transmission. The antenna had a low profile and a size of 35 × 20 mmde (CPW)  and oper2. Experimental tests showed that the antenna maintained its performance when positioned near to the human body. The antenna exhibited a safe SAR of 0.297 W/kg at a 0.5 W input power, thus indicating that the antenna can be used safely in wearable devices.A compact, flexible wearable antenna composed entirely of a textile material for the 2.45 GHz ISM band was discussed in . It compAnother previous study  discusse3 and exhibited an impedance bandwidth of 15% and an efficiency of 79%. These findings indicate that the antenna holds significant potential for use in wearable systems.A small textile antenna was designed and tested for use in the ISM band at 2.4 GHz. The antenna utilized a rectangular slot/notch with a strip line inserted to form an inverted E-shape . This deA wearable microstrip antenna made from conductive textile fabric was introduced in . It was Recently, fabric and textile antenna designs have gained widespread attention owing to the growing demand for multi-frequency and multi-function antennas in smart clothing and future consumer-centric communication technologies . The modThe performance of an antenna equipped with a textile substrate and an AMC was discussed in . This st2. According to the manufacturer, the surface resistance of the fabric was below 0.05 Ω/sq.The biological attributes of the human body, such as tissue properties and skin layers, play a crucial role in determining the propagation of radio signals through the human body . A texti3, and it exhibited an omnidirectional radiation pattern. The study assessed the performance of the antenna in both a free space and human body surface. Owing to its compact size, this antenna may find utility in numerous applications within the smart wearable textile industry.Antennas employed for healthcare applications usually operate in multiple band frequencies. A reconfigurable patch antenna is well-suited for biomedical applications. In , a compaA planar inverted-F antenna (PIFA) is the most preferable radiating element for transmitting signals in portable wireless devices. In , the perSeveral wearable antennas that are resistant to the body coupling effect have been reported in the literature . To achiWireless technology is integral to the advancement of flexible and stretchable electronics, which has gathered attention in view of addressing the increasing demand for devices that are compact, portable, and comfortable . MicrostIn , the pro2) and operates at a resonant frequency of 4.8 GHz, with a frequency shift range of 8% under different strains. Additionally, it is compatible with 5G communications. Additionally, the sensor exhibits excellent mechanical flexibility and maintains a stable response to repetitive stimulations. It exhibits a superior strain sensitivity of 20 compared with similar antenna sensors. Its resilience to human body proximity was tested by performing cantilever motion monitoring. The antenna exhibits satisfactory stability and sensitivity. It exhibits noticeably shifted resonant frequencies while maintaining a reflection coefficient of approximately −25 dB, indicating its potential for applications in the fields of healthcare monitoring, construction diagnosis, and IoT.Owing to rapid advancements in wearable electronics, flexible radio-frequency wireless antenna sensors have garnered considerable interest for their various IoT applications . HoweverA smart pH measuring device can provide vital health information and has various applications in detecting infections, diagnosing diseases, and personalized medicine . HoweverInterdisciplinary research focuses on routine healthcare objects to develop sensors that can monitor human biomedical parameters in an ergonomic and environmentally sustainable manner. In , a hybri2 and an excellent salt rejection rate of 99.96% over a 24 h period were achieved.In the past few decades, considerable efforts have been spent to develop simple and cost-effective methods for preparing superhydrophobic membranes using PDMS. In , a straiAnother previous study  discusse2. The antenna uses a PDMS substrate with a dielectric constant of 2.65 and a loss tangent of 0.02. The antenna has a rectangular slot on the ground and a single circular SRR on the patch. The SRR structure assists in achieving the desired frequency notching characteristics, compact size, minimal losses, and reduced backward radiation when the antenna is used near the human body. The proposed flexible antenna showcases a stable performance and a low SAR. The antenna performance was also evaluated under various moisture and bending conditions. The simulation results are consistent with the measured data.A polymer-based flexible antenna that operates at three different frequency bands  for WLAN and WBAN applications was developed in . The antModern wearable health monitoring systems utilize multiple biosensors embedded in wireless devices . This neAnother study  focused Another study  proposedPDMS is a versatile elastomer that possesses exceptional optical, electrical, and mechanical characteristics, rendering it highly suitable for various engineering applications . Its bio2 and is composed of a simple microstrip structure with two modified arc-shaped patches as the main radiator. The antenna also includes a full ground plane on the opposite side of the substrate to prevent interference from biological tissues and back radiation towards the human body. To ensure flexibility and durability, the antenna is fabricated using conductive fabric embedded into a PDMS polymer. The simulation and experimental results reveal that the antenna exhibits promising performances in both free-space and in vitro on-body cases. This is the first UWB antenna with a full ground plane that can withstand the harsh conditions that are typically encountered with wearable applications.A new UWB antenna was developed for wearable applications in the 3.7–10.3 GHz band . This anA flexible UWB antenna using a PDMS substrate was proposed in . The con−6 1/K at different temperatures from 103 K to room temperature (RT = 298 K) to 123 K. The results show that as the temperature decreased, the failure mode of PDMS changed from ductile to brittle, with evident brittle characteristics at 123 K.The abrasive jet machining (AJM) of PDMS is either slow or impossible at room temperature because PDMS can absorb the energy of the impacting particles. In , cryogenAnother study  summariz2 was developed [3) and low manufacturing cost, this antenna is well suited for health telemetry applications. Compared with other flexible antennas, the proposed antenna demonstrates smaller dimensions, better radiation efficiency, and higher gain when placed on a human body model.eveloped . The antA modified sinusoidal half-wave dipole antenna sensor that can be used for strain sensing applications was discussed in . Figure Microwave imaging is an efficient method used to diagnose cancer in its early stage. However, the efficiency of a microwave imaging system depends on the effectiveness of the antenna used for transmitting and receiving the microwave signals. Moreover, the antenna should be flexible. Extensive research has been conducted on designing a flexible antenna and increasing its efficiency to save the lives of people. An early detection of cancer can significantly enhance the chances for recovery, potentially saving numerous lives. In India, almost 2.5 million cancer patients have been registered, with 1 lakh new cases added annually. In 2018, 7 lakh deaths occurred owing to cancer. According to the Indian Council of Medical Research, India is likely to record over 17 lakh new cancer cases with over 8 lakh deaths by 2022. Breast cancer is the most prevalent type of cancer in women. These statistics underline the necessity of developing new methodologies for the early detection of breast cancer. Currently, image processing techniques, such as mammography, magnetic resonance imaging, and ultrasound, are available for breast-cancer diagnosis. To improve the efficiency of early breast cancer detection, a portable breast cancer detection device using the microwave imaging technique can be designed and developed. It involves designing a flexible wearable metamaterial antenna operating in a UWB frequency range and machine learning techniques. In addition, a flexible wearable metamaterial antenna can be used as a wearable device to address the limitations of the current detection technologies, which involve radiations that are painful and detrimental to the human body ,95,96,97A U-shaped slot for ultra-wideband microwave imaging applications was proposed in . The ant3 and uses an FR4 substrate [A printed monopole antenna was designed with staircase steps at the edge of the feed line, as shown in ubstrate . The opeMetamaterials are remarkable engineering novelties, and they are shown in 3 was proposed and examined, and it is shown in In , a modif2 (0.2 λo × 0.2 λo) and is fed using a CPW as shown in In , a biodeIn , a smallSeveral numerical techniques were reported for antenna miniaturization based on patch antenna loading with slots, lumped elements, and shorting posts. The slots introduced are of various shapes, and the lumped elements, based on similar reactive components, are designed at the resonating frequency. The etching of various slots facilitates the reduction in the antenna size for modern wireless communication .Antenna miniaturization is accomplished by fabricating a patch structure on a dielectric substrate with a dielectric value that is higher than that of the patch. However, this drastically increases the current distribution and leads to surface wave effects, which degrade the patch antenna characteristics such as the impedance bandwidth, radiation characteristics, and radiation efficiency .Currently, UWB antennas are the most preferred antennas for non-destructive testing and microwave imaging. UWB antennas operate in the frequency range of 3.1–10.6 GHz, which encompasses low-frequency to very-high-frequency signals; hence, the use of UWB antennas produces images with better resolution. A device for obtaining the three-dimensional scan of a breast model was developed in . The devEmploying notch cutting in the ground plane reduces the effects at low frequencies. Impedance matching is provided for the input feed from the finite ground plane, and slots are introduced in the radiator. This prompts the antenna to radiate in the UWB frequency range . The canRecently, digital mammography has been adopted for breast cancer detection. Digital mammography is almost similar to the traditional method of film screen mammography. However, the latter involves compressing and positioning the breast organ over the mammography machine in a manner that may be painful for the patients. Digital mammography primarily aims to detect breast abnormalities. Compared to the conventional method of mammography, digital mammography provides breast images with a better resolution at lower radiation levels. However, it suffers from high false positive and negative rates. This necessitates additional examinations to confirm cancer and higher expenses for the early diagnosis of breast cancer. A flexible wearable patch antenna with a jean substrate is proposed in . This anThe conductivity of the electro-textile material and its surface impedance was measured. Furthermore, the SAR analysis was conducted. The antenna exhibited increased bandwidth and efficiency. A metamaterial antenna was fabricated using a low-cost FR4 material, and the antenna characteristics were evaluated by applying metascreens over the patch.In , the useIn , a radarConventional antennas are designed and fabricated on PCBs using substrates such as FR4, Rogers, and PTFE. If these antennas are used in wearable applications, they may obstruct and prevent reactions with the human body during cancer diagnosis . Such anCertainly, the scientific community, the technical community, and the clinical community need to work closely together to figure out solutions that synergize with one another in order to successfully develop and implement wearable antennas in the medical field. Each of these groups plays an important role in ensuring that technical breakthroughs are successfully incorporated into applications that are used in the actual world of healthcare. The authors in  illustraThe research on wearable antennas focuses on developing towards low-cost, easy-to-fabricate BAN systems for medical applications and remote monitoring. This review begins by providing an overview of the different substrate materials and techniques used for wearable antenna fabrication. Substrate materials such as polymer, graphene, PDMS, textile materials, and microfluidic materials are discussed. Substrate materials play major roles in determining the coupling between the antenna and the human body and the characteristics of the wearable antenna under wet and humid conditions. Hence, the substrate material must be chosen carefully to ensure the robustness of the antenna’s characteristics against all environmental conditions.Increasing the accuracy and effectiveness of the present measurement and manufacturing processes;Releasing new yarns and conductive textiles on the market that have increased conductivity or decreased resistance;Introducing new flexible materials for clothing that can be embroidered or new suggested production methods;Introducing novel body-operated antenna sensors based on substrate materials used for various applications.The industry and the scientific community are becoming more interested in flexible wearable antenna sensors. Due to this, the following research problems and critical topics are provided for future studies in this field:For the impactful real-world application of wearable antennas, a further area of research is still required to be carried out in the field of materials science and system engineering. To enhance the performance of antennas as sensors in biomedical applications, new materials including conductive ink on textile substrates and graphene substances can be used. These novel materials are interesting components for the next generation of antenna design.Flexible wearable antennas have gathered considerable attention from both the industry and scientific communities. This may lead to some research challenges. Researchers may focus their efforts towards increasing the accuracy and effectiveness of the current measurement and manufacturing processes. Developing innovative approaches can enhance the conductivity of yarn and textile materials.Novel flexible materials can be used to fabricate wearable antennas for better performance. Future studies can focus on enhancing the performance and reliability of antennas used for medical and industrial applications. Further investigations can be conducted on textile-, microfluidic-, polymer-, and graphene-conductive-ink-based antennas to increase the performance of wearable antennas integrated to BAN systems. Advancements in wearable technology can facilitate the realization of diverse applications in the medical field.


Since the CubeSats have become inherently used for the Internet of space things (IoST) applications, the limited spectral band at the ultra-high frequency (UHF) and very high frequency should be efficiently utilized to be sufficient for different applications of CubeSats. Therefore, cognitive radio (CR) has been used as an enabling technology for efficient, dynamic, and flexible spectrum utilization. So, this paper proposes a low-profile antenna for cognitive radio in IoST CubeSat applications at the UHF band. The proposed antenna comprises a circularly polarized wideband (WB) semi-hexagonal slot and two narrowband (NB) frequency reconfigurable loop slots integrated into a single-layer substrate. The semi-hexagonal-shaped slot antenna is excited by two orthogonal +/−45° tapered feed lines and loaded by a capacitor in order to achieve left/right-handed circular polarization in wide bandwidth from 0.57 GHz to 0.95 GHz. In addition, two NB frequency reconfigurable slot loop-based antennas are tuned over a wide frequency band from 0.6 GHz to 1.05 GH. The antenna tuning is achieved based on a varactor diode integrated into the slot loop antenna. The two NB antennas are designed as meander loops to miniaturize the physical length and point in different directions to achieve pattern diversity. The antenna design is fabricated on FR-4 substrate, and measured results have verified the simulated results. With the advanced varieties of wireless applications along with addressing the requirements of end user demands which can be varied daily, especially during disaster situations, a flexible communication system is necessary. Numerous use cases require a more global, scalable, flexible, and robust solution, such as monitoring remote areas, internet provisioning to underserved or disturbed regions, or intelligent global transport management. CubeSats are recommended to achieve global communication systems between those different services ,2,3. Cubprojects ,9,10,11.In order to solve the connection problems between multiple CubeSats, the cognitive radio (CR) offers a potential solution. In CR communication, a transceiver is able to discern between channels that are being used and those that are not. It avoids occupied channels and rapidly enters vacated ones without interference with the licensed user. Thus, CRs are a class of intelligent transceivers with increased situational awareness due to their cognitive skills. This can result in the improvement of the efficient and robust use of communication resources and low delay of data exchange in the CubeSat constellation ,9,12,13 Due to space restrictions, achieving multifunctional antennas in the CubeSat is challenging. Indeed, the antenna is the main key for the CubeSat to provide those aforementioned services (CR and IoST); so, a wideband antenna for sensing and a reconfigurable narrowband antenna for communication in low profile and compact size is mandatory. Thus, some physically changing antenna techniques such as origami folding, hinges, soft robotics, spring forces, and telescopic actuation are implemented ,21,22,23Extensive work has been undertaken to provide antennas for cognitive radio applications ,31,32,33In this paper, a simple structure-folded slot antenna design has been presented. The proposed antenna consists of three antennas; one works as wideband antenna which is fed by two feedlines to provide circular polarization, while the other two are narrowband antennas that are fed by separate feedlines in a different orientation, to achieve radiation diversity. In addition, each NB antenna has a varactor diode. The NB antennas change their frequency over the operating band of the wideband antenna. By changing the value of the loading capacitor, the antenna will achieve frequency reconfigurability. The proposed antenna with reconfigurability features in addition to wideband at UHF can be a good candidate for the Cubesate of IoST applications.The proposed antenna is designed on a The sensing antenna is a semi-hexagonal-shaped slot antenna with a perimeter 8 pF see  results To better understand the CP generation in the left- and right-hand sense, the surface current distributions are provided in The narrowband antenna is a semi-ellipse-meander-shaped slot antenna; the meander shape is employed to reduce the antenna’s physical size. Similar to the sensing antenna, the NB antenna is loaded with various capacitance values from 0.84 pF to 5.08 pF. A varactor diode is connected to the antenna to reconfigure its operating frequency based on the bias voltage value, which changes the capacitor value. The proposed slot antenna has a total length of 86 mm and a width of 32 mm. Two NB antennas are printed on the same view with the sensing antenna. They are printed in two different directions to achieve pattern diversity. Five capacitance values  are used to tune the antenna’s resonant frequency over the wide frequency band. 1, L2 = 1 μH), and current-limiting resistor . The varactor diode (SMV 1233) is connected to the biasing circuitry through shorting posts. RF chokes are used to separate the radiating structure from the DC power source while the reverse-biased varactor diode serves as a DC blocking capacitor to ensure that the DC biasing component and the RF radiating structure are well isolated.The biasing circuitry of the reconfigurable antenna, as shown in Next, the board is placed in an etchant solution that selectively dissolves the unprotected copper areas, leaving behind the desired circuit pattern. The etchant solution usually contains chemicals such as ferric chloride, ammonium persulfate, or cupric chloride, which react with copper to dissolve it. Once the required amount of copper has been removed, the board is rinsed with water to eliminate any residual etchant solution, and the resist is removed, revealing the final circuit pattern on the copper-coated substrate. Chemical etching is a highly reliable and widely used method that enables the production of high-quality PCBs with precise circuit features. The proposed antenna was measured for its S-parameters and radiation characteristics.The far-field radiation pattern characteristics were also performed for the proposed MIMO antenna. To calculate the antenna’s performance, the peak gain and radiation efficiency values (%η) are determined for each element of the antenna. To conduct the measurement for any port, the rest of the MIMO antenna ports were terminated with a 50 Ω load to avoid any reflected power. For sensing and frequency reconfigurable antennas, the peak gain values were 1.079 dBi and 0.86 dBi, respectively, while %η varied from 80~85% to 73~78%, respectively. Anechoic chamber: The chamber is large enough to accommodate the antenna under test and other required testing equipment. The walls, ceiling, and floor of the chamber are covered with radiation-absorbing material to prevent reflections and create an environment free of external interference.Antenna positioning system: The antenna positioning system is used to precisely control the position and orientation of the antenna under test. This system typically includes a rotation stage and one or more translation stages, which allow the antenna to be positioned at various distances and angles from the measurement equipment.Signal generator: The signal generator is used to generate the RF signal that excites the antenna under test. The frequency and power level of the signal can be adjusted as needed.RF receiver: The RF receiver is used to measure the signal received by the antenna under test. The receiver is typically connected to an antenna or probe that is positioned at a fixed distance and angle from the antenna under test.Data acquisition system: The data acquisition system is used to collect and store the measurement data. This system includes a computer, software, and any necessary interfaces for controlling the measurement equipment and recording the data.Calibration equipment: The calibration equipment is used to calibrate the measurement system and ensure accurate results.The measured and simulated radiation patterns for the UWB antenna and narrowband reconfigurable antenna are shown in The patterns show omnidirectional radiation patterns in both planes for wideband antenna, indicating they are useful for UHF band communication applications. The NB antennas have omnidirectional radiation and wide-beam directive patterns, alternating in both planes which makes them useful for sensing behavior. The simulated and measured results show good agreement for both antennas in both XZ and YZ planes.ECC) is calculated to show how much antenna elements are independent in their performance. The values are found to be very low, less than 0.02, ideal for the MIMO operation. ECC values are calculated based on the radiation patterns of antenna elements as given below:ith antenna element. The diversity of the MIMO antenna in terms of envelope correlation coefficient (The proposed antenna features the benefits of sensing and communication integrated antenna, compatibility with unity CubeSat size, low profile, dual CP sensing, communication diversity, frequency reconfigurability, and UHF support. o tapered feed lines and loaded by a capacitor in order to achieve left/right-handed circular polarization in a wide bandwidth from 0.57 GHz to 0.95 GHz. The frequency reconfigurable antenna operates over a wide band from 0.6 GHz to 1.05 GH using a single varactor diode per antenna element. The two NB antennas are designed as meander loops to miniaturize the physical length and reactive loading, which further optimized it to be operated in sub-GHz bands. The antenna system is fabricated on FR-4 substrate with a dimension of 100 × 100 × 0.76 mm3. The measured results verified the simulated results and both are in good agreement. The proposed antenna design is well suited for IoST CubeSat applications.This work presents a low-profile WB and NB frequency reconfigurable antenna for IoST applications. The proposed antenna consists of a circularly polarized WB semi-hexagonal slot and two NB frequency reconfigurable loop slots integrated on the same substrate board. The semi-hexagonal-shaped slot antenna is excited by two orthogonal ±45