This study introduces an innovative MIMO antenna tailored for 5G millimeter-wave applications. By integrating a rectangular closed loop (RCL) and split-ring resonators (SRRs) with a monopole structure, the design achieves notable enhancement in impedance performance around the 26.5 GHz frequency. The MIMO configuration comprises four radiating elements positioned on a common PCB with a space-efficient footprint of 30 × 30mm2. The developed four-port antenna system offers a wide impedance bandwidth of 2 GHz (25.7-27.7 GHz) centred at 26.5 GHz, achieving a total efficiency of 85-95% over the operating band. Additionally, the antenna exhibits envelope correlation coefficient (ECC) values within acceptable limits, ensuring excellent isolation between the ports. The antenna achieves an average gain of 7 dBi, confirming its effectiveness for deployment in millimeter-wave 5G New Radio (NR) bands n257, n258, and n261.

This letter introduces a novel electrically small antenna (ESA) with an inductive–capacitive resonator (LC-R) design tailored for compact handheld devices such as dongles, routers, tablets, and mobile handsets. The ESA integrates an LC resonator parasitically with the driven element to achieve a dual-band/wideband response in sub-6 GHz 5G new radio (NR) bands. Its key innovation is independence from device printed circuit board (PCB) size, maintaining matched impedance without external matching circuits. The fabricated prototype achieves impedance bandwidths (VSWR < 2) of 27.78% [(3.15 GHz to 4.15) GHz] and 20.77% [(4.4 GHz to 5.42) GHz] for 5G NR bands n77/n78/n79. Impedance performance is further validated on various PCB sizes, highlighting its versatility for wireless handheld applications.

Seeing the rising applications of metamaterial in sensing and imaging, satellite communications, it becomes evident to design a high-gain microstrip patch antenna. To support these applications, this paper proposes a 7 x 7 array of planar novel metamaterial unit cells used as a superstrate to enhance the gain of microstrip patch antenna operating at 11.2 GHz. This proposed metamaterial structure yields a very low (near zero) value of effective refractive index at 11.2 GHz. Hence, the superstrate behaves as a near zero-indexed-medium (NZIM) around this frequency. NZIM superstrate are very popular because of their ability to focus the radiation and by utilizing this property, a significant gain enhancement has been achieved in the usage of patch antennas. Numerical simulations have been conducted using the CST Microwave studio, and obtained results corroborate that NZIM superstrate when suspended over a microstrip patch antennas significantly improves the gain around the value of 7.5 dB at 11.2 GHz, and efficiency is also improved.

This work presents a novel frequency reconfigurable electrically small antenna (ESA) with a quasi-isotropic radiation pattern for ISM band applications within the 2.4 GHz band. The key contribution of this work is that a split ring resonator (SRR) is used parasitically with the electric dipole to realize a magnetic dipole-type radiation pattern. In addition, the proposed configuration is further configured with two p-i-n diodes to facilitate frequency reconfigurability to the antenna within the 2.4 GHz band. The SRR is arranged orthogonally with an electric curved dipole to achieve a uniform or quasi-isotropic radiation pattern in 3D spatial coverage. The overall size of the fabricated prototype is 0.13λ×0.13λ mm2; here, λ is the free space wavelength that corresponds to operating frequencies. The proposed antenna offers 40MHz bandwidth centered at 2.44GHz when the diodes (D1 & D2) are ON and a 30MHz bandwidth centered at 2.47GHz when the diodes (D1 & D2) are OFF. In both states, the antenna exhibits a quasi-isotropic radiation pattern with over 60% efficiency.

Seeing the recent rise in applications of RFID tags in industrial internet of things (IIoT), it become very evident to design an efficient and compact antenna which is able to satisfy the uprising IoT demands. This work presents a new 3D quasi-isotropic electrically small antenna (ESA) for RFID applications in the 2.4 GHz band. The proposed antenna is designed on a single perfect electric conductor (PEC) sheet by loading an inverted L-shaped slot. An opened aperture is excited to realize magnetic dipole characteristics to achieve a quasi-isotropic radiation pattern in 3D spatial coverage. The overall volume of the prototype is O.18Ax0.07Ax0.0096A nm3; here, λ is the free space wavelength that corresponds to operating frequencies. The proposed antenna offers a 30MHz (2.42-2.45 GHz) impedance bandwidth centered at 2.43 GHz. The antenna exhibits a quasi-isotropic radiation pattern with a maximum efficiency of 85%, which makes it suitable for RFID applications.

Electrically small antennas (ESAs) have several inherent characteristics. These include a compact size, cost-effectiveness, lightweight design, and ease of integration. Due to these advantages, ESAs are widely preferred for use in miniaturized wireless devices such as mobile phones, laptops, routers, dongles, indoor base stations, and various other Internet of Things (IoT)-enabled devices. Numerous techniques, such as reactive element loading, metamaterial-inspired structure loading, and external matching circuit loading techniques, have been reported in the literature for designing ESAs. While these techniques are useful, they possess some limitations, such as scalability issues, complicated designs, etc. Moreover, the incorporation of additional reactive elements and external matching circuits with an antenna is challenging while maintaining compact surface area, low-quality factor, high gain, bandwidth, and acceptable radiation efficiency. This chapter discusses scalable techniques to mitigate challenges in designing multiband/wideband efficient electrically small antennas while maintaining a small surface area. The first part of this chapter discusses multiple stub–loaded triple-band electrically small antennas, where stubs act as distributed impedance-matching elements for the intended resonance frequency. In this chapter, the dimensions and position of the stubs are predicted by observing variations of the impedance curve in the Smith chart, which is an effective and efficient approach to designing ESAs while maintaining a compact surface area. The second design in this chapter is a multi-resonator-loaded wideband ESA. Here, the design technique involves merging two closely space resonating modes into a single passband to improve the bandwidth of ESA. The dimensional parameters of the stub are optimized to tune the impedance behavior of resonating modes. The stub resonators used in the presented antenna design are loaded by observing the field and current distribution on the radiating element to achieve maximum radiation efficiency with monopole-type radiation patterns. The proposed antenna configurations in this chapter satisfy Chu’s criteria for an electrically small antenna (ESA), which is achieved when the electrical size K × a is less than 1. This indicates that the proposed antennas are indeed electrically small. The design techniques discussed in this chapter are scalable and easy to implement, making them suitable for designing ESAs for miniaturized wireless devices operating at any frequency band.

This paper presents a frequency reconfigurable monopole antenna that uses a switchable defected ground structure to switch between two bands - UWB (2.6 GHz to 10 GHz) and sub-6 GHz from 2.6 GHz to 5.6 GHz. Two slots are created in the partial ground plane of the monopole antenna that act as defected ground structure resonators of length λg/2. The DGS alters the current distribution of the antenna and thereby causes a change in the operating bandwidth of the monopole. Two p-i-n diodes are used to control the surface current path along the DGS resonators. The radiation characteristics show good efficiency and gain in passband and reduction in gain and efficiency in the stopband indicating good stopband characteristics. The antenna is suitable for use in UWB and sub-6 GHz 5G applications.

This paper investigates an FSS-based, wide-band, polarization-insensitive, and lightweight EM wave absorber. The proposed design consists of four number of arrow shaped FSS patterns along with SMD resistors printed on 0.25 mm thin Duroid substrates. The top substrate is separated from the bottom side of the structure by an air spacer that is 5.5 millimeters thick. The bottom side of the structure is complete metal. The proposed design offered a wide absorption bandwidth of 14.9 GHz (5.8 - 20.7 GHz). The presented FSS unit cell has a surface area of 0.19λLg × 0.19λLg and a thickness of 0.108λL, where λLg is wavelength at 5.8 GHz. In this case, the thickness of the suggested structure is 5.6 millimeters, which is extremely close to the Razonov limit. The simulation results demonstrate that the designed FSS absorbs EM wave from 5.8 to 20.8 GHz band with angular stability of 50° for both polarizations. In addition to angular stability, the suggested design is polarization insensitive in the working band. The presented structure is also studied for its RCS, and to demonstrate its real time application in RCS reduction, the RCS (mono and bi-static) of the absorber structure is calculated and compared with the metal sheet's RCS of the same size. Here, the absorption mechanism inside the proposed FSS is further exploited with the help of input impedance plot, E-field, and surface current distribution.

This work presents an EM wave absorber with a band notch between the absorption band. The proposed work consists of two vertically arranged FSS-based resonators over a common metal on the bottom side. The SMD resistor loaded top FSS pattern offers wide absorption bandwidth, and the bottom FSS pattern provides the band notch between the absorption band. The simulation results show that the proposed structure offers more than 90% absorption in 5.8-12.9 GHz and 14.48-20.8 GHz frequency bands with a reflection notch at 13.5 GHz with a 3dB bandwidth of 500 MHz. The designed structure is also polarization-independent due to the four-fold symmetry inside the resonator. Analysis of the proposed structure's angular stability shows that the presented design is angularly stable up to 50° and 40° for TE and TM polarization, respectively. The proposed structure is compact in nature with the unit cell dimension of 0.19 L × 0.19 L × 0.12 L, where L is the wavelength's lowest frequency. Due to presence of the notch band along with absorption, this structure can be used for RCS reduction application of antenna where the notch band can be used as reflector of the antenna.

This work presents an electrically small antenna (ESA) for wireless applications, such as digital cellular systems (DCS1800), WiMAX, and sub 6 GHz–5G new radio (NR) systems. The proposed antenna offers a triple band resonance centered at 1.825, 3.3, and 3.58 GHz. Here, impedance matching networks of printed microstrip line sections, such as inverted ‘L’, open-ended line, meandered line, and capacitive stub, are used to achieve impedance matching at the desired frequencies. The total surface area of the proposed antenna is 0.14λ × 0.06λ, where λ is the wavelength at 1.825 GHz. The designed antenna is tested for its impedance and radiation characteristics. The fabricated prototype offers fractional bandwidth (FBW, with VSWR < 2) of 1.6%, 6%, and 6.7% centered at 1.825, 3.3, and 3.58 GHz, respectively, whereas for VSWR 3:1, the achieved fraction bandwidth(s) is 8.2% and 24.5% for the DCS1800 and 3.3 GHz band, respectively. The stable and nearly omnidirectional radiation pattern for each operating frequency bands indicates the suitability of the proposed antenna for the intended application(s).

This work presents a terahertz metasurface absorber-based biomedical sensor for cancer cell detection applications. The proposed metasurface structure is designed using the metallic split annular ring on GaAs substrate, which offers more than 97% absorption at 3.77 THz with the FWHM absorption bandwidth and Q factor of 110 GHz and 34.27, respectively. The absorption mechanism inside the THEMWA is exploited with the help of a normalized input impedance (Zeff) plot and electric and magnetic coupling. Four-fold symmetry inside the resonator makes this structure's polarization insensitive. This study further uses this proposed structure as a sensor where cancer cells are detected by the shift of resonance frequency caused by variations (changes) in the refractive index of biological samples placed on top of the absorbers. The simulation's output demonstrates that the proposed structure's resonance frequency shifts from 3.608 THz to 3.59 THz with a change in refractive index from 1.35 to 1.40. This TEMWA-based sensor offered high sensitivity and FOM of 360 GHz/RIU and 3.273, respectively, which make this proposed structure a good candidate for refractive index-based biomedical sensors for cancer detection applications.

A multi-functional metasurface structure is presented in this paper. This metasurface consists of two resonating structures printed on two FR-4 substrates, while the bottom side of the structure is completely laminated with copper. The proposed design offered absorption at 6.1 GHz frequency with 200 MHz bandwidth and polarization conversion in the X band from 7.8 to 11.9 GHz frequency band. The presented unit cell is compact with a length and width of 0.31 λ × 0.31 λ while thickness is 0.081 λ, where λ is the free-space wavelength at 6.1 GHz. The simulation results show that the proposed structure absorbs EM wave at 6.1 GHz in the C band with angular stability of up to 70° for both TE and TM polarization. Whereas the four-fold symmetry inside the resonator provides polarization insensitivity in nature. Along with this absorption phenomenon, this proposed structure also provides a polarization conversion phenomenon in the X band from 7.8 -11.9 GHz with angular stability of up to 50°. The absorbance mechanism in the proposed structure is further explicated with the help of surface current distribution, E-field distribution, and impedance plot, whereas the polarization conversion mechanism has been explained with the help of reflection due to cross-polarization.

This paper presents a compact high gain antenna for indoor communications. Here an electrically small antenna is suspended above an artificial magnetic conductor (AMC) surface to achieve a unidirectional radiation pattern within LTE 1800MHz band. The antenna is placed at the height of 0.18? above the AMC surface. The overall surface area occupied by the proposed prototype is 0.46?×0.46?. The electrically small antenna(ESA) is tested with an AMC reflector, and simulated S11response shows good agreement with the measured result. Here the proposed antenna (with AMC surface) offers fractional bandwidth of 3.3% with an average gain of 6.1dBi over the desired operating band.

This work presents a top-loaded wideband electrically small antenna (ESA). Here a 2D metallic (PEC) strip is loaded at the top of the conventional monopole to design an electrically small antenna. The bandwidth enhancement mechanism of the proposed antenna is analyzed by considering fringing field capacitance between the ground plane of the CPW feed and radiating element. In addition, to support the effectivity of the proposed method, the lower bound Quality factor (Q.Flb) of the proposed antenna is estimated by considering the theoretical limitations of an electrically small antenna. The overall surface area of the antenna is 0.2λ×0.15λ, where λ is the wavelength at 4.4GHz. The antenna exhibits -10 dB impedance bandwidth of 1950 MHz for the intended 5G WLAN and new radio (n79) applications. Furthermore, it offers more than 85% efficiency with an omnidirectional radiation pattern over the operating band. The achieved impedance response and radiation characteristics validate the suitability of the proposed antenna for indoor wireless applications.

This paper presents a frequency reconfigurable printed monopole antenna that can be reconfigured to two operating bands - UWB (3.1 - 10.2 GHz) and sub-6 GHz (3.1 - 6 GHz). To attain frequency reconfigurability, the partial ground plane of the printed monopole is loaded with a quarter wave stub resonator which can be either connected or disconnected with the ground plane with the aid of a p-i-n diode. The quarter wave stub resonator is designed in such a way that it provides a wide stopband in the UWB band of the antenna giving the sub-6 GHz band. The proposed resonator structure has minimal effects on the antenna's radiation characteristics while providing good stopband performance. The antenna is suitable for UWB, sub-6 GHz 5G and Cognitive Radio applications.

In this work, a polarization independent and wideband electromagnetic (EM) waves absorbing frequency selective surface (FSS) structure is presented. The unit cell of the proposed FSS consists of an assembly of cross arrow resonators with four SMD resistors mounted on it, to enhance the absorbance bandwidth. This unit cell also possesses a four-fold symmetry which makes it polarization insensitive. The designed unit cell is compact with the length and width dimensions as 0.19λL × 0.19λL, and thickness of 0.13λL, where λL is the guided wavelength corresponding to the lowest operating frequency. The proposed absorber is theoretically and experimentally tested for its absorbance, cross-polarization level, and radar cross section (RCS) characteristics. The computer-aided simulation and practical measurements indicate that the proposed absorber offers more than 90% (with a fractional bandwidth of 93%) absorbance for normal incidence at 4.5–12.4 GHz frequency band. The cross-polarization reflection coefficient analysis indicates that the proposed FSS configuration behaves as an absorber and not a polarization convertor. The input impedance plot, surface current distribution, and E-field distribution of the unit cell were also analyzed and presented to understand the absorbance mechanism. The RCS of the proposed FSS is compared with the RCS of a reflective (metallic) sheet to analyze its suitability for practical applications (RCS reduction) within the working band. The 3D simulated and 2D calculated RCS results indicate that the proposed FSS is suitable for wideband EM wave absorber applications.

This study presents an electrically small antenna loaded with a parasitic loop resonator for dual-band operations. The proposed configuration covers 2.4 GHz Bluetooth/Wi-Fi, 5G new radio (n79), and 5 GHz WLAN bands. In this study, a coplanar waveguide (CPW) feed L-shaped driven element is capacitively coupled with a parasitic loop resonator to get a dual-band response centered at 2.43 and 5.5 GHz, respectively. Further, an open-ended stub is attached with the driven element to achieve wide impedance bandwidth over the 5 GHz WLAN band. The overall dimension of the proposed antenna is 0.06λ × 0.2λ, where λ is the wavelength at 2.43 GHz. The parasitic loop resonator loaded electrically small antenna offers 60 and 1580 MHz impedance bandwidth (S11 < −10 dB). The stable impedance bandwidth and radiation characteristics of the proposed antenna validate its suitability for wireless application(s).

This paper presents an electrically small quasi-isotropic dipole antenna loaded with Split Ring Resonator (SRR) for applications in the 2.4GHz band. In this work, a near field parasitic element (NFPE) i.e., SRR is loaded beneath the electric dipole to generate quasi-isotropic radiation characteristics. The electric dipole (i.e., curved dipole) and NFPE are arranged to achieve a uniform radiation pattern in spatial coverage. Here, the SRR exhibits patterns like magnetic dipole which is orthogonal to the radiation pattern of an electric dipole. The overall dimension of the antenna is 0.13λX0.13λ mm2. The fabricated prototype of the proposed electrically small antenna(ESA) is measured to validate its performance. The measured S11 response shows good agreement with the simulated one. The fabricated prototype offers 48MHz bandwidth centered at 2.43GHz. The proposed antenna offers a quasi-isotropic pattern with 90% radiation efficiency over the operating band, ranging from 2.41 to 2.458GHz.

This paper presents a frequency reconfigurable parasitically coupled rectangular loop antenna that can be tuned to three different frequencies in the sub-6 GHz band. The antenna structure consists of two rectangular loops, one rectangular loop fed with a 50 ohm transmission line and the other loop is parasitically coupled with the first one. The frequency tuning is achieved by using four pin diodes which are placed at appropriate positions on the parasitic rectangular loop. By switching the diodes (ON/OFF) three bands from 2.7 - 3.1 GHz, 3 - 3.5 GHz and 3.5 - 4.5 GHz are obtained. The simulation is carried out in CST Microwave studio and analysis of the antenna is done using parametric study and surface current distribution. The antenna exhibits omnidirectional radiation pattern in all three frequency bands with good stopband characteristics and is suitable for 5G and cognitive radio applications.

In this paper, an electrically small chip antenna is presented for 5G WiMAX and WLAN applications. In this work, multiple vias and virtual ground (VG) are used to design a multiband miniaturized antenna. The feeding pad for the antenna is mounted on a 50-Omega microstrip feed line. The proposed antenna offers -10dB impedance bandwidth of 130 MHz and 440MHz in WiMAX and 5GHz WLAN band respectively. The surface area of the chip antenna is approximately 0.09× 0.04 textmm2, wherecorrespond to the wavelength at 3.5GHz. Due to its compact surface area, the proposed antenna can be mounted onto the circuit board of any wireless devices such as a dongle, Wi-Fi receiver, laptops smartphone etc.

This paper presents the design and analysis of dual band electrically small antenna loaded with meander line and loop resonator. The proposed electrically small antenna (ESA) is designed on the FR-4 substrate with modified ground plane. The radiating element of the proposed antenna consists of metallic strip loaded with thin inductive meander line and a resonant triangular loop. The presented configuration gives dual band response at 1.81 GHz and 2.56 GHz. The higher resonance frequency is controlled by tuning the effective length of metallic strip. The lower frequency response i.e. 1.81 GHz is achieved by using the combination of the shunt inductive meander lines topped with a triangular loop resonator. The surface area of the presented antenna is 40 mm× 15 mm. The designed antenna exhibits fractional bandwidth of 3.8% and 21% for 1.81 GHz, and 2.56 GHz respectively. The measured and simulated results are in near agreement proving the effectivity of the resonator.

This work presents dual band, polarization insensitive and angular stable radar absorber structure. Here, proposed absorber unit cell has two resonator structures M and N. Each resonator provides absorption at distinct frequencies in X and Ku band. Simulation results in different cases show that the structure is polarization insensitive and angular stable up to 600. Calculated effective impedance plot and surface current distribution at the top and bottom surface supports the absorption mechanism at the resonance frequencies. To verify the simulations, a prototype of absorber is fabricated on FR-4 substrate and tested in an anechoic environment.

In modern wireless application, wideband microstrip antenna plays a vital role. In this paper, we will discuss higher order mode dual beam 'Microstrip Antenna' instead of fundamental mode TM 01 to improve the bandwidth of the rectangular Microstrip antenna. Different techniques have been adopted to improve the bandwidth of planar antenna. A lot of work has been done using U-slot technique, here the antenna bandwidth is analyzed by combining single U, double U and triple U slots, with polygon slot on the radiating patch. This antenna operates between 5.1GHz to 7.1GHz having VSWR less than 2.15 and bandwidth increasing up to 33.3% with acceptable return loss response. This antenna exhibits two radiation beams directed at+40° and -40°. This proposed antenna is useful for indoor wireless applications such as cordless telephones, mobile communications, Wi-Fi etc.

In this paper, a novel design of a stacked two layer microstrip patch antenna with wideband characteristics is proposed. This paper follows fractal and stacking methodology to improve the characteristics of microstrip antennas. This antenna consists of two circular patches. The upper radiating patch is suspended with Teflon clamps over the lower driving element. The radiating patch is excited through EM coupling by the driving element. The rectangular slots on the ground plane are loaded for better impedance matching over the operating frequency range. The impedance bandwidth of single layer patch is 7%. After using stacking and fractal methodology the impedance bandwidth increases up to 69% ranging from 7.5GHz to 14.4GHz with acceptable return loss. This antenna offers Omni-directional radiation patterns in H-plane. This antenna is useful for X-band applications such as radar, mobile communication, satellite communication etc. as it's center frequency is 10GHz.

Ultra wideband Fractal shaped planar antenna is proposed in this paper. This paper followed Koch iteration technique to improve the bandwidth of the planar antenna. A circular slot is loaded on the radiating element to increase the current density over the surface of radiating patch. The Koch geometry can be formed by taking the help of a mathematical process i.e. Iterative Function Scheme (IFS). After second iteration the bandwidth is approximately 3GHz but return loss is found to be just below -15dB. After inserting a circular slot on the patch, fractional bandwidth improves up to 56.25% ranging from 3.6GHz to 7.2GHz with better reflection loss response. This designed slotted Koch fractal antenna presents Omni-directional radiation characteristics over the wide operating range. This proposed fractal antenna is suitable for C-band applications such as cordless telephones, mobile communications, Wi-Fi, Satellite communications etc.

In this article, an innovative structure of a high gain stacked fractal antenna is introduced. This article follows stacking and Sierpinski Carpet concept to achieve wide bandwidth and high gain of the antenna. The proposed design consists of five patches, the driving element is printed on the lower substrate and other four parasitic patches are suspended with dielectric clamps above the driving element. This designed antenna has 550MHz bandwidth with a gain of 10.3dB. As this antenna is operating at 6GHz frequency, this antenna is suitable for C-band applications.

In this paper, a novel design of a corrugated microstrip antenna with wideband characteristics is proposed. The suggested antenna consists of an arc-shaped edge and a ground plane which has been modified. The difference from the other traditional antennas is in the modification of the ground plane. The corrugated ground plane is present below the feed line and partially present just below the radiating element. By cutting square shaped slots on the arc side at regular intervals improves the frequency bandwidth. With this design the return loss curve was found to be below -10dB with frequency range of 2.6-17.7GHz and a radiation pattern just like a horizontal dipole antenna.