Free-space Wavelength Research Articles

Design and analysis of dual-band circularly polarized coplanar waveguide antenna for millimeter-wave 5 G applications

Abstract A dual-band circularly polarized antenna has been designed for millimeter-wave applications, operating over the frequency ranges of 27 GHz to 28.45 GHz and 34.3 GHz to 35.8 GHz. The proposed coplanar waveguide (CPW) antenna features a central feed line serving as the main signal conductor, with circular structures arrayed around it acting as radiating elements. These elements are strategically designed for optimal performance at millimeter-wave frequencies. The antenna, with physical dimensions of 8 mm × 7 mm × 0.757 mm, corresponds to approximately 0.72λ × 0.63λ × 0.068λ at 27 GHz, where λ represents the free-space wavelength. Fabricated on a Rogers RT/duroid 5880 substrate, the antenna’s practical measurements exhibit good agreement with simulated results. The antenna achieves an overall gain of up to 6 dBi across the operating bandwidth, maintaining an axial ratio of less than 3 dB. These results confirm the antenna’s efficacy, making it a superior choice for millimeter-wave 5 G applications.

Miniaturized Arrow-Shaped Flexible Filter-Embedded Antenna for Industrial and Medical Applications

This paper presents the design and characterization of a coplanar waveguide (CPW) fed, low-profile, and flexible arrow-shaped filtenna for ISM band applications at 2.45 GHz. The antenna design involves an innovative approach incorporating etching slots to achieve miniaturization by 34%, contrasting with a traditional quadrilateral-shaped antenna. After the attainment of desired miniaturization, the unwanted harmonics are also mitigated by deploying simple filtering methodology. A perpendicular rectangular stub is strategically introduced to the feedline, effectively minimizing harmonics across a broad frequency range of 3.3–11.0 GHz. Through simulations and measurements, the results indicate that the antenna’s operational band spans from 2.276 to 2.75 GHz, encompassing the entire ISM band (2.4–2.5 GHz). Notably, the antenna demonstrates promising radiation characteristics, including omnidirectional gain of approximately 2.2 dBi and a radiation efficiency exceeding 95%. With a compact overall size of 0.24λ × 0.20λ × 0.0005λ (where λ is the free-space wavelength at 2.45 GHz), coupled with wide harmonic rejection property, the proposed arrow-shaped flitenna emerges as a compelling candidate for ISM band applications.

Compact metasurface antenna for Sub-6 GHz applications with isolated n77/n78 bands using CSRR

Abstract A compact (0.35 λ0× 0.35 λ0 where λ0 is free space wavelength at the lower resonance frequency 3.50 GHz) bio-inspired tulip flower-shaped antenna (TFSA) is proposed. A double negative (DNG) metamaterial complementary split ring resonator (CSRR) is introduced near the feed in the hybrid triangular-circular patch which inserts a notch-band (4.20-4.38 GHz) in the wide bandwidth (3.15-7.05 GHz) and makes the antenna response dual-band. Consequently, this results in in-band interference reduction in 5G-Sub-6 GHz applications. A slotted FSS is placed at a distance of 28.507 mm beneath the monopole-reduced ground of the antenna to enhance the reduced gain from 4.39 dBi to 7.22 dBi. A further gain is improved to 12.84 dBi by placing a full copper surface (0.35 λ0× 0.35 λ0) as the reflector layer is placed below FSS at 1.6 mm. Finally, prototyped TFSA with FSS and reflector model achieve a dual bands reflection coefficient response (3.15-4.20 GHz): n77/n78, and (4.38-7.03 GHz): n46/n47/n96/n102/n79. The antenna reflection coefficient is tested using Keysight 14 GHz FieldFox Microwave Analyzer N9916A, and radiation patterns in the E-plane and H-plane are measured using an 18 GHz anechoic chamber. The comparison of simulated results with measured results is found an excellent match in bandwidth and with shapes of gain radiation patterns. The reflector and FSS jointly make the radiation pattern strong in the E-plane above the TFSA radiator. The antenna is well suited for n77/n78 (3.30-4.20 GHz), n79(4.40-4.99 GHz), n46 (5150-5925MHz), n47 (5855 – 5925MHz), n96/n102 (5925-6425MHz), 5.8 GHz HiperLAN, WiMAX 3.5GHz applications. An electrical equivalent circuit model of the proposed TFSA antenna is presented and validated using ADS software.

Low-profile miniaturized dual-band dielectric resonator antenna with a mountain-shaped ground

ABSTRACT A novel method is proposed to achieve a low-profile miniaturized dual-band dielectric resonator antenna (DRA) for wireless communication applications. The cylindrical dielectric resonator (DR) is fed by a microstrip loop on the top surface of the substrate and a mountain shaped ground on the bottom surface of the substrate. This structure not only effectively transfers energy to the DR but also plays a pivotal role in establishing a lower resonance frequency of 1.73 GHz, achieving this with a compact structure (0.21λ 0 × 0.18λ 0 × 0.02λ 0, and λ 0 is the free-space wavelength at 1.73 GHz). HEM11δ mode of the cylindrical DR is employed to cover the upper frequency band of 2.8 GHz. Ultimately, the effectiveness of our suggested approach and the antenna’s performance are confirmed through the measurement.

Metal-free ultrathin terahertz absorber with independently tunable dual narrow bands

Abstract A technique is introduced to precisely control the resonance behaviour of a metal-free graphene-based terahertz absorber by independently tuning dual resonant peaks. The proposed ultrathin absorber features a multilayer configuration, with two isolated resonator layers of patterned graphene on dielectric (SiO2) substrates, and a thin graphite sheet at the bottom serving as a reflector. The stacked arrangement enables independent tunability of the high-absorptivity resonant peaks at 7.33THz and 9.34THz. The structure, with a thickness of just λ/15 of the free-space wavelength, offers a compact design suitable for space-constrained applications. Its symmetrical geometry ensures polarization insensitivity and stable performance for incident angles up to 60°. Simulated results, analysed via CST Studio and validated with an Equivalent Circuit Model (ECM), demonstrate excellent thermal stability. Furthermore, the narrowband response of the proposed absorber improves its sensitivity for refractive index variations induced by biomolecular interactions validating its suitability in biosensing applications. The absorber demonstrates peak absorption across both the resonant frequencies with an analyte optimised at 1.5μm thickness. Sensitivity levels of 1.1THz/RIU and 1.05THz/RIU along with figure-of-merit (FOM) values of 2.11 and 2.23. are recorded for the lower and upper bands, respectively. The absorber offers enhanced selectivity owing to low values of full-width at half maximum (FWHM). High Q-factors of 12.85 and 19.3, confirm its strong potential for refractive index sensing. 

Miniaturized meandered ring graphene-metal metasurface with wide angle control on the transmitted wave

In this paper, a miniaturized transmissive metasurface using graphene-metal in the 3.5 THz frequency range is proposed and designed to control the wavefront of the transmitted wave. The designed unit cell has four identical ultra-thin layers. Each layer contains a meandered ring-shaped slot carved in a metal sheet, which is partially filled with four graphene patches in symmetrical places. By employing the meandered shape slots, the lateral dimensions of the unit cells are reduced to 0.19 of the free space wavelength, which, to the best of our knowledge, is the most miniaturized designed structure among the existing transmissive metasurfaces in the literature. Full wave simulations confirmed that without any physical changes and by just altering the spatial distribution of the chemical potential of the graphene patches, wave-front control is achieved. The achievements include beam steering and beam splitting with numerous discrete angles up to 63° and beam focusing with optional focal lengths. It is envisaged that besides 6G wireless telecommunications, this structure could also be beneficial for THz imaging, nano-photonic and opto-electronic devices.

Design of a high-gain, low-ECC 2x2 MIMO antenna for 28 GHz 5G wireless communication system

In this paper, a 2 × 2 MIMO antenna with inset feed is designed for the frequency Range 2 (FR2) millimeter wave frequencies such as n257 (26-29.5 GHz), n258 (24.25-27.5 GHz), and n261 (27.5-28.35 GHz). The MIMO antenna is designed and fabricated using low loss Rogers RT/duroid 5880 substrate having dimension of 1.4λ 0×2.8λ 0×0.073λ 0, where λ 0 is the free-space wavelength operating at 28 GHz.The defected ground structure (DGS) minimized the surface waves current. Thus DGS are used to increased the gain and the isolation of the proposed MIMO antenna design. The gain of the MIMO antenna reported is 10.3 dBi with 97.01% radiation efficiency at 28 GHz resonant frequency. The -10 dB impedance bandwidth lies between 26.95-29.50 GHz, which covers the 5G frequency bands. The isolation is ≥28 dB and envelope correlation coefficient (ECC) is 10 −5, respectively, in the complete operating band.

Wideband circularly polarized dielectric resonator antenna with multi-functional metasurface assistance for low profile

ABSTRACT A low-profile broadband circularly polarized (CP) dielectric resonator antenna (DRA) is proposed, utilizing DR reutilization and metasurface (MS) techniques. Two resonant frequencies and an AR minimum are achieved simultaneously, by exciting a rectangular DR with an inclined corner-truncated coupling slot, for it generates nearly degenerated TE111 modes. For significant bandwidth enhancement and low profile, a new resonator is formed by reusing the DR and loading an MS above, which works in orthogonal TM modes. To increase the axial ratio bandwidth (ARBW) further without enlarging the antenna size， two parasitic patches are printed on two adjacent side walls of the DR. To verify the rationality and feasibility, the antenna is fabricated and measured. The fabricated prototype possesses the profile of 0.06λ 0 (λ 0 is the free-space wavelength at the center frequency). The measured impedance bandwidth (IBW) and ARBW are 36.05% (4.23 ~ 6.09 GHz) and 22.46% (4.9 ~ 6.14 GHz), respectively. The proposed antenna has both broadband characteristics and a low profile, making it easy to integrate into space-limited wireless communication systems with high data rates.

Deep subwavelength topological edge state in a hyperbolic medium.

Topological photonics offers the opportunity to control light propagation in a way that is robust from fabrication disorders and imperfections. However, experimental demonstrations have remained on the order of the vacuum wavelength. Theoretical proposals have shown topological edge states that can propagate robustly while embracing deep subwavelength confinement that defies diffraction limits. Here we show the experimental proof of these deep subwavelength topological edge states by implementing periodic modulation of hyperbolic phonon polaritons within a van der Waals heterostructure composed of isotopically pure hexagonal boron nitride flakes on patterned gold films. The topological edge state is confined in a subdiffraction volume of 0.021 µm3, which is four orders of magnitude smaller than the free-space excitation wavelength volume used to probe the system, while maintaining the resonance quality factor above 100. This finding can be directly extended to and hybridized with other van der Waals materials to broadened operational frequency ranges, streamline integration of diverse polaritonic materials, and compatibility with electronic and excitonic systems.

An in‐band full‐duplex antenna for 2.4 GHz WLAN using differential‐feed based neutral coupling for isolation enhancement

AbstractThis article introduces a unique design approach for a compact in‐band full‐duplex (IBFD) antenna with good isolation in a wider bandwidth at the 2.4 GHz WLAN. The meander slot baluns are innovatively constructed in the feeding network, one balun on the top substrate layer and the other on the bottom substrate layer of the ground, to realize double differential feeding and polarization diversity. The metallic vias that connect one of the baluns in the feeding network with the co‐radiating patch further reduce the antenna's overall size. The balun's neutral coupling characteristics of differential potentials, which reduce the leakage currents by creating null potential, and differential filtering, which suppresses the leakage currents by non‐coupling fields, generate high isolation in the antenna. The designed balun offers a stable differential feed with a trivial magnitude and phase imbalances of (0.04–0.06) dB and , respectively. The antenna offers a minimum isolation of 78 dB with a wider bandwidth of 130 MHz. The far‐field measurement shows broadside radiation with low cross‐polar levels of less than −32 dB. A prototype is fabricated on FR‐4 substrate layers with an overall size of (0.8 × 0.8 × 0.012) ( is the free space wavelength of the frequency GHz) to validate the proposed design performance. The measured results of the prototype properly correlate with the simulated results.

Four‐port dual CP MIMO antenna with enhanced isolation for 5G applications

SummaryIn this paper, a 4 × 4 MIMO (multiple‐input multiple‐output) antenna with metasurface (MS), which is composed of dual circularly polarized (CP) patch antennas, is proposed for 5G (sub‐6 GHz) applications. The MIMO antenna consists of four microstrip patch antennas. In order to improve the isolation of the MIMO antenna, parasitic elements are placed on the MS and layer of patch antennas. In addition, a substrate‐integrated waveguide (SIW) structure is used at the center of the MIMO antenna for this purpose. The proposed MIMO antenna is fabricated for validation tests. The antenna has overall dimensions of 115 mm × 115 mm × 3.2 mm (1.219 × 1.219 × 0.033 , where is the free space wavelength at the lowest operating frequency in 10‐dB impedance bandwidth). The MIMO antenna has 10‐dB impedance bandwidth (IBW) from 3.3 to 3.8 GHz (14.08%), 3‐dB axial ratio bandwidth (ARBW) from 3.42 to 3.69 GHz (7.59%), and 6.36‐dBi peak gain. The isolation is greater than 28.14 dB in the n78 frequency band (3.3–3.8 GHz).

Metamaterial inspired superstrate loaded miniaturized quad port MIMO antenna for 5G C-band applications

This paper proposes a new quad-port Multiple-Input-Multiple-Output antenna with a unique Maze structure Epsilon Negative (ENG) Metamaterial superstrate for 5G NR C-band applications. The suggested 2x2 MIMO antenna has four microstrip antennas with a C-shaped stub inside the slot arranged orthogonally on a FR4 substrate. The overall dimension of the proposed 2x2 MIMO antenna is 0.62λ0 x 0.62λ0 x 0.02λ0, where λ0 is the free space wavelength at 3.7 GHz. The proposed MIMO antenna has excellent impedance matching over a bandwidth of 32% (3.2 GHz–4.4 GHz). The proposed antenna incorporates a superstrate layer composed of modified maze-structured metamaterial elements with a unit cell size of 0.16λ0 x 0.16λ0 x 0.02λ0 on a single-layer FR4 substrate to enhance the antenna's gain, improve isolation properties, and achieve size reduction. By strategically placing the metamaterial superstrate, it reduces the mutual coupling between the antennas and enhances peak isolation of < −30 dB. In order to accomplish the goals of isolation and gain improvement, the metamaterial superstrate is positioned 10.5 mm (0.13λ0) above the MIMO components. Furthermore, it attains a 3.54 dB peak realized gain, which is enhanced by 162% across the frequency ranges, and the overall size of the MIMO antenna is reduced to approximately 17%. Adequate values for factors such as the diversity gain, envelope correlation coefficient, channel capacity loss, and total active reflection coefficient are also determined for the MIMO antenna performance. The design prototype of the proposed antenna is built and verified by measurements that reveal a strong correlation with the simulation's output.

A closely spaced dual band polarization insensitive FSS for 5G applications

This study presents a novel single layer Frequency Selective Surface (FSS) for fifth generation (5G) applications with a polarization independent closely spaced dual band response. The proposed design consists of four split ring apertures etched on a square patch printed on a RT5880 dielectric substrate. The FSS has two stop-bands at 24.78 GHz and 28 GHz center frequencies with attenuations around 55 dB. The S21<−10 dB bandwidths (BW) of these bands are 14.48 % and 9.25 %, respectively and these closely spaced bands succeed 1.13 frequency ratio. It shows a stable frequency response for both TE and TM polarizations. Furthermore, the FSS represents a single layered and quite thin (thickness 0.042λl) structure with its unit cell size (0.70λl × 0.70λl, where λl is the free-space wavelength at lower frequency). The novelty of the presented FSS is not only achieving a small closely spaced band ratio in the mmWave band and exhibiting polarization insensitivity but also providing these features with a simple geometry and, uncomplicated single layer structure. The simulation results were confirmed by well accordant measurement results. All these results make the presented FSS a good candidate for 5G electromagnetic interference (EMI) shielding applications.

An efficient and miniaturized ultra-thin tunable UWB graphene metasurface absorber for terahertz gap regime

This work introduces an ultra-thin tunable ultra-wideband (UWB) metasurface absorber (MSA) for the terahertz (THz) gap. The polarization-insensitive MSA provides an absorptivity (A(f)) ≥ 90% from 0.1 to 11.5 THz, corresponding to 196.6% fractional bandwidth. The usage of resonant slots engraved on top patterned graphene sheet (Gpat) and strong plasmonic coupling in the Fabry-Perot cavity formed between top Gpat and bottom continuous graphene (Gcont) in bilayer stack configuration ensures absorptivity over a UWB THz spectrum. An equivalent circuit model (ECM) closely follows the A(f) response of the proposed MSA. The proposed DC-biasing mechanism can regulate the chemical potential (μc) of the connected Gcont efficiently. A DC bias voltage of 0 to 6.1 V is adequate to vary μc of Gcont from 0 to 0.6 eV for achieving tunable A(f). The structure maintains its ultra-thin nature and has a thickness of only λ0/1500, where λ0 is the free space wavelength calculated at 0.1 THz. In addition, the periodicity is only λ0/300. The MSA also provides stable absorption response from 0.1 to 11.5 THz with A(f) ≥ 80% for incidence angle (θ) up to 60∘ under both transverse magnetic (TM) and transverse electric (TE) polarization.

Ultra-Wideband Circular Polarized Implantable Patch Antenna for Implantable Blood Glucose Detection System Applications.

To address the current demands for antenna miniaturization, ultra-bandwidth, and circular polarization in advanced medical devices, a novel ISM band implantable antenna for blood glucose monitoring has been developed. This antenna achieves miniaturization by incorporating slots in the radiation patch and adding symmetric short-circuit probes, resulting in a compact size of only 0.054λ0 × 0.054λ0 × 0.005λ0 (λ0 is the wavelength in free space in respect of the lowest working frequency). By combining two resonance points and utilizing a differential feed structure, the antenna achieves ultra-broadband and circular polarization. Simulations indicate a |S11| bandwidth of 1.1 GHz (1.65-2.75 GHz) and an effective axial ratio (based on 3 dB axis ratio) bandwidth of 590 MHz (1.89-2.48 GHz), able to cover both the ISM frequency band (2.45 GHz) and the mid-field frequency band (1.9 GHz). The antenna exhibits CP gains of -20.04 dBi at a frequency of 2.45 GHz, while it shows gains of -24.64 dBi at 1.9 GHz. Furthermore, a superstrate layer on the antenna's radiating surface enhances its biocompatibility and minimizes its impact on the human body. Simulation and experimental results indicate that the antenna can establish a stable wireless communication link for implantable continuous blood glucose monitoring systems.

Offset-fed Slotted Antenna Practically Loaded with Split Ring as Water Quality Sensor for X-Band Industrial Applications

This article communicates an offset-fed split ring loaded slotted-antenna design, testing, and analysis for different water quality sensor. The antenna was designed to resonate at 10GHz on a low-cost FR-4 substrate of dimensions 0.621λo×0.467λo×.053λo, where λo is the free space wavelength. The measured antenna parameters are found in excellent agreements. The antenna achieves a gain of 7.61dBi with nearly unidirectional radiation pattern and a radiation efficiency of 76% at 10GHz. Further, the research is explored to use the antenna as a water sample sensor. Different water samples are tested with the antenna by dipping the antenna into the water samples and in the second case contactless measurements at 10mm apart from the upper water level in the container. The quality of water is examined by observing the shift in the resonant frequency (fr), antenna quality factor with different total dissolved solvents (TDS) water samples, and changes in the reflection coefficient (S11) values in the water samples. It is observed that the antenna shows less than 1.5% numerical sensitivity (NS) with fr and high NS with the S11. The S11 and bandwidth of the antenna vary with different water samples. This antenna is suitable for X-band industrial and microwave laboratory applications.

A novel ultra-miniaturized 2.5-D frequency selective surface temperature sensor with linear frequency–temperature behavior

This paper presents the design and proposal of a new ultra-miniaturized Frequency Selective Surface (FSS) sensor configuration for applications in temperature sensing systems. A 2.5-D (2.5 Dimensions) FSS is proposed with elements inspired by convoluted metal lines with metal vias inserted and printed on an FR4 dielectric substrate. The vias contribute to the capacitive and inductive effects in the structure, providing ultraminiaturization of the unit cell dimensions. The size of the unit cells of the proposed FSS is equal to 4.42 % of the wavelength in free space for the frequency of 2.21 GHz (resonance frequencies). The principle of operation of the FSS is evaluated using the equivalent circuit model proposed in this work. A new application for ultra-miniaturized FSS based on convoluted geometries as non-contact temperature sensors is analyzed in this work. According to the literature, the electrical permittivity of the dielectric material used as the FSS substrate changes as the temperature of the environment in which the circuit is inserted changes, thus altering its frequency response. Numerical analyses were carried out and found that the FSS has an almost linear relationship between the resonance frequency and the electrical permittivity. The numerical results simulated for the prototype were obtained using the ANSYS HFSS software and the equivalent circuit model. The prototype sensor was built and the transmission coefficient and resonance frequency were experimentally characterized. The proposed sensor was experimentally analyzed from a temperature of 20° to 120°C and showed a sensitivity of 0.640 MHz/°C. The values obtained in the experiments were compared and discussed with the results of the simulations, which showed good agreement.

Near field food contamination detection technique employing a compact Antipodal Vivaldi antenna

This paper presents a simple yet robust technique for identification of the presence of contaminants in food samples by detecting the variation in the transmission coefficient (S21) in a near field measurement setup. A compact step-notched antipodal Vivaldi antenna with a frequency range of operation 3 - 18 GHz, and realized gain of 12.81 dB at 16 GHz having compact dimensions 60mm×40mm×0.51mm, i.e., 0.6×0.4×0.005λ03 (where λ0 is the free space wavelength at the lowest frequency of operation) is designed for contamination detection due to its compact size, high directivity and high boresight gain for near-field measurement. An equivalent image is constructed from the S - parameters, measured at different positions and different antenna polarizations over the frequency range of 3-18 GHz for metallic contaminants, i.e., iron ball and aluminum foil. An algorithm is developed for detection of contamination from the images using the reference case of no-contamination scenario. The proposed algorithm is validated using full-wave simulation.

A low-profile frequency- and pattern-reconfigurable metantenna for UAV joint RadCom systems

To address the specific requirements of antennas in Unmanned Aerial Vehicle (UAV) joint radar-communication (RadCom) systems, a novel low-profile reconfigurable metantenna with the capability of frequency and pattern reconfiguration is proposed in this paper. The proposed antenna consists of a metasurface layer with 3 × 3 square unit cells and a simple feeding network with two pairs of PIN diodes. Specifically, the designed metantenna has a low profile of 0.064 λ0 (λ0 is the free space wavelength at 5.5 GHz). And measured results show that, for the broadside radiation mode, the −10 dB operating bandwidth is about 12.1 %, ranging from 5.05 to 5.7 GHz with a maximum gain of 8.9 dBi. For the conical radiation mode, the −10 dB operating bandwidth is about 21.9 %, ranging from 5.88 to 7.33 GHz with a maximum gain of 6.83 dBi. Given its excellent radiation performance, the metantenna designed for UAV joint RadCom systems holds significant research significance and value in the field of multifunctional reconfigurable antennas.

Reconfigurable metamaterial processing units that solve arbitrary linear calculus equations

Calculus equations serve as fundamental frameworks in mathematics, enabling describing an extensive range of natural phenomena and scientific principles, such as thermodynamics and electromagnetics. Analog computing with electromagnetic waves presents an intriguing opportunity to solve calculus equations with unparalleled speed, while facing an inevitable tradeoff in computing density and equation reconfigurability. Here, we propose a reconfigurable metamaterial processing unit (MPU) that solves arbitrary linear calculus equations at a very fast speed. Subwavelength kernels based on inverse-designed pixel metamaterials are used to perform calculus operations on time-domain signals. In addition, feedback mechanisms and reconfigurable components are used to formulate and solve calculus equations with different orders and coefficients. A prototype of this MPU with a compact planar size of 0.93λ0×0.93λ0 (λ0 is the free-space wavelength) is constructed and evaluated in microwave frequencies. Experimental results demonstrate the MPU’s ability to successfully solve arbitrary linear calculus equations. With the merits of compactness, easy integration, reconfigurability, and reusability, the proposed MPU provides a potential route for integrated analog computing with high speed of signal processing.