Slot Dipole Research Articles

Hierarchical Phased-Array Antennas Coupled to Al KIDs: A Scalable Architecture for Multi-band Millimeter/Submillimeter Focal Planes

We present the optical characterization of two-scale hierarchical phased-array antenna kinetic inductance detectors (KIDs) for millimeter/submillimeter wavelengths. Our KIDs have a lumped-element architecture with parallel plate capacitors and aluminum inductors. The incoming light is received with a hierarchical phased array of slot dipole antennas, split into 4 frequency bands (between 125 GHz and 365 GHz) with on-chip lumped-element band-pass filters, and routed to different KIDs using microstriplines. Individual pixels detect light for the 3 higher-frequency bands (190–365 GHz), and the signals from four individual pixels are coherently summed to create a larger pixel detecting light for the lowest frequency band (125–175 GHz). The spectral response of the band-pass filters was measured using Fourier transform spectroscopy (FTS), the far-field beam pattern of the phased-array antennas was obtained using an infrared source mounted on a 2-axis translating stage, and the optical efficiency of the KIDs was characterized by observing loads at 294 K and 77 K. We report on the results of these three measurements.

Dual‐band inkjet printed coplanar waveguide‐fed stepped‐impedance slot dipole antenna for ISM application

AbstractIn this work, a dual‐industrial, scientific, and medical (ISM)‐band flexible slot dipole antenna is investigated. It is based on quarter‐guided‐wavelength () stepped impedance resonator (SIR) slots fed by coplanar waveguide. Compared to the mostly used SIR, the use of the type SIR not only enables compact size but also leads to broadside radiation without gain decline at the first harmonic. The analysis of fundamental and spurious resonance conditions was also elaborated to reveal the theory behind compact size and harmonics suppression. Planar measurements show the impedance bandwidths are 500 MHz (20.4%) for 2.2–2.7 GHz, and 1200 MHz (21.4%) for 5–6.2 GHz, with peak gain of 3.7 and 5.8 dBi at 2.4 and 5.5 GHz, respectively. Furthermore, in curving measurement, both the reflection coefficient and radiation pattern remain stable during bending. Our proposed antenna will benefit a bunch of flexible and compact applications operating in dual‐ISM‐band.

Optically Invisible Artificial Magnetic Conductor Subarrays for Triband Display-Integrated Antennas

This article proposes a novel concept of an optically invisible artificial magnetic conductor subarrays for bandwidth improvement of display-integrated antennas in millimeter-wave spectrums. The proposed subarrays consist of two unit-cell types that are arranged as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$ </tex-math></inline-formula> super cells to cover target bands of a slotted dipole antenna with triband resonances. The optical transparency is realized by using thin-metal meshes, and both solid and thin-metal mesh prototypes are fabricated to demonstrate the proposed concept from antenna characteristics standpoints. The mesh prototype exhibits the measured 10-dB matching bandwidth of 25.9% at 28.2 GHz with an average gain of 1.12 dBi, which is similar to 21.1% at 27.5 GHz and 1.25 dBi of the simulated results. These results confirm that the proposed concept is feasible to broaden bandwidths of the triband antenna, while maintaining the optical transparency of 85.1%.

A portable non-invasive microwave based head imaging system using compact metamaterial loaded 3D unidirectional antenna for stroke detection

A metamaterial (MTM) loaded compact three-dimensional antenna is presented for the portable, low-cost, non-invasive microwave head imaging system. The antenna has two slotted dipole elements with finite arrays of MTM unit cell and a folded parasitic patch that attains directional radiation patterns with 80% of fractional bandwidth. The operating frequency of the antenna is 1.95–4.5 GHz. The optimization of MTM unit cell is performed to increase the operational bandwidth, realized gain, and efficiency of the antenna within the frequency regime. It is also explored to improve radiation efficiency and gain when placed to head proximity. One-dimensional mathematical modelling is analyzed to precisely estimate the power distribution that validates the performance of the proposed antenna. To verify the imaging capability of the proposed system, an array of 9 antennas and a realistic three-dimensional tissue-emulating experimental semi-solid head phantom are fabricated and measured. The backscattered signal is collected from different antenna positions and processed by the updated Iterative Correction of Coherence Factor Delay-Multiply-and-Sum beamforming algorithm to reconstruct the hemorrhage images. The reconstructed images in simulation and experimental environment demonstrate the feasibility of the proposed system as a portable platform to successfully detect and locate the hemorrhages inside the brain.

Single-Fed Dual-Circularly Polarized Stacked Dielectric Resonator Antenna for K/Ka-Band UAV Satellite Communications

A single-fed dual-band dielectric resonator antenna (DRA) with orthogonal circular polarizations (CPs) in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> - and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ka</i> -bands is proposed for satellite communications on unmanned aerial vehicle (UAV). The antenna overcomes the challenges of dual-band dual-CP operation, narrow axial-ratio bandwidth (ARBW) of single-fed antennas, and limited payload and space of UAVs. A shared-aperture merged-structure technique of DRA and slot-dipole antenna is proposed for dual-band dual-CP radiation, thus enabling full-duplex operation with compact size for high isolation systems. The orthogonal CPs in two frequency bands can be controlled independently by a phase compensation method. Besides, broadened ARBW and enhanced gain are attained from the stacked DR, from which high capacity and reliability communication can be achieved. A prototype operating at right-handed CP (RHCP) in the lower band, whereas left-handed CP (LHCP) in the upper band has been designed and measured. It features 10-dB impedance bandwidths of 6.4% and 12.8%, and 3-dB ARBW of 5.2% and 4.1% in the lower and upper bands, respectively. The antenna provides a low cost solution for high isolation, high throughput, and small payload full-duplex UAV satellite systems.

Second Iteration of Slotted Fractal Log Periodic Dipole Antenna for UHF Digital TV Band Application

This paper discusses the simulations and measurements of the antenna with and without slot implementation in terms of reflection coefficient (S11) and radiation pattern. The slot implementation on each of the radiating elements on the 2nd iteration log periodic fractal Koch antenna (LPFKA) was described in this paper. This method is utilised to reduce the antenna's size while also preventing the lower designated frequencies from shifting to the higher band as the iteration increases. The antenna is designed to test and observe performance in the Ultra High Frequency (UHF) band, which ranges from 0.5 GHz to 3.0 GHz. Computer Simulation Technology (CST) software is used to design and model the antenna, which was then built using the wet etching technique. The antenna's substrate is made of FR-4 laminated board with a dielectric constant of 4.6, tangent loss of 0.019, and a thickness of 1.6mm. The results demonstrate good agreement, with a steady radiation pattern over the operational bandwidth and a reflection coefficient of less than -10 dB for the frequency range of interest. The antenna is being tested with Digital TV decoder and the result is observed towards the picture of the Digital TV.

Graphene-Modulated Terahertz Metasurfaces for Selective and Active Control of Dual-Band Electromagnetic Induced Reflection (EIR) Windows.

Currently, metasurfaces (MSs) integrating with different active materials have been widely explored to actively manipulate the resonance intensity of multi-band electromagnetic induced transparency (EIT) windows. Unfortunately, these hybrid MSs can only realize the global control of multi-EIT windows rather than selective control. Here, a graphene-functionalized complementary terahertz MS, composed of a dipole slot and two graphene-integrated quadrupole slots with different sizes, is proposed to execute selective and active control of dual-band electromagnetic induced reflection (EIR) windows. In this structure, dual-band EIR windows arise from the destructive interference caused by the near field coupling between the bright dipole slot and dark quadrupole slot. By embedding graphene ribbons beneath two quadrupole slots, the resonance intensity of two windows can be selectively and actively modulated by adjusting Fermi energy of the corresponding graphene ribbons via electrostatic doping. The theoretical model and field distributions demonstrate that the active tuning behavior can be ascribed to the change in the damper factor of the corresponding dark mode. In addition, the active control of the group delay is further investigated to develop compact slow light devices. Therefore, the selective and active control scheme introduced here can offer new opportunities and platforms for designing multifunctional terahertz devices.

Complementary SRR-Based Reflector to Enhance Microstrip Antenna Performance

In this paper, complementary split ring resonator (SRR) based reflector to enhance the printed slot dipole (PSD) antenna performance is introduced. The numerically calculated return-loss, directivity and radiation pattern results of the PSD antenna, with (w/) and without (w/o) CSRR element etched on reflector plane are presented and investigated. Numerical analysis and modelling of the proposed design are carried out using CST Microwave Studio simulator based on the finite integration technique. According to the simulation results, with the inclusion of the CSRR-based reflector into the PSD antenna, the directivity is increased by values changes from 0.6 dB to 4.25 dB through the operation band, while an improvement in bandwidth (~2.1%) is seen. It is also shown that this improvement in antenna performance is due to the -negative (ENG) behavior of CSRR structures. Prototype of the proposed antenna is fabricated using Arlon DiClad 880 substrate with electrical permittivity ofεr= 2.2. A quite good agreement between simulation and measurement is obtained. In this study, it is shown that the radiation performance of the antenna can be increased easily by using the CSRR element as a reflector in the antenna structure with a new enhancement approach. Also, the proposed antenna with a compact size of 0.27λ× 0.41λ is appropriate for operating in IEEE 802.11b/g/n/ax (2.4 GHz) WLAN applications.

Narrowband to Narrowband Frequency Tunable Slotted Dipole Antenna

In this paper, the slotted dipole antenna structure is proposed to have four narrowband frequencies with ability to be reconfigured. Narrowband reconfiguration can be achieved by controlling the length of slotted dipole by using switches. The narrowband frequency is to be at 1.8 GHz (GSM), 2.4 GHz (WLAN), 2.6 GHz (4G), and 3.5 GHz (5G) respectively. The longest dipole length produced 1.8 GHz, the second-longest dipole length produced 2.4 GHz, the third-longest dipole length produced 2.6 GHz, while the smallest dipole length produced 3.5 GHz. To maintain the stability of the RF current in the system, sixteen capacitors were used. As well eight inductors were used to isolate the RF current and power supply. The PIN diode was used as a switch to allow the induced current to stop and pass into the slot which means that it can be used to select the desired frequency. Depending on switching configuration, the operating frequency is tuned. Good matching is achieved for all configurations. The simulated result of gain for the four operating is higher than 2 dB while the omnidirectional radiation pattern has been obtained thus makes the proposed antenna suitable for wireless application.

A Portable Electromagnetic Head Imaging System Using Metamaterial Loaded Compact Directional 3D Antenna

A non-invasive, low-powered, and portable electromagnetic (EM) head imaging system is presented using metamaterial (MTM) loaded compact directional 3D antenna. The antenna consists of two slotted dipole elements with $2\times 3$ and $3\times 3$ finite MTM array elements in top and ground, respectively, and folded parasitic elements that operate within the frequency range of 1.12 GHz to 2.5 GHz. The MTM array elements are optimized to enhance the overall performance regarding antenna bandwidth, realized gain, efficiency, and directionality in both free space and proximity to the head model. The mathematical modelling is also analyzed to justify the integration of MTM unit cells to the top and ground side of the antenna. The impact of MTM on SAR analysis is also performed. A tissue-mimicking 3D head phantom is fabricated and measured to validate the antenna performance. A nine-antenna portable setup is used with the fabricated phantom to measure and collect the scattering parameters that are later analyzed to detect and reconstruct the haemorrhage images by applying the updated IC-CF-DMAS algorithm. The overall performance demonstrates the feasibility of the proposed system as a portable platform to successfully detect, locate and monitor the haemorrhages inside the head in EM imaging system.

Design of CPW fed multiband antenna for wearable wireless body area network applications

This communication presents a multiband on-body conformal and wearable antenna for Wireless Body Area Network (WBAN) applications. The suggested wearable CPW-fed slot dipole antenna is incorporated with inductively coupled meander shape, T and O shaped resonators that lead to provide multiband operation. The resonant frequency is controlled by a definite resonant path, which leads to high degree of freedom in design paradigm. The proposed wearable antenna covers the 2.4 GHz/5.2 GHz/5.8 GHz WLAN, 3.5 GHz WiMAX, and 4.4 GHz C-bands and has an overall dimension of 60 × 40 × 0.254 mm3. The SAR analysis has also been presented for the antenna at several resonant frequencies which are well under the normal SAR criteria of 1.6 W/kg that suggests that the model performs satisfactorily for wearable applications. To characterize the performance of the antenna, the specimen of the antenna is rigorously tested in terms of antenna gain, S-parameters and flexibility under different bending configurations for radii values ranging from 90 to 30 mm. The reflection coefficient of the suggested antenna is also evaluated and the outcomes are compared under distinct on-body circumstances. Measured and simulated results of S11, radiation pattern and gain are in good agreement.

Design and Optimization of Genetic Algorithm (GA) based High Gain and Directive CPW-Fed Slot Dipole Antenna for Wideband Applications

Genetic Algorithm (GA) is proposed in this paper for the design of a wide bandwidth, high gain and directive CPW-fed slot-dipole antenna. The proposed antenna is built on a FR4 substrate that is cheap and easy to produce. Genetic Algorithm is used to select parameters that reflect antenna geometry to achieve wider bandwidth and reduced return loss (parameter S11) and high gain values at resonant frequency. The antenna design shows a wide operating bandwidth of 1.4 GHz (simulated) and 1.3 GHz (measured) over the X-band, a return loss (S11) of -25.83 dB (simulated) and -23.08 (measured) and a gain and directivity of 5.61 dB (simulated) and 11.87 dB (simulated) at 10.5 GHz resonating frequencies. In this work, all simulations were performed using the ANSYS HFSS v14.0 software. A prototype antenna was produced and then characterized using VNA to validate the design. Measurement results were in good agreement with the results simulated using ANSYS HFSS.

UWB MIMO antenna implemented with orthogonal quasi‐circular slot dipole radiators

In this paper, a very low-profile two-port ultra-wideband antenna for multiple input-multiple output applications is proposed. The antenna is implemented by using two orthogonal quasi-circular slot dipole radiators fed by coaxial lines. The antenna performs from 2 to 10 GHz, with an average peak-gain of 4 dB, and high port isolation, with values around S21 = −20 dB and below. The radiation patterns of both antennas are opposite to each other and hence, the diversity gain reaches values around 20 dB. The low inter-port coupling and low correlation are verified by obtaining the envelope correlation coefficient, which is lower than 0.003. These calculations were made by the S-parameter and far-field methods. The total active reflection coefficient shows that the antenna operative bandwidth does not change for different input signals with random phases, preserving the operation from 2 to 10 GHz. The antenna performance is compared to different state of the art slot configurations, showing advantages to previously published work.

A New Compact, Stable, and Dual-Band Active Frequency Selective Surface with Closely Spaced Resonances for Wireless Applications at 2.4 and 2.9 GHz

This paper presents a dual-band active frequency selective surface (AFSS) with closely spaced bands and angular stability for wireless applications at 2.4 and 2.9 GHz. The proposed AFSS element geometry is composed of a slotted cross dipole combined with four ring patches, where the diameter of the ring patches at the top of the geometry is 1.618 times greater than the diameter of the ones at the bottom. The choice of this multiplying factor, used to define the geometry of the proposed patch element, is based on the Fibonacci sequence of numbers. In addition, to perform frequency reconfiguration, two p-i-n diode switches are used, which are placed at the input of the ring patches placed at the top of the AFSS element geometry. The AFSS simulation is performed using Ansoft HFSS software and using generalization of the WCIP, i.e., GWCIP, method. The simulated results are compared with the experimental ones for validation purpose. A very good agreement is observed between the simulated and measured results.

Novel L-Slot Matching Circuit Integrated with Circularly Polarized Rectenna for Wireless Energy Harvesting

Radio frequency (RF) power harvesting allows wireless power delivery concurrently to several remote RF devices. This manuscript presents the implementation of a compact, reliable, effective, and flexible energy harvesting (EH) rectenna design. It integrates a simple rectifier circuit with a circularly polarized one-sided slot dipole antenna at 2.45 GHz Industrial, Scientific, Medical (ISM) frequency band for wireless charging operation at low incident power densities, from 1 to 95 μ W/cm 2 . The rectenna structure is printed on a single layer, low cost, commercial FR4 substrate. The integration of the rectifier and antenna produces a low-profile and high performance circularly polarized rectenna. In order to maximize the system efficiency, the matching circuit introduced between the rectifier and antenna is optimized for a minimum number of discrete components and it is constructed using multiple of L-slot defects in the ground plane. For a given input power of − 6 dBm intercepted by the circularly polarized antenna with 3 dBi gain, the peak RF-DC (radio frequency-direct current) conversion efficiency is 59.5 % . The rectenna dimensions are 41 × 35.5 mm 2 . It is demonstrated that the output power from the proposed rectenna is higher than the other published designs with a similar antenna size under the same ambient condition. Thanks to its compact size, the proposed rectenna finds a range of potential applications for wireless energy charging.

Dynamical switching of electromagnetically induced reflectance in complementary terahertz metamaterials

Active manipulation of group delay of electromagnetic waves is highly desirable for telecommunications and information processing. However, most control means of the group delay currently demonstrated experimentally in the artificial metamaterials require different external excitations necessitating complex setups. Here, electrical manipulation of resonance strength of electromagnetically induced reflectance (EIR) are theoretically and numerically demonstrated in a hybrid metal-graphene complementary metamaterial for actively tunable slow light applications. Combining a monolayer graphene with a metal-based complementary metamaterial composed of a dipole slot and a quadrupole slot, a sharp EIR window in the complementary structure is excited due to strong coupling between two resonators. As shifting the Fermi energy of graphene implanted under the dark mode resonator via electrostatic doping, the EIR window can realize an on-to-off switch, and the modulation depth of 73.3% for the EIR resonance strength is achieved with actively switchable group delay of 6.44 ps. Further investigations show that the active modulation can be attributed to the change in the damping rate of the dark mode caused by the tunable conductivity of graphene. This work provides an alternative way for innovative design and realization of dynamically controllable terahertz slow light devices, which may show potential applications in future terahertz wireless communications.

Miniaturized-Element Bandpass FSS by Loading Capacitive Structures

A bandpass frequency-selective surface (FSS) element loaded with capacitive structures is proposed to miniaturize FSS unit cell size. In the FSS design, the capacitive structure, implemented by convoluted slot grids (CSGs), is introduced to increase the equivalent capacitance of the bandpass FSS, thus leading to a lower resonance frequency. The FSS unit cell size is then reduced accordingly. To validate this design concept, a double-layered bandpass FSS consisting of convoluted slot dipole and CSG structures is designed to provide a unit cell size as small as $0.035\lambda _{0} \times 0.035\lambda _{0}$ , where $\lambda _{0}$ refers to the resonance wavelength in the free space. Equivalent circuit of this FSS is established for explaining the resonance mechanism and modeling the frequency performance. Finally, a prototype of the proposed FSS is fabricated and measured. The measured results exhibit the stable filtering response under different polarizations and incidence angles (up to 60°), which also agree well with those obtained by full-wave simulations.

Design of a wideband bowtie antenna using a modified T‐shaped slot

AbstractThis article proposes a bowtie antenna with a modified T‐slot and compares it with a normal slot antenna and a T‐slot antenna in terms of wideband characteristics. The proposed antenna is a simplified version of the bowtie dipole antenna with a reflector. The proposed antenna obtains wideband characteristics by adding a T‐shaped slot, whose width is gradually increased toward the ends of the antenna, to the slot dipole antenna. The proposed antenna also has the radiating element of a bowtie form that decreases return loss at the frequencies above 2 GHz. As the proposed antenna has a simple structure, it can achieve the desired wideband characteristics with a small number of parameters. Its height is λ/5 of the center frequency, so it is a low‐profile antenna. The return loss of the proposed antenna is below −15 dB at 1.6–2.7 GHz. Despite a low‐profile antenna often having a small gain, the gain of the proposed antenna reaches up to 7.5‐9 dBi. The proposed antenna shows little variation over the operating frequency range, which makes it suitable for wideband applications.

Miniaturized uniplanar triple‐band slot dipole antenna with folded radiator

AbstractA miniaturized uniplanar slot dipole for triple‐frequency operation is presented. The antenna consists of a folded slot radiator with an increased number of degrees of freedom that allow for efficient size reduction. Rigorous electromagnetic (EM)‐driven design optimization is applied in order to achieve the smallest possible size while maintaining acceptable levels of antenna reflection at the required operating frequencies. The latter is ensured by using suitably defined design constraints. The size of the antenna is 51 mm × 33.4 mm (footprint area of around 1700 mm2) which corresponds to 0.42λ0 × 0.27λ0 for the lowest operating frequency. Experimental validation confirms good electrical and field performance of the structure.

Wide bandwidth microstrip antenna with defected patch surface for low cross polarization applications

A simple and single element wide slot dipole loaded shorted rectangular microstrip antenna has been proposed and investigated experimentally for broad impedance bandwidth and improved cross polarized (XP) radiation compared to maximum co-polarized (CP) gain without changing the co-polarized (CP) radiation pattern. Around 23-35 dB isolation between CP and XP radiation along with 25% impedance bandwidth is achieved with the proposed structure. The measured gain of the antenna is around 6.2 dBi over the entire band. The present antenna is very simple and easy to manufacture. Unlike the other structures, the present one is free from back radiation in terms of XP fields. The design of the antenna structure is theoretically justified and rigorously analyzed. The present investigation provides an insightful, clear visualization-based understanding of the concurrent improvement in both the impedance bandwidth and XP performance with the present structure.