Antenna Impedance Research Articles

A cavity model microwave patch antenna for lubricating oil sensor applications

This paper presents a single port micro strip patch cavity antenna for identifying lubricant oil level as well as its quality. The antenna sensor has a compact structure with a ground plane of 52 mm × 45 mm and radiating patch of 40 mm × 31 mm. The substrate is made up of FR-4 (εr = 4.3) material with 1.6 mm thickness and the copper clad of 0.035 mm thickness. The cavity height is 1.5 mm and cavity is made up of FR-4 material. The parameters of the sensor are optimized using the CST-Microwave Studio tool (CST-MWS) and designed at 3.16 GHz operation, under unloaded conditions. When the cavity is filled with the fresh engine oil, then the resonance frequency reduces to 2.79 GHz. The proposed antenna provides a sensitivity of 554 MHz/ε. A prototype of the designed antenna is fabricated and its characteristics are found to match with simulation. The antenna impedance is found to increase with volume of oil, for all conditions. Moreover, the resonant frequency of sensor is gradually decrease with increase oil volume inside the cavity of antenna sensor.

A Novel Method for Sensing Local Electron Density via Measuring the VSWR of Spaceborne Antenna

The performance of an antenna is impacted by the electromagnetic characteristics of the media surrounding the antenna. Most antennas work in neutral air. However, the surrounding media for the spaceborne antenna is space plasma, which is dispersive dielectric media. It could significantly change the performance of a spaceborne broadband antenna. In the present study, a broadband dipole antenna was taken for example to investigate the impacts led by space plasma. The working parameters in neutral air and space plasma were compared. The space plasma taken into account in the present study was supposed to be time-varying dispersive media. The study revealed that the space plasma could significantly influence the antenna voltage standing wave ratio (VSWR) and the antenna impedance. For those spaceborne radars working in active mode, there was a minimum detection range which makes it hard to detect the plasma area within the range. Since antenna working parameters vary with the variation of the surrounding plasma, a method to sensing the local plasma electron density based on VSWR of spaceborne broadband antennas was proposed. The method makes the antenna system work as a plasma sensor and could complement the radar minimum detection range. The results show the good performance of the method.

Four-Arm Sinuous Antenna With Low Input Impedance for Wide Gain Bandwidth

An improved method of reducing the input impedance of a four-arm sinuous antenna is demonstrated for a wide gain bandwidth. The proposed antenna has a dual-linear polarized response for electronic support measures (ESM) systems and is designed with a planar substrate. The structure for reducing the input impedance is developed based on the transmission and coupled line theory and is shown to be in excellent agreement with theoretical predictions. The proposed antenna achieves an impedance bandwidth in the range of 0.45–6 GHz with a reference impedance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100 ~\Omega $ </tex-math></inline-formula> . Simulations for comparison according to the difference in input impedance of designed antennas with feeding structures are also presented. Finally, the performance of the fabricated antenna with wideband balun is verified by measuring co- and cross-polarization radiation patterns. As a result, the proposed antenna achieves a wide gain bandwidth (>2.5 dBi) and a cross-polarization isolation (>−13 dB) of more than 12:1 in the frequency range over 0.6 GHz, which can be used in ESM systems.

A Simplified Derivation of Causality From Passivity for the Impedance Representation of Transmitting Antennas

A relatively simple, straightforward, self-contained derivation, sufficiently general for most engineering purposes, is given to show that passivity implies causality for the input-impedance representation of linear, single-port, time-invariant transmitting antennas. The necessary and sufficient condition on the time-domain input impedance for the electrical stability of these antennas is also derived. It is shown that a series resistance-reactance representation of the input impedance of an antiresonant passive antenna has a noncausal and nonpassive time-domain resistance and reactance, even though the total time-domain input impedance satisfies the passivity, causality, and stability conditions.

Wideband, Millimeter Wave Domain SI Canceling (&gt;50dB) In-Band Full-Duplex Circulator Receiver

This paper describes a 26-GHz fully integrated In-band Full-duplex Circulator (IBFD) Receiver (RX), which employs passive and active Self-interference Cancellation (SIC) techniques in the mm-wave domain. Coverage of wireless networks at mm-wave frequencies can be enhanced by deploying a large number of base stations economically based on Integrated Access and Backhaul (IAB) relays and repeaters. However, to retain the channel capacity, IAB needs to be implemented using full-duplex schemes that suffer from a strong Transmitter (TX) to RX SI. This SI leakage can significantly impact the receiver sensitivity and increase the baseband/ADC dynamic range requirements. Canceling SI at mm-wave applications is particularly challenging given the high frequency of operation, wide bandwidth, and antenna (ANT) impedance sensitivity to the surroundings. Proposed mm-wave RX with a shared ANT interface based on a circulator with active SI cancelers provide ~53 dB SIC over 400 MHz and ~40 dB SIC over 400 MHz in mm-wave domain to meet the link budget requirements. Proposed architecture achieves SIC by (i) introducing a shared ANT interface based on a hybrid-coupler and a non-reciprocal delay line that provides wideband SIC and additionally creates a SI replica (ii) subsequent active cancellation using SI replica processed with variable gain amplifiers and phase shifters. This system also accommodates SI channel variations due to surroundings. Proposed 26-GHz circulator RX has >100x better SIC at high TX power (>10dBm) levels in comparison to the state-of-the-art and it consumes ~111 mW power. The system is implemented in 45nm SOI CMOS and has an active area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.54\, mm^{2}$ </tex-math></inline-formula> . Stand-alone RX NF is ~5.8 dB and TX to ANT insertion loss (IL) is ~3.1 dB. Over-the-air measurements with modulated TX (128 QAM 2.1 Gb/s) and RX (128 QAM 4.2 Gb/s) signals show an EVM of 3.3%.

Miniaturized Antenna for High Data Rate Implantable Brain-Machine Interfaces

Technological advancements in medical care have necessitated the development of efficient and miniaturized implantable medical devices. This paper presents an ultra-wide-band implantable antenna for use in scalp-based biomedical applications covering the industrial, scientific, and medical (ISM) (2.4&#x2013;2.48 GHz) band. The proposed antenna is mounted on a 0.1&#x2013;mm thick liquid crystalline polymer (LCP) Roger ULTRALAM (tan&#x03B4; = 0.0025 and &#x03B5;_r = 2.9), serving as a dielectric material for both the superstrate and substrate layers. LCP materials are widely used in manufacturing electronic devices owing to their desirable properties, including flexibility, conformable structure, and biocompatibility. To preserve the capability of an electrically small radiator and achieve optimum performance, the proposed antenna is designed to have a volume of 9.8 mm³ (7 mm &#x00D7;7 mm &#x00D7; 0.2 mm). The addition of a shorting pin and open-ended slots in the radiating patch, and close-ended slots in the ground plane facilitates antenna miniaturization, impedance matching, and bandwidth expansion. Notably, the antenna exhibits a peak gain of &#x2013;20.71 dBi and impedance-matched bandwidth of 1038.7 MHz in the ISM band. Moreover, the antenna is safe to use according to the IEEE C905.1-2005 safety guidelines based on low specific absorption rates. To evaluate the performance of the implantable antenna, finite-element simulation was performed in homogeneous and heterogeneous environments. For validation, measurements were performed in a minced pork-filled container. The simulation results are consistent with the measurements. In addition, a link budget analysis is performed to confirm the robustness and reliability of the wireless telemetric link and determine the range of the implantable antenna.

A Compact Wideband Circularly Polarized Planar Monopole Antenna With Axial Ratio Bandwidth Entirely Encompassing the Antenna Bandwidth

The antenna presented in this study is a compact wideband monopole with wideband circular polarization that can be used across the whole antenna bandwidth. A rectangular C-shaped patch is partially covered by a ground plane in the proposed planar monopole antenna. Inserting a rectangular stub to the ground plane, etching a slit at the antenna patch, and adding a semicircular stub at the top of the antenna feed line increase the antenna impedance bandwidth (BW) and axial ratio bandwidth (ARBW). An FR4 substrate with overall dimensions of 25 mm&#x00D7;25 mm&#x00D7;1.6 mm is used to create the antenna. The antenna&#x2019;s observed impedance BW is 70% (4.55 GHz in the 4.3-8.85 GHz band), while the measured broadside ARBW is improved to a value of 82.2 percent (5.3 GHz along the range 3.8-9.1 GHz). The impedance BW is perfectly covered by the ARBW; hence the antenna can be considered circularly polarized throughout its operational spectrum. Within the antenna BW, the measured gain is greater than 1.5 dB.

High Gain of UWB Planar Antenna Utilising FSS Reflector for UWB Applications

In this paper, a high gain and directional coplanar waveguide (CPW)-fed ultra-wideband (UWB) planar antenna with a new frequency selective surface (FSS) unit cells design is proposed for UWB applications. The proposed UWB antenna was designed based on the Mercedes artistic-shaped planar (MAP) antenna. The antenna consisted of a circular ring embedded with three straight legs for antenna impedance bandwidth improvement. The modelled FSS used the integration of a two parallel conductive metallic patch with a circular loop structure. The FSS provided a UWB stopband filter response covering a bandwidth of 10.5 GHz, for frequencies from 2.2 to 12.7 GHz. The proposed FSS had a compact physical dimension of 5 mm × 5 mm × 1.6 mm, with a printed array of 19 × 19 FSS unit cells. The FSS unit cells were printed on only one side of the dielectric FR4 substrate and placed as a sandwich between the antenna and the reflector ground plane. An equivalent circuit configuration (ECC) was used to verify the FSS unit cell structure’s performance. The simulated results indicated that the UWB MAP antenna and FSS reflector provided a fractional bandwidth of 136% and a high gain of 11.5 dB at 8.5 GHz with an acceptable radiation efficiency of 89%. Furthermore, the gain was improved across the operating band and kept between 8.3 and 11.5 dB. The proposed antenna was in good agreement between theoretical and experimental results and offered a wide enough bandwidth for UWB and vehicle applications.

Investigation into the impedance characteristics of magnetoelectric antennas

Mechanical antenna is recently considered a novel scheme for realizing very low frequency (VLF) and portable transmitters. In this paper, the impedance characteristics of 1-1 typed and 2-1 typed magnetoelectric (ME) mechanical antennas are systematically studied and compared. Based on measured frequency-impedance curves and the corresponding MBVD (Modified Butterworth-Van Dyke) model, three characteristic frequency points, i.e., the minimum impedance frequency &lt;i&gt;f&lt;sub&gt;m&lt;/sub&gt;&lt;/i&gt;, the series resonance frequency &lt;i&gt;f&lt;sub&gt;s&lt;/sub&gt;&lt;/i&gt; and the resonance frequency &lt;i&gt;f&lt;sub&gt;r&lt;/sub&gt;&lt;/i&gt; are obtained and discussed. On this basis, the influence of driving voltage, bias magnetic field, and the quality factor (Q value) on ME antenna impedance characteristics is experimentally explored. Finally, the reactance components of both 1-1 typed and 2-1 typed ME antenna are collected by referring to the actual working frequency &lt;i&gt;f&lt;sub&gt;d&lt;/sub&gt;&lt;/i&gt;. Experimental results prove that resonant ME antennas are basically pure resistive vibrators, while a ME antenna with high Q value normally fails to support high driving field because of the low resistance (&lt; 100Ω) and the strong nonlinearity. Thus, the field radiation capability in 2-1 typed ME antenna is higher than that of 1-1 typed one. This work provides perspectives for Q value selection and further optimization of a magnetoelectric antenna based on the understanding of its impedance characteristics.

Dual-Band Patch Antenna Matching Network Comprised of Separated Ground Layers and via Posts for Adjustable Return Current Path

This paper proposes a dual-band antenna impedance matching network concept that features identical radiation characteristics. The concept is exemplified for millimeter-wave mobile devices but can be scaled to lower and higher frequency spectrum. The method is deduced through an introduction of an additional matching network consisting of inductive distributed elements to formulate adjustable return current paths. This is realized using fragmented ground plane and a series of vias. No modification of the antenna radiating element is required. This new class of matching network enables independent adjustment of the resonance frequencies while maintaining nearly-identical radiation patterns at both frequencies. For experimental verifications, the proposed antenna impedance matching network is fabricated using a low-temperature co-fired ceramic process. The measurement of this single element exhibits dual-band operations at 28.0 GHz and 39.0 GHz, obtaining the realized gain of 5.15 dBi and 5.42 dBi, respectively. In addition, a 1×4 phased array antenna is devised and studied to validate beamforming performances at both frequencies. With the integration of the beamforming circuit, a reconfigurable beamforming is demonstrated at 28.0 GHz, in which the peak measured gain is 10.83 dBi. At the second resonance frequency (39.0 GHz), a passive feeding network is employed to evaluation its beam scanning abilities, and the main beam peak realized gain of 10.40 dBi is ascertained. The result can be extended to any other frequencies while maintaining near-identical far-field characteristics.

Computer Simulation of Magnetoelectric Antenna and Performance Comparison With Micro-Loop

Electromagnetic radiation can be produced using functional materials such as magnetoelectric (ME) composites, in which the magnetoelasticity and piezoelasticity of material are involved. The mechanical nature of the vibrations is used to miniaturize the ME antenna to micro-scale size. The antenna performance evaluation requires a multiphysics analysis of the structure. An ME antenna design and simulation is detailed using the finite element method (FEM) in COMSOL Multiphysics&#x00AE; in which the structural mechanics, electrostatics, and magnetic field physics are coupled together to address the simulation needs. An antenna size of 250 &#x03BC;m &#x00D7; 50 &#x03BC;m &#x00D7; 1 &#x03BC;m is simulated within a static magnetic bias field of 20 mT. The nonlinear isotropic model is used for magnetostrictive material definition in which the prestress is defined by the magnetic bias. The model is linearized for radio frequency (RF) simulations to account for the AC simulation. The antenna farfield radiation pattern and the gain are computed using finite difference time domain (FDTD) by incorporating the extracted nearfield of the ME antenna in COMSOL. The simulated antenna impedance, radiation pattern and antenna gain are compared to an equivalent micro-loop magnetic antenna. In addition, electromagnetic computations are used to evaluate the coupling performance between the ME antenna and a larger loop antenna over a distance up to 20 mm in free space and biomedical tissues to address the potential of using ME antenna in medical implants for wireless communication and wireless power transfer.

Computational Intelligence-Based Methodology for Antenna Development

The antenna design is a challenging task, which might be time-consuming using conventional computational methods that typically require high computational capability, due to the need for several sweeps and re-running processes. This work proposes an efficient and accurate computational intelligence-based methodology for the antenna design and optimization. The computational technical solution consists of a surrogate model application, composed of a Multilayer Perceptron (MLP) artificial neural network with backpropagation for the regression process. Combined with the surrogate model, two multiobjective optimization meta-heuristic strategies, Non-dominated Sorting Genetic Algorithm (NSGA-II) and Multiobjective Evolutionary Algorithm based on Decomposition (MOEA/D), are used to overcome the mentioned issues from the traditional antenna design method. A study of case considering a dipole antenna for the 3.5 GHz 5G band is reported, as proof of the proposed methodology concept. Comparisons of antenna impedance matching obtained by the proposed methodology, numerical full-wave results from ANSYS HFSS and experimental result from the antenna prototype are performed for demonstrating its applicability and effectiveness for antenna development.

Design and Simulation “Ha”-Slot Patch Array Microstrip Antenna for WLAN 2.4 GHz

This paper presents a linear 1 × 2 “Ha ( )”–slot patch array microstrip antenna. The proposed design of an array microstrip antenna is intended for Wireless Local Area Network (WLAN) 2.4 GHz devices. From the previous research concerning the single patch “Ha ( )”–slot microstrip antenna, the gain that can be achieved is 5.77 dBi in simulation. This value is considered too small for an antenna to accommodate WLAN devices if compare to a Hertzian antenna. To enhance the gain of microstrip antenna, some methods can be considered using linear 1 × 2 patch array and T-Junction power divider circuit to have matching antenna impedance. The distances between two patches are one of the important steps to be considered in designing the patch array microstrip antenna. Thus, the minimum distance between the patch elements are calculated should be greater than λ/2 of the resonance frequency antenna. If the distance less than λ/2 electromagnetically coupled will occur, vice versa when it is to widen the dimension of the antenna will less efficient. Epoxy substrate Flame Resistant 4 (FR4) with dielectric constant 4.3 is used as the platform designed for the array antenna and it is analyzed using simulation software Computational Simulation Technology (CST) studio suite by which return loss, Voltage Standing Wave Ratio (VSWR), and gain are calculated. The simulation result showed that the designed antenna achieve return loss (S11) -25.363 dB with VSWR 1.1 at the frequency 2.4 GHz, and the gain obtained from simulation is 8.96 dBi, which is greater than 64.4 % if compared to the previous one. The proposed antenna design shows that increasing the number of patches in the array can technically improve the gain of a microstrip antenna, which can cover a wider area if applied to WLAN devices

Design and Modeling of Wideband Planar Antennas Using Characteristics Modes

Origin of wideband nature and radiation behavior in many broadband antenna structures is not clearly understood. In this article, we have attempted to clarify those phenomena using characteristic mode (CM) analysis along with equivalent circuit (EC) modeling. By modeling the modal impedance of antenna for a large bandwidth, considering natural resonances and anti-resonances, the EC models are developed for various wideband antennas. It is observed that the reactive loading and resonant mode coupling effects are largely contributing in the formation of wideband and far fields of antenna. These models can be used in SPICE simulators to study the effective communication between wireless transmitter and receiver systems without an EM solver. A novel design method is proposed on the development of wideband antennas using a modal impedance model and coupled mode theory of resonant modes. This method yields accurate design to achieve desired center frequency and bandwidth using structural modifications.

Development of Proximity Sensor Focusing on Variations in Antenna Impedance

Development of Proximity Sensor Focusing on Variations in Antenna Impedance

Development of a wideband symmetric pillbox antenna with low side lobes in gap waveguide technology

In this work, a symmetric pillbox antenna with low side lobes is designed, simulated and fabricated by using gap waveguide technology. The proposed antenna operates on the basis of the reflector antenna principle and provides a fan-beam radiation pattern. In the proposed structure, the antenna aperture is loaded by a stepped discontinuity and a corrective pin to improve the side-lobe level (SLL) and gain. The designed antenna impedance bandwidth (S11 < −10 dB) is 42% at the Ku band. Also, −15 dB < SLL < −10 dB and a gain of 16.6–18.7 dBi are achieved over the operating bandwidth. There is a good agreement between the simulated and measured results.

Antenna Impedance Matching Using Deep Learning.

We propose a deep neural network (DNN) to determine the matching circuit parameters for antenna impedance matching. The DNN determines the element values of the matching circuit without requiring a mathematical description of matching methods, and it approximates feasible solutions even for unimplementable inputs. For matching, the magnitude and phase of impedance should be known in general. In contrast, the element values of the matching circuit can be determined only using the impedance magnitude using the proposed DNN. A gamma-matching circuit consisting of a series capacitor and a parallel capacitor was applied to a conventional inverted-F antenna for impedance matching. For learning, the magnitude of input impedance S11 of the antenna was extracted according to the element values of the matching circuit. A total of 377 training samples and 66 validation samples were obtained. The DNN was then constructed considering the magnitude of impedance S11 as the input and the element values of the matching circuit as the output. During training, the loss converged as the number of epochs increased. In addition, the desired matching values for unlearned square and triangular waves were obtained during testing.

Thin and flexible printed antenna designed for curved metal surfaces

This paper presents a flexible low-profile antenna suitable for tagging onto metal curved surfaces. The novelty of the proposed antenna lies in the design of an extended ground plane and folding it to realize the bottom layer to shield against metal surfaces. This method reduces the manufacturing complexity as no vias are required in the fabrication process. In addition, the antenna impedance for metal and non-metal surfaces could be obtained through a slight tuning of the slot length. The antenna was realized using a novel low-cost thermal ink transfer process and integrated with a radiofrequency identification chip to successfully demonstrate passive wireless communication at 915 MHz. From the wireless results, a maximum read distance of 1.86 m was obtained for the proposed antenna on metal, compared to a distance of 0.31 m for a reference dipole antenna on metal. Furthermore, the return signal strength indicator pattern obtained show a good correlation to the radiation pattern. The effect of different metal sizes and different metal curvatures were investigated, and results suggest that the effect of these parameters on the impedance mismatch and corresponding power transfer coefficient is not significant. The results are promising for the use of antennas in tagging metal surfaces in the airplane, automotive and unmanned aerial vehicle industries.

A wideband and directive metasurface FPC antenna with toroidal metal structure loading

Abstract In this paper, a novel metasurface-based Fabry−Perot cavity antenna loaded with toroidal metal structures is presented. The antenna is compact, wideband, and has high directivity and a high front-to-back ratio. The idea of the antenna is based on loading a microstrip narrow band patch antenna resonating at 4.5 GHz by a single layer metasurface superstrate and with a toroidal metal structure. The metasurface superstrate comprises a periodic array of square patch cells. Compared to conventional microstrip antenna, the front to back lobe ratio is increased from 7 to 20 dB and the directivity is increased by 7 dB. Also, the antenna impedance bandwidth is 34% which is increased four times. This is the first-ever antenna with enhanced bandwidth and directivity using a single layer of metasurface and that too made up of periodic cell array and has application as an energy harvester.

Optimization of power matching and transfer in the helicon plasma discharge

Helicon plasma source is being developed at the Budker Institute of Nuclear Physics SB RAS, Novosibirsk. The parameters are studied of the plasma confined in a mirror trap configuration of the magnetic field at an operating frequency of 13.56 MHz. For matching the antenna impedance and generator load, the Π-type matching box was designed and successfully tested at powers of 20–25 kW. The low reflected power (1–2%) was obtained, as compared to that for the L-type matching network used previously (the reflected power was more than 15% at the generator output power of 18 kW). The triple Langmuir probe is used to determine the plasma density. The plasma resistive characteristics were determined using the Rogowski coil measuring the RF antenna current. In the experiments, the plasma with a density of ∽5⋅1012 cm-3 and an electron temperature on axis of 10 eV was obtained, and the RF power transfer efficiency was ∽85% at the RF power of 25 kW.