Tunable Antenna Research Articles

Highly tunable directional optical antennas with large local angular chiroptical effects

The highly localized field of the plasmonic nanostructures can amplify the chiroptical effects. While most efforts have been focused on spectral responses in real space for chiroptical effects of the plasmonic nanostructures, we present alternative extrinsic chiroptical effects with respect to angular emission patterns in momentum space based on the designed directional nanoantennas. First, the chiroptical effects with respect to spectral responses for the antenna are investigated and decomposed based on the multipolar expansion method. Through the traditional spectral responses, there seems to be no chirality. However, when we turn to the angular emission patterns in the momentum space for the nanoantenna, large local angular chiroptical effects are observed. The chiroptical effects assessed by the difference of azimuth angle emission lobes under left- and right-circularly polarized light illumination can reach 180°. The multipolar analysis combined with Green's function method in a stratified medium is constructed to explain the unidirectional emission and chiral phenomenon, which agrees well with the simulation results. Moreover, the local angular chiroptical effects are also highly tunable by changing the refractive index of the surrounding medium. Our study on local angular chiroptical effects provides a new perspective to understand the chirality, and the large extrinsic chirality for the nanoantenna sheds a new light for biosensing and chiral photon detection.

Dielectric rod loaded tunable substrate integrated waveguide slot antenna

This paper presents a novel passive tuning technique to mechanically tune the resonant frequency of a substrate integrated waveguide (SIW) slot antenna, by using cylindrical rods of different dielectric materials in the air holes. A full-wave 3-dimensional Electromagnetic simulator software is used to estimate tunability in the resonant frequency of the SIW slot antenna, which is then analysed using its equivalent circuit, and then verified experimentally. Tunability is obtained by changing relative permittivity of dielectric rods. Measurements show good frequency tunability even with a limited number of dielectric rods and gains over 5 dBi. The similarity in the radiation patterns with tuning, demonstrates a good characteristic for tunable antennas. The technique is simple but effective and does not require external direct current bias circuitry, which removes parasitic effects and less power consumption. The low field perturbation of dielectric rods provides better loss performance and a higher Q-factor over a wider bandwidth. The initial design demonstrates a cost-effective tuning technique achieving return loss (>10 dB) in the X-band. This technique is also suitable for practically overcoming the performance deviation due to fabrication inaccuracies and temperature variation.

QoE-driven Antenna Tuning in Cellular Networks With Cooperative Multi-agent Reinforcement Learning

Antenna tuning plays an essential role in ensuring high quality wireless communications. Targeting for higher Quality of Service (QoS), many existing network antenna tuning schemes are based on expert knowledge, rule-based policies or conventional optimization theory. However, maximizing the traffic-related QoS does not guarantee that all customers experience good services. In addition, existing schemes are often limited to some handcrafted rules or heuristics and lack of adaptability especially in a time-varying environment. Quality of Experience (QoE), a user-centric metric, can better measure users' satisfaction for services in wireless networks. This paper proposes the cooperative tuning of antennas based on QoE, a paradigm shift from network-centric QoS to user-centric QoE domain. In a normal cellular network, besides the need of improving the overall QoE, it requires handling faults from different cells. As Multi-agent Reinforcement Learning (MARL) has the capability of self-learning the dynamics of environment, we propose an antenna configuration algorithm based on multi-goal MARL. In our framework, agents from different cells not only need to cooperate with each other to achieve the global goal of increasing the overall QoE of the wireless network but also complete some personal goals by combating the faults encountered in their own cells. To accelerate the training efficiency, we introduce a novel two-stage curriculum learning. To reduce the collection time of each QoE sample, we develop an accurate and timely QoE/QoS mapping model with the cascading of a Random Forest Classifier (RFC) and a Deep Neural Network (DNN) (abbreviated as RFC-DNN), which can help us obtain QoE by collecting QoS measurements and perform QoE-based antenna configurations with smaller time granularity. Our proposed RFC-DNN model can reduce the time by 70% when predicting the QoE of a single sample. A huge amount of time will be saved in MARL when tens of thousands of transitions/samples need to be collected. The performance results show that our proposed antenna tuning schemes can not only address specific faults in each cell, but also significantly improve the global average QoE with a faster and more stable convergence speed.

Transparent Saltwater in Glass Structure: Simultaneous Tunable UHF Antenna and EMI Shielding Window

Transparent Saltwater in Glass Structure: Simultaneous Tunable UHF Antenna and EMI Shielding Window

Designing and Simulating of Tunable Microstrip Patch Antenna for 5G Communications Utilising Graphene Material

The patch antennas are considered one of the widespread antennas that are extensively utilized due to their capability to combine and unite with various devices, and their manufacturing cost is low, in addition to their low weight. On the other hand, in contrast to these advantages, these antennas are tainted by their narrow bandwidth and low efficiency, in addition to their weak gain. The use of high frequencies such as 60-GHz for indoor uses and the future of the next generation of wireless communications allows users to obtain a high data transfer speed of up to many gigabits per second but at the expense of losses in this frequency band, which must be rationed as much as possible through the antenna design. In this article, a Microstrip Patch (MP) antenna with the rectangular patch shape will be simulating and improved for 60-GHz applications based on graphene material. This material has amazing and unique characteristics one of which is the variable surface impedance which can be tuned via practised DC voltage on the material layer. This property allows constructing the tunable antennas that are considered as a good solution to eliminate the narrow bandwidth of the MP antennas. The introduced antenna structure comprises of fully copper radiated patch inside it two graphene slots are inserted, a substrate with 2.2 relative permittivity and 0.1 mm thickness, and a fully copper ground plane. The suggested antennas design is done by using the finite integration that is offered by the CST software. The obtained gain results for the simulated antenna is diverse among 6.19-4.6dBi for both states of the surface impedance (i.e. low graphene surface impedance and high graphene surface impedance).

Improved Multifunctional MIMO Cognitive Radio System for Integrated Interweave-Underlay Operations

This article presents the design of an integrated system involving multiple-input–multiple-output (MIMO) and cognitive radio (CR) technologies for sub-6 GHz applications. Two types of CR techniques, i.e., interweave and underlay CR, have been discussed in this article. The design model has a four-port multifunctional MIMO antenna system involving lumped elements for three selectable operation choices. Based on the switching conditions, the MIMO antenna system can operate as a wideband antenna (for sensing purpose), or narrowband frequency tunable antenna (for communicating purpose in interweave CR), or a wideband antenna with frequency tunable band notch (for communicating purpose in underlay CR). The sensing frequency range is 2.45–5.3 GHz. The interweave CR communicating antenna frequency tuning range is 3.6–4.2 GHz. To cover the entire desired spectrum range, i.e., from 2.5 to 4.2 GHz, another four-port narrowband MIMO antenna system with resonance frequency tuning from 2.5–3.6 is designed on the other/backside of the substrate. In the underlay CR communicating antenna, the stopband frequency tuning range is 3.1–3.85 GHz. The complete structure is having dimensions of 110 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 70 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 1.52 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The measurements are performed, and good matching is found between simulated and measured results.

Linearity Analysis of High-Voltage RF Switches for Antenna Tuning Applications

An analysis describing nonlinearities in shunt aperture tuning radio frequency (RF) switches operating in OFF-state is presented in this article. The focus is put on the analysis of second- and third-order nonlinear products and their power distribution as a function of geometry of high-voltage (HV) field-effect-transistor (FET)-based RF switch. According to the results of analysis, the third-order nonlinear product can be reduced by 6 dB at the expense of 4.1 dB increase in the second-order product by doubling the stack size and transistor width used in the switch. The analytical findings are verified with measurements for which two integrated circuits (ICs) were designed and manufactured in Infineon 130-nm RF switch technology. The experiment demonstrated reasonable hardware-to-model correlation, showing around +8 and −7 dB difference in second and third harmonic and intermodulation (IM) products between high-voltage (HV) and low-voltage (LV) RF switches, respectively.

A Frequency-Reconfigurable Wearable Textile Antenna With One-Octave Tuning Range

A reconfigurable wearable textile antenna with wide frequency tuning range is demonstrated in this work. Frequency agility is realized by adding a coplanar reconfiguration module to a planar inverted-F antenna (PIFA) constructed in textile technology. The reconfiguration module consists of a small flexible printed circuit board (PCB) which integrates a tuning circuitry with commercial snap-on buttons as electronic-to-textile connectors. Using this module equipped with a varactor diode, the frequency reconfigurability of the PIFA is investigated and optimized parametrically for maximum tuning range, exploiting a smooth transition from a quarter-wave to a half-wave patch resonant mode. A fabricated prototype demonstrates a very wide tuning range of approximately 70% (or one octave) with stable directive radiation characteristics, as predicted by simulations. The robust performance and mechanical stability of the reconfigurable antenna in various on-body and bending configurations validates the viability of the antenna tuning concept and the practicality of the proposed coplanar reconfiguration module.

Analysis of tunable THz antennas integrated with polarization insensitive frequency selective surfaces

Analysis of tunable THz antennas integrated with polarization insensitive frequency selective surfaces

Mechanically Tunable Nanogap Antennas: Single‐Structure Effects and Multi‐Structure Applications (Advanced Optical Materials 20/2021)

Plasmonic nanogap antennas offer attractive properties in terms of their adjustable coupling and high electric near-fields within the gap region, e.g. for sensing purposes or plasmon rulers. By changing the width of a nanometer gap, the coupling condition, plasmon resonance wavelength, and hotspot intensity can be seamlessly modified. In their Review (article number 2100326), Florian Laible, Anke Horneber and Monika Fleischer highlight recent realizations and applications of single-structure and mechanically tunable nanogap antennas based on flexible substrates, break junctions, or alternative stimuli.

A multi-physics informed antenna sensor model through the deep neural network regression

A passive wireless strain sensing method using antenna sensors has significantly advanced structural health monitoring systems. Since the dimensions of antenna sensors are sensitive to their strain sensing performance and operating frequency, an iterative tuning process is required to achieve a final optimized design. Although multi-physics finite element simulation enables accurate estimation of antenna performance for each turning iteration, the simulation process requires high computational resources. Therefore, antenna tuning processes are recognized as obstacles to delay the final design process. In this study, we explore the potential of multi-physics informed models as an alternative approach for analyzing antenna sensors. Through deep neural networks, as a branch of the machine-learning algorithms, we formulate multi-physics informed models with six input parameters (antenna dimensions) and two outputs (resonance frequency and strain sensitivity). Twenty-two hundred high fidelity data sets are prepared by simulating multi-physics models: 1,600, 400, and 200 data sets are applied to deep neural network regression (DNNR) training, validating, and testing, respectively. From extensive data investigation, an optimized DNNR architecture is obtained to be two layers, with 16 neurons in each layer. Its training, validating, and testing values of mean square errors are 13.01, 44.22, 37.27, respectively. Finally, the proposed multi-physics informed model predicts the resonance frequency and strain sensitivity with errors of 0.1% and 0.07%, respectively. In addition, since the average computation speed for each tuning process is 0.007 seconds, the practical usefulness of the proposed method is also proven.

Impedance characteristics and radiation efficiency of partially submerged antenna in seawater

In view of the radiation performance of buoy antenna in the marine environment, based on the characteristics of the high attenuation in short-wave and ultra-short-wave frequency bands in seawater, this paper proposes an assumption that the antenna is divided into two parts, the water and underwater, using the sea surface as the interface, and an antenna model that is partially submerged in seawater is established. Based on the theoretical calculation model of the antenna in seawater, the hypothesis and the model are verified by carrying out the antenna input impedance test experiment. Using the model, the working frequency range of the underwater part and the underwater impedance conjugate matching conditions are determined, and how the length of the underwater part and the dielectric parameters of the insulating layer affect the radiation efficiency are analyzed. The results show that the effective radiation of the buoy antenna can be achieved by adjusting the antenna frequency, the impedance of the antenna tuner, the material and thickness of the insulating layer, and so on, thus, providing support for marine electromagnetic wave communication.

Planar analog memimpedance behavior in reduced GO-Based Metal-Semiconductor-Metal

Tunable electronics are of great potential for intelligent, adaptable systems. Memristors and memcapacitors have been extensively investigated recently as low power, high density, and high-speed elements to provide tunable-state needed by many emerging applications. Examples of such systems are tunable filters, tunable antennas, multi-level memory, and computing components. This work reports on a novel tunable analog memimpedance device. For the first time, it is proved that analog change in both resistance and capacitance can be achieved simultaneously in the same metal–semiconductor-metal structure. The novel planar geometry device consists of silver-reduced graphene oxide-silver. The multistate memimpedance behavior is observed and investigated for different oxide widths and the results confirmed the scaling of the device capacitance accordingly. Detailed study based on experimental findings shows that the capacitance of the novel system presented in this work follows n-type MOS capacitance behavior. The device is fabricated on a flexible substrate which extends its value to be deployable in smart wearable devices, in addition to its compatibility with CMOS Technology.

Sub-6 GHz quad-band frequency tunable MIMO antenna for 5G applications

This paper describes a slot-based, reconfigurable multiple-input multiple-output (MIMO) quad-band antenna for sub-6 GHz 5G applications. The structure contains a simple arrangement of closely spaced stub-loaded monopole radiating elements and a partial ground plane, realized on FR-4 epoxy substrate with a board dimension of 50 mm × 25 mm × 1 mm. The design has a C-shaped slot and PIN diodes for frequency reconfigurability. The ground plane includes two stubs embedded in it to improve port isolation. The antenna works in four frequency bands: 3.22–5.82, 3.3–4.4, 3.7–5.1, and 4.68–5.64 GHz with port isolation below −20 dB. Scattering parameters, envelope correlation coefficient (ECC), diversity gain (DG), total radiation efficiency, mean effective gain (MEG), and multiplexing efficiency are all determined to validate the fabricated MIMO antenna. The calculated values confirm that the developed antenna is quite promising for sub-6 GHz 5G MIMO systems.

Mechanically Tunable Nanogap Antennas: Single‐Structure Effects and Multi‐Structure Applications

AbstractBy mechanically changing the width of a nanometer gap between two optical antennas, the coupling condition for the antennas can be seamlessly modified. This leads to a shift in the antenna's localized surface plasmon resonance wavelength, and a modification of the intensity in the antenna hotspot, which can reach extraordinarily high values for nanometer gaps. Such systems have in recent years been realized, for example, by using flexible polymers as substrates that are mechanically stretched or bent, or by combining break junctions with plasmonic antennas. Applications can be found, amongst others, in plasmonic strain sensing via color shift sensors, or tunable surface‐enhanced Raman spectroscopy platforms. In this article an overview is given over recent work on mechanically tunable gap antennas, with a specific focus on studies at the single‐nanostructure level. Different techniques used for mechanical tuning, optical read‐out signals that are influenced by the gap width, and potential applications of the resulting structures are presented. Plasmonic break junctions offer a new perspective that allows for added functionalities. The mechanical activation is discussed within the context of single nanoantenna gap tuning by using alternative stimuli.

Phase Control of an Infrared-Frequency Current Wave on a Microstrip Line with dc Diode Bias

Antenna tuning using voltage-controlled elements such as diodes or varactors has been challenging in the infrared. We present measurements of an antenna-coupled metal-oxide-metal (MOM) diode with a time constant fast enough to rectify at infrared frequencies. This diode loads a microstrip infrared antenna, and the dc diode impedance is a function of voltage. When a dc bias voltage was applied across the diode, phase shifts of the current standing waves on the antenna were observed using scattering scanning near-field optical microscopy. This is the first experimental evidence of a dc bias voltage on a MOM diode controlling the phase of current waves at infrared frequencies.

Frequency-Tunable Slot-Loop Antenna Based on KNN Ferroelectric Interdigitated Varactors

A miniature frequency-tunable slot-loop antenna (0.128 λ 0 × 0.077 λ 0) based on ferroelectric K0.5Na0.5NbO3 (KNN) interdigitated varactors is investigated at Ku-band. KNN material has been selected among the ferroelectric oxide family because of its competitive properties for microwave applications. Its high permittivity value ( ϵr a 360 at 10 GHz) and its wide frequency tunability under an external static electric field E bias make it a promising candidate for frequency-agile antennas and circuits at microwaves. The antenna prototype has been designed and elaborated on MgO substrate ( ϵr = 9.8 and tan δ a 10−4 at 10 GHz). Fabrication details including laser microetching process of the ferroelectric layer are also described. The center frequency of the slot-loop antenna can therefore be tuned monotonously from 15.22 to 15.97 GHz under E bias = 88 kV/cm, leading to a frequency tunability rate equal to 4.6%. These results demonstrate for the first time the ability of the KNN material to be used for miniature tunable antennas, in comparison with BaxSr1−xTiO3, currently considered as the most relevant material for such applications.

Characterisation of density linear control in a helicon plasma source with tunable antenna wavenumber spectra

The helicon plasma source is widely used in various fields due to its high ionisation rate. The helicon wave dispersion relationship indicates that the density is proportional to axial wavenumbers. In this study, we systematically investigated how the plasma density varies with the axial wavenumber by employing several phased antenna systems. The antenna comprised different numbers of loops, and each loop was connected to an individual radio frequency power source. We adjusted the plasma density from approximately 1011 to 1013 cm−3. Such two orders of magnitude adjustments may provide a novel operation mode for helicon applications. The density was linearly proportional to the axial wavenumber, when the axial wavenumber was not exceptionally large. In addition, in a low magnetic field, density peaks were observed in all three antenna configurations. The density peak appears irrespective of whether the Landau damping frequency is higher than collision frequency. This finding suggested that Landau damping and other mechanisms can lead to such a phenomenon of low field density peak.

Tunable high-gain and multiband microstrip antenna based on liquid/copper split-ring resonator superstrates for C/X band communication

We proposed a tunable, high-gain and multiband metamaterial microstrip antenna. The design structure is analysed using simulation results and measured results. The split-ring resonator superstrate and complementary split-ring resonator are used as metamaterial elements and loaded in microstrip patch antenna. The high gain is achieved by using the stacking of metamaterial superstrate above the microstrip patch antenna. We have presented the comparison of gain by loading split-ring resonator superstrate layers. The tunability is achieved by switching on and off p-i-n diodes. Three different combinations of six p-i-n diode switches are used for tuning the frequency spectrum. The improvement in bands is also achieved by different switching conditions. The liquid metamaterial superstrate shows a better response compared to the copper metamaterial superstrate. The results in terms of electric field are also presented. The design results are compared with previously published results. The proposed antenna with its tuning capacity and the high gain feature can be applied in wireless communication applications for C/X band communication.

Method for automatic antenna matching with transmitter output stage

This work is devoted to the study of automatic antenna tuning units of the short-wave range. Devices of narrowband matching based on discrete sets of reactive elements are considered. A classification of the most frequently used automatic matching methods has been made. The advantages and disadvantages of each method are analyzed. Examples of using different approaches in commercially available devices are given. Particular attention is paid to the calculation method of matching, as the most promising for use in modern communications. Assumptions are made about the reasons for its rare use in serial devices. Circuits have been developed to simulate the influence of parasitic parameters of the components of the matching circuit and the body of the tuning unit on the resulting standing wave ratio when using this method. Based on the simulation results, conclusions were drawn about the reasons for the low quality of the calculation method. As an alternative, a new method of automatic tuning is proposed, combining the advantages of computation and search methods, which is based on modeling the search process using a simulation model. The conditions for its application in automatic antenna tuning units are determined. Acomparative analysis of the features of both the known methods of automatic tuning and the newly proposed one ismade.