Antenna Response Research Articles

Improving the isolation of a tunable terahertz multi-input-multi-output dielectric resonator antenna using graphene coating

A technique is developed for enhancing the isolation between the ports of a terahertz (THz) dielectric resonator (DR) antenna (DRA) with two ports and single radiator. A two-port DRA provides the isolation of 6.88 dB which is further enhanced to 16.78 dB by inserting a circular slot in the ground plane of this antenna structure. The sidewalls of the DR at opposite to the source ends are then coated with the graphene material which enhances the value of isolation between the ports up to 25.05 dB. The coating of top surface of DR with graphene material enhances the isolation up to 35.10 dB. Coating of graphene material at all the open surfaces of the DR can enhance the isolation up to 63.06 dB. The frequency response of antenna can be tuned by applying the electrostatic field on the graphene coating at top surface of the DR. Moreover, the multi-input-multi-output performance parameters like envelope correlation coefficient and diversity gain remains less than 0.06 and 9.8 in the passband. The orthogonal feed arrangement used in the antenna structure can provide the polarization diversity.

Graphene-Based Full-Duplex Antenna for Future Generation Communication in THz Frequency Range

A proximity-coupled graphene patch-based full-duplex antenna is proposed for terahertz (THz) applications. The antenna provides a 10 dB impedance bandwidth of 6.06% (1.76 − 1.87 THz). The input ports of the proposed design are isolated from each other by −25 dB. The aspect ratio of the graphene-based radiating patch and the physical parameters of the antenna is selected for obtaining the single-mode operation. The dimensions (length and width of graphene) of the proposed antenna have been opted to operate in two higher-order orthogonal modes, and these modes remain intrinsically isolated. The utilization of the graphene material provides flexibility in tuning the antenna response. Graphene-based patch exhibits good electrical conductivity, electrical conductance controllability, and plasmon properties. The graphene-based antennas perform better than their metallic counterparts, especially in the THz frequency range. The radiation properties of the graphene material are more prominent due to no-ohmic losses. Moreover, its chemical potential may be altered by applying a bias voltage to its surface conductivity, which modifies the surface impedance value of graphene. Therefore, with a small footprint, graphene acts as an excellent radiator at extremely high frequencies.

Rapid antenna optimization with restricted sensitivity updates by automated dominant direction identification

Meticulous tuning of geometry parameters turns pivotal in improving performance of antenna systems. It is more and more often realized using formal optimization methods, which is demonstrably the most efficient way of handling multiple design variables, objectives, and constraints. Although in some cases a need for launching global search arises, a typical design scenario only requires local optimization, especially when a decent initial design can be rendered using engineering experience or parametric studies. At the same time, antenna optimization is typically conducted using full-wave electromagnetic (EM) simulations, which entails considerable computational expenses. In this paper, we introduce a novel procedure for expedited antenna tuning. Its fundamental mechanism is to restrict the antenna response sensitivity updates to the selected dominant directions within the parameter space, determined based on the problem-specific knowledge, in particular, the estimated changes of antenna characteristics when moving across one-dimensional affine subspaces spanned by these directions. Thus, the said dominant directions affect the most the responses of the antenna structure under design as assessed using the introduced metrics. The decision making process concerning the number of directions to be used relies on quantification of the aggregated system response variability metrics. The proposed approach is demonstrated by means of several antenna structures and benchmarked against conventional trust-region algorithm, but also its accelerated versions. The results indicate considerable (up to over 60%) speedup over the reference procedure without noticeable quality degradation.

Study of the Radiation Pattern and Frequency Response of a Short Linear Antenna Surrounded by Discharge Tubes for the Development of Rapidly Adjustable Wideband Antenna Systems

Plasma antenna systems consisting of discharge elements have great practical application prospects due to their ability to quickly adjust parameters over a wide range. In this work, the radiation patterns of a 30 mm long linear antenna surrounded by 16 standard T8 fluorescent lamps were measured by using a spectrum analyzer with a tracking generator. The radiation pattern of the system is measured by connecting the output of the spectrum analyzer tracking generator to a linear antenna and connecting the input of the spectrum analyzer to the receiving broadband horn antenna. The work features experimental measurements over a wide frequency range of 0.5 to 1.5 GHz and a wide discharge with current values from 35 to 200 mA. The specific frequency band and uniquely selected geometry allowed for the investigation of both the in-phase and out-of-phase antenna modes, while some modes were found to have a narrow directional radiation pattern, within 50 degrees, with a beam width of −3 dB. The parameters of the gas-discharge plasma were also evaluated using drift theory, as well as using the microwave transmission of the 20 GHz signal. The electron density value corresponding to the used discharge currents was approximately from 4 × 1011 to 7 × 1010 cm−3.

Implementing the circularly polarized THz antenna with tunable filtering characteristics

An ultra-wideband (UWB) terahertz (THz) antenna is designed and numerically analyzed. A technique is implemented for obtaining the filtering characteristics in the antenna response. A graphene sheet is placed in antenna structure for achieving the filtering response. The variation in the surface conductivity of the covered area by graphene sheet provides the variable field confinement in antenna structure. This way helps in generating the filtering characteristics in UWB response of antenna. Also, the variation in the electrical properties of graphene material provides the tunability in the generated notched frequency band. The antenna utilizes the feeding with the orthogonal stubs associated with it which helps in providing the circularly polarized response. Furthermore, the antenna operation is verified with the electrical circuit model.

Autoencoder-extended Conditional Invertible Neural Networks for Unfolding Signal Traces

The reconstruction of cosmic ray-induced air showers from measurements of radio waves constitutes a major challenge. In this work, we focus on recovering the full three-dimensional electromagnetic field from two recorded signal traces of an antenna station covering two horizontal polarization directions. The simulated field is folded by a direction and frequency-dependent characteristic antenna response pattern, resulting in voltage signal traces as a function of time. Both signal traces are contaminated by simulated background noise. We use conditional Invertible Neural Networks (cINNs) to learn posterior distributions, from which the most likely electromagnetic field given a measured signal trace can be inferred. To improve robustness, we extend the method with an autoencoder by reducing the parameter phase space and decoupling the cINN from specific data shapes. Thereby, each signal trace is condensed into a small number of abstract parameters in the latent space on which the cINN operates. The presented method shows promising results and can be transferred to other unfolding problems where the recovery of the pre-measurement state is of interest.

Terahertz antenna with tunable filtering.

A terahertz (THz) antenna with tunable filtering is designed and numerically studied. A slotted monopole radiator with defected ground structure is used for operating with wideband response with an impedance bandwidth in the range of 3.80-11.98THz for S 11≤-10d B. A slot is engraved in the radiator for obtaining the filtering characteristics in the antenna response. By varying its chemical potential, the frequency band 5.05-6.69THz with graphene material can provide the tunability in the frequency and bandwidth of the filtered band in the antenna response. Furthermore, the antenna can provide radiation efficiency of more than 90% and gain with a peak value of 6.6dBi in the passband.

An Implementation of Galactic White Dwarf Binary Data Analysis for MLDC-3.1

The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way. However, the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation. In this paper, we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data. To quickly determine the rough parameters of the target sources, the following algorithms are adopted in a coarse search process: (1) using the downsampling method to reduce the number of original data points; (2) using the undersampling method to speed up the generation of a single waveform template; (3) using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space; (4) combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template. A fine search process is applied to further determine the parameters of the signals based on the coarse search, for which we adopt the particle swarm optimization. Finally, we detect double white dwarf signals, validating the feasibility of our method.

Terahertz antenna with controllable and tunable filtering characteristics

− A terahertz (THz) wideband antenna is implemented and numerically studied for achieving the controllable and tunable filtering characteristics. A rectangular-shaped metal-based monopole antenna is designed for obtaining the wideband response. A slot is engraved in the radiator to obtain the filtering characteristics. The slot in radiator is filled with graphene material which acts as the controller and tuner of obtained filtering characteristics. The surface conductivity of graphene strip is tuned and hence the field confinement in the covered area is varied which tunes and controls the obtained filtering characteristics. The antenna provides monopole like radiation pattern with a high value of gain and radiation efficiency which decay in the filtered frequency band with a sharp roll-off rate to attain their minimum value. The gain and efficiency of antenna remain approximately unchanged in the passband even after application of graphene in antenna structure. This signifies the effectiveness of the proposed technique for obtaining the filtering characteristics in antenna response. Moreover, the antenna response is validated through an electrical circuit theory approach.

Compact tunable terahertz self-diplexing antenna with high isolation

A tunable terahertz (THz) slotted monopole antenna is implemented with self-diplexing capability. The radiating arms of antenna are filled with the graphene strips. The variation in electrical parameters of graphene alters the surface current distribution in the radiating arms which results in tuning the antenna response through individual input ports. Antenna operates in frequency range 4.75–5.34 THz and 5.57–6.76THz with the application of input at port-1 and 2, respectively which can further be tuned with the reported biasing schemes. The antenna structure utilizes the orthogonal radiating slots which provides high isolation more than 150 dB between the ports in compact antenna geometry. An electrical equivalent circuit is prepared to verify the antenna operation. In addition, antenna offers the peak gain 3.83 dBi at port-1 and 6.06 dBi at port-2 in the operating passband along with the efficiency of more than 80%. Antenna provides the compact geometry with tunable self-diplexing capability and can be suitable for future wireless applications requiring the simultaneous transmit and receive systems.

Altering the THz Antenna Response: by Merging the Resonance of Tunable Surface Plasmons in Fringing Field

Altering the THz Antenna Response: by Merging the Resonance of Tunable Surface Plasmons in Fringing Field

Nonlinear Dynamics of a Space Tensioned Membrane Antenna during Orbital Maneuvering

Due to the super flexibility and strong nonlinearity of space membrane antennas, the dynamic response of a space membrane antenna will be affected by the rigid–flexible coupling effect in the process of orbital maneuvering. In this case, the dynamic model of a tensioned membrane antenna is significantly different from that under the general condition (fixed boundary). In this study, a nonlinear dynamic model of a tensioned space membrane antenna experiencing maneuvering is established, and the influence of the rigid–flexible coupling effect on structural stiffness and damping characteristics is described. Through a numerical solution, the effects of rigid body motion and structural natural frequency on the rigid–flexible coupling effect are discussed. The results show that the vibration frequency and amplitude of the antenna are positively correlated with the acceleration and initial velocity of rigid body motion. With the increase of the natural frequency of the antenna, the vibration frequency increases but the amplitude decreases. The rigid–flexible coupling nonlinear dynamic model proposed in this work is more applicable in intelligent vibration control compared to finite element software.

Simulation of electric field response of horizontal circular electric half wave dipole antenna for seabed logging

Seabed logging (SBL) is a direct and remote application of controlled source electromagnetic (CSEM) method to detect hydrocarbon resources beneath the seafloor in offshore conditions. In this method, electromagnetic waves are used to detect the resistivity contrast between various sediment layers. The current source of electromagnetic waves is a horizontal electric dipole (HED) antenna. The antenna design represents a challenge in shallow waters (less than500 m seawater depth) due to the presence of airwaves that lead to a low signal-to-noise ratio, hence hindering the detection of a hydrocarbon reservoir. A horizontal circular electric half-wave dipole will be used in this work as the source of electromagnetic waves. The numerical solution for the electric field response will be developed based on solving the Maxwell equations in two modes: the poloidal and toroidal modes. Simulation results have shown that the new antenna is able to detect the presence of deep hydrocarbon reservoirs (up to 5000 m) in shallow-water environment. Comparison of the average percentage difference in delineation between the circular and the HED was carried out. The new antenna results in 61 % delineation compared to 15 % for the HED at 5000 m hydrocarbon depth and 200 m seawater depth, indicating the ability of the antenna to disperse the airwaves. The results also show that the airwaves are significantly reduced from nearly 15000 m (for the HED) to 10000 m offset for the proposed antenna, hence increasing the signal-to-noise ratio. These results seem to indicate the potential for the new antenna to be used as an EM source for SBL in shallow-water environment.

Constraint on the mass of graviton with gravitational waves

We consider the effects of the mass of graviton on both the waveform of gravitational waves and the antenna response to gravitational waves. We find the effect on the response function is negligible for small mass. By using the Fisher matrix method, we make parameter estimations with space-based gravitational wave detectors for massive black hole binaries in massive gravity theory. The wavelength of massive graviton is constrained to be $\lambda_g\gtrsim 10^{17}$ m and the mass is constrained to be $m_g\lesssim 10^{-60}$ kg by one year's observation of massive black hole binaries with space-based gravitational wave detectors.

Double Sided Wideband Concentric Ring Spatial Filters for Mid-Band 5G Devices

This paper presents the methodology, development, and implementation of the double concentric ring band-pass frequency selective surface (FSS) based spatial filters. The filters are designed to improve the active responses of the 5G antennas by incorporating them as superstrate or as substrates. A comparable circuit model is used to anticipate the resonant frequency bands required for predicting the FSS band-pass behavior. The designed spatial filter is composed of a combination of periodic circular loop structures engraved on both sides of a thin dielectric substrate. The proposed design of a double circular loop FSS exhibits band-pass characteristics for n77, n78, and n79 bands of the mid-band 5G spectrum (ranging from 3 GHz - 6 GHz) and provides insensitivity to polarization angles of the incident plane wave. The computed, simulated, and measured findings are all depicting a similar pattern that validates our structure.

Quantitative protein sensing with germanium THz-antennas manufactured using CMOS processes.

The development of a CMOS manufactured THz sensing platform could enable the integration of state-of-the-art sensing principles with the mixed signal electronics ecosystem in small footprint, low-cost devices. To this aim, in this work we demonstrate a label-free protein sensing platform using highly doped germanium plasmonic antennas realized on Si and SOI substrates and operating in the THz range of the electromagnetic spectrum. The antenna response to different concentrations of BSA shows in both cases a linear response with saturation above 20 mg/mL. Ge antennas on SOI substrates feature a two-fold sensitivity as compared to conventional Si substrates, reaching a value of 6 GHz/(mg/mL), which is four-fold what reported using metal-based metamaterials. We believe that this result could pave the way to a low-cost lab-on-a-chip biosensing platform.

Excitation of higher order modes in terahertz antenna using graphene strip

A terahertz (THz) antenna is implemented with a technique of achieving the multiband response by exciting the higher order modes without changing the antenna structure. A patterned triangular shaped THz microstrip patch radiator is designed and numerically analyzed for providing the dual-band response with TM10 and TM20 modes. A graphene strip is applied in the antenna structure which can act as a controller or tuner responsible for the generation and mitigation of resonant modes. The insertion of graphene strip can generate the higher order resonances of TM11 and TM21 mode and antenna response can be attained with dual, triple or four operating passbands by varying the chemical potential of the applied graphene strip. The antenna operation is verified with the electrical equivalent circuit model. Moreover, conical or bi-conical radiation beam can be obtained from the antenna corresponding to the nature of the excited resonant mode.

Low-cost yield-driven design of antenna structures using response-variability essential directions and parameter space reduction

Quantifying the effects of fabrication tolerances and uncertainties of other types is fundamental to improve antenna design immunity to limited accuracy of manufacturing procedures and technological spread of material parameters. This is of paramount importance especially for antenna design in the industrial context. Degradation of electrical and field properties due to geometry parameter deviations often manifests itself as, e.g., center frequency shifts or compromised impedance matching. Improving antenna performance at the presence of uncertainties is typically realized through maximization of the fabrication yield. This is normally carried out at the accuracy level of full-wave electromagnetic (EM) analysis, which incurs considerable computational expenses. The involvement of surrogate modeling techniques is the most common approach to alleviating these difficulties, yet conventional modeling methods suffer to a great extent form the curse of dimensionality. This work proposes a technique for low-cost yield optimization of antenna structures. It capitalizes on meticulous definition of the domain of the metamodel constructed for statistical analysis purposes. The domain is spanned by a limited number of essential directions being the most influential in terms of affecting antenna responses in the frequency bands of interest. These directions are determined through an automated decision-making process based on the assessment of the circuit response variability. Our approach permits maintaining small domain volume, which translates into low cost of surrogate model setup, while providing sufficient room for yield improvement. The presented method is validated using three antenna structures and favorably compared to several surrogate-assisted benchmark methods. EM-driven Monte Carlo simulation is also conducted to verify reliability of the yield optimization process.

Wind/Waves Antenna Length Determined Using Quasi-Thermal Noise Spectroscopy

The Wind/Waves instrument has been collecting in situ electric field measurements in the solar wind as well as Earth's magnetosphere and geotail since 1994. The Thermal Noise Receiver (TNR) sub-instrument uses a wire dipole made of very long and thin whip antennas, highly convenient for Quasi-Thermal Noise (QTN) measurements. The instrument team has determined that twice during the mission, in 2000 and 2002, one of the antenna arms broke, changing the antenna response to plasma fluctuations. In this note, we use the QTN spectroscopy method developed specially for the TNR to determine the antenna length after each of these breaks. By parametrically varying the value of the antenna length used in the QTN calculation, we find that initial 50 m long antenna arm was initially shortened to ∼25.5 m in 2000, and then to ∼20 m in 2002.

Generalized redundant calibration of radio interferometers

Redundant calibration is a technique in radio astronomy that allows calibration of radio arrays whose antennas lie on a lattice by exploiting the fact that redundant baselines should see the same sky signal. Because the number of measured visibilities scales quadratically with the number of antennas but the number of unknowns describing the individual antenna responses and the available information about the sky scales only linearly with the array size, the problem is always overconstrained as long as the array is big and dense enough. This is true even for nonlattice array configurations. In this work we study a generalized algorithm in which a per-antenna gain is replaced with a number of gains. We show that it can successfully fit data from an approximately redundant array on square lattice with pointing and geometry errors, but that the model's parameters are difficult to link to the quantities of interest. We discuss the parametrization, limitations, and possible extensions of this algorithm.