Asymmetric Antenna Research Articles

Sensitive Room-Temperature Graphene Photothermoelectric Terahertz Detector Based on Asymmetric Antenna Coupling Structure

A highly sensitive room-temperature graphene photothermoelectric terahertz detector, with an efficient optical coupling structure of asymmetric logarithmic antenna, was fabricated by planar micro-nano processing technology and two-dimensional material transfer techniques. The designed logarithmic antenna acts as an optical coupling structure to effectively localize the incident terahertz waves at the source end, thus forming a temperature gradient in the device channel and inducing the thermoelectric terahertz response. At zero bias, the device has a high photoresponsivity of 1.54 A/W, a noise equivalent power of 19.8 pW/Hz1/2, and a response time of 900 ns at 105 GHz. Through qualitative analysis of the response mechanism of graphene PTE devices, we find that the electrode-induced doping of graphene channel near the metal-graphene contacts play a key role in the terahertz PTE response. This work provides an effective way to realize high sensitivity terahertz detectors at room temperature.

An ultra-thin high-efficiency plasmonic metalens with symmetric split ring transmitarray metasurfaces

Metasurface lenses (or metalenses) have aroused great attentions and efforts in the community of metamaterials or metasurfaces due to its ultrathin device dimension and superior focusing performances. High-efficiency transmissive metalenses with an ultra-thin device thickness are an important aspect especially in the low frequency by using plasmonic transmitarray antennas. In this paper, an ultra-thin plasmonic metalens with only 0.1λ (λ is working wavelength, the aperture size is 7λ) device thickness is designed by changing the radius of the proposed symmetric complementary split ring resonator antenna metasurfaces. Thanks to its high transmittance and large phase shift of the plasmonic meta-atoms, the designed metalens achieves both high transmissive efficiency of 80% and high focusing efficiency of 50% on the focal plane of F = 4.6λ in the simulations. The designed ultra-thin plasmonic metalens has a moderate large numerical aperture of 0.67 (NA = 0.67). In order to verify its high working efficiency of the proposed plasmonic metalens, a sample is also fabricated and a much higher focusing efficiency of 65% is realized in the measurements. The influence of the open angles of the symmetric split ring transmitarray metasurface on the focusing performances such as working efficiency and NA of the designed metalens is also studied and analyzed finally, which can add new degree of freedoms to optimize its focusing performance. The presented studies can facilitate the development of high-efficiency metalenses in the low frequency and have significant potential applications in high-resolution microwave imaging, high-gain metalens antennas and others.

Highly Compact 4 × 4 Flower-Shaped MIMO Antenna for Wideband Communications

This paper introduces an MIMO antenna with a highly compact size of 30 mm width and 30 mm length. Four symmetrical MIMO antenna radiators are utilized with decoupling stubs in the top and bottom planes of the substrate to improve the isolation level. The simulated and measured outcomes are validated to investigate the impact of the suggested MIMO antenna for wideband applications. The suggested MIMO antenna has an impedance matching less than −10 dB from 5.8 GHz up to 11 GHz, and the isolation between the four radiators exceeds 20 dB over this band. Moreover, the antenna provides an envelope correlation coefficient not exceeding 0.004, a diversity gain above 9.97 dB, and a mean effective gain of ≤−3 dB over the achieved frequency range. The suggested MIMO antenna exhibits a nearly omnidirectional radiation pattern in one plane and a bi-directional radiation pattern in the other plane with an acceptable average value of the realized gain (4 dBi) over the achieved frequency band. A comparison with the state-of-the-art is tabulated to show the distinct performance of the suggested MIMO antenna for wideband applications.

Г-Shaped Asymmetrical Monopole Antenna on Truncated DGS For Multiband RF Energy Harvesting Applications

In today's world, through the advancement of technology, wireless communication has become an integral part of our lives with the utilization of versatile electronic devices such as cell phones, tablets, and computers that contain wireless communication modules. The idea of utilizing different frequencies and power of RF signals in the environment has led to the concept of harvesting RF signals to produce DC output voltage. In this paper, a printed multiband monopole antenna is presented. The proposed antenna is composed of two Г-shaped asymmetrically positioned feeding lines which are located on slotted truncated ground plane with three stubs loaded on both ground plane sides. The antenna design covers the frequently used frequencies for electronic device communication, such as GSM 1800, UMTS 2100, WLAN 2450 and LTE 2600 With the numerically computed gain values of 3.89dBi at 1.8GHz, 4.51dBi at 2.1GHz, 5.02dBi at 2.45GHz, and 5.03dBi at 2.6GHz, respectively. The proposed antenna design has permissible gain values to be used for RF energy harvesting applications.

Diagnosis of a brain stroke using wideband microwave scattering.

This paper presents a new computer-aided microwave monitoring system as a promising, portable and inexpensive tool to detect and localize brain stroke using a bank of a new wavelet-matched filters. The head is exposed to microwave radiation over the band from 1.1 to 3 GHz, and the backscattered signals at a hemi-elliptical array of 16 antenna elements surrounding the head are filtered to analyse the perturbation in the microwave signals from the brain. A novel technique is applied to remove the strong reflection from the air-skull interface as a way to estimate the target response and is compared with different techniques from literature to portray their role in the performance. The study results approve that the intensity and the distribution of wavelet energy and Shannon wavelet entropy in the filtered microwave signal, and the novel tool based on the distance between the wavelet energies at symmetric opposite antennas are promising candidate signatures for computer-aided detection and localization of a stroke.

High-Gain Millimeter-Wave Antenna-in-Display Using Non-Optical Space for 5G Smartphones

This article presents a high-gain display-integrated antenna topology, for the first time, embedding radiating traces into a nonoptical space, referred to as the dead space (DS), which is the edge part of the display panel; however, it does not perturb the optical illumination of the display. Thus, the proposed antenna topology is denoted as antenna-in-display (AiD). To fit the extremely narrow embedding conditions of the given DS (= <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.03 \lambda _{0}$ </tex-math></inline-formula> at 28 GHz), a new-shape coplanar waveguide (CPW)-fed folded dipole antenna was devised and efficiently tailored in the DS area. The bottom side of the panel was modified to render the effect of a coplanar defected ground structure (CDGS) for antenna minimization, and a new asymmetrical antenna geometry was proposed for wideband impedance matching and broadside radiation pattern. Compared with conventional studies, the proposed antenna concept provides an improved gain resulting from the good conductive metal in DS, the complete display visibility, and touch sensor compatibility, whereas the previous antenna-on-display (AoD) approaches inherently suffer from the limited gain obtained at the expense of lower conductivity of the optically invisible antenna electrodes. Because the proposed AiD concept enables the direct fabrication of antenna traces into the DS area of the display panel, eliminating need for an additional film, a lower package profile, and cost reduction can be achieved. The proposed prototype was fabricated and verified using an actual smartphone. The measured data confirm 12.32 dBi gain, 54.3% radiation efficiency, and 3 dB gain bandwidth larger than 3 at 28 GHz.

Parameters of a Short Dipole Antenna Placed Over a Two-Layer Lunar Soil

In this paper, the performance characteristics of a horizontal symmetrical dipole antenna, located in the immediate vicinity of the Moon’s surface, are numerically analyzed. The lunar soil is assumed as a flat-layered medium composed of two lossy dielectrics, the upper layer with a thickness of 5–10[Formula: see text]m, filled with regolith, and solid bedrock in the form of granite or basalt. Calculations were performed in the frequency range of 1–100[Formula: see text]MHz, which is interesting for low-frequency (LF) and very low-frequency (VLF) radio astronomy. The frequency dependences of the impedance, the radiation efficiency, and the effective area of a thin wire dipole with a short length are investigated. All calculations were carried out by simulation of the dipole using the well-known Altair Feko software. As a result of the calculations, it was found that the frequency characteristics of the dipole parameters above the two-layer medium have characteristic differences from the same for the dipole above a homogeneous medium, namely, they have oscillating components, the period and magnitude of which depend on the parameters of these media and the thickness of the upper layer. The presence of this oscillating component is largely manifested in the dipole efficiency and effective area but to a lesser in its impedance. The dependence of the dipole radiation pattern (RP) on the frequency also is analyzed in detail, making it possible to detect the quasi-periodic changes in its shape, which are clearly synchronized with the oscillating component of the dipole radiation efficiency.

Defected Ground–Structured Symmetric Circular Ring Antenna for Near-Field Scanning Plasmonic Applications

Defected Ground–Structured Symmetric Circular Ring Antenna for Near-Field Scanning Plasmonic Applications

New approach to monitoring and characterizing the directionality of electromagnetic radiation generated from rock fractures

Electromagnetic radiation (EMR) is a common phenomenon widely used in engineering and geology fields for detection and monitoring. Although there are some attempts to monitor the directionality of electromagnetic radiation, they are limited by the inability to perform multi-directional measurements at the same time. As a result, the directionality of electromagnetic radiation induced by rock fracture is less involved. Here, four symmetrical three-axis antennas are used to monitor the fracture-induced electromagnetic radiation signals and characterize directionality during uniaxial compression experiments of limestone and granite. The synthesized signals of the four antennas are obtained based on the principle of vector synthesis. Signals monitored on the three axes differ significantly with the direction as the three electromagnetic field components are at the same position. The resultant vectors at the maximum intensities and the equivalent vectors calculated by energy ratio are used to characterize the directionality of electromagnetic radiation caused by fractures. The direction of those vectors shows an obvious correlation with the crack surface. Based on the above research, a new approach using electromagnetic radiation directionality to monitor the stress state and failure in engineering and geological sites is established.

Graded index all-dielectric lens antenna designed by phase manipulation and optical path rescaling

A rotationally symmetric all-dielectric lens antenna is designed by defining the phase function inside the dielectric directly via a closed-form series formula. The refractive index of the lens is modified using state-of-the-art optical path rescaling to keep the refractive index within practical values. The lens optimization is done using the genetic algorithm in MATLAB, where each case is evaluated by conducting linked ray tracing and full-wave electromagnetic simulation in COMSOL. A lens prototype is shown to provide a directivity enhancement of 5.1 dB compared to the optimal conical horn antenna, an improvement of 2 dB compared to the Luneburg lens, and an improvement of 3.8 dB compared to a reference graded index lens. All the examined cases shared a similar length of 5λ for the center frequency of 10 GHz. The prototype lens antenna has a maximum refractive index of 2.1, a reflection coefficient of −22 dB, and a side-lobe level of −25 dB at the center frequency of 10 GHz. The lens’ performance is consistent in the 9–11 GHz band supported by the standard circular waveguide. The results from a prototype with a discretized refractive index simulated in CST Studio Suite are in excellent agreement with the ones with a continuous refractive index profile simulated in COMSOL.

Mutual coupling reduction for monopole MIMO antenna using l-shaped stubs, defective ground and chip resistors

In this paper, a symmetrical and compact monopole multiple input multiple output (MIMO) antenna is designed with two feeding ports. To reduce the mutual coupling between antenna elements, the l-shaped stubs and the defective ground structure (DGS) are used, and additionally the chip resistors are loaded. By optimizing the length of stub, the elements isolation can be improved remarkably. Then, two rectangular slots are etched on the metal ground as DGS to change the path of electric current so as to enhance the isolation further. Also, through loading the chip resistors to control the coupling current on the stubs, the isolation can be strengthened once more. The simulation and measurement results show that this antenna has the mutual coupling of −36 dB, the envelope correlation coefficient (ECC) of 0.002 and the diversity gain (DG) of 9.99 dB at resonance along with the radiant peak gain of 4.03 dBi.

Multibeam half radial line slot array (RLSA) antennas

ABSTRACT An original design of a multibeam Radial Line Slot Array (RLSA) antenna having two beams directed to the broadside and two beams directed to the backside is discussed in this research. The uniqueness of this design is the implementation of multibeam as a half-cut RLSA instead of a full-circle RLSA, which aims to make them more suitable for smaller devices. In order to produce a beam to the backside, the slots were placed on the backside ground plane. Furthermore, the use of the half-circle RLSA and the backside ground plane to generate the beam disrupted the power flow within the antenna’s cavity, which caused a problem of center frequency shift. A frequency design shift technique is then proposed to overcome this problem in this research with the modeling and simulation of 120 four-beams half RLSA in order to determine the most efficient model to be fabricated. The measurements carried out to verify the accuracy of the fabricated model were in good agreement with the simulation results and proved the validity of the antenna design. The result shows the possibility and effectiveness of designing four symmetrical beam antennas with gain of 8.1 dBi, directions of 60°, 150°, 210°, and 330°, and beamwidth of 22°. The gain of 8.1 dBi is 9 dB less than the gain of a single beam antenna, which is consistent with the theory of beam splitting. Moreover, the antenna offers low reflection and broad bandwidth for Wi-Fi needs.

A super asymmetric cross antenna structure with tunable dual-frequency resonances.

The detection performance of traditional infrared spectroscopy can be very limited in the case of molecular vibrational modes with low absorption cross-sections. On account of its electric field enhancement, plasmonic antenna can be combined with infrared spectroscopy to realize surface enhanced infrared detection and characterization of molecules. In this work, a super asymmetric cross antenna structure with tunable dual-frequency resonance and a high enhancement factor is designed. By systematically studying the transmission spectrum and charge distribution of this super asymmetric cross antenna structure, the physical origin of the dual-frequency resonance and its tunability are characterized in detail. In addition, in order to target desired molecular ensembles, the relationship between the resonance frequency and electric-field intensity of the two resonance modes and the parameters of structure and incident light are examined, yielding an enhancement factor close to 100 in the desired frequency region. Finally, the experimental results show that the proposed super asymmetric cross antenna structure can indeed generate dual-frequency resonances, agreeing reasonably with the theoretical results. It is believed that the super asymmetric cross antenna structure can be widely used to sensitively detect trace molecules, and in monolayered chemistry and bio-molecules, allowing their structures and dynamics to be studied using nonlinear infrared spectroscopy.

Spatial Radiation Field Distribution of Underwater VLF Two-Element Antenna Array

In this communication, we analyze the field distributions of underwater very-low-frequency (VLF) two-element array composed of two symmetrical antennas. This analysis is carried out with the improved parallel total-field scattered-field source (TSS) finite-difference time-domain (FDTD) method with sea–air boundary field value conversion and thin-wire algorithm. We specifically analyze the field distribution in the range close to the antenna array in seawater. Furthermore, we also study the field propagation law in air propagating across the air–sea interface.

An SIW Pillbox-Based Compact Dual-Polarized Multibeam Antenna With Passive 2-D Beam Scanning Capability

In this brief, a dual-polarized multi-beam antenna is proposed based on substrate integrated waveguide (SIW) pillbox beamforming networks (BFNs). By using a rotationally symmetrical frequency scanning leaky-wave antenna (LWA) array and four SIW pillbox BFNs, the 2-D beam steering capability is realized for two polarizations. Due to the rotationally symmetrical geometric characteristic of the LWA, the orthogonally placed BFNs can excite orthogonally polarized beams. A stable gain with a wide beam scanning range in the limited bandwidth is realized, where only the backward to broadside scanning region of the LWA is used, and the forward radiation is compensated by the axisymmetric BFN. Moreover, the stacked layout of the multi-layer antenna structure greatly helps realize miniaturization. The proposed antenna can provide ±35° beam scanning range by switching 7 ports in the multi-beam plane and ±31° frequency beam scanning range within the bandwidth of 21 GHz to 27.5 GHz. The advantages of the proposed antenna, including dual-polarization, 2-D beam scanning, low profile, compact size, and low cost, make it a very appropriate choice in millimeter-wave multi-beam radars systems.

A Novel Diagonally Symmetric Fractal Antenna with Wideband Characteristics for Internet of Things Applications

A Novel Diagonally Symmetric Fractal Antenna with Wideband Characteristics for Internet of Things Applications

Short Asymmetrical Inductive Dipole Antenna for Direct Matching to High-Q Chips

A planar antenna structure based on a folded asymmetrical dipole is presented, whose geometrical parameters are seen to independently determine either the real or the imaginary parts of the complex radiation impedance. This unique feature allows very efficient and wideband conjugate matching coupling to nonconventional RF sources of arbitrary internal impedance, i.e., small resistance with large and negative reactance. The antenna theoretical framework is developed and an optimized design to match a photodiode is manufactured and measured. The results show a fractional bandwidth of about 20% in the 28 GHz band.

Dual-Band MIMO Antenna with Enhanced Isolation for 5G NR Application.

A two-port multiple-input and multiple-output (MIMO) antenna with dual-band characteristics operating at the fifth-generation (5G) new radio (NR) sub-6 GHz n7/n38/n41/n79 bands is proposed. The proposed MIMO antenna is composed of two symmetric antenna elements and a defected ground plane. The antenna element consists of an incomplete circular patch with two L-shaped branches. By applying the defected ground structure and the slotted stub, the current distribution on the ground plane is changed to reduce the mutual coupling between the antenna elements. The measured -10 dB reflection coefficients cover 2.34-2.71 GHz and 3.72-5.10 GHz, while the measured isolation is larger than 20 dB at the whole operating frequency band. The paper has investigated different performance parameters in terms of the envelope correction coefficient (ECC), diversity gain (DG), radiation patterns, antenna gain, and efficiency. The proposed MIMO antenna is suitable for 5G applications.

Intuition and Symmetries in Electromagnetism: Eigenstates of Four Antennas

Symmetries play an essential role in the field of physics. In this paper, we examine the relationship between the eigen-amplitudes of four (2 × 2) symmetrical antennas and the symmetry of the amplitudes of their sources (excitations) using mirroring effects. In our case, we find that changing mirrors using symmetry is identical to the point group theory. By exploiting the symmetry problem, we can show the advantage of reducing the size of the analysis domain, at least by a factor of two or more (2, 4, and 8…etc.) (depending on the problem). Several simulation examples have been developed by the MoM-GEC and HFSS to validate this approach.

A High-Efficiency Microstrip Antenna Pair with Similar Pi-Shaped Decoupling Structure for 3.5 GHz 5G Ultrathin Smartphones

In this paper, a low profile and high-efficiency decoupling antenna pair for multiunit smartphones is proposed using a similar π-shaped feed structure that can excite the dipole radiation mode of microstrip antenna. Ordinarily, symmetrical single-port T-shaped microstrip antennas can only excite monopole modes of bilateral radiation. This paper changes the vertical feeding microstrip structure into two oblique, similar π-shaped feeding structures. This oblique feeding structure can excite the dipole mode of unilateral radiation of the microstrip antenna. Using this method, the antenna design can be simplified, and the low-coupling independent radiation on both sides of the microstrip antenna can be freely controlled without the need for additional structures. Considering the ultra-thin characteristics of 5G smartphone devices, the parameters of the antenna are further optimized: the optimized antenna profile is only 3.7 mm. The measured results show that the 2 × 2 microstrip antenna pairs can effectively cover the 3.5 GHz band (3.4–3.6 GHz), with a coupling that varies from −16.14 dB to −11.01 dB and an efficiency that varies from 80% to 94.1%. The 8 × 8 MIMO smartphone antenna results show that the coupling varies from −20.1 dB to −12.17 dB, the efficiency varies from 79.72% to 93.7%, and the envelope correlation coefficient (ECC) is lower than 0.05. The microstrip antenna decoupling pair with a similar π-shaped feed structure proposed in this paper has high efficiency and low-profile characteristics have important application value in the decoupling design of 3.5 GHz 5G ultra-thin smartphone antennas.