Unidirectional Radiation Research Articles

Pin‐loaded ultrathin magnetoelectric dipole antenna with unidirectional radiation

AbstractA wide‐beam magnetoelectric dipole antenna with an ultralow profile of 0.01λ0 is proposed in this letter. The magnetic dipole (M‐dipole) is formed by placing a turnstile‐shaped patch above a circular ground, establishing the foundation of a thin profile. Then, a pair of crossed strips with one end shorted is introduced, exciting the electric‐dipole without affecting the radiation of M‐dipole and increasing the antenna profile. In that way, stable wide‐beam unilateral radiation in both the E‐ and H‐planes can be achieved. At the same time, a high front‐to‐back (F/B) ratio of 22 dB is obtained for the measured result. Besides, by adjusting the number and position of shorting pins, the proposed antenna shows beam steering capability, which makes it quite promising for future scanning applications.

Modeling of unidirectional radiation of microdisk resonators with small piercing holes by Galerkin method with accurately computed matrix elements

Using the integral-equation-based in-house guaranteed-convergence numerical code, we study the effect of a circular air hole on the frequency, threshold gain and directionality of emission of the whispering-gallery modes of a two-dimensional model of circular-disk microcavity laser. It is shown that a small hole can enhance the directionality greatly and leave the threshold gain intact, if the disk‘s refractive index is large enough and the hole‘s location is chosen properly. This location should be close to the area, in which the same uniform disk, if illuminated with a plane wave, would display a broadband focusing in the form of a hot spot called a photonic jet.

Dual‐band full‐duplex antenna with high isolation using differential fed and dual‐polarization

AbstractThis study proposes a new design approach for a dual‐band full‐duplex antenna to achieve high interport isolation using the differential fed technique. It consists of a single radiating patch, a differential fedline, and a direct fedline. A slotline‐based balun is used in the design to implement the differential fed, which offers minimum phase and magnitude imbalances to the patch of the antenna. The differential fed and direct‐fed lines are orthogonally connected to the radiating patch to realize dual polarization. Both the dual‐polarization and differential fed techniques help to improve the interport isolation of the antenna. It offers an interport isolation of more than 51 and 53 dB over the entire lower and higher operating bands, resonating at 3.22 and 4.1 GHz with 84 and 110 MHz bandwidths. To validate the proposed antenna, a prototype has been fabricated on an FR‐4 substrate with the dimensions of (1.79 × 1.79 × 0.017)λg (λg is the guided wavelength in the substrate at the lower frequency f1), with measured results consistent well with simulations. The far‐field measurement exhibits that the proposed antenna provides a unidirectional broadside radiation pattern and achieves a minimum cross‐polarization of less than −38 dB in all directions and less than −42 dB in the direction of the main lobe in both E‐ and H‐planes at the resonant frequencies. The antenna has insignificant backward radiation with the front‐to‐back ratio 20 dB when port1 is active and the front‐to‐back ratio 30 dB when port2 is active. Moreover, the proposed antenna design is simple and easy to fabricate as the differential fed is implemented using the slotline‐based balun within the same general purpose FR‐4 substrate layer. This eliminates the need for any additional and separate circuits for differential fed and minimizes the overall volume of the antenna.

Parasitic Elements Shorted to Ground to Enhance the Bandwidth of a Dual-Polarized Antenna

An ultra-wideband dual-polarized antenna covering multiple communication standards such as LTE700/GSM850/GSM900 is proposed in this paper. The antenna consists of two dipoles that are perpendicularly placed to each other. The two dipoles can generate +45°/−45° linear polarizations, respectively. Dual-loop structure is utilized as the arm of the dipole, while four parasitic patches with shorting walls are coupled to the dipoles to extend the operating bandwidth. The measured results show that the antenna has an impedance bandwidth of 101.4% (0.54 GHz–1.65 GHz) with a reflection coefficient less than −10 dB. The isolation between the two ports is larger than 22 dB, and the cross-polarization is less than −20 dB over the band. Good unidirectional radiation patterns are obtained.

Mirror-Less Unidirectional Radiation in an Asymmetric Single Resonator

We propose a novel approach to realize unidirectional radiation in an asymmetric single resonator without using an external mirror, which is based on mutual coupling between two degenerate resonant modes through the background scattering of the asymmetric resonator. In the proposed approach, only one of the resonant modes experiences optical gain and the other works just as an internal reflector. So, our approach is conceptually to mimic a one-port system by introducing the internal reflector in a two-port system. Due to this intuitive and simple operation concept, the design of such devices is straightforward. We described the operation principle by using the temporal coupled-mode theory, from which a practical design method was derived. An example device of the proposed approach was designed based on guided-mode resonances in a slab waveguide grating and its performance was analyzed with the finite-difference time-domain simulation. A ratio of 4.6 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> between the upward and the downward radiations was numerically demonstrated.

Design of Antenna-Multiplexer for Seamless On-Body Internet of Medical Things (IoMT) Connectivity

Here, a compact design of antenna-multiplexer is engineered specifically to meet the stringent requirement imposed by intricate subsystems operating at 5.2, 5.5, and 5.8 GHz frequency bands for Internet of Medical Things (IoMT) applications. The proposed design includes a hexagonal-shaped substrate integrated waveguide (HSIW) cavity, tripole-shaped radiating slot, tuning vias, and three inset microstrip feedlines. A tripole-shaped slot is imprinted on the top of the SIW. This slot subdivides the cavity into trio-radiating segments and each segment offers a single frequency band. Further, the frequency bands are tuned at 5.2/5.5/5.8 GHz. The design maintains mutual port isolation better than 23.9 dB. Compared with the conventional tri-frequency antennas, the proposed design is highly compact and doesn’t need any additional circuitry to improve the port isolations. The measured results confirm the expected performance of the design. Furthermore, the proposed antenna is optimized within an implantable medical device (IMD) and simulated inside a realistic Human Head model at a depth of 3 mm and the Specific Absorption Rate (SAR) value is estimated. The SAR values are well below 0.362 W/Kg at the functioning bands due to the unidirectional radiation pattern from the antenna.

Improved bandwidth and F/B ratio of a CPW-fed planar monopole antenna

A directional planar monopole antenna is described. The antenna comprises of a circular monopole, coplanar waveguide (CPW) feed line and a ground plane. To achieve unidirectional radiation, a stub is also attached to on the ground plane to increase the lower end impedance bandwidth and also increase the Front-to-Back ratio (F/B). The proposed antenna is etched on a 50 × 50 mm2 FR4 substrate. Simulated and experimental results reveal that the proposed antenna can achieve an impedance bandwidth from 2.3 – 10.5 GHz for S11 < −10 dB, and unidirectional radiation patterns with high gain and high efficiency.

Self-quadplexing slot antenna for S and C-band applications

This paper demonstrates a novel kind of cavity-backed self-quadplexing slot antenna for the S and C-band applications. The proposed antenna consists of 4 distinct “U”-shaped slots of different lengths and produces the quad frequency band for wireless communication systems. These slots are excited through the separate and orthogonal placed microstrip feed lines of 50 Ω; generates four distinct operating bands at 3.2 GHz, 4.1 GHz, 5.8 GHz, and 7.2 GHz. Due to the perturbation of different U-shaped slots over the substrate integrated waveguide (SIW) cavity with defined positions, the high intrinsic port isolation value is better than 30.5 dB. Thus, the proposed unique antenna structure combines the four independent operating bands with minimum mutual coupling and negligible interference among input ports, which shows the self-quadplexing feature of the antenna. The proposed antenna also has the property of frequency tunability with uni-directional radiation pattern and gain of 5.8 dBi, 5.4 dBi, 4.01 dBi, and 3.47 dBi at corresponding operated frequency. The cross-polarization is 17.3 dB and the front-to-back ratio higher than 21.5 dB at all operating quad bands. There is a good agreement between simulated |S|-parameters results and equivalent circuit model results.

Self-quadplexing slot antenna for S and C-band applications

This paper demonstrates a novel kind of cavity-backed self-quadplexing slot antenna for the S and C-band applications. The proposed antenna consists of 4 distinct “U”-shaped slots of different lengths and produces the quad frequency band for wireless communication systems. These slots are excited through the separate and orthogonal placed microstrip feed lines of 50 Ω; generates four distinct operating bands at 3.2 GHz, 4.1 GHz, 5.8 GHz, and 7.2 GHz. Due to the perturbation of different U-shaped slots over the substrate integrated waveguide (SIW) cavity with defined positions, the high intrinsic port isolation value is better than 30.5 dB. Thus, the proposed unique antenna structure combines the four independent operating bands with minimum mutual coupling and negligible interference among input ports, which shows the self-quadplexing feature of the antenna. The proposed antenna also has the property of frequency tunability with uni-directional radiation pattern and gain of 5.8 dBi, 5.4 dBi, 4.01 dBi, and 3.47 dBi at corresponding operated frequency. The cross-polarization is 17.3 dB and the front-to-back ratio higher than 21.5 dB at all operating quad bands. There is a good agreement between simulated |S|-parameters results and equivalent circuit model results.

Broadband Dielectric Resonator Antenna Array With Enhancement of Isolation and Front-to-Back Ratio for MIMO Application

Dielectric resonator antenna (DRA) arrays with enhanced isolation and front-to-back ratio (FBR) are proposed in this letter. Specifically, each DRA element is mounted on a small and separated ground plane; all the DRA elements (with small ground planes) share a large common ground plane. Each DRA element is excited by two differential probes at its edges. The DRA element in its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\boldsymbol{TE}}_{{\boldsymbol{\delta }}11}^{\boldsymbol{x}}$</tex-math></inline-formula> mode is equivalent to a magnetic dipole. Meanwhile, the differential probes also excite electric current on the small grounds that can be viewed as an electric dipole. The equivalent magnetic and electric dipoles are orthogonal, behaving like a magnetoelectric dipole (ME-dipole). By properly adjusting the small ground planes’ size and their height above a sizeable common ground plane, a broadside unidirectional radiation pattern with low backward radiation is realized; moreover, the small ground structures can provide neutralization paths to counteract the original coupling waves. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1 \times 4$</tex-math></inline-formula> single-polarized DRA array is designed, fabricated, and measured. Measurements align well with the simulations, demonstrating significant isolation and FBR improvements compared with the conventional DRA array. The proposed array has about 20% relative bandwidth.

A dual‐band dual‐sense circularly polarized self‐diplexing SIW cavity‐backed antenna with elliptical slot for millimeter‐wave 5G applications

In this paper, a substrate integrated waveguide (SIW)-based circularly polarized (CP) self-diplexing antenna is proposed and discussed. The proposed antenna makes use of an elliptical slot in the metallic ground plane which is excited with the help of two separate microstrip feed lines, placed face-to-face with each other. This arrangement produces two different frequencies, centered around 21.70 and 27.10 GHz when separately excited by port-1 and port-2, respectively. The CP operation in both frequency bands can be brought by rotating the elliptical slot, which gives 3 dB axial-ratio bandwidth (ARBW) of 3.01% and 6.62% in lower and upper-frequency bands, respectively. A unidirectional radiation pattern and a peak gain of 7.70 and 9.84 dBic are obtained in lower and upper-frequency bands, respectively. The radiation efficiency of more than 80% in both the operating frequency bands has been achieved. The behavior of the cavity modes is explained using an equivalent circuit model. The proposed antenna has been fabricated and the measured results are experimentally verified with the simulated ones. The attractive features such as low profile and low weight make the proposed SIW antenna suitable for satellite and millimeter-wave 5G applications.

Antena Vivaldi Konvensional untuk Penerapan pada Radar Cuaca (9.4 GHz)

To predict weather conditions as an anticipation act towards natural disasters, a weather radar is needed. In weather radar technology, antennas play an important role in supporting the performance of the weather radar. Vivaldi antenna is the right choice because it has an unlimited bandwidth so it is able to operate at the desired work frequency, including the working frequency of weather radar (9.4 GHz). This research discusses the modification of tapered slots, circular stub, radial stub, length and width of the reference vivaldi antenna [1] using CST Studio software. After modifications and measurements, a return loss value of -23.25336989 dB, bandwidth of 500 MHz, VSWR 1.188463357, gain of 3.99 dBi, and unidirectional radiation patterns. All the resulting antenna parameter values are in good condition and qualify the weather radar antenna for a working frequency of 9.4 GHz.

Designing and Implementing a Microstrip Antenna on LoRa Frequency for Smart Meter Communication

The long-range wide area network (LoRaWAN) has been widely used for sensor networks, including smart meter (SM). The SM can report power consumption to the control center automatically via a communication link. An antenna is a key component to indicate an effective communication system. The microstrip antenna (MSA) works based on the unidirectional radiation pattern. The advantages of MSA are its light weight, small size, and ability to be easily etched on a print circuit board. These advantages are needed for the SM communication because SMs are installed on electric poles that have limited space. In this pa- per, we implement the MSA for SM communication on LoRaWAN technology that operates at a frequency of 920–925 MHz in Thailand. The proposed MSA is used to design a new path loss model for LoRaWAN in urban areas. Results show that our MSA is effectively close to commercial antennas in a 2.2 km range, with the packet delivery ratio reaching 52.93%. We analyze the results by using a mathematical equation that includes the free space model, the Okumura–Hata model, root mean squared error, and coefficient of determination.

Radiation Properties Improvement of 1 × 4 Array of Wideband Printed Antenna Supported by AMC Surface for Vehicular MIMO Systems

AbstractA 1 × 4 array of printed dipole antenna (PDA) with a broadband rhomboid artificial magnetic conductor (AMC) is introduced. A suggested PDA using a pair of microstrip dipoles with unequal arms excited by a T‐shaped microstrip feedline expands the bandwidth in the measured range of 5.27–6.74 GHz. Then, the suggested 3 × 3 AMC reflector is inserted into the PDA to exhibit −10 dB measured impedance bandwidth from 4.20 to 7.11 GHz for WLAN and WiMAX applications. The suggested PDA with AMC compared to the PDA without AMC exhibits a size reduction of 46.72%, enhanced gain up to 8.4 dBi, and excellent impedance matching with unidirectional radiation patterns. The novel AMC unit cell operates at 6.20 GHz with an AMC bandwidth of 5.09–7.21 GHz. Also, by loading a 3 × 8 AMC periodic array on a FR4 substrate with 3 mm thickness underneath the four‐element array of PDA with a gap distance of 3 mm, a low‐profile wideband structure with enhanced radiation properties is achieved. The measured S‐parameters show the broad bandwidth from 4.26 to 7.28 GHz with enhanced gains and efficiencies of all elements. Besides, the suitable isolation between the array elements of more than 30 dB for multiple‐input multiple‐output (MIMO) systems is achieved by applying various polarized directions of PDAs and loading the 3 × 8 periodic AMC reflector. Finally, the proposed MIMO design introduces remarkable advantages of good size reduction and bandwidth enhancement, low‐profile antenna with high stable gain, high efficiency and large isolation, and unidirectional radiation patterns with reduced backside direction.

Wearable Wideband Circularly Polarized Array Antenna for Off-Body Applications

A wideband circularlypolarized (CP) wearable antenna for 5 GHz (5.15–5.825 GHz) wireless body area network is presented and analyzed. The emphasis of this work is on the additional resonance generated by the mutual coupling of a 2×2 compact patch array. As the proposed antenna is fed by a sequential-phase feeding network, the resonance can be used to achieve unidirectional radiation with improved CP bandwidth. To alleviate the loading effects of the human body, a modified strip feedline, comprising two pairs of arc-shaped slots cut on the bottom ground, is introduced. Moreover, the adoption of textiles as substrate and conductor provides flexibility and conformability, allowing the antenna to be integrated with garments. The prototype with the dimensions of 40 mm × 40 mm × 4 mm (0.73 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.73 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.07 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) was fabricated. The measured results indicate that a wide impedance bandwidth of 43% (4.25–6.63 GHz), a half-power beamwidth of 60°, and a 3 dB AR bandwidth of 34% (4.71–6.67 GHz) are achieved. Furthermore, the antenna performance is proved to be stable under structural deformation and human body loading. Finally, transmission losses and link budgets are evaluated, enabling the antenna to be a robust solution for off-body communications.

Design of a wideband patch antenna and performance enhancement using an AMC reflector surface for on-body communication at 2.45 GHz

ABSTRACT Wireless biotelemetry enables the formation of communication link from living body to an external monitoring device. Isolation of near field electromagnetic (EM) waves from body tissue, and wide bandwidth to avoid frequency detuning in different biological environments are the important parameters of on-body antennas. In this paper, a conformal defected ground patch antenna with artificial magnetic conductor (AMC) is introduced for on-body communication. Initially, a quarter wave wide band antenna with a shorting pin is designed to operate at 2.45 GHz. It resonates effectively on body tissue but most of the near field EM radiations are absorbed by tissue. Poor radiation efficiency of 10% and high specific absorption rate (SAR) value of 7.73 W/Kg were obtained. Thus, to reduce the effect of tissue loading on antenna performance an AMC-based structure is added. Better impedance matching, high efficiency (65%) and directivity (7.3 dBi) is achieved with AMC structure. Furthermore, unidirectional radiation pattern with SAR value of 1.43W/Kg is attained. Wide bandwidth of 600 MHz on phantom enables the antenna to withstand frequency detuning effect due to body postures and movements. Antenna robustness is analysed by bending the structure at different radii along X-axis and Y-axis.

Unidirectional radiation control of quantum emitters coupled to spiral nano-antennas using optoelectronic material in near-infrared

In this paper, we propose a new architecture of reconfigurable spiral nano-antenna utilized for the applications of modulators and switches by tailoring intensity, efficiency, and beam-steering. The property of real-time tuning is realized by DC-bias voltage applied to DAST layer as a lossless optoelectronic material. The proposed nano-antenna, coupled to a quantum emitter, is investigated and optimized using three-dimensional software with the FDFD method and parametric simulation. The numerical results show that altering bias voltage from −10 to 10 V tailors a unidirectional radiation pattern with a gain in the range of 5.54 to 0 dB. It is also shown the proposed array of spiral nano-antenna increases directivity to the 13.5 dB and rotates radiation pattern of the structure, equal as 24Deg using different bias voltages.

Hybrid epsilon-near-zero modes of photonic gap antennas

We demonstrate that in photonic gap antennas composed of an epsilon-near-zero (ENZ) layer embedded within a high-index dielectric, hybrid modes emerge from the strong coupling between the ENZ thin film and the photonic modes of the dielectric antenna. These hybrid modes show giant electric field enhancements, large enhancements of the far-field spontaneous emission rate, and a unidirectional radiation response. We analyze both parent and hybrid modes using quasinormal mode theory and find that the hybridization can be well understood using a coupled oscillator model. Under plane-wave illumination, hybrid ENZ antennas can concentrate light and achieve local electric field amplitudes more than two orders of magnitude greater than that of the incident wave. This places them on par with the best plasmonic antennas. In addition, the far-field spontaneous emission rate of a dipole embedded at the antenna hotspot can be increased by more than three orders of magnitude as compared to that in free space, with nearly perfect unidirectional emission.

Enhancement of the Unidirectional Radiation Pattern of Shear Horizontal Ultrasonic Waves Generated by Side-Shifted Periodic Permanent Magnets Electromagnetic Acoustic Transducers With Multiple Rows of Magnets

Shear horizontal (SH) guided waves are widely used in non-destructive evaluation and can be generated by permanent magnet electromagnetic acoustic transducer (PPM EMATs). PPM EMATs generate SH waves that propagate both forwards and backwards. This is often an undesirable characteristic. Unidirectional generation can be achieved by the interference mechanism produced by two independent sources. This, however, is non-feasible for the conventional PPM EMATs due to the arrangement of PPM array and racetrack coil. Recently, we presented a design of an SH EMAT with side-shifted PPM arrays that generates SH waves nominally in a single direction. Due to the shift of the produced wavefronts from each array, that design produced side-lobes in the backward semi-plane. In this paper, we enhance the unidirectional generation of SH waves with side-shifted PPM EMATs by evaluating the effect of the separation between individual arrays as well as the number of rows of magnets in each array. An analytical model is used to calculate the radiation pattern. The amplitude of the backward side-lobes decreases either with increasing the number of magnets rows or decreasing the lateral gap between rows. This behaviour is explained by the amount of wavefront misalignment introduced by each design. Increasing the number of magnets rows also increases the directivity and the energy of the forward generated waves. Twelve different configurations were fabricated, with a reasonably short wavelength of 12 mm, and experimentally evaluated, agreeing with the theoretically calculated radiation pattern. The magnitude of the backward side-lobes was roughly halved when compared with the original design.

Substrate integrated waveguide‐based simultaneous transmit and receive antenna for full‐duplex wearable devices

In this paper, a low-size and compact substrate integrated waveguide (SIW)-based simultaneous transmit and receive antenna is developed for full-duplex wearable telemetry applications. The antenna operates at 4.9 GHz (Wireless Local Area Network [WLAN]) and 5.8 GHz (Industrial, Scientific and Medical [ISM]) bands with acceptable gains. Keeping a proper gap between the two ports achieves an isolation of better than 29.8 dB. This antenna is kept compact (0.20 λg2, where λg is the wavelength at 4.9 GHz) by additional arc-shaped slot in each radiator, which adds additional capacitance. The suggested antenna is simulated inside a 52 × 63 × 17 mm3 dummy wearable telemetry device and is worn on the subject's chest. Thanks to SIW technology, it has unidirectional radiation patterns, allowing a minimum beam towards the human body, and thus, offers lower specific absorption rate (SAR) at both frequency bands. The unique advantage is its capacity to receive and transmit the telemetry signals simultaneously. Its low profile, flexibility in the resonant bands, simultaneous transmission and reception, and lower SAR values make this antenna suitable for full-duplex wearable telemetry devices.