Dielectric Superstrate Research Articles

Ultrawideband and high-efficient polarization conversion metasurface based on multi-resonant element and interference theory.

In this work, an ultrawideband and high-efficient polarization conversion metasurface (PCM) is proposed, which can efficiently convert linearly polarized waves into cross-polarized waves in an ultra-wide frequency range. The unit cell of the proposed PCM is composed of two pairs of L-shaped metallic patches covered by a dielectric superstrate and an air-based substrate attached with a metallic ground. The PCM has an operating band from 3.37 to 22.07 GHz with the polarization conversion ratio (PCR) over 90% under the normal incidence, which the ratio bandwidth (fH/fL) is 6.5:1. The PCR can achieve 100% at seven resonant frequencies. The equivalent circuit model is analyzed to explain the fundamental cause of the PCM's multi-resonance and polarization conversion behaviors. In addition, all possible near-field interactions among the resonator, the superstrate, and the ground sheet can be accurately calculated using interference theory, which reveals the underlying physical mechanisms of the multi-resonance metasurface. The theoretical calculated, numerically simulated, and measured results are in good agreement. Compared to other PCMs, the proposed PCM has a simple geometry structure but an ultrawideband and high PCR property.

Radiation Improvement of Microstrip Antenna by Metamaterial Superstrate

In this paper, a new approach to enhance the radiation efficiency of microstrip patch antennas by a quarter-wavelength antireflection superstrate is proposed. It is based on dielectric right-handed metamaterial (MM) build with U-shape cells. The moments method in the spectral domain predicts a maximum radiation efficiency of 78% for disk microstrip antenna combined with quarter-wavelength dielectric antireflection superstrate. Design, optimization and characterization of the metamaterial layer are well described. A numerical analysis of the microstrip patch antenna disk with and without metamaterial antireflection layer is performed with commercial specialised software. The results of the simulation show significant performance improvement of the antenna in the presence of the metamaterial antireflection layer. Radiation efficiency, directivity and gain are respectively increased by 9%, 2dBi and 2.6dB. This approach enabled to improve the total radiated power up to 18%.

Proximity-coupled high gain graphene patch antenna using holey dielectric superstrate for terahertz applications

This paper presents the concept of a superstrate microstrip graphene antenna feed with a proximity-coupled technique. The proposed structure is based on a resonance cavity antenna (RCA) method, which significantly improves the gain and radiation efficiency. The investigated electric properties of graphene confirm the exceptional role of material for realizing an antenna in the THz band. Firstly, a triangular shape graphene antenna configured at 1.5 THz frequency, which illustrates reconfigurable properties by changing the chemical potential via bias voltage and antenna radiation performance in the frequency band from 1-to-2 THz. Furthermore, holey superstrate layers are placed over the graphene antenna at an appropriate distance to improve the radiation characteristics. Based on the findings, a superstrate graphene antenna advances the gain, radiation efficiency, and impedance bandwidth significantly compared to the conventional design. The projected high gain graphene antenna can be used for sensing, imaging, and detection applications via spectroscopic and Doppler radar techniques. The numerical simulation and analysis of the antenna are performed by CST microwave studio (CST MWS).

Mutual Coupling Reduction With Dielectric Superstrate for Base Station Arrays

This letter proposes a dielectric superstrate to reduce the couplings between copolarized and cross-polarized antenna elements in realistic base station (BS) arrays. The mutual couplings are reduced by adjusting the permittivity and profile of the dielectric superstrate to create “reflected” waves to neutralize the original coupling wave. The dielectric superstrate is a simple structure that is easy to design and manufacture. A large dielectric board and four small dielectric blocks help reduce the couplings between horizontal and vertical antenna elements, whereas a dielectric pillar is added to suppress the coupling between diagonal elements. The superior decoupling performance (>25 dB isolation) is demonstrated for dual-polarized BS arrays over the fifth generation frequency band of 3.3–3.8 GHz, without affecting the matching and radiation performances of the array elements.

1-D Wide-Angle Beam-Scanning Linear Phased Array With Enhanced Gain by Using 3-D Printed Dielectric Slab Superstrate

A 1-D wide-angle beam-scanning linear phased array with enhanced gain by using dielectric slab superstrate (DSS) is presented. In this scenario, the beams of array elements in the scanning plane should be wide enough and that in the orthogonal plane should be as narrow as possible. Different from the existing DSS technology, the DSS in this letter is used to satisfy the requirements of the beams in both planes. The parameters of the DSS and its position are optimized by setting the narrowest beam in the orthogonal plane as the objective function under the constraint of the specified wide beam in the scanning plane. To validate the proposed scheme, an eight-element DSS linear phased array operating at 10 GHz was designed, fabricated, and measured. Using the simple measure, the measured 3.5 dB gain enhancement in the scanning range of ±43° has been achieved with the aperture efficiency of 98%, the low profile of 1.39 wavelength, and the acceptable side-lobe levels (SLL) of better than −8.7 dB.

Compact Pattern Diversity Antenna with 3-D Printed All-dielectric Superstrate for WLAN Access Points

ABSTRACT This paper presents a four-port pattern diversity antenna with a 3-D printed all-dielectric superstrate for 5.2 GHz Wireless Local Area Network (WLAN) access points. The topology of four-port coaxial-fed circular patch antennas provides a beam tilt of ±45° and ±15° with an angular coverage of ±60°. The beam tilt is obtained through this unique topology, without the need for any additional phase shifting circuits. Then, a low-cost 3-D printed dielectric superstrate is designed to enhance and equalize the gain without compromising on the beam tilt and polarization purity of the antennas. The antenna module has an impedance bandwidth of 80 MHz (5.16 GHz–5.24 GHz), covering the IEEE 802.11ac band, for a gain of 9 dBi throughout the band and across the ports. The dielectric superstrate provides a gain enhancement of 3.8 dB for antennas 1 and 4, and 5.4 dB gain enhancement for antennas 2 and 3, respectively.

Switched Beam Multi-Element Circular Array Antenna Schemes for 2D Single-Anchor Indoor Positioning Applications

This research investigates four switched-beam multi-element circular array antenna schemes operating at 2.4-2.5 GHz for two-dimensional (2D) single-anchor indoor positioning applications. The realization of the proposed antenna schemes involved two evolutionary stages: rectangular microstrip antenna with dielectric superstrate (i.e., element) and multi-element circular array antenna with radio frequency (RF) switch network. The number of elements of circular array antennas was varied between 4, 5, 6, and 8 elements. Multiple signal classification (MUSIC) algorithm was used to determine the direction of incoming signal and Friis transmission equation to estimate the transmission distance. Simulations were carried out, and results showed that the rectangular microstrip antenna with dielectric superstrate (one single element) achieved impedance matching ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10\,\,\text {dB}$ </tex-math></inline-formula> ) in the frequency range of 2.4-2.5 GHz, with unidirectional radiation pattern and 6.65 dBi antenna gain. In addition, four-, five-, six-, and eight-element circular array antenna prototypes were fabricated and experiments carried out in an indoor environment with two, three, and four incoming signals. The experimental results indicated that the eight-element circular array antenna could be deployed to reliably determine signal direction and distance, particularly for indoor localization with two incoming signals. The novelty of this work lies in the potential use of switched-beam multi-element circular array antenna schemes in place of conventional adaptive array antennas for 2D indoor localization. Compared with the conventional adaptive array antennas, the proposed multi-element circular array antenna schemes are relatively low-cost and easy to fabricate.

Dual-Polarized Antenna Gain Enhancement Using Dielectric Slab Superstrate and its Application in Forming an Array

The use of dielectric slab superstrate (DSS) is proposed for gain enhancement of dual-polarized patch antenna and the corresponding arrays. The DSS for a single antenna is investigated firstly to lay a solid foundation for the design of DSS for large arrays. The DSS is placed in front of the dual-polarized aperture-coupled patch antenna and is proved to be available for gain enhancement for both polarizations. The measured results show that the DSS has little effect on the impedance bandwidth but can increase the gain by 10.7 and 11.2 dB for the two ports, respectively. Different from the existing research work, the DSS used to enhance the gain for large arrays is discussed. A piecewise homogeneous DSS with slots is proposed and fabricated for 2 ×2 array with a measured peak gain of 18.3 and 18.4 dBi for two polarizations. The piecewise homogeneous DSS and source antenna array hold the advantages of high gain, large aperture efficiency and easy processability. The piecewise homogeneous DSSs for 4×4 and 8×8 array are also designed and the simulated results show that the DSS can be effective for larger arrays.

Scan Blindness Free Design of Wideband Wide-Scanning Open-Ended Waveguide Phased Array

A wideband wide-scanning open-ended rectangular waveguide phased array in a triangular lattice is presented. Dielectric or metamaterial wide-angle impedance matching superstrates have been widely used in phased arrays to improve the scanning performance. However these dielectric-containing covers cannot solve the problem of scan blindness caused by the surface waves, or even further aggravate the surface wave effect. The modulated surface structures, which consist of the impedance-gradient structures and the surface wave bandgap structures are designed to maximize the wideband wide-scanning performance of the array. The proposed array achieves 40% bandwidth (8–12 GHz), while covering a scanning range of ±65° in the E-plane (VSWR < 2.3) and H-plane (VSWR < 2). The practical working frequency band occupies the whole potential operating frequency band between the waveguide TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> cutoff frequency and the onset frequency of the first grating lobe. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$11\times11$ </tex-math></inline-formula> prototype is fabricated and measured. Good agreement is achieved between the simulated and measured results.

A tightly coupled dipole array used for radiation power improvement on finite radiation aperture

Radiation power of an electromagnetic wave plays a decisive role in its transmission distance. Traditionally, the radiation power can be improved by expanding the radiation aperture size of the antenna array or increasing input power of the unit cell. However, the radiation aperture size is always restricted by assembly space. The input power improvement of the unit cell is always limited by the signal source. It is difficult to improve radiation power on a finite radiation aperture. However, the radiation power on a finite radiation aperture is related closely to the number of antenna elements and the radiation efficiency of the antenna array. It is useful to arrange more elements and improve radiation efficiency of the antenna array to improve the radiation power on a finite radiation aperture. Wideband wide-angle scanning phased array is able to make full use of a finite radiation aperture. The wide-angle scanning properties make it possible for the radiated power to cover a wide area. In this paper, a compact wideband wide-angle scanning tightly coupled dipole array (TCDA) is proposed. A high permittivity substrate and compact wideband balun are used for miniaturizing the antenna array. The period of the unit cell is only 0.144&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;high&lt;/sub&gt; × 0.144&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;high&lt;/sub&gt; (&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;high&lt;/sub&gt; is the wavelength at the highest operation frequency in free space). Parameters of the balun are optimized to improve impedance matching between the balun and the antenna array. Two bilateral frequency selective surfaces (FSSs) are used to replace traditional dielectric superstrate to improve the impedance matching between the antenna array and free space. A low-loss dielectric substrate is used to reduce dielectric loss of the antenna array. In these ways, the radiation efficiency is greatly improved. The simulation results show that the proposed antenna array operates at 1.7–5.4 GHz (3.2:1) while scanning up to 65° in the E plane, 45° in the H plane and 60° in the D plane with following a rigorous impedance matching criterion (active VSWR &lt; 2). A 16 × 16 prototype array is fabricated and measured. Good agreement is achieved between the simulation results and the measurement results. Compared with the designs in the literature, the proposed antenna array has an excellent performance in radiation power on a finite radiation aperture.

To tailor the conical beam by using planar superstrate

Here, the planar superstrate is used to tailor the conical beam. In the applications of conical beam antenna, making a good balance between the wider coverage and the higher gain is always a challenge, while the planar superstrate provides the freedom of design. Through adjusting the parameters of the planar superstrate, it is possible to change the coverage range and to make the beam more flat. To verify the proposed method, some simulated results are presented and two prototypes with homogeneous dielectric slab superstrate and with patterned dielectric slab superstrate are fabricated and measured. The simulated results and the measured ones are in good agreement.

A superstrate loaded aperture coupled dual-band circularly polarized dielectric resonator antenna for X-band communications

AbstractA superstrate loaded cylindrical dielectric resonator antenna is developed and demonstrated for dual-band circular polarization. The proposed antenna employs a microstrip-fed rotated cross-shaped slot coupling technique for exciting the dielectric resonator (DR). The design is developed in a straight forward way. Firstly, the DR is coupled with a conventional plus-shaped slot and operates in linear polarization mode at 7.4 and 11.2 GHz. Secondly, the slot is rotated by 10° to enable out-of-phase excitation and ensure circular polarization at the above-mentioned frequencies. In the third step, a square dielectric superstrate is placed above the DR which creates multiple reflection and enhance the gain up to ~8 dBi in both the frequencies without affecting other performances. The development stages are discussed in detail. The proposed design is demonstrated through prototype fabrication and characterization. This antenna can be used for X-band satellite communications.

Characteristics of TCDA With Polarization Converting Ground Plane

In this study, we propose a tightly coupled dipole array (TCDA) with a polarization convertor (PC) to overcome the bandwidth limitation at h = 0.5 λ and 1 λ of a conventional TCDA. Ultrawideband and low-profile array antennas are gaining considerable attention with widespread of wireless electronic systems. Although TCDA has such characteristics and several advantages compared with others, their bandwidth is still limited by the ground plane (GP) reflection. The use of resistive frequency selective surface (FSS) to overcome this limitation entails ohmic losses which deteriorate the radiation efficiency of the array antenna. In the present study, we propose a 20.9:1 TCDA antenna without resistive FSS. The proposed array antenna employs a PC to overcome the limitation of bandwidth due to GP reflection when the height of the array antenna is 0.5 λ and 1 λ. The concept neither involves any dielectric superstrates nor does it introduce any resistive loss. Thus, beam steering is possible without surface wave generation. As a result, the proposed array antenna is expected to be successfully applied to wideband and beam-scannable array with improved performance of wireless electronic devices.

Dielectric Slab Superstrate Electrically Small Antennas With High Gain and Wide Band

The gain enhancement using superstrate has been widely investigated. Different from the existing research work, this letter focuses on the study of dielectric slab superstrate (DSS) antenna element with electrically small size. For the electrically small DSS antenna, the gain enhancement mechanism based on the multireflections between interfaces with infinite sizes is no longer available. By using a plug-in optimizer based on Python programming and HFSS simulation software, the optimized designs of electrically small two-layer and three-layer DSS patch antennas operating at 6 GHz are introduced. To validate the predicted results, the two optimized antennas are fabricated and measured. For the two-layer DSS patch antenna, the measured peak gain, 3 dB gain bandwidth, impedance bandwidth, and the aperture efficiency are 10.47 dBi, 22%, 20.7%, and 379%, respectively. For the three-layer DSS patch antenna, the measured peak gain, 3 dB gain bandwidth, impedance bandwidth, and the aperture efficiency are 10.55 dBi, 42%, 28.7%, and 386%, respectively.

Design, Simulation and Experimental Analysis of Square Microstrip Patch Antenna with Superstrates at 2.4GHz

Microstrip antenna is used in wide area of applications such as high speed vehicles, missiles, tanks and satellite communications. In these applications dielectric superstrate (or cover) is used above the square patch antenna for providing the protections from severe environmental conditions such as rain, snow, heat, and damage etc. The proposed square microstrip patch antenna is designed using coaxial probe feed technique and transmission line model and operated at center frequency of 2.40 GHz, which is lying in the S-band region. The proposed model is used in linear polarization applications. The square patch is fabricated on low loss dielectric substrate material having dielectric constant is 2.2 and loss tangent of the substrate material is 0.0009. Ansoft electromagnetic simulator software such as HFSS is used for simulating proposed model and studied the effect cover or superstrate on different parameters of square patch antenna. This paper mainly focuses on the performance of square patch antenna without superstrate, and with superstrate at different height of dielectric superstrate above the patch antenna. The result found of patch antenna without superstrate the bandwidth is 0.04GHz and gain is obtained 8.9 dB and 7.51 dB in azimuth and elevation respectively. The result observed of patch antenna with dielectric cover (or superstrate) at height H =0, the antenna performance characteristics are slightly degraded and also comparing the antenna with the bandwidth is decreased to 0.02GHz from 0.04 GHz and gain is decreases to 6.44 dB and 6.6 dB from 8.9 dB and 7.51 dB in both azimuth and elevation plane respectively. The decreased performance characteristics of antenna will be improved by varying height of the superstrate above the patch antenna.. At particular optimum height, the performance characteristics patch antenna will be almost same as the patch antenna without superstrates. The obtained simulated results good match with measurement results.

High Aperture Efficiency Array Antenna for Wireless Power Transfer Applications

We propose a novel array antenna with high aperture efficiency by employing an array element operating in a high-order mode to improve the transmission efficiency of wireless power transmission applications. The proposed array element, operating at a frequency of 5.8 GHz, consists of a square patch with four metallic shorting pins, an extended cavity, and a high dielectric superstrate. The four metallic shorting pins derive the high-order operation, which can enhance the bore-sight gain, resulting in the high aperture efficiency of the array. The extended cavity structure can help further improvement the aperture efficiency and minimize the mutual coupling strength between adjacent elements. The proposed antenna element is extended to 2 × 2 and 4 × 4 arrays, resulting in aperture efficiencies of 74.2% and 80.5%, respectively. For the 2 × 2 array, maximum measured gains of 19.9 dBi in the zx-plane and 18.8 dBi in the zy-plane are observed. For the 4 × 4 array, the maximum measured gains of 24.3 dBi in the zx-plane and 24.5 dBi in the zy-plane are obtained in a full-anechoic chamber. Finally, the transmission efficiency of 6% with a distance of 0.8 m between the transmitter (Tx) and the receiver (Rx) is measured when setting up the wireless power transfer system, which consists of the Tx with the proposed 4 × 4 array and the Rx with a single element.

Design, Simulation and Experimental Analysis on Rectangular Microstrip Patch Antenna with Superstrates

This paper focuses on design, simulation and experimental analysis of rectangular MSA with and without superstrates. The rectangular MPA is designed at frequency range of 2.40 GHz, which is lying in the S band region. The transmission line model analysis and High Frequency Simulation Software (HFSS) is used for designing of proposed rectangular MPA. The proposed antenna is fabricated on Arlon diclad 880 substrate, whose dielectric constant is 2.2, thickness of the substrate is 1.6mm and loss tangent is 0.0009. In this paper the effect of dielectric superstrates on rectangular MPA and the height of superstrate are varying above the rectangular MPA is investigated experimentally and compared with simulated and measured results. The proposed antenna has been analyzed using different dielectric superstrates. From the study it was observed that in antenna without superstrate the VSWR is 1.21, return loss is -18.51dB, bandwidth is 0.038GHz. However, gain is 8.77dB. In the antennas with superstrates, center frequency is shifted from 2.40 GHz to 2.33 GHz as well as other parameters are slightly degraded. As superstrate height increases, the performance antenna is degraded and at particular optimum height the performance characteristics of antenna with and without superstrate will be same. The frequency range 2.40 GHz is used in wireless applications.

A New Model to Determine Effective Permittivity and Resonant Frequency of Patch Antenna Covered With Multiple Dielectric Layers

This paper reports a model to determine effective permittivity ( $\varepsilon _{\mathrm {eff}}$ ) and resonant frequency ( $f_{r}$ ) of microstrip patch antenna (MPA) covered with multiple dielectric layers. This model is augmented with a newly developed empirical expression to determine the $\varepsilon _{\mathrm {eff}}$ of multi-layered superstrates over a substrate. The development of empirical formulation makes use of conformal mapping approach (CMA) and series–parallel combination of dielectric boundaries between the ground plane and patch of the MPA. In this work, the MPA is designed on substrate having dielectric constant of $\varepsilon _{1}$ whereas the superstrate layers have dielectric constants of $\varepsilon _{2}$ , $\varepsilon _{3}\ldots \varepsilon _{\mathrm {n}}$ . It is shown that the proposed technique is able to predict the $f_{r}$ of MPA with error of 1.8%, 3.5%, and 1.4% when it is covered with a single dielectric layer with superstrate height of 4.5mm for respective conditions of $\varepsilon _{1}= \varepsilon _{2}$ , $\varepsilon _{1}> \varepsilon _{2}$ and $\varepsilon _{1} ( $\varepsilon _{1}=3.66$ , $\varepsilon _{2}=2.2$ /4.7). Furthermore, the developed technique is analyzed for distinct combination of substrate and two superstrate layers for the cases $\varepsilon _{1}= \varepsilon _{2}> \varepsilon _{3}$ , $\varepsilon _{1}= \varepsilon _{2} , $\varepsilon _{1} \varepsilon _{3}$ , $\varepsilon _{1}> \varepsilon _{2} , and $\varepsilon _{1}> \varepsilon _{2}> \varepsilon _{3}$ . Subsequently, the viability of the proposed technique is demonstrated in practical scenarios for body centric communications by considering single (e.g., jeans cotton, pure cotton, rayon, polyester, felt fabric, terry wool, and leather) and multiple (e.g., wool over jeans cotton and polyester, felt fabric over pure cotton and rayon) layers of textiles over MPA. The measurement results on various dielectric superstrates and textiles show excellent agreement with the corresponding theoretical results and thereby validate the reported theory. Finally, a comparison with the seminal works clearly shows the promise of the reported technique in this paper.

Theoretical Analysis and Design of High-Stable-Gain Antenna with Ultrawide Band Capabilities and Suppressed Back Radiations

In this paper, a novel shaped microstrip antenna is proposed for millimeter wave wireless applications. Dual band performance is achieved by embedding the defect in the ground plane. Then, a metallic reflector is used in the near-reactive region beneath the ground plane of the antenna to achieve ultrawideband performance at millimeter wave range. Further, a dielectric superstrate is placed again in the near-reactive region just above the upper face of the antenna which deflects the radiated waves of near-reactive region and influenced the surface wave on the antenna surface and results in the enhanced antenna bandwidth and gain. Simulation and analysis of proposed antenna is done by High Frequency Structure Simulator which is based on Finite Element Method. Again, theoretical analysis of structure is carried out using equivalent circuit theory approach and designed structure is fabricated by standard photolithography process. Simulated, theoretical, and measured results are in accordance with each other.

Wideband high‐gain SIW‐fed antenna array for mm‐Wave applications

AbstractA wideband high‐gain mm‐Wave antenna array operating in Ka‐band is reported. The antenna element consists of an antipodal Vivaldi antenna (AVA) with plated through vias on the edges of the radiating arms, which is utilized to eliminate the harmful gap resonance due to the electrically discontinuity. A modified wideband 8‐way substrate integrated waveguide (SIW) power divider is proposed to feed the linear array. In addition, in order to enhance antenna gain, a stacked dielectric superstrate is employed, which achieves 2.3 dBi average gain improvement over 25‐40 GHz. The proposed structure provides superior bandwidth of 25.4‐40 GHz with S11 &lt; −9.5 dB (corresponding to VSWR &lt; 2). The modified SIW power divider, 1 × 8 AVA array and the dielectric superstrate are designed and fabricated, resulting in a wideband and high‐gain structure as compared to other SIW‐fed antennas. A prototype is experimentally verified. The measured results show that the impedance bandwidth ranges from 25.37 to 39.48 GHz (S11 &lt; −9.6 dB, relative bandwidth of 43%). The measured gain varies from 15.5 to 18.5 dBi in the frequency range with an average gain of 16.6 dBi.