Showing papers on "Slot antenna published in 2021"

Wideband Decoupling of Integrated Slot Antenna Pairs for 5G Smartphones

Abstract: This communication proposes a wideband decoupling technique to suppress the strong coupling between two extremely closely spaced open-slot antennas and implements a wideband integrated slot antenna pair for fifth-generation (5G) metal-rimmed smartphones. By simply inserting a connecting line between two closely spaced open-slot antennas, a top slot structure can be constituted with odd- and even-mode resonances in the lower and higher bands, respectively, to cancel the original strong mutual coupling. In addition to the decoupling effect, the top slot can also expand the effective radiation aperture of the antenna pair for the bandwidth improvement. The proposed slot antenna pair, with a compact footprint of $28 \,\, \times 7\,\,\times1.8$ mm3, shows good impedance matching, isolated and diversity performance across 3.3–5.0 GHz. Then, an $8 \times 8$ multiple-input multiple-output (MIMO) system, constituted by four sets of slot antenna pairs, is simulated, fabricated, and measured. Both the simulated and experimental results show that the $8 \times 8$ MIMO system can offer isolations of better than 10.8 dB and envelope correlation coefficients (ECCs) of less than 0.14 between all eight ports across 3.3–5.0 GHz. Also, a total efficiency of 55.0%–83.1% and 52.5%–83.1% is achieved for Ant1 and Ant2, respectively. Featuring wide bandwidth, compact size, high integration level, and metal rim compatibility, we forecast the proposed solution has great potential for future 5G smartphones.

A Miniaturized MIMO Antenna With Triple Band-Notched Characteristics for UWB Applications

Abstract: In this paper, a novel compact four-element ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with triple band-notched characteristics is proposed. The proposed antenna is composed of four slot antenna elements with a common rhombic slot, each feeding by a microstrip-fed line to greatly reduce the overall size of the antenna. It has a compact size of 34 mm $\times34$ mm $\times1.6$ mm. The high isolation and polarization diversity are achieved by placing the four microstrip-fed lines perpendiculars to each other, while a parasitic strip is employed as a decoupling structure between adjacent microstrip-fed lines to further improve isolation. Moreover, the proposed antenna can achieve triple band-notched characteristics by embedding L-shaped and C-shaped slots on each radiator and loading electromagnetic band gap (EBG) structures next to micro-strip feeders respectively. As a result, the proposed antenna obtains three notched bands of 3.3-3.9 GHz, 5-6 GHz, and 7.4-8.5 GHz, which are in good agreement with the interference bands of WiMAX (3.3-3.7 GHz), WLAN (5.15-5.875 GHz) and X-band (7.3-8.5 GHz), respectively. The antenna prototype has been fabricated and measured. The results show that the antenna has an impedance bandwidth of 2.5-12 GHz (except for the three notched bands). Besides, the isolation among the elements, envelope correlation coefficient, radiation characteristics, efficiency, realized gain, and total active reflection coefficient are also investigated. The experimental results indicate that the proposed antenna can be a good candidate for UWB-MIMO wireless communication applications.

A Planar Dual-Polarized Phased Array With Broad Bandwidth and Quasi-Endfire Radiation for 5G Mobile Handsets

Abstract: A planar dual-polarized phased array is proposed for 5G cellular communications. The array has the properties of dual-polarization, wideband, and quasi-endfire radiation, which is printed on one side of a single-layer substrate. The design contains two eight-element subarrays including horizontally polarized endfire dipole antennas and vertically polarized endfire periodic slot antennas, employed on the PCB ground plane of the 5G mobile platform. Both subarrays provide wide bandwidth to cover 28 and 38 GHz (promising 5G candidate bands). The −10 dB impedance bandwidth of the proposed CPW-fed dipole and slot antennas are 26.5–39.5 GHz and 27.1–45.5 GHz, respectively. Moreover, for −6-dB impedance bandwidth, these values could be more than 20 GHz (24.4–46.4 GHz for the dipole antenna) and 70 GHz (22.3–95 GHz for the slot antenna). The fundamental characteristics of the proposed dual-polarized 5G antenna array in terms of the impedance bandwidth, realized gain, polarization, radiation pattern, and beam steering are investigated and good results are obtained. The clearance of the proposed dual-polarized 5G antenna array is less than 4.5 mm which is sufficient for cellular applications.

Wideband Dual-Layer Huygens’ Metasurface for High-Gain Multibeam Array Antennas

Abstract: A wideband dual-layer Huygens’ unit cell based on offset electric dipole pair (OEDP) is proposed. Different from traditional designs with a combination of electric and magnetic polarizabilities, the proposed Huygens’ unit cell exclusively employs electric polarizabilities. By doing so, it practically avoids the unbalanced resonant frequencies between the two polarizabilities, thereby achieving wideband transmission. Based on the proposed unit cell, a wideband and high-gain multibeam array antenna is developed. First, a Rotman lens is designed by using a substrate-integrated waveguide (SIW) technology. Then a parallel-fed slot antenna array is connected to the Rotman lens to generate multiple beams. Without using a series-fed slot antenna array, the multibeam array antenna based on Rotman lens can operate within a relatively wide bandwidth (28–32 GHz). Second, a wideband dual-layer Huygens’ metasurface is developed that serves as a superstrate of the multibeam array antenna for increasing the antenna gain further. A wideband and high-gain multibeam array antenna is finally realized, which is comprised of a Rotman lens, a parallel-fed slot antenna array, and a Huygens’ metasurface. To verify the performance of this design, a prototype is fabricated and its measured results are compared to the simulated counterparts.

An Orthogonal Hybrid Analog–Digital Multibeam Antenna Array for Millimeter-Wave Massive MIMO Systems

Abstract: A hybrid analog–digital multibeam antenna array (MBAA) consisting of two types of 1-D beamformers for two orthogonal planes, respectively, is proposed for massive multiple-input multiple-output (MIMO) communication systems at millimeter-waves. In the vertical direction, the multiple beams are generated by a passive beamformer, i.e., a Butler matrix, whereas the multibeam coverage in the horizontal plane is achieved digitally at the baseband. Comparing to a full-digital multibeam array, the digital beamforming (DBF) processing is simplified in the proposed scheme, significantly alleviating the computational burden of data processing. Since the radiation beams are generated by only a part of the radio frequency (RF) channels in the hybrid multibeam array, the power consumption could be reduced by powering down the idle channels. To verify the concept, a two-dimensional (2-D) array comprised by 16 columns of eight-beam tapered slot antenna subarrays is designed and fabricated, in which each subarray contains a pair of $4 \times 8$ modified Butler matrices based on the substrate-integrated waveguide technology. The measured results exhibit that the operating bandwidth is 13.45% for the subarray fed by the modified Butler matrices implemented by substrate-integrated waveguides. The RF receivers, intermediate frequency (IF) chains, and analog-to-digital converters (ADCs) are also implemented to enable the DBF in the horizontal plane. The maximum simulated directivity of the array is 27 dBi. A wide 2-D spatial angle is covered simultaneously by the proposed hybrid passive-DBF scheme. The demonstrated 2-D millimeter-wave hybrid array may find widespread potential applications in future communication systems.

Surrogate-Assisted Quasi-Newton Enhanced Global Optimization of Antennas Based on a Heuristic Hypersphere Sampling

Abstract: This communication presents a novel surrogate-assisted quasi-Newton enhanced global optimization (SA-QNEGO) algorithm. In this proposed method, the heuristic hypersphere sampling (HHS) method is used to obtain representative samples. The surrogate model is built based on the low-fidelity model. The quasi-Newton enhanced differential evolution (DE) method is designed to optimize the surrogate model. Finally, the optimal design of a high-fidelity model is obtained through a space mapping procedure. The proposed algorithm is verified through two antenna design examples including a dipole antenna with balun and an SIW cavity-backed slot antenna. The results show that the proposed algorithm finds a more accurate minimum value with less computational time than direct optimization using DE.

E-Shaped H-Slotted Dual Band mmWave Antenna for 5G Technology

Abstract: The aim of this work is to propose a dual band millimeter wave (mmwave) MIMO antenna system for 5G technology. In addition, the arrangement of the antenna elements in an array should be in such a manner that without using the traditional decoupling structures and/or techniques, a reasonable isolation level must be achieved. To demonstrate this, a system consists of four radiating elements that are etched on a 0.508 mm-thick Rogers-5880 substrate. The dielectric constant of the substrate is 2.2 and the loss tangent is 0.0009. Each radiating element consists of three parts; an E-shaped patch, an H-shaped slot within a patch, and a transmission line. The system is resonating at two different mmwave frequencies, i.e., 28 GHz and 38 GHz with a minimum port isolation of 28 dB. The mean measured gain is found to be at 7.1 dBi at 28 GHz and 7.9 dBi at 38 GHz with average efficiency, and envelope correlation coefficient (ECC) of the system at 70%, and 0.0005 respectively. The proposed system is designed and simulated in a full-wave electromagnetic wave software Computer Simulation Technology (CST), fabricated using LPKF D104 milling machine, and measured using R&SZNA67 vector network analyzer. An excellent agreement is observed between the simulated and the measured results and a detailed comparison with the previous works is also presented. Due to attributes such as low-cost, easy to fabricate, and dual-band, it is believed that this system will find its application for future 5G systems.

Dual-Polarized mm-Wave Endfire Chain-Slot Antenna for Mobile Devices

Abstract: This article describes a dual-polarized endfire antenna array for millimeter-wave (mm-wave) frequencies. The antenna consists of a chain-slot-shaped pattern on a mobile phone metal frame. The antenna is fed using a transmission line, which would cause only a negligible capacitive loading of the sub-6 GHz antenna realized on the same metal frame and, therefore, would not significantly degrade its performance. This makes colocating the sub-6 GHz and mm-wave antennas in the same, shared volume possible. Measurements indicate that a four-element array placed within a mobile phone provides a realized gain between 8 and 12.6 dBi for both polarizations across the entire band from 24.5 to 29.5 GHz. The total efficiency of a single element is better than −2 and −3 dB for the whole band for horizontal and vertical polarizations, respectively.

High-Isolation In-Band Full-Duplex Cavity-Backed Slot Antennas in a Single Resonant Cavity

Abstract: High-isolation in-band full-duplex (IBFD) cavity-backed slot antennas (CBSAs) in a single resonant cavity are presented in this article. The TE101 and TE011 cavity modes combined with a modified orthogonal feeding structure are first used to design the duplex antenna. The proposed feeding structure can reduce the port-to-port coupling strength and produce a very high isolation. By replacing the crossed radiation slots with two pairs of parallel radiation slots, enhanced radiation gain is achieved. To tackle the narrow bandwidth for the single-mode operation, two orthogonal resonant-iris modes produced by the two feeding slots are introduced to design a dual-mode wideband IBFD antenna. The simulated bandwidth is increased from 0.8% to 5.7%. All the presented antennas with improved performances are designed and realized in a single full-metal resonant cavity. Compared with the conventional design method, high isolation, enhanced gain, and enhanced bandwidth are simultaneously achieved without enlarging the antenna size. Finally, the prototype of the wideband IBFD slot antenna is measured and presented to validate the design concept, which has a 5.8% bandwidth, higher than 95% total efficiency, especially an isolation higher than 72 dB.

Low-Sidelobe Cavity-Backed Slot Antenna Array With Simplified Feeding Structure for Vehicular Communications

Abstract: In this article, low-sidelobe cavity-backed slot antenna array with simplified feeding structure for vehicular communication is proposed. Conventional low-sidelobe antennas were realized using power dividing network to obtain the in-phase and nonuniform-amplitude excitation, which causes complicated antenna's structure and design. To tackle these challenges, a simplified feeding method without using power dividing network is introduced to design the low-sidelobe slot antenna array. The slots at the top walls serve as the radiation elements, and the slots are directly fed by the electric field of the cavity mode. Nonuniform amplitude is obtained by simply modifying the slots’ sizes and positions, while the in-phase excitation of the elements is remained. The nonuse of power dividers brings out a simpler antenna structure than conventional full-metal waveguide-based antennas. Besides, the full-metal structure introduces a high power-handling capacity. Then, two linear arrays with 1 × 4, 1 × 7 elements and a planar array with 5×4 elements are presented to show the design feasibility. Finally, the 5 × 4 antenna array is fabricated and measured, which can achieve 18.2 dBi gain, −20 dB sidelobe level, 94% radiation efficiency, and -42 dB cross-polarization. Good agreement between measurement and simulation verifies the feasibility of the proposed design concept.

Design of a Stacked Co-Polarized Full-Duplex Antenna With Broadside Radiation

Abstract: This article presents a co-linearly polarized (LP) stacked two-port antenna with compact size and broadside radiation patterns for in-band full-duplex (IBFD) application. The proposed IBFD antenna consists of a patch antenna and a substrate integrated waveguide (SIW) cavity-backed slot antenna (CBSA). The patch antenna and the CBSA are used as the transmitter (Tx) and receiver (Rx), respectively. The Rx is placed above the Tx for compact size. Linear polarization and broadside radiation patterns are achieved in this article. A cavity-patch coupling (CPC) path is added for canceling the slot-patch coupling (SPC) by using four probes to connect the top layer of the SIW cavity and the metal ground. Parametric studies show that the two coupling paths can be adjusted independently. Experimental results illustrate that the measured highest isolation over 40 dB is obtained with a compact size of $30\times 30\times {4}$ mm3 ( $0.63\lambda _{0} \times 0.63\lambda _{0} \times 0.08\lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at the center frequency of about 6.29 GHz). The measured −10 dB bandwidths of the Tx and Rx antennas are 430 and 100 MHz, respectively. The proposed stacked IBFD antenna is validated with the merits of identical polarization, same radiation direction, and compact size.

Compact Dual-Frequency Antenna Array With Large Frequency Ratio

Abstract: A dual-fed dual-frequency shared-aperture antenna array with a large frequency ratio is investigated. Its unit cell consists of a microwave ground-surrounded patch antenna and a millimeter-wave substrate-integrated $2\times {2}$ slot antenna subarray. The former is excited in the fundamental TM10 mode, whereas the slot elements are excited in their fundamental mode. Based on the dual-frequency antenna unit, a dual-frequency antenna array is designed. To demonstrate the idea, a prototype that consists of a $C$ -band $2\times {2}$ patch antenna array and a $Ka$ -band $8\times {8}$ slot antenna array was designed, fabricated, and tested. Its matching and radiation characteristics are studied for both bands. Reasonable agreement between the measured and simulated results is observed. Excellent measured intraband isolations of over 32 dB are obtained.

Dual-Polarized Slot Antenna for Full-Duplex Systems With High Isolation

Abstract: A single-layered slot antenna system working at 5.8 GHz Industrial, Scientific and Medical (ISM) band is proposed for in-band full duplex (IBFD) operation applications without the use of a coupler. First, high isolation is achieved by strong separation of even- and odd-mode feeds. The microstrip-coupled coplanar waveguide (CPW) is used at Port 1 (TX port) to excite a stepped-slot antenna in the CPW odd mode. On the opposite side, a microstrip T-junction power divider is employed at Port 2 (RX port) to feed two offset-fed stepped-slot antennas in even mode. Second, isolation is further improved by 30 dB by using a lumped capacitor at the termination of the CPW. The measured isolation between the two ports is about 50 dB across the bandwidth. The measured −10 dB bandwidth of Port 1 is 0.49 GHz (8.5%), while that of Port 2 is 1.06 GHz (18.3%). The gains of TX and RX antennas are 5.4 and 5.8 dBi at 5.8 GHz. The proposed antenna can also be deployed as a dual-polarized antenna. Mathematical analysis and equivalent transmission line circuit models are provided to give physical insight into the working principals of the antenna with validation from ANSYS HFSS simulation.

A compact double-band planar printed slot antenna for sub-6 GHz 5G wireless applications

Abstract: A planar rectangular slot antenna with dual-band operation and realized higher peak gain is proposed, designed, and fabricated for sub-6 GHz 5G applications. The antenna possesses a rectangular radiating slot with the inverted stub on its upper edge excited simultaneously by a micro-strip feed line having a double folded T-shaped structure. The fabricated design is of compact size with the radiating portion of 0.3 λ0 × 0.17 λ0 (λ0 represents free-space wavelength) and profile of 0.009 λ0. The measured results show the operating frequency bands of 3.29–3.63 GHz and 4.3–5.2 GHz, with a peak gain of around 7.17 dBi. The higher frequency band is generated by the feed patch and the slot whereas lower resonant frequency band is generated by the stub loaded on the slot. The measured results are in a good agreement with the simulated results. The proposed design is suitable for the International Telecommunications Union sub 6 GHz applications.

A 5 × 8 Butler Matrix Based on Substrate Integrated Waveguide Technology for Millimeter-Wave Multibeam Application

Abstract: A 5 × 8 Butler matrix (BM) operating in the millimeter-wave band is presented in this letter. The matrix is extended from two 3 × 4 Butler matrices by adding two couplers and one power divider, providing an equal amplitude signal distribution with five phase differences between the adjacent output port (0°, ±45°, ±135°). In order to reduce the number of crossover and complexity of the matrix structure, a dual-layer and symmetrical substrate integrated waveguide (SIW) structure is used to design the proposed BM. To verify the concept, an experimental BM is designed and fabricated as the feeding network of a slot antenna array, achieving five beams in the frequency range of 27.8–30.8 GHz.

Efficient Wireless Power Transfer System for Implantable Medical Devices Using Circular Polarized Antennas

Abstract: In this article, we present a novel approach for designing a rotation insensitive, biocompatible, circular polarization-based efficient wireless power transfer (WPT) system for implantable medical devices (IMDs) in the radiative near-field region. Initially, a wideband, biocompatible, flexible circular polarized (CP) slot antenna is designed inside a single-layer skin tissue model to use as a receiving (Rx) element. To create the WPT link, a simple square patch antenna with the truncated corners is constructed to utilize as a transmitting (Tx) element. Furthermore, a polarization conversion-based metamaterial (MTM) structure is built particularly to improve the power transfer efficiency (PTE) of the proposed WPT system. Also, to show the versatility, the performance analysis of the proposed MTM integrated WPT system is conducted inside the human torso and head model. Moreover, a detailed study of the specific absorption rate (SAR) is accomplished regarding the safety of the human body in the light of IEEE regulation. Finally, the prototypes of the proposed WPT system are fabricated and experimentally verified in skin-mimicking gel and minced pork. The experimental result confirms the feasibility of the proposed concept by enhancing the PTE of the presented system by the usage of the MTM slab.

Efficient SIW-Feed Network Suppressing Mutual Coupling of Slot Antenna Array

Abstract: In this communication, an effective method to suppress mutual coupling between two substrate-integrated waveguide (SIW) slot antenna arrays is presented. To achieve that, a decoupling feed network is used. The feed network is composed of a two-layer directional coupler that is connected to two SIW-slot antenna arrays directly to establish an indirect coupling with controlled magnitude and phase, which can effectively reduce the direct coupling generated by surface waves between the array elements. A $2 \times 4$ array of slot antenna as well as the proposed decoupling network is designed, fabricated, and measured to illustrate the effectiveness of the proposed technique. The measured and simulated results verified the good decoupling performance. The measured mutual coupling is about −35 dB at the center frequency without negatively affecting the return loss and radiation patterns. The proposed mechanism of the decoupling network is simple and successfully used in SIW slot antenna arrays.

Wideband Single-Layer Substrate Integrated Waveguide Filtering Antenna With U-Shaped Slots

Abstract: A wideband single-layer substrate integrated waveguide (SIW) filtering slot antenna with compact structure is investigated, which is originated from a SIW resonant cavity operating at its TE110 mode. A straight radiating slot is integrated on the top surface of the cavity. The resonator can be splitted into two half-mode resonators, generating a radiation null at higher edge of the passband. At same time, two U-shaped slots are etched on the bottom surface of the cavity. One of the U-shaped slots is used to introduce a radiation null at the left edge of the passband while the other U-shaped slot introduces the modified half-TE110 mode in the right half cavity, broadening the bandwidth of the antenna. Finally, the third-order filtering antenna is obtained with 11.84% impedance bandwidth in only one SIW resonant cavity. To validate design, a prototype is fabricated and measured. Compared with other designs, the proposed antenna owns features of simple structure, wide bandwidth, and compact size, satisfying the increasing requirement for the miniaturization and integration of RF devices.

A K -Band Broadband Circularly Polarized Slot Antenna Based on L-Shaped Waveguide Cavity

Abstract: A new broadband circularly polarized antenna is presented for K -band application in this letter. The circularly polarized radiation is realized by orthogonal-polarized slots based on a special structure of the L-shaped waveguide cavity. To verify the proposed idea, a single element and a 2 × 4-element array are designed, fabricated, and measured. The simulations are agree well with experiments. The results show that the single element achieves the 10 dB impedance bandwidth of 27.5% (18.5–24.5 GHz) and the 3 dB axial ratio bandwidth of 7.1% (19.6–21.2 GHz), while the 2 × 4 element array achieves the 10 dB impedance bandwidth of 27.1% (18.5–24 GHz) and the 3 dB axial ratio bandwidth of 18.7% (19.3–22.6 GHz). Moreover, all-metal structure of the proposed antenna is very appropriate for tough environment applications.

A Compact Dual-Band Slot Antenna With Horizontally Polarized Omnidirectional Radiation

Abstract: A dual-band horizontally polarized omnidirectional antenna for WiFi applications is proposed in this letter, which consists of a 3-D radiation slot on a metal box and three folded patches inside. The 3-D slot is formed by connecting two trapezoid slots at top and bottom of the box with a rectangle slot at the vertical side. Then, the radiation slot is excited by a folded patch connected to the feed line and produces two resonances at 2.45 and 5.5 GHz. With the help of two parasitic patches beside the excited patch, the higher frequency band is broadened. Measured results show that the antenna has two 10 dB return loss operating bandwidths of 5.32% and 20.56%. Moreover, the measured out-of-roundness for the horizontal radiation pattern is less than 2.4 dB in lower frequency band and that of higher frequency band is less than 5.3 dB. Besides, the antenna maintains a compact size of only 22 mm × 10 mm × 25 mm (0.18 λ 0 × 0.08 λ 0 × 0.20 λ 0, where λ0 is the wavelength of the lowest operating frequency), with the gain about 2 dBi and the cross-polarization ratio greater than 20 dB in the entire band.

High Selectivity and High Gain X-Band Waveguide Filtering Antenna Based on Triple-Mode Resonator

Abstract: In this communication, a high-selectivity and high-gain filtering slot antenna operating in $X$ -band is designed based on a triple-mode cavity resonator. Three modes of the cavity resonator, namely, TE101, TE011, and TM110, are excited by properly selecting the position and size of the coupling aperture. By adjusting the frequency and external coupling of the three modes, transmission zero can be introduced on both sides of the passband, achieving high selectivity of antenna gain. Because the cavity has a high unload quality factor, the radiation efficiency in the passband is high and flat. In order to increase the gain of the filtering waveguide antenna, a grid-slotted patch is added on the top of the slot. To demonstrate the concept, an $X$ -band waveguide filtering antenna is designed and fabricated. Measured results show the filtering antenna can obtain a gain of greater than 8.5 dBi in the frequency range of 9.8–10.2 GHz.

Radiation Pattern Reshaping of A Narrow Slot Antenna for Bandwidth-Enhancement and Stable Pattern Using Characteristic Modes Analysis

Abstract: A novel design concept to reshape radiated fields of a slot antenna for improved bandwidth and stable radiation pattern is proposed. Initially, the radiated fields of the traditional slot antenna are theoretically studied using characteristic modes (CMs). The results demonstrate that its CM1, CM2, and CM3 are resonated of around 2.39, 4.78, and 7.17 GHz, respectively. For CM1 and CM3, both of them maintain the bidirectional radiation patterns. Whereas, the CM2 generates a radiation null in the broadside direction. Then, in order to utilize the nearby CM1 and CM2 for wide-bandwidth, the linear slot is properly folded so as to transform the non-bidirectional pattern of CM2 into the bidirectional one. After that, the narrow slot is reformed as the stepped scheme, thus reallocating these dual modes in proximity to each other. With these arrangements, the impedance bandwidth of the antenna is dramatically widened with two attenuation poles, while keeping a compact size and stable radiation pattern. Finally, the proposed antenna is fabricated and tested. Measured results show that the antenna without any extra feeding network has gained a wide-bandwidth (|S11|<−10 dB) of around 31.4% ranging from 3.22-4.42 GHz, which is about 2.24 times wider than its traditional counterpart (14%). Besides, the overall size of the slot radiator is kept as small as about 0.42λ0×0.06λ0(λ0 is the free-space wavelength). Particularly, the bidirectional radiation pattern, stable gain of around 5 dBi, and low cross-polarization of below −12.3 dB are all satisfactorily generated during the operating band.

Novel Reconfigurable Full-Metal Cavity-Backed Slot Antennas Using Movable Metal Posts

Abstract: Novel design concept of reconfigurable full-metal cavity-backed slot antennas (CBSAs) using movable metal posts is proposed in this article. It is found that the cavity mode with purely directional electric field is only affected by the metal post to be placed in parallel to its electric field. Thus, two orthogonal cavity modes TE101 and TE011 can be perturbed by two respective metal posts so as to independently tune the resonant frequencies of these two modes. Electromagnetic energy of the cavity modes can be radiated out through the slots on the top wall of the cavity. In this context, reconfigurable slot antennas with different functionalities, such as single-band, dual-band, dual-mode wideband, the tunable frequency with constant bandwidth, and tunable bandwidth with constant frequency, are thus constituted to demonstrate its attractive design feasibility. The frequency-reconfigurable cavity-back slot antenna with movable metal posts is proposed for the first time. The utilization of the metal posts allows us to achieve a continuous frequency tuning property, while the full-metal structure of the proposed antenna holds a high power-handling capacity and a high radiation efficiency. In final, a prototype of the dual-mode wideband slot antenna is designed, fabricated, and tested to reveal its total efficiency higher than 88% and stable radiation pattern over the tuning band. Good agreement between the measured and the simulated results well validates the presented design concept.

Miniaturized Antipodal Vivaldi Antenna with Improved Bandwidth Using Exponential Strip Arms

Abstract: In this paper, a miniaturized ultra-wideband antipodal tapered slot antenna with exponential strip arms is presented. Two exponential arms with designed equations are optimized to reduce the lower edge cut-off frequency of the impedance bandwidth from 1480 MHz to 720 MHz, resulting in antenna miniaturization by 51%. This approach also improves antenna bandwidth without compromising the radiation characteristics. The dimension of the proposed antenna structure including the feeding line and transition is 158 × 125 × 1 mm3. The results show that a peak gain more than 1 dBi is achieved all over the impedance bandwidth (0.72–17 GHz), which is an improvement to what have been reported for antipodal tapered slot and Vivaldi antennas with similar size.

Compact UWB Vivaldi Tapered Slot Antenna

Abstract: In this paper compact Ultra Wideband (UWB) Vivaldi Tapered Slot Antenna (VTSA) is designed simply by changing its Microstrip to Slot line (M/S) transition. To explain the effect of transition’s shapes on the size and the performance of the UWB VTSA, four models (A–D) with detailed parametric studies are analyzed, designed, and fabricated. As compared to Model A, in Model D the size (42.9 mm × 29.28 mm = 1256.112 mm2) is reduced by 19.25%, and the bandwidth (10.34 GHz) is enhanced by 24.56%, in addition, it provides 6.51 dBi maximum realized gain, and stable end-fire radiation pattern. The validity of the proposed antennas is proven by hardware measurement results.

A dual-mode double-sided 4 × 4 MIMO slot antenna with distinct isolation for WLAN/WiMAX applications

Abstract: A novel compact four-element antenna system is presented for MIMO applications. The MIMO antenna has four slot radiators perpendicular to each other with two radiating elements on the top layer of the substrate, and the two other elements are on the bottom layer. This MIMO antenna has an overall compact size of 60 × 60 × 0.8 mm3. The four antenna elements are in inverse positions on both sides of the dielectric material to accomplish a minimal size. Furthermore, the best possible arrangement of components along the dielectric material enhances the isolation between components besides the use of decoupling structures. The proposed MIMO antenna can operate at WLAN band running from 2.4 to 2.485 GHz, and WiMAX band running from 3.4 to 3.6 GHz. The four elements MIMO antenna has dual independent modes of operation to increase the data rate for each application independently since the first mode resonates at 2.46 GHz, and the second mode resonates at 3.5 GHz. A closed consensus between simulation and measurement results confirms the effectiveness of this MIMO antenna for the use in multi-band environments with high isolation level, elevated DG, and very low ECC.

Radar Cross Section-Based Chipless Tag With Built-In Reference for Relative Humidity Monitoring of Packaged Food Commodities

Abstract: Dry food commodities like grains and pulses can be stored safely for several years under controlled storage conditions. The equilibrium moisture content of the packaged grain is one of the most important parameters required to be monitored and controlled for extended safe storage. This paper presents a single element dual-polarized sensing tag based on an annular slot antenna operating at two closely spaced resonant frequencies for radar cross-section-based monitoring of relative humidity in hermetically packaged food commodities. One of the resonant frequencies is functionalized for sensing while the other acts as a built-in reference, mitigating the effects of environmental loading. A polyvinyl alcohol coated interdigitated capacitor, integrated onto the antenna is used as a capacitive transducer for the sensing element. Laboratory scale measurements were carried out using the saturated salt solution method. Results show that the proposed sensor can be used for monitoring a wide range of humidity conditions.

Bandwidth-Enhanced High-Gain Full-Metal Filtering Slot Antenna Array Using TE 101 and TE 301 Cavity Modes

Abstract: In this letter, a bandwidth-enhanced high-gain full-metal cavity-backed filtering slot antenna array is proposed. By replacing one radiating slot with 2 × 2 radiating slots, the enhanced gain is obtained without enlarging the antenna size. Besides, two cavity modes, i.e., TE101 and TE301, are combined to obtain an enhanced bandwidth. Metal ridges and metal posts are employed to make the two modes close to each other. Due to a similar radiating field of the two specific cavity modes under the proper perturbation and placement of the 2 × 2 radiating slots, a high gain over the enhanced bandwidth is obtained. In addition, the high-quality factor of the two cavity modes can inherently produce a filtering performance in terms of the realized gain and efficiency. The final measurement shows that the proposed slot antenna array can achieve 6.2% bandwidth, 97% total efficiency, and 10.4–11 dBi stable realized gain with a small aperture size of 0.84 λ 2. Good agreement between the simulation and measurement has well validated the proposed design concept.

A Broadband High Gain Tapered Slot Antenna for Underwater Communication in Microwave Band

Abstract: A broadband high gain Tapered slot antenna array for under water communication is presented in this paper. The procedure to design the unit element antenna is followed by applying a linear tapered array-slot structure to the conventional Vivaldi antenna; hence the bandwidth, gain and radiation efficiency of the antenna are improved. The proposed antenna array is designed on the low-cost FR4 epoxy substrate material with value of dielectric constant $$\varepsilon _r= 4.4$$ , and loss tangent $$\delta = 0.02$$ . The reduction of the feed line width and location adjustment is used to expand the impedance bandwidth of the proposed antenna. Moreover, the single antenna element is expanded to $$1\times 2$$ , $$1\times 4$$ and $$2\times 4$$ to form an antenna array respectively. The dimensions of the developed array antenna are satisfying the proper impedance matching. The simulated reflection coefficient results confirm that the proposed antenna array achieves an impedance bandwidth of above 55% obtained at 10 dB return loss, the peak realized gain of 10.75 dBi and radiation efficiency of more than 90%. The measured results show a good agreement and hence making the designed antenna array appropriate to work in the underwater communication band.