Compact circularly polarized beam‐switching wireless power transfer system for ambient energy harvesting applications

In this work, we propose a circularly polarized (CP) beam‐switching wireless power transfer system for ambient energy harvesting applications operating at 2.4 GHz. Beam‐switching is achieved using a low profile, electrically small CP antenna array with four elements and a novel miniaturized 4× 4 butler matrix. The CP antenna is designed with an e‐shaped slot and four antennas. The CP antenna measures 0.32 λ₀× 0.32 λ₀× 0.006 λ₀ at 2.4 GHz. The antenna has a gain of 3 dBic and an axial ratio less than 3‐dB at 2.4 GHz. A linear antenna array consisting of four elements is designed with the CP antenna element with an inter‐element distance of 0.29 λ₀ . A 4× 4 butler matrix with miniaturized couplers and crossovers are used to feed the four antenna array elements. Based on the input port of excitation, the main beam of the antenna array is demonstrated to be switched to four directions: ?5°, 65°, ?55°, and 20°. A CP rectenna is used to demonstrate the wireless power transfer capability of the combination of the butler matrix and the CP‐antenna array. The rectenna consists of a Teo‐shaped CP antenna and a rectifier. The open circuit voltage at the output of the rectenna is found to peak value of 30 mV at ?3°, 61°, ?53°, and 17°. Thus a complete system for CP wireless power transfer including the power transmission system as well as the RF energy harvesting sensor is designed and experimentally verified.     

Compact triband slotted printed monopole antenna for WLAN and WiMAX applications

This work presents a triband antenna, which is compact, low profile, and covers the bandwidth requirements for WLAN and WiMAX applications. The proposed design is a modified and miniaturized printed monopole antenna. It consists of beveling rectangular patch, a Pi‐shape slot element, and an inverted‐L slot element to achieve resonance in three bands. The physical size of the antenna is 27.5 × 20 mm² while the electrical size is 0.26 λ₀ × 0.23 λ₀ at the lower operating frequency which is very compact as compared to other triband designs. It works in three bands, that is, 2.37 to 2.52 GHz, 3.35 to 3.90 GHz, and 4.97 to 7.85 GHz with |S₁₁| < ? 10 dB within these operating bands. The prototype of the proposed miniaturized antenna has been fabricated and the measured results are provided for validation. Antenna performance is studied in terms of input match, gain, radiation efficiency, surface current distributions, and radiation pattern. The antenna shows a nearly omnidirectional radiation pattern with peak efficiency of 90% and acceptable gain of 4 dBi over the three operating bands of WLAN and WiMAX. The prototype of the antenna is fabricated, and simulated results have been verified through measurements.     

A dual‐polarized cross‐dipole antenna with wide beam and high isolation for base station

In this paper, a dual‐polarized cross‐dipole antenna with wide beam and high isolation is designed and analyzed for base station. The proposed antenna consists of two planar cross dipoles with four square patches, two L‐shaped microstrip lines, two ground plates, four parasitic patches, and a reflector. The square patches are placed between the center of cross dipoles to couple with L‐shaped microstrip lines. By introducing the parasitic patches, the wide beam can be realized. The measured results show that the proposed antenna achieves an impedance bandwidth (|S₁₁| < ?10 dB) of about 18.7% (1.9‐2.35 GHz) and an isolation better than 30 dB. A measured gain of 5.7 dBi and a half‐power beamwidth over 120° at the center frequency are obtained. Furthermore, the size of the proposed antenna is only 0.5λ₀ × 0.5λ₀ × 0.22λ₀ (λ₀ is wavelength at the center frequency).     

Miniaturized low‐profile antenna based on uniplanar quasi‐composite right/left‐handed metamaterial

In this article, a metamaterial‐based broadband low‐profile antenna is presented. The proposed antenna employed an array of uniplanar quasi‐composite right/left‐hand (CRLH) metamaterial cells. This structure contributes to exciting the operating modes in lower frequencies. The antenna has an overall electrical size of 0.75 × 0.60 × 0.07 λ₀³ (λ₀ is the center operating wavelength in free space) and provides a 25% measured bandwidth with the center frequency of 5.1 GHz and maximum gain of 6.6 dB. The proposed antenna is an appropriate candidate for WLAN, WiMAX, and other wireless communication applications.     

A high‐gain compact circularly polarized microstrip array antenna with simplified feed network

A broadband high‐gain circularly polarized (CP) microstrip antenna operating in X band is proposed. The circular polarization property is achieved by rotating four narrow band linearly polarized (LP) microstrip patch elements in sequence. Since the conventional series‐parallel feed network is not conducive to the miniaturization of the array, a corresponding simplified feed network is designed to realize the four‐way equal power division and sequential 90° phase shift. With this feed network, the impedance bandwidth (IBW) of the CP array is greatly improved compared with that of the LP element, while maintaining a miniaturized size. Then, parasitic patches are introduced to enhance the axial ratio bandwidth (ARBW). A prototype of this antenna is fabricated and tested. The size of proposed antenna is 0.93λ₀ × 0.93λ₀ × 0.017λ₀ (λ₀ denotes the space wavelength corresponding to the center frequency 10.4 GHz). The measured 10‐dB IBW and 3‐dB ARBW are 13.6% (9.8‐11.23 GHz), 11.2% (9.9‐11.07 GHz) respectively, and peak gain in the overlapping band is 9.8 dBi.     

A compact dual band short ended metamaterial antenna with extended bandwidth

A compact dual‐band CPW–fed metamaterial inspired antenna using Composite Right/Left Handed (CRLH) resonant approach is presented in this article. The antenna is designed such that it can be operated in series resonant mode where resonance behavior is characterized by series LC parameters. Proposed antenna comprises two annular ring resonators connected with the signal patch intended to excite the higher order modes. This results extension of second band from 51.4% (f_c = 6.92 GHz) to 69.2% (f_c = 7.35 GHz). In addition to that proposed antenna shows compact nature with an electrical size of 0.14 λ₀ × 0.21 λ0 × 0.01 λ₀ at f₀ = 2.18 GHz. The antenna is operating over 2.14–2.23 GHz, 4.81–9.90 GHz with simulated peak gain of 0.66 and 4.44 dB, respectively. Simulated radiation efficiencies of proposed antenna are 69.8 and 94.1% throughout first and second band, respectively. To examine the resonance and radiation characteristics prototype is fabricated and measured. Observed experimental results are in good agreement with those simulated one. These characteristics makes this antenna is a good candidate for modern wireless communication systems such as Bluetooth, WLAN/Wi‐Fi band. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:435–441, 2016.     

A miniaturized circularly polarized multi‐dipole antenna with wide axial‐ratio beamwidth via loading loop resonators

A miniaturized, loop resonators (LRs)‐loaded, circularly polarized (CP) multi‐dipole antenna with wide axial‐ratio (AR) beamwidth is proposed and demonstrated in this article. The radiator of this CP antenna consists of two pairs of parallel dipoles loaded with four LRs at their corners. By increasing the length of the LR, or decreasing the coupling space between the dipole and the LR, the effective length of the dipole can be lengthened significantly and thus the working frequency can be reduced without increasing the whole aperture size. As a result, a miniaturized radiator structure is completed. A feeding network consisting of a T‐shaped coupling feeding structure and four coplanar striplines having different lengths are specially designed to feed these dipoles with approximately the same magnitude and 90° phase quadrature. What is more, a cavity reflector is employed to achieve a unidirectional radiation with wide axial‐ratio beamwidth. The radiator of the proposed CP antenna has a small aperture size of only 0.34λ₀ × 0.34λ₀, where λ₀ is the free space wavelength at the working frequency. Measured results are in a good agreement with the corresponding simulated counterparts. Especially, the experimental results show that the antenna has achieved a wide AR beamwidth of 182° and 174° at the center frequency in the xoz and yoz planes, respectively.     

Low profile antenna based on a fractal shaped metasurface for public safety applications

In this article, design and analysis of a fractal shaped metasurface (FSMS) antenna for public safety applications is presented. It comprises of two layers, upper layer and lower layer. The upper layer has the metasurface (MS) and lower layer has the fractal inspired monopole antenna. MS is made up of Sierpinski Knopp fractal shaped unit cell, which is arranged in 4 × 6 layout to achieve miniaturization. Ansys Electronic Desktop tool is utilized for analyzing the performance of the MS antenna. The projected FSMS antenna is fabricated using FR4 dielectric material and experimented with the help of an anechoic chamber and Vector Network Analyzer (VNA). Results show that the FSMS antenna exhibits a bandwidth of 200 MHz and a gain of 1.56 dBi at 4.89 GHz. The results obtained in simulation and measurement are in good agreement. Consequently, the proposed antenna with a low profile of 0.43λ₀ × 0.43λ₀ × 0.03λ₀, where λ₀ is the free space wavelength at 4.89 GHz is well fit for public safety applications.     

Wideband and compact horizontally polarized omnidirectional antenna using composite dipole elements

A wideband horizontally polarized (HP) omnidirectional antenna is constructed and experimented in this article. The antenna consists of four composite dipoles forming a circular array in the azimuth plane and four pairs of parallel strip lines as impedance transformer networks. Two kinds of dipoles compose the composite dipole to achieve a wideband operation. By utilizing the composite dipole, four resonances can be simultaneously excited and manipulated to increase the bandwidth. A prototype is manufactured to validate the method. The dimensions of the antenna are just 0.62λ₀ × 0.62λ₀ × 0.03λ₀ (λ₀ is the free‐space wavelength at center frequency). The measured results show that the presented antenna has a impedance bandwidth of 58.6% (1.63–2.98 GHz) for VSWR ≤2. The gain variations are less than 0.6 dB at the azimuth plane in the operating band. Meanwhile, the cross‐polarization is less than 20 dB and the peak gain reaches 1.7 dBi among in the band. These advantages of the antenna make it suitable for 4G mobile communication applications.     

A compact monopolar patch antenna with bandwidth‐enhancement under dual‐mode resonance

A compact monopolar microstrip patch antenna (MPA) with enhanced‐bandwidth is proposed. In order to achieve the miniaturized patch, the zeroth‐order mode of the MPA instead of its higher‐order modes is employed at first by loading the shorting pin around the center of the patch. After that, a L‐shaped microstrip line with a shorting pin is introduced at the periphery of the patch radiator to excite an additional non‐radiative mode for bandwidth enhancement. In final, the proposed MPA is fabricated and measured. The results illustrate that the antenna generates an enhanced‐bandwidth of about 4.1% ranging from 2.39 to 2.49 GHz, which is significantly larger than that of the traditional MPA around 1%. Meanwhile, the dimensions of the radiating patch are obviously decreased down due to the employment of zeroth‐order mode, which are kept as small as about 0.17 λ₀ × 0.22 λ₀ × 0.026 λ₀ (λ₀ is the free‐space wavelength).     

Millimeter‐wave antenna with wide‐scan angle radiation characteristics for MIMO applications

A three‐element quasi Yagi‐Uda antenna array with printed metamaterial surface generated from the array of uniplanar capacitively loaded loop (CLL) unit‐cells printed on the substrate operating in the band 25‐30 GHz is proposed. The metamaterial surface is configured to provide a high‐refractive index to tilt the electromagnetic (EM) beam from the two dipole antennas placed opposite to each other. The metamaterial region focuses the rays from the dipole antenna and hence increases the gain of the individual antennas by about 5 dBi. The antenna elements are printed on a 10 mil substrate with a center to center separation of about 0.5 λ ₀ at 28 GHz. The three‐element antenna covers 25‐30 GHz band with measured return loss of 10 dB and isolation greater than 15 dB between all the three ports. The measured gain of about 11 dBi is achieved for all the antenna elements. The three antenna elements radiate in three different directions and cover a radiation scan angle of 64°.     

Novel ultra‐compact two‐dimensional waveguide‐based metasurface for electromagnetic coupling reduction of microstrip antenna array

A novel ultracompact two‐dimensional (2D) waveguide‐based metasurface is proposed herein and applied for the first time to reduce mutual coupling in antenna array for multiple‐input multiple‐output applications. The unit cell of the proposed 2D waveguide‐based metasurface is ultracompact (8.6 mm × 4.8 mm, equal to λ₀/14.2 × λ₀/25.5) mainly due to the symmetrical spiral lines etched on the ground. The metasurface exhibits a bandgap with two transmission zeros attributing to the negative permeability in the vicinity of magnetic resonance and the negative permittivity in the vicinity of electric resonance. Taking advantage of these two features, a microstrip antenna array is then designed, fabricated, and measured by embedding an 8 × 1 array of the well‐engineered 2D waveguide‐based metasurface elements between two closely spaced (9.2 mm, equal to λ₀/13.3) H‐plane coupled rectangular patches. There is good agreement between the simulated and measured results, indicating that the metasurface effectively reduces antenna mutual coupling by more than 11.18 dB and improves forward gain. The proposed compact structure has one of the highest reported decoupling efficiencies among similar periodic structures with comparable dimensions. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:789–794, 2015.     

Metamaterial‐based antennas for integration in UWB transceivers and portable microwave handsets

Two planar antennas based on metamaterial unit‐cells are designed, fabricated, and tested. The unit‐cell configuration consists of H‐shaped or T‐shaped slits and a grounded spiral. The slits essentially behave as series left‐handed capacitance and the spiral as a shunt left‐handed inductance. The unit‐cell was modeled and optimized using commercial 3D full‐wave electromagnetic simulation tools. Both antennas employ two unit‐cells, which are constructed on the Rogers RO4003 substrate with thickness of 0.8 mm and ε_r = 3.38. The size of H‐shaped and T‐shaped unit cell antennas are 0.06λ₀ × 0.02λ₀ × 0.003λ₀ and 0.05λ₀ × 0.02λ₀ × 0.002λ₀, respectively, where λ₀ is the free–space wavelength. The measurements confirm the H–shaped and T–shaped unit‐cell antennas operate across 1.2–6.7 GHz and 1.1–6.85 GHz, respectively, for voltage standing wave ratio (VSWR) < 2, which correspond to fractional bandwidth of ～140% and ～ 145%, respectively. The H‐shaped unit‐cell antenna has gain and efficiency of 2–6.8 dBi and 50–86%, respectively, over its operational range. The T‐shaped unit‐cell antenna exhibits gain and efficiency of 2–7.1 dBi and 48–91%, respectively. The proposed antennas have specifications applicable for integration in UWB wireless communication systems and microwave portable devices. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:88–96, 2016.     

Wideband high aperture efficiency antennas with beam switching for mmWave 5G base stations

A compact metamaterial inspired sub‐wavelength unit cells are integrated into wideband Vivaldi antenna. A high gain Vivaldi antenna with 50% impedance bandwidth is proposed. The dimensions of the antenna are 1.55 λ₀ × 3.2 λ₀ at 28 GHz. Gain enhancement of 3‐dB achieved by placing metamaterial unit cells in the aperture of the antenna. These unit cells aid in phase correction of the antenna. The 1‐dB gain bandwidth of antenna is 42% with a peak gain of 12.5 dBi indicating high pattern integrity. Corrugations of varying length are introduced in the ground plane to improve front‐to‐back ratio without altering the input impedance bandwidth. The aperture efficiency of the metamaterial loaded Vivaldi antenna is 78% at 28 GHz. The proposed element is used in a stacked module to achieve wide angular coverage of 120°.     

Compact broadband circularly polarized slot‐patch antenna array

A simple design of circularly polarized slot‐patch antenna array with broadband operation and compact size is presented in this article. The antenna element consists of a circular slot and a semicircular patch, which are etched on both sides of a substrate. For the gain and axial ratio (AR) bandwidth enhancement, its array antennas are implemented in a 2 × 2 arrangement and fed by a sequential‐phase feeding network. The final 2 × 2 antenna array prototype with compact lateral dimension of 0.8λ_L × 0.8λ_L (λ_L is the lowest frequency within AR bandwidth) yielded a measured impedance bandwidth of 103.83% (2.76‐8.72 GHz) and a measured AR bandwidth of 94.62% (2.45‐6.85 GHz). The peak gain values within the AR bandwidth are from 2.85 to 8.71 dBi. A good agreement between the simulated and measured results is achieved. This antenna array is suitable for multiservice wireless systems covering WiMAX, WLAN and C‐band applications such as satellite communications.     

A beam scanning Fabry–Pérot cavity antenna for millimeter‐wave applications

A beam scanning Fabry‐Pérot cavity antenna (FPCA) for 28 GHz‐band is presented in this article. The proposed antenna consists of a slot‐fed patch antenna and several layers of perforated superstrates with different dielectric constant. The beam of the antenna can be controlled by moving the superstrate over the antenna. By increasing the offset between the feeding antenna and the superstrate, a larger tilt angle can be obtained. The size of the antenna is 0.95λ₀ × 0.95λ₀ × 0.48λ₀ at 28.5 GHz. The results show the proposed antenna achieves an impedance bandwidth (S₁₁ < ‐10 dB) of 10.5% (27.2‐30.2 GHz), and the beam can be scanned from 0° to 14° in the yoz‐plane with the offset changed from 0 mm to 2 mm. The gain of the antenna is enhanced by 5 dBi in comparison with the feeding antenna without the superstrate, which ranges from 10.91 to 11.53 dBi with the different offset. The proposed antenna is fabricated and shows a good agreement with simulated result.     

New Compact antenna based on simplified CRLH‐TL for UWB wireless communication systems

This letter presents the experimental results of a novel planar antenna design which is synthesized using simplified composite left/right‐handed transmission‐line (SCRLH‐TL), which is a version of a conventional composite left/right handed‐transmission‐lines (CRLH‐TL), however, with the omission of shunt‐inductance in the unit‐cell. SCRLH‐TL exhibits a right‐handed response with nonlinear dispersion properties and a smooth Bloch‐impedance distribution. Arranged within the inner slot of the antenna are three smaller rectangular patch radiators. Each patch radiator is embedded with an E‐shaped notch, and located in the antenna conductor is a larger E‐shaped notch next to the 50‐Ω termination. The E‐shaped notches constitute SCRLH‐TL property. The gap in the slot between the smaller patches and the conductor next to the larger E‐shaped notch determines the impedance bandwidth of the antenna. The dimensions of the smaller patches determine the radiation characteristics of the antenna. The antenna is excited using a conductor‐backed coplanar waveguide transmission‐line. The antenna covers a bandwidth of 7.3 GHz between 0.7 GHz and 8GHz, which corresponds to 167.81%. In this band, the antenna resonates at 4.75 GHz and 7 GHz; the gain and radiation efficiency at these frequencies are 4 dBi—80% and 3.6 dBi—73%, respectively. The antenna's performance was validated through measurement. The antenna has dimensions of 0.0504λ₀ × 0.0462λ₀ × 0.0018λ₀, where λ₀ is free‐space wavelength at 700 MHz. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:217–225, 2016.     

Triple band omnidirectional miniaturized metamaterial inspired antenna using flipped rectangular stub for LTE,WiMAX, and WLAN applications

In this article, a miniaturized metamaterial (MTM) inspired antenna with triple band characteristics is presented for LTE/WLAN/WiMAX applications. The antenna mainly consists of a square shaped split ring resonator (SRR) with rectangular stub connected in the outward direction. Due to inward flipping of the same rectangular stub leads to 20% antenna miniaturization without degrading the resonance behavior. The SRR produces first and second band, while the third band is enhanced due to flipping of inward stub and addition of rectangular type slot in the partial ground plane. The antenna exhibits tri‐band characteristics with each bands centered at 2.23, 3.65, and 5.13 GHz, having ?10 dB impedance bandwidth of 9.42%, 12.88% and 15.34% for the first, second, and third band, respectively. The antenna has a footprint size as low as 0.16 λ₀ × 0.18 λ₀ × 0.012 λ₀ corresponding to 2.23 GHz with a measured gain of 2.22, 2.31, and 1.98 dBi., and measured radiation efficiency of 70%, 72.75% and 82.57% in the three bands, respectively. The prototype of the antenna is fabricated and simulated results are verified through measurements.     

Broadband and high-aperture-efficiency metasurface antenna using multi-mode radiator

A high-aperture efficiency and broadband metasurface antenna array with multi-mode radiator is put forward in this article. The abnormal slot is etched at the center of the ground plane and fed to the antenna via a microstrip line. Resonant along the slot line, and in the electric field, two short horizontal lines with uniform gaps are symmetrically added near zero. Additional radiation modes have been introduced. Then, broadband slot antenna with two resonances is obtained by combining full-wavelengths provided by the first slot. Working bandwidth increased from 7.6% to 21.1%. By introducing a ring slot, the antenna gain is increased by 0.9 dBi. At the same time, the aperture efficiency is modified by 12.9%. A 2 × 2 array was made to verify the design, with an overall size of 2.01λ₀× 2.01λ₀ × 0.07λ₀. The simulation and measurement results show that the operating bandwidth is 38.9% with maximum gain is 15.8 dBi.     

Broadband compact CPW‐fed metasurface antenna for SAR‐based portable imaging system

A broadband and compact coplanar waveguide (CPW) coupled‐fed metasurface (MS)‐based antenna for C‐band synthetic aperture radar (SAR) imaging application is proposed in this article, which is consisted of 16 uniform periodic square patches performed as radiators. The CPW feeding structure gives two following functions: (1) It excites an aperture coupling slot structure underneath the center of MS patch array. (2) It acts as a ground plane for the metasurface patch units. Different slots were investigated and eventually an hourglass‐shaped slot is applied to enhance bandwidth for imaging applications. A prototype with a dimension of 60 × 60 × 1.524 mm³ (1.1λ₀ × 1.1λ₀ × 0.03λ₀) operating at the center frequency 5.5 GHz (f₀) has been fabricated and measured to verify the design principle. This antenna has a measured impedance bandwidth of 12.4% from 5.14 to 5.82 GHz, a peak gain of 9.2 dBi and averaged gain of 7.2 dBi at broadside radiation. Microwave imaging experiments using the proposed antenna have been carried out and a good performance is achieved.