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Antennas with complex radiation characteristics can enhance the adaptability of radiofrequency systems in complex electromagnetic environments. However, The realization of complex targets is extremely challenging for conventional antenna design methods. It is difficult to find a suitable initial topology of the antenna with complex radiation characteristics. Therefore, in this paper, topology optimization is used to explore the initial structure with complex radiation properties. A two‐dimensional lossy thin layer model based on the transitional boundary condition is constructed, and target field functions for complex radiation are proposed. To verify the effectiveness of the algorithm, a high gain antenna with 10.2 dBi is realized, which has the highest aperture efficiency compared with the literature in similar directions. Then, for more complex targets, the radiation patterns of arbitrary direction null, arbitrary direction beam, and equal‐amplitude dual beam are realized, respectively. The topology optimization algorithm provides a new approach for the design of complex multitarget antennas. [ABSTRACT FROM AUTHOR]

This letter presents a design of a high gain uniplanar end‐fire electrically small antenna. The design starts from an equivalent antenna of an antenna array with two half‐wavelength dipoles, which consists of two linear strips and produces the end‐fire unidirectional radiation. Two U‐shaped strips are utilized to replace the linear strips, which makes the antenna compact. In addition, a spilt‐ring resonator is loaded to make the realized gain of the electrically small antenna increase by ~2 dB. An antenna prototype is fabricated and measured. The measurements reveal that the proposed antenna has a peak realized gain of 6.02 dBi and a front‐to‐back ratio of 12.71 dB at its resonance frequency of 747.8 MHz. Its size is only 0.254 λ0 × 0.184 λ0 × 0.0037 λ0, and ka = 0.984. The measured realized gain exceeds both the Harrington and Kildal–Best ka‐based upper limits. [ABSTRACT FROM AUTHOR]

In this paper, a fractal antenna is proposed for wideband application. It has a resonance frequency of 5 GHz, and has been designed using an FR4 substrate with a width and a length of 40 mm and patch with a width, length of 35.288 mm. The proposed antenna has been made with five iterations, and the result obtained multiband behavior and agrees with the various efficient wireless applications. In the proposed antenna, there are four bands response at frequencies 1.6, 2.9,5.2, and 6 GHz, and bandwidth percentage are 4.56%, 7.89%, 12.13%, and 4.6%. It also covers application in 1.5–1.7, 2.8–3.1, 4.8–5.4, and 5.9–6.2 GHz. The gain and the directivity of the proposed antenna is measured as 15.885 dBi greater than other fractal antennas to date, and 7.422 dBi respectively. The proposed antenna has been implemented successfully using IE3D and the result has been tested successfully using a key sight vector analyzer. [ABSTRACT FROM AUTHOR]

This article proposes a high‐gain quasi‐Yagi antenna using nested metaresonator structures with a systematic design approach. The nested metaresonators are used as a director element instead of conventional strip directors. The gain enhancement of the proposed antenna is based on strong electromagnetic coupling between the driver and metaresonator director elements. The proposed antenna has a gain of 7.6–9 dBi with a bandwidth of 8.6% between 2.43 and 2.65 GHz (S11≤−10 ${S}_{11}\le -10$ dB). It achieves a maximum gain increase of 4 dBi compared to the conventional quasi‐Yagi antenna and 2 dBi compared to the four‐director quasi‐Yagi antenna. The proposed antenna can be used for wireless communication applications that require high gain. [ABSTRACT FROM AUTHOR]

In this article, a narrow and a wide band high gain antenna with improved front to back ratio using highly reflecting surface are proposed. A highly reflecting compact ultrathin metasurface (MS) of thickness 0.0134 λ with >90% reflection band of 1.42 GHz from 4.55 to 5.97 GHz is designed. The open air field Fabry–Perot cavity resonator antenna is designed by placing this MS over a microstrip patch antenna radiator first and next on standard wide band C‐band wave guide port radiator at an optimum height to get narrow and wide enhanced gain band width, respectively. The proposed antennas are fabricated and measured experimentally. A low profile narrow band FPC antenna with measured broad side gain enhancement of 8.54 dB having maximum measured gain of 16.5 dBi at 5.3 GHz is designed first. Next, a wide band FPC antenna having broad side measured enhanced gain band width of >1 GHz from 4.75 GHz to about 6.00 GHz with maximum gain enhancement of 8.32 dB with maximum measured gain of 17.85 dBi at 5.30 GHz is observed. A wide improved front to back ratio (FBR) band of 1 GHz with maximum FBR of 39.5 dB at 5.30 GHz is presented. This antenna can be used for 5G long range services. [ABSTRACT FROM AUTHOR]

This article proposed a dual band dipole antenna with a curved reflector that can be used in the wireless local area network (WLAN). The shape of the proposed antenna is similar to quasi‐yagi antenna as it combines the dipole antenna with folded dipole.When designing the antenna with a reflector using the standard antenna reflector uses a 2.45 GHz band, and the size of the band used here was relatively large at 5.5 GHz. As a result, a null occurred in the main lobe of the radiation pattern at the 5.5 GHz band, which ultimately reduced the gain. To solve this problem, a parabolic curved reflector was applied in this study. The designed antenna satisfied the condition of return loss smaller than −10 dB at the 2.45 GHz and 5.5 GHz WLAN bands. The gain of the antenna was larger than 8 dBi at 2.45 GHz and at 5.5 GHz. [ABSTRACT FROM AUTHOR]

Abstract: This article presents electrically steerable passive array radiator inspired high gain, mechanical beam steering configuration, operating in the wide frequency band with frequency dependent radiation characteristics. Monopole antenna in combination with twelve parasitic elements is fed through impedance matching network and offered impedance bandwidth of 32.0% and approximate gain of 9.0 dBi. [ABSTRACT FROM AUTHOR]

Abstract: This letter presents and analyses a novel parasitic U‐slot patch array antenna, designed by combining the characteristic of U‐slot patch antenna and the characteristic of parasitically coupled antenna elements. Characteristic mode analysis is performed on the novel antenna to reveal the potential of the new radiating structure. [ABSTRACT FROM AUTHOR]

Two frequency selective surfaces (FSSs), each with 12 patch elements; have been exploited to enhance the gain of an extended size microstrip patch antenna up to 18.5 dBi at X-band (8-12 GHz) frequencies. The antenna gain is further improved to 19.2 dBi just by adding two reflectors across E-field radiation. The concept of gain enhancement is first examined mathematically and them it is analysed with numerical method based on CST microwave studio simulations. Both of the proposed high gain antennas have been fabricated and tested at around 10 GHz frequencies. The measured and simulation results showed a good agreement. [ABSTRACT FROM AUTHOR]

ABSTRACT An antipodal Vivaldi antenna (AVA) with ultra-wideband performance is designed for microwave imaging of construction materials and structures. A step-by-step procedure has been employed to design and optimize performance of the proposed antenna. First, conventional AVA (CAVA) is designed. Second, to extend low end of frequency band, the inner edges of the top and bottom radiators of the CAVA have been bent (referred to as AVA-B). Third, to enhance gain at lower frequencies, regular triangular slit is applied to the antenna (referred to as RTSAVA-B). The proposed RTSAVA-B operates at frequency range from 2 to 27 GHz. The proposed RTSAVA-B enhances gain up to 1.5-2 dB. Additionally, it has low cross-polarization < −15 dB at the entire frequency range and capable of improving front-to-back ratio over AVA-B. A prototype of the antenna is fabricated and employed for the imaging of concrete- based specimens. High-range resolution images and high penetration depth inside specimens are achieved. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1259-1264, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT A Q-band planar lens with four substrates separated by air gaps is investigated. The efficiency, gain, and back lobe level are improved by shifting the sizes of the cells with dual square slot loops on different substrates. Besides, the compensated phase of each compound cell which consists of the corresponding square slot loop cells distributed in the four substrates is calculated using an equivalent phase other than the phase at the center of the cell. Three hundred and sixty degree compensated phase can be achieved by changing the sizes of the outer and inner slot loops of the cell. The side length of the lens is 144 mm or 20 wavelengths. The air gap between the substrates is 2 mm. The number of cells is 2025 or 45 by 45. The lens is fed by a linear polarized horn antenna with a gain of 15 dBi approximately. The measured peak gain is more than 33 dBi at 44 GHz, and the half power beam width of E-plane and H-plane are about 2.9°. The lens could cover from 43 to 47 GHz or more than 9% bandwidth. The side lobe level is under −20 dB, and the measured front-back-ratio is better than 20 dB. The measured data are in agreement with the simulated results. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2322-2330, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT Ultrawide band (UWB) nondestructive testing and evaluation techniques can provide the detection of defects and damages in construction materials and members. The development of UWB antennas with proper dimensions and high performance for these systems is one of the major challenges. In this letter, an antipodal Vivaldi antenna (AVA) has been developed to be used in UWB techniques for nondestructive detection of cracks in concrete members. To obtain a desirable antenna performance including the wider impedance bandwidth, the higher directivity, and higher front-to-back ratio rectangular-shaped slits (RSS) and a half-circular-shaped lens (HCSL) have been added in the design of a conventional tapered slot AVA. A parametric study on the dimensions of the slits is provided to optimize performance and size of the proposed antenna. The optimum size of the proposed antenna is 40 × 80 × 0.508 mm3, and it operates over the frequency range from 3.4-40 GHz. It is shown that the RSS increase impedance bandwidth especially at the lower frequencies. Directivity of the proposed antenna at higher frequencies has been increased by the HCSL. The feasibility of the proposed antenna for nondestructive evaluation of concrete members is demonstrated by investigation into its performance with concrete specimens possessing an air-gap inside a concrete specimen. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1573-1578, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT A millimeter-wave antipodal Fermi tapered slot antenna configured with a new corrugation is presented. The corrugation has a sine wave profile for improved design flexibility and radiation performance. The effect of the sine-corrugation parameters is presented in detail, and the optimized design is compared with the measured prototype. The antenna is fabricated using a low-cost printed circuit board process. The measured bandwidth of the antenna covers a wide band (55-65 GHz) with a measured gain of 18.75 dB at 60 GHz. With these features, the antenna is suitable for short-range wireless communications and imaging applications . © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:6-9, 2015 [ABSTRACT FROM AUTHOR]

In this letter, we report the design, fabrication, and measurement of a metamaterial-based Fabry-Perot (F-P) resonator antenna. The F-P resonator antenna is constructed of a fishnet superstrate and a printed patch antenna based on a mushroom-like electromagnetic bandgap substrate. Simulated and measured results show that the proposed F-P resonator antenna achieves an ultra-low profile as well as a high-gain enhancement. The thickness of the metamaterial-based F-P resonator is only λ/125. Compared to the traditional superstrate patch antenna, the forward gain of the new metamaterial F-P resonator antenna is enhanced and the back radiation is suppressed effectively. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2620-2623, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27155 [ABSTRACT FROM AUTHOR]

This letter presents a compact double-flip trapezium monopole antenna (D-FTMA) for ultra wideband (UWB) application. A significant impedance bandwidth improvement of 7:1 can be achieved at a centre frequency of 7.96 GHz compared to the conventional antenna when the dual bevel technique is deployed near the ground plane. The proposed compact antenna consists of 22 mm × 25.8 mm radiating element and 64 mm × 40 mm rectangular ground plane and fed by a 50 Ω coaxial connector. Furthermore, the low cost D-FTMA is fabricated on the FR4-PCB. The antenna agrees between simulation and measurement of return loss, which covers the UWB frequency range (3.1-10.6 GHz). The D-FTMA has a very constant and high relative gain at particular frequency up to 6 dBi. Moreover, the D-FTMA is observably capable in producing divisive radiation patterns with linear polarization at four different frequencies: 4, 6, 8, and 10 GHz. The parameter optimization analysis has been studied using CST Microwave Studio. The presented simulated results are supported by the measurement as well. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1882-1886, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26960 [ABSTRACT FROM AUTHOR]

This article proposes a low cost efficient high gain antenna using array of parasitic patches for wireless applications. The antenna structure consists of a microstrip antenna which feeds an array of square parasitic patches fabricated on a low cost FR4 superstrate. The patches on superstrate are suspended in air at λ0/2. The structure with 5 × 5 array of square parasitic patches is designed, fabricated, and tested. The measured voltage standing wave ratio (VSWR) is <2 over 5.725–5.875 GHz frequency band. The antenna with a single square patch provides a gain of 12.6 dB, whereas the antenna with 5 × 5 array of square parasitic patches provides a gain of 18.0 dB with 92% efficiency, SLL of -18.4 dB and front to back lobe ratio of more than 20 dB. The proposed structure can be packaged inside an application platform. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 733–739, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24156 [ABSTRACT FROM AUTHOR]