Analysis and design of a novel hat feed with narrow beamwidth for the Fresnel zone plate antenna

Conventional hat feeds have the best performance in very deep reflector antennas because of their wide beamwidth. They also have the advantage of being self‐supported. The disadvantage of this type of feed is its wide beamwidth. To solve this problem, a new hat feed is proposed that can be used as prime‐focus feed for Fresnel zone plate antennas. The novel design, called parabolic hat feed is achieved by appropriate shaping of the hat feed profile. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Highly‐isolated unidirectional multi‐slot‐antenna systems for enhanced MIMO performance

In this article, an improved approach is presented for designing Electromagnetic Bandgap (EBG) reflectors for slot antennas by using a waveguide aperture source in simulating reflection phase test. In this manner the nonplanar nature of the near field at the location of the source, that is, antenna, as well as its loading effect on the reflector are incorporated in the design of a mushroom‐type EBG structure operating at 5.3 GHz. This EBG design performs as an efficient reflector in normal wave incidence while suppressing the substrate‐bound modes propagating in the azimuthal directions. The designed EBG reflector is employed in several two‐slot‐antenna structures to establish excellent antenna isolation of at least 25 dB and single antenna gain of 5 dB at 5.3 GHz in each scenario. To further reduce coupling, the antennas are reoriented to benefit from polarization mismatch and radiation pattern nulls, resulting in isolation values of above 40 dB for antennas spaced one wavelength apart. The two‐antenna structures are also characterized for MIMO performance in a reverberation chamber and demonstrate an impressive diversity gain of better than 8 dB in a rich multipath environment. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:289–297, 2014.     

Coaxial cavity waveguide antennas excited by stacked circular microstrip patches for use as prime‐focus reflector feeds

A coaxial cavity antenna excited by a stacked circular microstrip antenna is investigated as a feed for prime‐focus parabolic reflector antennas. The radiation pattern of the proposed cavity‐backed antenna is saddle shaped, which widens the ?10 dB beamwidths and increases the reflector efficiency especially for deep reflectors with small focal length‐to‐diameter ratios. With a single‐probe feed, the co‐polar radiation pattern is slightly asymmetric in the E‐plane, but is made symmetric by a differential feeding technique, using two probes. The impedance bandwidth of the proposed feed antenna is 20%. The antenna was fabricated and tested, and it exhibited good agreement between simulation and measurement results. The gain factor of the feed was also studied with a circular‐symmetric reflector and provided a gain factor of 79% at f/D = 0.375. This type of feed can be used as an alternative to conventional horn or waveguide feeds, where reduced size and light‐weight are desirable with added advantage of easy integration with electronics.     

Investigation of ultra‐wideband Bowtie antennas for phased array feed application

In this article, two new ultra‐wideband (UWB) dual‐polarized Bowtie antennas are investigated as the elements for a phased array feed for reflectors. In addition to its UWB impedance matching characteristic, the Bowtie antennas have stable large beam‐width and a low cross‐polar level over a wide frequency band with a compact size, which is an essence for phased array applications. The simulated and measured results state a low ohmic loss, good impedance matching (S₁₁ below ?15 dB) and good radiation performance, with a simple structure for easy manufacturing. The proposed antennas can be good candidates for phased array feed (PAF) in FAST and the SKA (square kilometer array) pathfinder PHAROS2 projects, and massive MIMO antennas in wireless communication systems.     

Polarization‐independent and electrically tunable liquid‐crystal Fresnel lenses based on photoalignment in dye‐doped liquid crystals

Abstract— This work demonstrates polarization‐independent and electrically tunable liquid‐crystal (LC) Fresnel lenses based on photoalignment in dye‐doped liquid crystals (DDLCs). The LC alignments in the adjacent odd and even zones of the LC Fresnel lens are orthogonally hybrid alignments. Those are generated by surface treatment of homeotropic and homogeneous alignment layers, and the dye‐adsorption layer onto the UV‐cured surface‐relief Fresnel zone plate. The maximum focusing efficiency (～34.14%) of the fabricated LC Fresnel lens by applying a suitable AC voltage is close to the maximal theoretical focusing efficiency of a binary phase LC Fresnel lens (～40.5%). Additionally, the focusing efficiency is polarization‐independent and electrically tunable.     

A novel microstrip Yagi antenna with an improved end‐fire radiation pattern under operation of the TM20 mode

In this article, a novel microstrip Yagi antenna under operation of the TM₂₀ mode is proposed to obtain an enhanced end‐fire radiation pattern. First, a two‐element microstrip Yagi antenna is theoretically analyzed under different dimensions of the parasitic element. The results demonstrate that the parasitic element can act as either a reflector or director when its size is smaller or larger than the size of the driven patch, respectively. After that, the equivalent magnetic currents and electric fields of the two‐element antenna are formed to provide physical insight into the working principle and radiation performance of the antenna. With these arrangements, an array of four patch elements including one driver, one director, and two reflectors are selected for the antenna design. Unlike the traditional microstrip Yagi operating with the TM₁₀ mode, all the patch elements involved in this design resonate with the TM₂₀ mode, thus effectively enhancing the tilted beam angle toward the desired end‐fire direction on an infinite ground. Finally, the proposed antenna is designed, fabricated and tested. The measured results show that its impedance bandwidth is maintained at approximately 3.3%, ranging from 4.76 to 4.92 GHz. Most importantly, the maximum deviation angle of the antenna is significantly improved to approximately 58° from the broadside direction at the center frequency (4.84 GHz), while maintaining a low profile and compact size.     

Fast Inverse Reflector Design (FIRD)

This paper presents a new inverse reflector design method using a GPU‐based computation of outgoing light distribution from reflectors. We propose a fast method to obtain the outgoing light distribution of a parametrized reflector, and then compare it with the desired illumination. The new method works completely in the GPU. We trace millions of rays using a hierarchical height‐field representation of the reflector. Multiple reflections are taken into account. The parameters that define the reflector shape are optimized in an iterative procedure in order for the resulting light distribution to be as close as possible to the desired, user‐provided one. We show that our method can calculate reflector lighting at least one order of magnitude faster than previous methods, even with millions of rays, complex geometries and light sources.     

Matched feeds for offset reflector antenna using circular microstrip patch antenna

This article presents two designs of matched feed for an offset fed reflector. Circular microstrip patch antennas are used in the proposed designs. Both the matched feeds achieve conjugate field matching by generating TM₂₁ mode at an appropriate ratio to the fundamental TM₁₁ mode. The first matched feed generates the required dual mode field distributions using a dual layer stacked patch antenna. The second matched feed is a novel design using centered circular array with the central element generating the required TM₂₁ mode and the surrounding circular ring antenna elements operating in the TM₁₁ mode. Both the designs are studied analytically using cavity model and are implemented in High frequency System Simulator (HFSS) and Computer Simulation Technology (CST). The matched feed designs are investigated for an offset reflector with the projected diameter, D = 50λ, focal length, F = 30λ and clearance height, H = 5λ operating at 20 GHz. The secondary field patterns of the offset reflector fed by the matched feeds are evaluated numerically using a MATLAB code based on geometrical optics technique and verified by HFSS‐PO results. Offset reflector performance such as cross‐polarization, ?30 dB cross‐polar bandwidth, gain, and first side‐lobe level are investigated for the both matched feeds.     

Fundamental analysis of harmonic reflection in microwave frequency triplers

Harmonic reflection is a vital technique for microwave frequency multiplier design, including the design of frequency triplers. In this article, principles of frequency tripler design with reflector networks are analyzed via harmonic‐balance simulation of an idealized MESFET/HEMT transistor model. The use of an idealized model allows fundamental mechanisms of 3f0 output power and conversion‐gain improvement via reflector networks to be characterized. Several reflector configurations are analyzed including: a 3f0 input reflector; a f0 output reflector; and a combination of both reflectors. The effects of reflector offset length on tripler performance are analyzed in terms of conversion gain, output power, reflected power, and time‐domain waveforms. As a result of this work, a greater understanding of harmonic‐reflector networks and their importance to tripler design is achieved. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Pattern squint elimination for quad‐ridged conical and pyramidal horn antennas using bended probes

This article describes a new technique for pattern squint elimination of quad‐ridged conical and pyramidal horn antennas by introducing bended coaxial probes. Because of the phase difference and mutual coupling between vertical and horizontal polarizations, the radiation patterns of the conventional quad‐ridged conical and pyramidal horn antennas squint over a wide bandwidth. The proposed technique substantially reduces the phase difference and coupling between the two probes, so a significant improvement in the radiation patterns over the frequency band of 8–18 GHz can be achieved. The designed modified horn antennas are most suitable as a feed element in reflectors of radar systems and EMC applications. The proposed modified antennas have a voltage standing wave ratio (VSWR) less than 2.2 for the frequency range of 8–18 GHz. Moreover, the proposed antennas exhibit high gain, dual‐polarization performance, good isolation, low SLL, low back lobe, low cross polarization, and satisfactory far‐field radiation characteristics for the entire frequency band. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2010.     

A compact feed horn with wide‐distributed operating bands of Ku/Ka/W

This paper presents a design of a compact tri‐band feed horn for reflector, which has sufficient wide‐distributed operating bands at 14.5, 35, and 94 GHz. A single cavity is used to downsize and simplify the whole structure, replacing multiple transition sections, or dielectric rods. To maintain a good isolation, two 3‐order low‐pass filters are applied in the waveguide ports of Ku/Ka‐band respectively, meanwhile retaining a good coupling and minimal destruction on transmission modes. The prototype of the proposed tri‐band feed horn is fabricated and measured, showing an adoptable candidate for multiband reflector antennas.     

声表面波传感器Q值改善的理论与实验分析

用P矩阵方法分析带变迹叉指换能器(IDT)和倾斜金属反射栅的高Q值Y型声表面波(SAW)质量沉积传感器的通带纹波,并分别在振荡和非振荡模式下比较了这些传感器的通带纹波和Q值.分析了获得高Q值的原因.理论和实验结果表明:均匀孔径无反射栅的传感器旁瓣抑制为10dB,振荡模式下其Q值为5 289;通过孔径变迹设计,传感器的旁瓣抑制和Q值分别改善到25dB和8689;而对孔径变迹并加入倾斜反射栅的传感器,这两个参数提高到25dB和12477.非振荡模式下带反射栅的传感器比没有反射栅器件的通带纹波约低2dB.因此,变迹IDT和金属反射栅的应用是SAW质量传感器Q值的改善的两个重要因素.由于Q值改善,质量沉积灵敏度达到5.24 GHz·cm2/g     

Isolation enhancement between tightly spaced compact unidirectional patch‐antennas on multilayer EBG surfaces

In this article, ultracompact unidirectional patch antennas are used in different two‐antenna systems for biomedical applications at 5.2 GHz. Multilayer mushroom type electromagnetic bandgap (EBG) structures are designed as slow‐wave medium to reduce the size of the individual patch antennas to 0.1λ₀ by 0.18λ₀. Various techniques are investigated herein to improve antenna isolation for an enhanced Multiple‐Input Multiple‐Output (MIMO) performance. First, the coupling between 0.3λ₀‐spaced antennas is verified to occur dominantly through radiation and near‐field coupling between the patches rather than through substrate‐bound modes. Second, various configurations are proposed to suppress antenna coupling. These approaches include reorientation of the antennas and employment of parasitic radiators between the patches. A novel design is presented in which a unidirectional parasitic slot radiator on an EBG reflector is inserted between the antennas to decouple them. Measurement results confirm efficacy of these approaches in mitigating antenna coupling by more than 11 dB in the operating bandwidth of the antennas. The compact patch antennas maintain efficiency values of higher than 70%. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:30–38, 2015.     

Design of conical DRH antennas for K and Ka frequency bands

Two conical double‐ridged horn (DRH) antennas for K and Ka frequency bands are presented. Detailed simulation and experimental investigations are conducted to understand their behaviors and optimize for broadband operation. The designed antennas were fabricated with 0.01 mm accuracy and satisfactory agreement of computer simulations and experimental results was obtained. The designed conical DRH antennas have voltage standing wave ratio (VSWR) less than 2.1 and 2.2 for the frequency ranges of 18–26.5 GHz (K band) and 26.5–40 GHz (Ka band), respectively. Meanwhile, the proposed antennas exhibit low cross‐polarization, low sidelobe level, and simultaneously achieve slant polarization as well as symmetrical radiation patterns in the entire operating bandwidth. An exponential impedance tapering is used at the flare section of the horns. Moreover, a new cavity back with a conical structure is used to improve the VSWR. Numerous simulations via Ansoft HFSS and CST Microwave Studio CAD tools have been made to optimize the VSWR performance of the designed antennas. Simulation results show that the VSWR of the proposed antennas is sensitive to the probe spacing from the ridge edge and the cavity back structure. The designed conical DRH antennas are most suitable as a feed for the reflectors of radar systems and satellite applications. Results for VSWR, far‐field E‐plane and H‐plane radiation patterns, and gain of the designed antennas are presented and discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Fabrication of Fresnel zone plates with high aspect ratio by soft X-ray lithography

High focusing efficiency Fresnel zone plates for hard X-ray imaging is fabricated by electron beam lithography, soft X-ray lithography, and gold electroplating techniques. Using the electron beam lithography, Fresnel zone plates which has an outermost zone width of 100 nm and thickness of 250 nm has been fabricated. Fresnel zone plates with outermost zone width of 150 nm and thickness of 660 nm has been fabricated by using soft X-ray lithography.     

Fabrication of X-ray imaging zone plates by e-beam and X-ray lithography

X-ray imaging and microscopy techniques have been developed in worldwide due to their capabilities of large penetration power and high spatial resolution. Fresnel zone plates is considered to be one of the most convenient optic devices for X-ray imaging and microscopy system. The zone plates with aspect ratio of 7 and 13 have been fabricated by e-beam lithography combined with X-ray lithography in this paper. Firstly, the X-ray lithography mask of zone plates with outermost zone width of 100 nm was fabricated by e-beam lithography and gold electroplating techniques. Secondly, the zone plates with gold profile thickness of 700 and 1,300 nm were replicated by X-ray lithography and gold electroplating techniques. X-ray imaging and microscopy techniques were introduced to characterize the high-aspect-ratio zone plates’ inner structures. At the X-ray energy of 7.5 keV, the first-order focusing efficiency of zone plates with gold profile thickness of 700 nm is about 8.63%.     

声表面波传感器Q值改善的理论分析与实验结果

报道了带变迹叉指换能器（IDT）和倾斜金属反射栅的高Q值Y型声表面波（SAW）质量沉积传感器。用P矩阵方法分析了三种不同传感器的通带纹波。分别在振荡和非振荡模式下比较了这些传感器的通带纹波和Q值。分析了获得高Q值的原因。理论和实验结果表明：均匀孔径无反射栅的传感器旁瓣抑制为10dB，振荡模式下其Q值为5289；通过孔径变迹设计，传感器的旁瓣抑制和Q值分别改善到25dB和8689；而对孔径变迹并加入倾斜反射栅的传感器，这两个参数提高到25dB和12477。非振荡模式下带反射栅的传感器比没有反射栅器件的通带纹波约低2dB。因此，变迹IDT和金属反射栅的应用是SAW质量传感器Q值的改善的两个重要因素。由于Q值改善，质量沉积灵敏度达到5.24GHz?cm2/g     

Investigation of high extraction efficiency flip-chip GaN-based light-emitting diodes

In order to obtain higher light output power, the flip-chip structure is used. We studied the ratio of the light of GaN sides before and after fabricating metal reflector on p-GaN. The SiO₂/SiN _x dielectric film reflectors were deposited through plasma enhance chemical vapor deposition following the fabrication of metal reflector, and then the dielectric film reflectors on the electrodes were etched in order to expose the electrodes to the air. It is found that comparing with the flip-chip GaN-LED without dielectric film reflectors, light output power can be increased by as high as 10.2% after the deposition of 2 pairs of SiO₂/SiN _x dielectric film reflectors on GaN-LEDs, which cover the sidewalls and the areas without the metal reflector. This result indicates that the high reflector formed by multi-layer dielectric films is useful to enhance the light output power of GaN-based LED, which reflects light from step sidewalls and p-GaN without metal reflector to internal, and then light emits from the surface. Supported by the National Basic Research Program of China (Grant No. 2006CB604902), and the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality (Grant No. 05002015200504)     

高分辨率SAR辐射定标中两种角反射器响应测量方法的应用对比研究

利用角反射器进行SAR图像辐射定标是一种简单、实用、精度较高的绝对定标方法。其关键技术包括角反射器响应测量、天线方向图拟合和定标常数确定。针对机载分米级高分SAR影像定标问题,在同一场景中布设了30和10cm两组三面角反射器,依据雷达中心入射角估计值、均方根误差和变异系数等指标,分析了已有的两种角反射器响应测量方法,即峰值法和积分法的适用性,并提出了一种新的天线方向图拟合方法。最后给出了两种方法对高分辨率SAR辐射定标的适用性结论。     

Design of 4-element microstrip array of wideband reflector antenna with stable high gain characteristics

In this paper, three microstrip antennas with and without reflector are proposed with stable and high gain characteristics. The proposed antennas are simple to design and do not involve loading of any active elements on the patch or ground plane. The designed antennas cover the total frequency range of 10.5–44.5 GHz and operate well within the 5G communication frequency band of 27–30 GHz; consequently, making proposed antennas suitable for upcoming wireless technology. Furthermore, a 2 × 2 antenna array with phase diversity is proposed which offers an almost stable gain of about 14 dBi within the operating band. The proposed antennas are analyzed by finite element method based Ansys HFSS simulator. The fabricated prototypes of the optimized designs are made and simulated results are found in good agreement with the measured results.