Earticle

A novel metal-only reflectarray element with double split square ring slot laser cut into a metallic thick stainless steel plate is proposed in this paper. By using this unified slot structure, the dielectric substrate usually used in traditional reflectarray designs can be removed. The proposed technique can provide a more than 400° phase range with relatively smoother slope. In order to verify the phase data, a 25°-beam-steering metal-only reflectarray operating at 12.5 GHz is designed and simulated. A 1-dB gain bandwidth of 12% is achieved, which is slightly wider than that of reflectarray designs consisting of conventional patch elements. The proposed metal-only structure can better withstand the extreme outer space environment and effectively reduce the antenna cost.

Phase-only optimization of asymmetric multiple beams reflectarray with single feed is investigated in this paper. The conventional design approaches are first reviewed. Secondly, for design of asymmetric multiple beams reflectarray with arbitrary gain levels and beam directions, a general method based on invasive weed optimization is proposed. Then, practical considerations for applying the proposed method to design multiple beams reflectarray are talked over. For illustrating the effectiveness of the proposed method, several multiple beams design cases with different design requirements are optimized through this method, and the optimized results are analyzed through simulation approach based on array theory. The simulation results show that the optimized cases demonstrate the satisfactory multiple beams performance.

요약 리플렉트어레이 안테나는 반사경 안테나의 단점을 보완하여 대체할 새로운 형태의 안테나로 대두되고 있다. 하지만 반사판이 단층구조일 경우 대역폭이 매우 좁다는 단점이 있고, 대역폭을 넓히기 위하여 다층구조의 반사판을 사용할 경우 설계가 어렵고 제작 단가가 높아지게 된다. 본 논문에서는 이러한 단점들을 극복하기 위하여 단층구조를 사용하여 제작 단가를 낮추면서 협대역 특성을 극복할 수 있는 정사각형에 U자 모양 슬롯을 낸 패치를 이용하여 리플렉트어레이 안테나를 설계하였다. 제안된 리플렉트어레이 안테나는 12.5 GHz에서 55.5 %의 효율과 14 % 이상의 1 dB gain bandwidth 특성을 갖는다.

The microstrip reflectarray antenna is rapidly becoming an attractive alternative solution to the traditional parabolic reflector antenna. However, the bandwidth of the microstrip reflectarray using the single layer structure is very narrow. To obtain wide bandwidth characteristic, the microstrip reflectarray using the multi-layer structure has been used, but it has some disadvantages such as high cost and complicated design. In this paper, to obtain low cost and wide bandwidth, the microstrip reflectarray antenna composed of square patch with two U-slots using the single-layer structure is proposed. The proposed antenna demonstrate radiation efficiency closed to 55.5 % and 1 dB gain bandwidth over 14 % at 12.5 GHz.

As the important case of conformal arrays, conformal arrays on cylindrical surfaces have been widely used in radar and communication systems. This paper explores the chances of designing conformal reflectarray on cylindrical platform. An extended array theory method is proposed in this paper for analyzing the radiation patterns of cylindrical conformal reflectarray. The radiation characteristics of conformal reflectarray on convex and concave cylindrical surfaces are studied, and the performances of the two cases are compared with planar cases. It is shown that the cylindrical conformal reflectarray can be a good candidate of high gain antennas for applications where a slightly curved conformal platform is available.

In this paper a new cell is proposed for reflectarray antenna and is used to design the antenna to obtain to maximum gain and efficiency using phase synthesis in a frequency band of 11 GHz up to 11.7 GHz for different beam angles. The proposed cell is a double ring of hexagon which introduces multiple resonances which can provide more than 360 degrees phase variation by changing the loop size. Design method is based on phase-only algorithm where amplitude of the field on the reflectarray surface is forced by the feed. A 1.2 m reflectarray is designed for different beam directions. The results show maximum directivity of 42 dB and maximum efficiency of 73% for the required bandwidth. Focal length is 1.5 m which is set for maximum efficiency.

Reflectarray antenna with multiple simultaneous beams is a promising antenna candidate for the multiple beam applications. A comprehensive and systematic study on the design of single-feed multi-beam reflectarray antenna is presented in this paper. The traditional direct design method, called aperture field superposition method, is investigated first. It is demonstrated that although this method can generate a multi-beam pattern, it cannot provide satisfactory performances, mainly because of high side lobe level, gain loss and beam deviation. The iterative Fourier technique is then applied to optimize the performances of the multi-beam reflectarray antenna. The required mask and cost function for multi-beam design and the flow of the iterative Fourier techniques are represented. Finally, a Ku-band four beam reflectarray with a single feed is designed using the iterative Fourier techniques and the radiation performances are analyzed and compared with that of single beam, as reference case, and multiple beam designed by aperture field superposition. The numerical results show that a good four beam performance can be obtained by using the iterative Fourier techniques, which suggests that the iterative Fourier technique is suitable for the design of the multi-beam reflectarray antenna with a single-feed.

In the design procedure of the reflectarray antennas, the fast analysis of the aperture efficiency and radiation patterns is necessary before manufacture to forecast the antennas performance proximately. The fast calculation of the aperture efficiency and radiation patterns of reflectarray antennas is presented in this paper. A more general approach is introduced to calculate the spillover efficiency of a reflectarray. Meanwhile, the taper efficiency of the reflect-array is calculated with a unified set of equations. Two different fast approaches of the radiation patterns analysis-array theory and aperture field are described, and the discrete Fourier transform is applied to speed up the computational speed. On the basis of these derivations, numerical results of a Ku band reflectarray with offset feed are presented to show the performance of these approaches, and to provide the guidelines for designing and analyzing reflect-array antennas.

This paper presents a new reflectarray antenna capable with 1-bit switchable capability for W-band beamforming network. The proposed antenna has been optimized using two unit-cells with sizes of 1.0 mm and 1.3 mm to form a total number of 193 radiating elements on a square aperture surface of length 30 mm. These radiating elements are spaced 0.5 wavelengths apart and fed by a 15 dBi pyramidal horn antenna as the feed antenna placed 53 mm away from the aperture center. The proposed reflectarray achieves a realized peak gain of 22.52 dBi, a half-power beamwidth of 5.1° in both E- and H-planes at the test frequency of 80 GHz and operates over a wide bandwidth from 74 GHz to 90 GHz.

본 논문은 94GHz를 중심 주파수로 하며, 모노펄스 형식의 추적 레이다 시스템에 사용되는 folded reflectarray 안테나를 제안한다. 추적 레이다는 대부분 목표물로부터 반사되어 돌아온 반사 신호들을 비교하여 목표물을 찾으며, 모노펄스 형식에서는 이러한 신호들의 비교를 동시에 수행한다. 본 논문에서 제안한 모노펄스 형식의 folded reflectarray 안테나는 polarizing grid, reflectarray, 다중 모드 feed horn, 그리고 도파관으로 제작된 comparator로 이루어져 있다. 제작된 안테나는 다중 모드 feed horn과 comparator의 모노펄스 급전부에 의해 sum 모드, azimuth 모드, 그리고 elevation모드, 이렇게 세 개의 방사 패턴 형식을 나타낼 수 있다. 측정 결과, sum 패턴에서는 36dB, azimuth 패턴에서는 33.5dB, 그리고 elevation 패턴에서는 27.2 dB의 이득을 확인할 수 있었다

This paper proposes a high-gain monopulse antenna using the folded reflectarray for a monopulse target-tracking radar systems designed at the center frequency of 94 GHz. In target-tracking radar systems, the angle of arrival of the incoming wave Is determined by comparing the signal received on two or more non-coincident antenna patterns. This is the physical basis of most target-tracking techniques and the comparison is made simultaneously in a monopulse radar systems. In this paper, the antenna consists of polarizing grid, reflectarray, multimode feed horn, and comparator implemented by wavguide. The antenna is able to have three radiation patterns by using the monopulse feed systems assembled by multimode feed horn and comparator. The antenna demonstrates maximum gains 36dB, 33.5dB and 27.2dB at sum mode, azimuth mode, and evevation mode respectively.

The scattering solutions for multiple rectangular metallic gratings in a perfectly conducting plane excited by the TE and TM delta sources are presented using an overlapping T-block method. A reflectarray composed of rectangular metallic gratings shows fanbeam radiation patterns that are useful for an electromagnetic fence. The scattering characteristics of multiple rectangular gratings were computed in terms of total radiated power and antenna directivity. The design method of a fan-beam reflectarray to obtain high directivity was also compared with superdirective radiation and parabolic reflector phase.

본 연구는 파라볼릭 반사기의 체적을 줄일 수 있는 프린트 리플렉터어레이 안테나 설계에 대한 연구이다. 이를 위해 시뮬레이션과 제작된 도파관 시뮬레이터 측정을 통해 리플렉트어레이 안테나 단일소자의 위상변위 특성을 확인하였다. 그 결과, 10GHz에서 시뮬레이션시 최대 $298^{\circ}$의 위상 변위를 나타내었으며, 제작 측정시 $309^{\circ}$의 평균 위상변위 특성이 나타남을 확인하였다. 또한, 프린트 리플렉트어레이 안테나 이득은 28.3dBi, 3dB 빔폭은 E-plane $5.1^{\circ}$, H-plane $5.2^{\circ}$, 부엽은 E-plane -11.4dB, H-plane -17.6dB를 나타내었다.

In this study, we discuss about the printed reflectarray antenna design for parabolic reflector volume reduction. For this, we simulated and measured the phase characteristics of the unit array element of reflectarray antenna using waveguide simulator. As a results, the maximum phase variation is $298^{\circ}$ by simulation, the average phase variation is $309^{\circ}$ by measurement in 10GHz. And the printed Reflectarray antenna gain is 28.3dBi, 3dB beamwidth is E-plane $5.1^{\circ}$, H-plane $5.2^{\circ}$, sidelobe level is E-plane -11.4dB, H-plane -17.6dB.

마이크로스트립 리플렉트어레이는 다수의 반사소자를 이용하여 방사패턴을 조절하는 안테나로서, 일반적으로 곡면형 반사판 안테나를 대체하기 위하여 연구되어왔다. 본 논문에서는 리플렉트어레이에 관한 간략한 설계 이론을 정리하고, 고이득 및 광대역 리플렉트어레이의 연구동향을 살펴본다. 리플렉트어레이의 이득 특성을 개선하기 위해서는 리플렉트어레이에서 구현되는 반사위상의 오차를 최소화해야 하는데, 이를 위해서는 충분히 넓은 반사위상 범위 및 낮은 반사위상 민감도를 얻어야 한다. 리플렉트어레이의 대역폭을 확장하기 위해서는 반사소자의 반사위상이 주파수에 대해 선형적인 특성을 가지도록 설계해야 한다. 본 논문에서는 적층형 구조, 단층 다중공진 구조 등, 고이득 및 광대역 리플렉트어레이를 위해 반사소자의 반사위상 특성을 개선하고자 하는 다양한 연구에 대해 살펴본다. 또한, 안테나를 보다 소형화하기 위해 리플렉트어레이를 이중 반사판 형태로 구현하는 연구를 소개하고, 마지막으로 Contoured 빔, 근거리 빔 집중, RCS 감소 등 다양한 리플렉트어레이 적용 사례에 대해 정리한다.

Microstrip reflectarray is an antenna which controls its radiation pattern with a number of reflective elements. Conventionally, the reflectarray has been researched to replace curved reflector antennas. In this paper, design theories of reflectarray is briefly introduced, and research trends of high gain and broadband reflectarrays are reviewed. To improve the gain of the reflectarrays, it is required that the reflection phase errors on the reflectarray surface be minimized. For this purpose, sufficiently wide reflection phase range and low phase sensitivity should be realized with the designed element. For bandwidth improvement, the reflection phase of the element should be linear with the frequency variation. In this paper, various researches to improve the reflection phase characteristics of the element for high gain and broadband reflectarrays, such as multi-layer and single-layer multi-resonant structures, are reviewed. Also, dual-reflectarray configuration for compact antenna design is reviewed. Finally, various applications of reflectarrays such as contoured beam, near-field focusing, and RCS reduction are reviewed.

본 논문에서는 반사배열안테나 시스템을 기반으로 고 이득 방사성능과 원활한 이중 빔 형성 기능을 동시에 구현하기 위한 기법(위상 가중치)을 제시하였다. 제시된 기법은 부 배열 간 차 전계강도를 유도하는 위상 가중치를 적용하여 분할 빔 기반 이중 빔을 형성하는 방식으로, 빔간 중첩 현상을 개선하는 것을 목표로 한다. 제시된 기법을 검증하기 위해 반사배열안테나의 방사특성을 분석할 수 있는 수학적 모델을 제시하였고, 일반적인 부 배열 기반 이중빔 형성 기법과의 비교 분석을 수행하였다. 다양한 조건에서 모의실험 결과, 제시된 기법이 빔 중첩 현상을 개선할 할 수 있을 뿐만 아니라, 다양한 요구 빔 조향 각도에 대응하여 효율적인 이중 빔을 형성할 수 있음을 확인하였다.

In this paper, a method (phase weighting) is presented to achieve high-gain radiation performance and dual-beamforming functionality based on a reflectarray antenna system. The proposed method aims to mitigate the beam overlap phenomenon by implementing split dual-beamforming, using phase weighting that induces differential electric field strength between sub-arrays. To validate the proposed method, a numerical model for analyzing the radiation characteristics of the reflectarray antenna was developed, and a comparative analysis was conducted with a conventional sub-array-based dual-beamforming method. Simulation results under various conditions confirmed that the proposed method not only improves the beam overlap phenomenon but also efficiently forms split dual beams across a range of required beam steering angles.

밀리미터파 대역인 W-대역에서 초고이득 반사배열안테나를 구현하기 위하여 이중 반사판형태 중 주 반사판으로 향하는 전파가 급전부로 되돌아오지 않도록 하여 안테나의 효율 및 이득 특성을 크게 개선한 축이동 그레고리안 안테나를 금속 반사배열안테나 형태로 구현하였다. 금속 반사배열안테나의 경우, 유전체를 이용한 반사배열의 안테나와 달리 기판에 의한 손실이 없으며, 금속가공만으로 제작될 수 있는 제작의 편의성을 갖고 있다. 본 논문에서는 사각형 금속 개구의 배열을 이용하여 50 dBi 이상의 초고이득 축이동 금속 반사배열안테나를 설계하고, 일반적인 기계 가공을 이용하여 안테나를 제작하였으며, 제작된 안테나는 밀리미터파 컴팩트 레인지 안테나 측정시스템을 이용하여 검증하였다.

We design a displaced-axis Gregorian dual antenna in the form of a metal reflectarray antenna for millimeter wave region, W-band. Unlike a reflectarray composed of printed patch antennas on a dielectric substrate, metallic rectangular waveguide unit-cells are proposed to avoid the loss of substrate and take an advantage of ease of typical metal machining fabrication. In this paper, the radiation characteristics of constructed metal reflectarray antennas show ultra high-gain antenna over 50 dBi at a target frequency in W-band. The experimental measurements are conducted in millimeter-wave compact range antenna measurement system.

본 논문에서는 반사배열 안테나 구조를 이용한 W대역 모노펄스 추적 시스템을 제안하였다. 제안한 반사배열 안테나 모노펄스 추적 시스템은 단일 반사 방식의 4개의 급전 혼 안테나과 마이크로스트립 반사배열을 이용한 평판형 반사판으로 구성된다. 4개의 급전 혼 안테나는 10 dBi의 이득, E/H평면에서 대칭적으로 56도 반치각을 가지고 있다. 1개의 급전 혼 안테나를 사용한 반사배열 안테나는 41.8 × 41.8 mm²의 크기로, 26.8 dBi의 이득과 약 5.6도의 반치각 빔폭을 가지고 있다. 4개의 급전 혼 안테나를 사용한 반사배열 모노펄스 추적 시스템은 75 GHz에서 90 GHz까지 정합되어 있으며, 각 안테나 사이의 격리도는 10 dB 이상 확보되어 있다. 또한 전파신호의 추적범위는 5.98도를 가지고 있으며, 추적오차범위는 0.02도임을 확인하였다.

In this paper, we proposed a new W-band monopulse tracking system based on reflectarray antenna structure. The proposed reflectarray antenna monopulse tracking system consists of four feed horn antennas and a planar reflector using a microstrip reflectarray. The four feed horn antennas have a gain of 10 dBi and a half-power beam-width of 56 degrees symmetrically in the E/H plane. It was confirmed that the reflectarray antenna using one feed horn antenna has a size of 41.8 × 41.8 mm², a gain of 26.8 dBi, and a half-power beam-width of about 5.6 degrees. The reflectarray monopulse tracking system using 4 feeding horn antennas is well matched from 75 GHz to 90 GHz, and the isolation is secured by more than 10 dB. Finally, the proposed system shows the tracking range of 5.98 degrees and the tracking error range was 0.02 degrees.

본 논문에서는 위성 탑재용 반사 배열 안테나 시스템을 대상으로, 위상 제어만을 이용하여 빔 조향 영역 내에서 균일한 송신 강도를 유지하기 위한 확장 빔 형성 기법과, 위성 운영 시 자세 변화에 따른 영향을 보상하기 위한 확장 빔 회전 기법을 제안하였다. 제안된 기법은 다중 편향 빔 형성과 빔 중첩 현상을 기반으로 한다. 제시된 기법의 성능 검을 위해, 분석용 반사 배열 안테나를 활용하여 다양한 편향 빔 형성 조건에서 확장 빔의 형성 및 회전 성능을 분석하였다. 분석 결과를 바탕으로, 최적의 확장 빔 형성 및 회전을 위한 편향 빔 형성 조건을 도출하였다.

In this paper, a beam broadening technique is presented to maintain uniform transmission intensity within the beam steering range, along with a broadening beam rotation technique to compensate for attitude changes during satellite operation. These techniques are designed for a satellite-mounted reflectarray antenna system. The methods are based on the principles of multiple deflected beam formation and beam overlapping phenomena. To evaluate the effectiveness of the presented techniques, an analytical reflectarray antenna was used to analyze the formation and rotation performance of broadened beams under various deflected beam formation conditions. Based on the analysis results, the optimal conditions for deflected beam formation were identified to achieve the most effective beam broadening and rotation.