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To overcome the performance limit of multi-branch switch and stay combining (SSC) systems, the branches are divided into a pair of sub-SSC systems that are connected to selection combining. To evaluate the proposed system, the general mathematical expressions of average output signal-to-noise ratio (SNR) for the independent Nakagami-m fading branches are provided. There are deduced for the case in which one branch has higher or lower average SNR than the other branches. We also perform a numerical analysis, and demonstrate that this simple structure reconfiguration considerably increases the performance of SSC systems in several environments.

This paper proposes an optimization algorithm to determine the optimal coherent combination candidates of distributed local beams in a wireless sensor network. The beams are generated from analog uniform linear arrays of nodes and headed toward the random directions due to the irregular surface where the nodes are mounted. Our algorithm is based on one of the meta-heuristic schemes (i.e., the single-objective simulated annealing) and designed to solve the objective of minimizing the average interference-to-noise ratio (INR) under the millimeter wave channel, which leads to the reduction of sidelobes. The simulation results show that synthesizing the beams on the given system can form a deterministic mainlobe with considerable and unpredictable sidelobes in undesired directions, and the proposed algorithm can decrease the average INR (i.e., the average improvement of 12.2 dB and 3.1 dB are observed in the directions of &pi, 6 and 2 &pi, 3 , respectively) significantly without the severe loss of signal-to-noise ratio (SNR) in the desired direction.

In this letter, a rectangular microstrip antenna operating on the X-band (10 GHz) is miniaturized using transformation electromagnetics. Considering the characteristics of this technique, it is assumed that the antenna's length, width, and height are reduced independently or simultaneously while maintaining the resonant frequency. In order to validate this assumption, a full-wave simulation is utilized and the frequency responses are provided. The results confirm that the overall size of the antenna is decreased by 50% while the 10-dB return loss bandwidth is increased by 34% (0.61 to 0.82 GHz).

An SIW cavity is a useful tool to design an FSS which shows a rapid roll-off rate and insensitivity to polarizations and incident angles of electromagnetic waves. However, due to its high Q-factor, the FSS also shows narrow bandwidth which is undesirable for high-capacity communication. To address this drawback, we propose a novel technique to enhance the bandwidth while maintaining similar frequency response characteristics and minimizing the increase of the overall thickness of the SIW cavity FSS. In order to verify the performance of the technique, simulated frequency responses will be provided. Also, a parameter which affects the bandwidth will be studied. Finally the stability to polarizations and incident angles will be observed through the simulated results. Keywords: frequency selective surfaces, substrate integrated waveguide, radomes, periodic structures I. 서론 오늘날에 이르러 저잡음 및 고속 데이터 전송이 가능한 대용량 무선통신의 수요가 증가함에 따라 높은 롤오프율(rapid roll-off rate), 저손실성(low loss), 광대역성(wide bandwidth) 및 높은 안정성(high stability)을 갖는 필터 등의 통신부품 개발이 활발히 진행되고 있으며[1,2] 이러한 추세에 힘입어 주파수 선택적 표면(FSS: Frequency Selective Surface) 또한 광범위하게 연구되고 있다. FSS는 마이크로파 및 밀리미터파용 공간필터 혹은 물리적인 보호 장치로서 사용되고 있으며, 대역통과 및 대역저지 필터로 동작하기 위해서 일반적으로 다이폴 및 슬롯 등과 같은 금속성 공진형 구조물이 주기적으로 배열되어 있다[3-9]. 이러한 공진형 구조물로 이루어진 FSS는 분석과 제작이 쉽다는 장점이 있는 반면에 개방형 구조로 인하여 낮은 롤오프율과 높은 내부 손실을 가지며 또한 입사각과 입사편파에 민감하다는 단점 또한 가지고 있다. 최근 위에서 언급한 단점들을 해결하기 위해 기판 집적형 도파관(SIW: Substrate-Integrated Waveguide) 기술이 FSS 설계에 적극적으로 활용되고 있다. SIW는 기존의 3차원 도파관을 유전 기판에 내장한 평면 도파관으로서 서로 평행한 두 개의 금속판들과 금속판들 사이에 위치한 유전기판 그리고 유전기판 경계면을 따라 설치된 전도성 중공원통(hollow cylinder)들로 구성되어 있다[10]. 이러한 SIW의 열려 있는 양단을 추가적인 중공원통 열로 폐쇄하여 기존의 3차원 공동과 동작원리가 유사하며 높은 Q-factor를 갖는 SIW cavity [11]가 개발되었으며 최초로 대역통과 FSS의 단위셀로 이용되었다[12]. 또한 [13]에서 다중 모드를 이용한 편파회전 FSS로 개발하기도 하였으며, Luo 교수의 연구팀은 매우 높은 롤오프율과 입사각 및 편파에 대한 최대 안정성을 가지는 다층 SIW cavity FSS로 제작하기도 하였다[14]. [12-14]의 연구결과에서 볼 수 있듯이 SIW cavity를 FSS의 단위셀로 이용할 경우 매우 가파른 롤오프율과 불필요한 공진(spurious resonance)이 없는 명확한 주파수 응답을 얻을 수 있다. 하지만 높은 Q-factor에 의한 좁은 대역폭에 의해 대용량 통신에는 부적합하다는 단점을 가지고 있다. 본 논문에서는 가파른 롤오프율, 낮은 내부 손실, 입사각과 입사편파에 대한 높은 안정성을 유지한 체 SIW cavity FSS의 대역폭을 개선시킬 수 있는 기술을 제안하였다. 제안된 기술이 전반적으로 간단하고 FSS의 두께를 미약하게 증가시켰음에도 불구하고 대역폭은 두드러지게 증가되었다. 서론에 이어 제 II 장에서는 SIW cavity FSS의 대역폭을 개선하기 위한 구조물의 설계 방법과 동작원리를 다루었으며 또한 주파수 응답을 통해 성능 개선을 검증하였다. 그뿐만 아니라 편파 및 입사각에 대한 성능의 안정성도 살펴보았다. 마지막으로 제 III 장에서는 제안한 방식에 대한 평가와 결론을 맺었다. II. 설계 및 시뮬레이션 제안된 광대역 SIW cavity FSS 단위셀(unit cell)의 측면 및 정면 구조가 그림 1에 제시되어 있다. 단위셀은 총 4개의 금속 층으로 이루어져 있으며 각 층들 사이에는 상대 유전율(

Admittance spectroscopic analysis was used to examine the effect of a CF X plasma surface treatment on indium tin oxide (ITO) anodes using CF 4 gas and model the equivalent circuit for organic light emitting diodes (OLEDs) with the of ITO anode surface treated with CF X plasma. This device with the ITO/ N , N ′-diphenyl- N , N ′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine/tris-(8-hydroxyquinoline) aluminum/lithium fluoride/Al structure was modeled as a simple combination of two resistors and a capacitor. The ITO anode surface treated with the CF X plasma showed a shift in the vacuum level of the ITO, which resulted in a decrease in the barrier height for hole injection at the ITO/organic interface. Admittance spectroscopy measurements of the devices with the CF X plasma treatment on the surface of the ITO anodes showed a change in the contact resistance, bulk resistance and bulk capacitance.

We investigated frequency tunability of a microfluidic-based antenna using on-demand manipulation of a gallium-based liquid metal alloy. The fluidic antenna was fabricated by polydimethylsiloxane (PDMS) and filled with the gallium-based liquid metal alloy (Galinstan ® ). It is composed of a digital number “7”-shaped feedline, and a square-shaped and a digital number “6”-shaped patterns, which are all implemented with the liquid metal. The gallium-based liquid metal was adhered to the channel surface due to its viscous oxide layer originating from the gallium oxide forming when it exposed to the air environment. We treated the liquid metal with hydrochloric acid solution to remove the oxide layer on the surface resulting in easy movement of the liquid metal in the channel, as the liquid metal surface has been transformed to be non-wettable. We controlled the physical length of the liquid metal slug filled in feedline with an applied air pressure, resulting in tuning the resonant frequency ranging from 2.2 GHz to 9.3 GHz. The fluidic antenna properties using the liquid metal’s electrical conductivity and mobility were characterized by measuring the return loss (S11), and also simulated with CST Microwave Studio.

This letter presents a novel wideband miniaturized-element frequency selective surface (MEFSS). The simulation and measurement results show that the bandwidth of the proposed MEFSS is remarkably enhanced compared to that of an original second-order MEFSS while its size and total thickness are still small. A parametric study is also conducted to understand the operating mechanism of the proposed structure. The phenomenon observed in the parametric study is explained with an equivalent circuit model.