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Analysis and Measurement of a Coaxial Power Cable, Composite Multiband Antennas, and a Periodic Frequency Surface

Analysis and Measurement of a Coaxial Power Cable, Composite Multiband Antennas, and a Periodic Frequency Surface
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This dissertation proposes a time-domain transmission (TDT) method to extract the propagation constant of a coaxial power cable from a pulse transmitted through the power cable. The TDT system consists of a pulse generator, adaptors, and an oscilloscope that measures pulse waveforms. Coaxial cables connected to the instruments for the TDT system were calibrated using pulses reflected from the adaptors and the short termination, and using a pulse transmitted through the coaxial cables. The transmission coefficients of a 22.9 kV power cable measured by the proposed TDT method and conventional time-domain reflectometry (TDR) method were compared. For the TDR method, the measurement error increased at frequencies higher than 430 MHz due to an incomplete open termination
but for the TDT method, the propagation constant can be extracted up to 1.1 GHz because the termination was not used. The effect of pulse width of incident pulse and loss of the power cable on the measurement bandwidth were studied. The propagation constant at high frequency can be measured because the bandwidth of the pulse increased as its width decreased. The measurement bandwidth for the extraction increased because the attenuation of the pulse transmitted through the power cable decreased as the length of the power cable decreased. A composite antenna comprised of an annular ring antenna in the GPS/DMB band and a 4 x 4 array antenna in the DBS band was designed on one surface. The composite antenna has a sandwich structure reinforced by glass-fiber reinforced plastic (GFRP) on the top and carbon-fiber reinforced plastic (CFRP) on the bottom
that structure can increase the impact strength and the compression strength of the antenna. The CFRP acts as a reflector which suppresses the back radiation of the array antenna. The gains of the composite antenna decreased slightly due to loss caused by the composite materials, but the maximum gain satisfied the requirements for receiving communication signals. Impact tests and compression tests of the composite antennas were performed according to the regulations of ASTM D7137 and C393. The composite antenna had higher maximum contact force and compression load than the antenna without the composite materials. After an impact on the critical point of the composite antenna, the electrical characteristic of the antenna was maintained because the composite materials protect it. A composite periodic surface that operates from 9 to 10 GHz was proposed. The proposed structure comprised of patch, grid layer, and GFRP was designed considering the interaction of high-order modes between the layers. The transmission coefficient of the frequency selective surface (FSS) in consideration of GFRP was analyzed in terms of the equivalent circuit. The resonant frequency decreased because the capacitance related to the fringing field between the patches increased as the thickness of the GFRP increased. The proposed FSS was less sensitive to polarization and incident angle than a conventional slot FSS because the unit cell of the proposed FSS is symmetric and small. The measured transmission coefficient was lower than the simulated result due to loss caused by the adhesive film, and the resonant frequency was decreased due to the adhesive film and the thickness difference of GFRP. Simulated results that consider these effects agreed with the measured results.
본 박사학위 논문에서는 coaxial 전력 케이블을 투과 및 반사하는 pulse들로부터 이의 전파 상수를 추출하는 time-domain transmission (TDT) 방법을 제안하였다. 이 TDT system은 pulse generator, adaptor와 pulse waveform을 측정하는 oscilloscope로 구성된다. TDT system 장비를 연결하는 coaxial cable들은 adaptor에서 반사되는 pulse, short termination 에서 반사되는 pulse와 coaxial cable을 투과하는 pulse를 이용하여 calibration 한다 제안된 TDT 방법과 기존의 time-domain reflectometry (TDR) 방법으로 측정한 22.9 kV 전력 케이블의 투과계수를 비교하였다. TDR 방법의 경우, 불완전한 open termination으로 인하여 430 MHz이상의 주파수에서는 측정 오차가 증가하지만, TDT 방법의 경우 termination 을 사용하지 않기 때문에 전파상수를 약 1.1 GHz까지 측정할 수 있다. 입사 pulse의 pulse width와 전력케이블의 손실이 측정 대역폭에 미치는 영향에 대하여 고찰하였다. Pulse width가 줄어들수록 pulse의 대역폭이 증가하기 때문에 높은 주파수 대역의 전파상수를 측정할 수 있다. 케이블 길이가 짧아질수록 전력 케이블을 투과한 pulse 의 감쇠가 줄어들어 측정 대역폭이 증가하였다. GPS/DMB대역의 annular ring 안테나와 DBS 대역의 4 x4 배열 안테나를 한 평면에 통합된 복합구조 안테나를 설계하였다. 복합구조 안테나는 앞면과 뒷면이 유리섬유와 탄소섬유로 보강된 샌드위치구조이고, 이는 안테나의 충격 및 굽힘 하중을 증가시킨다. 탄소섬유는 배열안테나의 후방방사를 억제하는 reflector 역할을 한다. 복합재료의 손실로 인하여 복합구조 안테나의 이득은 약간 감소하지만, 신호를 수신하기 위한 요건은 만족한다. ASTM D7137와 C393 규정에 따라 안테나의 충격 및 좌굴 실험을 수행하였다. 복합재료로 인하여 maximum contact force와 compression load가 증가하였다. 복합재료가 안테나를 보호하기 때문에, 안테나 동작에서 가장 중요한 급전 부분에 충격을 가하여도 안테나의 특성이 유지되는 것을 확인하였다. 9~10 GHz에서 동작하는 composite periodic surface를 제안하였다. 제안된 구조는 유리섬유와 주기적인 패치와 격자로 구성되며, 고차모드로 인한 층간의 상호작용을 고려하여 설계하였다. 유리섬유를 고려한 frequency selective surface (FSS)의 투과 특성을 등가회로 관점에서 분석하였다. 유리섬유의 두께가 두꺼워질수록 패치 사이의 fringing field로 인한 capacitance 가 증가하기 때문에 공진주파수가 낮아진다. 제안한 FSS는 구조가 작고 대칭이기 때문에 slot FSS보다 polarization과 입사각도에 덜 민감하다. 접착 필름의 손실로 인하여 측정된 투과계수는 시뮬레이션 결과보다 낮았고, 유리섬유의 두께 차이와 접착필름으로 인하여 공진주파수가 낮아졌다. 이 영향을 고려한 시뮬레이션 결과는 측정결과와 일치하였다.
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