Korean Journal of Optics and Photonics (한국광학회지)

Optical Society of Korea (한국광학회)
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Squint-less Phased Array Antenna Near-field Subwavelength Focusing with True-time Optical Delay Line

광 지연선로를 이용한 스퀸팅이 없는 위상배열 안테나의 근접장 서브파장 포커싱

  • 정영진 (울산과학대학교 전기전자공학부)
  • Received : 2019.02.07
  • Accepted : 2019.04.15
  • Published : 2019.06.25
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Abstract

The near-field subwavelength squint-less focusing system of a phased array antenna is designed and demonstrated by numerical simulation. The Huygens-Fresnel principle is applied to numerical simulation for calculation of the phased array antenna at microwave frequency. It was shown that beam squinting can be eliminated, utilizing true-time optical delay lines based on a chirped fiber grating in the proposed system. Furthermore, subwavelength focusing with high numerical aperture can be achieved by considering the fact that the array elements of the phased-array antenna can be treated as diffractive elements in an optical lens system. Also, side lobes can be suppressed by decreasing the distance between element antennas to less than half of the wavelength.

본 연구에서는 광 지연선로를 이용한 스퀸팅(squinting)이 없는 위상배열 안테나의 근접장 미세파장 포커싱(subwavelength focusing)을 디자인하고 전산모사를 통해 검증하였다. 마이크로파 파장에서 위상배열 안테나의 수치적 계산을 위해 호이겐스-프레넬(Huygens-Fresnel) 원리를 적용하였다. 제안하는 시스템은 첩 광섬유 격자(chirped fiber grating)에 기반한 광 지연선로를 이용하여 빔 스퀸팅이 생기지 않는다는 것을 전산모사를 통해 확인하였다. 그리고 개별 안테나의 배열은 광학렌즈시스템에서 회절 소자로 간주할 수 있음에 착안해 높은 개구율(numerical aperture)을 구현하고 미세파장 포커싱을 얻었다. 또한, 위상배열 안테나의 안테나 사이 거리를 반파장 이하로 줄여 사이드 로브를 억제할 수 있음을 보였다.

Keywords

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Fig. 1. Coordinate definition for the calculation of electromagnetic field distribution.

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Fig. 2. Arbitrary time delay feeding system employing tunable filters and chirped fiber grating; EOM: electro-optic modulator; PD: photodiode.

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Fig. 3. Controllable area of the phased array antenna system.

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Fig. 4. Description of the phased array antenna under numerical simulation system.

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Fig. 5. Comparison of beam squinting characteristics between conventional phased array antenna and array antenna with true time delay lines.

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Fig. 6. Required group delay for focusing at x = 5 [cm] and z = 15 [cm] in the case of the proposed array antenna employing true time optical delay lines.

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Fig. 7. Required phase difference for focusing at x = 5 [cm] and z = 15 [cm] in the case of general phased array antenna.

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Fig. 8. Comparison of the spot size of focal point with numerical aperture variation.

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Fig. 10. Comparison of intensity profile while varying the space between antennas.

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Fig. 11. Comparison of the lateral direction (x-axis) intensity profile of focal spot with varying the gap between antennas.

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Fig. 9. Subwavelength focusing characteristics. (a) Lateral direction (x-axis) intensity profile of the focal spot with numerical aperture variation. (b) Spot size as a function of the numerical aperture.

Table 1. Simulation parameters for observing beam squinting caused by frequency detuning

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Table 2. Simulation parameters for observing subwavelength focusing

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Table 3. Simulation parameters for observing side lobes

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