Dual-Circularly Polarized 60 GHz Beam-Steerable Patch Antenna Array With 8×8 Butler Matrix

Abstract

본 논문에서는 밀리미터파 기반의 5G 무선통신 시스템에서 넓은 빔 커버리지 확보와 높은 데이터 전송률을 얻기 위해 60 GHz 비면허 대역에서 빔 조향이 가능하고 이중의 원형편파 특성을 갖는 패치 배열 안테나를 제안하였다.

먼저, 밀리미터파 5G 대역에서의 높은 경로 손실을 보상하고 빔 조향 네트워크 회로와의 연결성을 고려하여 1×4 패치 배열 안테나를 구성하여 설계하였다. 패치 안테나에 기생 패치를 적층하여 넓은 대역폭 특성을 확보하였고, 두 개의 급전선로로 이중의 급전점을 갖도록 설계하여 ±90°의 위상 차이를 통해 원형편파를 형성하였다. 또한, 적층한 기생 패치의 크기와 모양을 최적화하여 원형편파를 형성하도록 했다.

두 번째로, 1×4 패치 배열 안테나로 인가되는 신호의 위상을 제어하기 위해 빔 조향 네트워크 회로를 버틀러 매트릭스로 구성하여 설계하였다. 배열 안테나와의 연결성을 고려하고 원하는 출력위상을 얻기 위해 하이브리드 커플러와 크로스오버로 구성된 일반적인 4×4 버틀러 매트릭스 두 개와 추가적인 회로가 결합된 8×8 버틀러 매트릭스 구조이다. 4×4 버틀러 매트릭스는 네 개의 입력포트에 따른 출력위상들 간의 위상 차이가 각각 ‒45°, +135°, ‒135°, +45°가 되도록 설계하였으며, 제안된 8×8 버틀러 매트릭스는 원형편파 형성을 위해 한 개의 안테나로 연결되는 인접한 두 출력포트가 ±90°의 위상 차이를 갖도록 설계하였다. 제안한 안테나를 제작 및 측정하였으며 시뮬레이션 결과와 유사함을 보였다.

결과적으로, 제안된 8×8 버틀러 매트릭스를 결합한 패치 배열 안테나는 반사계수 ‒10 dB를 기준으로 55.3 GHz – 64.9 GHz의 대역폭 특성을 갖고 57.5 GHz – 63.2 GHz 대역에서 10 dB 이상의 격리도 특성을 갖는다. 60 GHz의 주파수에서는 ‒38°, ‒11°, +11°, +39°의 빔 조향 각도를 가지며, 해당 각도에서 각각 9.39 dBi, 10.67 dBi, 10.63 dBi, 9.38 dBi의 이득을 갖는다. 또한, 버틀러 매트릭스의 입력포트에 따라 포트 1부터 포트 4까지는 우회전 원형편파가 형성되고 포트 5부터 포트 8까지는 좌회전 원형편파가 형성된다.

따라서, 제안된 안테나는 넓은 커버리지 확보와 동시에 편파 다이버시티가 요구되는 60 GHz 5G 무선통신 어플리케이션에 활용하기에 적합하다.|In this thesis, I propose a patch antenna array that operates in the unlicensed 60 GHz band to enable beam-steering and generates dual-circular polarization for wide beam coverage and high data rate in millimeter-wave based 5G wireless communication systems.

Firstly, a 1×4 patch antenna array is designed to compensate for the high path loss in the millimeter-wave 5G band and to consider the integration with the beam steering network circuit. The patch antenna has a wide bandwidth characteristic by stacking parasitic patches and is designed to have two feed lines with a double feed point to form a circular polarization with a phase difference of ±90°. Also, the size and shape of the stacked parasitic patches are optimized to radiate the circularly polarized wave.

Secondly, a Butler matrix is designed to control the phase of the signal applied to the 1×4 patch antenna array. The 8×8 Butler matrix consists of two typical 4×4 Butler matrices and additional parts to get the desired output phase. Each input port of the 4×4 Butler matrix produces a different set of 4 orthogonal phases of ‒45°, +135°, ‒135°, and +45°. The proposed 8×8 Butler matrix is designed so that two adjacent output ports connected by one antenna have a phase difference of ±90° to form a circular polarization.

The proposed antenna array system demonstrates good reflection coefficients in the frequency band ranging from 55.3 GHz to 64.9 GHz and has a mutual coupling of less than ‒10 dB over the frequency range of 57.5 GHz – 63.2 GHz. At 60 GHz, the maximum gains and beam-steering angles for input ports 2, 4, 5, and 7 are 9.39 dBi at ‒38°, 10.67 dBi at ‒11°, 10.63 dBi at +11°, and 9.38 dBi at +39°, respectively. It is also demonstrated that the dual-polarization is well formed by switching the excitation ports. The RHCP (right-handed circular polarization) is formed when four ports from port 1 to port 4 are excited and LHCP (left-handed circular polarization) is formed when four ports from port 5 to port 8 are excited.

The proposed antenna array system could be a good candidate for millimeter-wave 5G applications that require wide beam coverage and polarization diversity.; In this thesis, I propose a patch antenna array that operates in the unlicensed 60 GHz band to enable beam-steering and generates dual-circular polarization for wide beam coverage and high data rate in millimeter-wave based 5G wireless communication systems.

Firstly, a 1×4 patch antenna array is designed to compensate for the high path loss in the millimeter-wave 5G band and to consider the integration with the beam steering network circuit. The patch antenna has a wide bandwidth characteristic by stacking parasitic patches and is designed to have two feed lines with a double feed point to form a circular polarization with a phase difference of ±90°. Also, the size and shape of the stacked parasitic patches are optimized to radiate the circularly polarized wave.

Secondly, a Butler matrix is designed to control the phase of the signal applied to the 1×4 patch antenna array. The 8×8 Butler matrix consists of two typical 4×4 Butler matrices and additional parts to get the desired output phase. Each input port of the 4×4 Butler matrix produces a different set of 4 orthogonal phases of ‒45°, +135°, ‒135°, and +45°. The proposed 8×8 Butler matrix is designed so that two adjacent output ports connected by one antenna have a phase difference of ±90° to form a circular polarization.

The proposed antenna array system demonstrates good reflection coefficients in the frequency band ranging from 55.3 GHz to 64.9 GHz and has a mutual coupling of less than ‒10 dB over the frequency range of 57.5 GHz – 63.2 GHz. At 60 GHz, the maximum gains and beam-steering angles for input ports 2, 4, 5, and 7 are 9.39 dBi at ‒38°, 10.67 dBi at ‒11°, 10.63 dBi at +11°, and 9.38 dBi at +39°, respectively. It is also demonstrated that the dual-polarization is well formed by switching the excitation ports. The RHCP (right-handed circular polarization) is formed when four ports from port 1 to port 4 are excited and LHCP (left-handed circular polarization) is formed when four ports from port 5 to port 8 are excited.

The proposed antenna array system could be a good candidate for millimeter-wave 5G applications that require wide beam coverage and polarization diversity.