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1 Lab-: Antenna Mutual Coupling. Theory. 안테나상호결합 (mutual coupling) - 안테나상호결합 : 두안테나사이의전력이전달되는현상 그림 : 안테나상호결합개념 [Wang, "DOA estimation under unknown mutual coupling and mutlipath with improved effective array aperture", ensors, 05] - 동일편파안테나사이의상호결합 : 거리가가까울수록증가. 두안테나가마주보는방향으로이득이작을수록작다. - 서로편파가수직인안테나사이의상호결합 : 작다 ( 이론적으로 0) - 편파가서로수직인경우 : 수평편파 수직편파, 우원편파 좌원편파 - 편파다이버시티통신 : 상호결합 -0dB 이하요구 - 원편파구현시 개의직교하는편파사이의분리도 : 0dB 이상필요 - 배열안테나 : 동일한안테나를 개이상배열하여이득을높이거나안테나빔을특정방향으로향하게한안테나 - 배열안테나에서소자사이의간격이보통 파장이하이므로한안테나에서다른안테나로전력이잘전달된다.. 안테나간전력전달공식자유공간 (free space; 아무것도없는무한공간 ) 에서동작하는두안테나사이의전력전달은아래공식을사용하여계산 ) 두안테나사이의거리가작은경우 ( 이격거리가안테나크기보다작은경우 ): 측정또는시뮬레이션으로두안테나간의전달계수 을구한후다음공식사용

2 P P 0 0 0, 0 : 안테나 과 의포트전송선특성임피던스 ) 두안테나사이의거리가충분히큰경우 ( 이격거리가안테나크기보다큰경우 ): Friis 전송공식사용 P P 4 R GG P : 안테나 의송신전력 P : 안테나 의수신전력 R: 두안테나사이의이격거리 : 안테나동작주파수에서의파장 G, G : 안테나 과 의이득 ( 서로마주보는각도 ( 보통이득이최대인각도 ) 에서의이득 ) 3) Friis 전송공식의응용 - 안테나이득측정 : 두안테나사이의거리와송신안테나는고정시키고수신안테나 A( 이득을알고있는안테나 ; 표준이득안테나라부름 ) 에서측정된전력과수신안테나 A를수신안테나 B( 이득을측정하고자하는안테나 ) 로교체하였을때측정된전력을비교 - 가시거리 (LO; line of sight) 통신링크 budget 계산 : 가시거리통신링크에서송신전력대비수신전력을계산하여통신링크설계시사용 3. 안테나상호결합의효과 - 배열안테나에서상호결합에의해부엽준위 (sidelobe level) 증가 - 배열안테나의주빔을스캔할경우반사계수가크게증가하는경우발생 : 이경우표면파공진모드에의해소자간상호결합크게증가, 반사계수증가, 안테나의전력이방사파로방사되지않고배열안테나표면을따라표면파로진행. 위와같은현상을 'scan blindness' 라한다. 4. MMO 안테나에서의상호결합 - MMO (multiple input multiple output) 안테나 : 동일주파수에서다수의안테나로송신하고다수의안테나로제한된주파수대역폭을사용하여더용량의정보를전송하거나용량이정해진경우더빠른속도로전송하기위해사용 - MMO 통신의통신용량증가효과 : 이론적최대치 = 송신안테나수와수신안테나수중에서 작은수배수만큼증가

(a) (b) Figure: (a) MMO exploits multipath propagation to multiply link

(b) MMO antenna concept [Mohammadkhani, "MMO capacity improvement in the

04] Figure: Capacity of a MMO wireless communication system - MMO

- MMO 안테나설계의중요한부분은상호결합감소이다. - MMO 안테나에서상호결합감소방법 : 안테나소자구조를상호결합감소를고려하여설계.

communication standards: EEE 80.n (Wi-Fi), EEE 80.

3 (a) (b) Figure: (a) MMO exploits multipath propagation to multiply link capacity [Wikipedia]. (b) MMO antenna concept [Mohammadkhani, "MMO capacity improvement in the presence of mutual coupling", 00] (a)[wiki for T] (b)[ghayoula, JETR, 7(3), 04] Figure: Capacity of a MMO wireless communication system - MMO 안테나에서의상호결합 : 통신대역폭내에서소자간전달계수 -5dB 또는 -0dB 이하가요구됨. - MMO 안테나설계의중요한부분은상호결합감소이다. - MMO 안테나에서상호결합감소방법 : 안테나소자구조를상호결합감소를고려하여설계. 안테나소자사이에상호결합감소구조을적용하고여기에회로소자 ( 능동, 수동 ) 를결합 - MMO 응용 : ) Wireless communication standards: EEE 80.n (Wi-Fi), EEE 80.c (Wi-Fi), HPA+ (3G), WiMax (4G), Long Term Evolution (LTE 4G) ) Power-line communication: 3-wire, TU G.hn, HomePlug A 3) MMO radar: 예시 = 3개의송신안테나가서로직교하는신호송신, 4개의수신안테나에서 matched filter와 DP 기술을이용하여총 종류의신호수신함으로써 개의배열안테나와동일한분해능을얻는다. - Massive MMO: Gbps 전송속도를목표로하는 5G 이동통신의 core technology. 4G LTE 에서는 개또는 4 개소자 MMO 사용. Massive MMO 에서는수십, 수백개안테나사용. Huawei, TE, 3

4 Facebook 회사에서 96 개, 8 개소자 massive MMO 통신시연완료 Figure: 5G massive MMO concept. Left: Junil Choi 5. Dipole Mutual Coupling Figure: Dipole mutual coupling [D. Jenn, NP] 4

5 . Experiments 치수단위 : mm 전원 : Discrete port across the gap g. ource impedance = 50Ω Frequency: GHz Figure: imulation geometry for two-dipole mutual coupling. A ingle Dipole Make a dipole and find its resonant frequency. No ground plane. The dipole is in a free space Dipole center at the origin (0, 0, 0) Dipole arm in y direction Dipole length: one arm's end to the other arm's end = L = 4mm Dipole feed gap: g = mm Dipole wire cross section: square, W x W = x mm imulation frequency: GHz ) 3D perspective view of the antenna structure ) (db), Cartesian 3) R and X on the same graph 4) Find the resonance frequency f r.. Mutual Coupling: Two Parallel Dipoles We will study the mutual coupling between two parallel dipoles. Use two dipoles of the same dimensions as obtained in. Frequency: GHz d x = a half wavelength at f r obtained in. d y = 0 ) 3D perspective view of the antenna structure ), in db on the same graph for GHz 3) R and X on the same graph for GHz 5

6 4) Compute the power transfer ratio using the Friis formula and compare it with the simulation. 3. Mutual Coupling of Two Parallel Dipoles vs Antenna Distance Observe (db) as d x decreases until both dipoles almost touch each other. 4. Mutual Coupling: Two Collinear Dipoles Use two dipoles of the same dimensions as obtained in. Frequency: GHz d x = 0 d y = a half wavelength at f r (obtained in ) + L (=40mm) ) 3D perspective view of the antenna structure ), in db on the same graph for GHz 3) R and X on the same graph for GHz 4) Compute the power transfer ratio using the Friis formula and compare it with the simulation. Why the calculation is different from the simulation? 5. Mutual Coupling of Two Collinear Dipoles vs Antenna Distance Observe (db) as d y decreases until both dipoles almost touch each other. 6

7 . Mathematics for Antenna Mutual Coupling Analysis ) mpedance matrix [] for antenna mutual coupling : self impedance of antenna (measure the input impedance of antenna with antenna 0 open-circuited) : mutual impedance between two antennas, 0 0 : self impedance of antenna 0 ) Admittance matrix [Y] for antenna mutual coupling Y Y Y Y 3) cattering matrix [] for antenna mutual coupling, : reflected wave (equivalent voltage), : incident wave 0 : reflection coefficient at antenna input terminal (measured with the antenna terminated with 0 ) 7

8 , 0 0 : transmission coefficient between two antennas 0 : reflection coefficient at antenna input terminal With the antenna terminated with a matched load 0 : in, 0 in, 0 ; ( )/ 0 in,0 ( ) ; ( ) Re( 0 ) P Y : incident power P P ( ) : reflected power Re( 0 ) P Y Re( Y ) P P 0 Re( Y0) With the antenna excited with a matched source: in in in in 0 0 in in in in out in in in out 0 in 0 in out 40 P []-to-[] conversion: 8

9 ( )( ) ; ( ) z z 0 0 ( 0); ( 0)( 0) z 0 z ( )( ) z 0 0 []-to-[] conversion: ( )( ) ; 0 0 s s ; ( )( ) 0 0 s s ( )( ) s References: N-port matrix conversions, 9

THE JOURNAL OF KOREAN INSTITUTE OF ELECTROMAGNETIC ENGINEERING AND SCIENCE Mar.; 28(3),

THE JOURNAL OF KOREAN INSTITUTE OF ELECTROMAGNETIC ENGINEERING AND SCIENCE. 2017 Mar.; 28(3), 163 169. http://dx.doi.org/10.5515/kjkiees.2017.28.3.163 ISSN 1226-3133 (Print) ISSN 2288-226X (Online) PCB