05940842 Lte a Compact Mimo Ant Japan

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Muual Coupling Cancellaion for Compac MIMOAnenna wih 3 dB Hybrid

Nobuo Nakajima, Tomoko Yamazaki and Wei NiScoo of Infoatics

e Univesit of Eectro-CommunicationsCo-shi, okyo, Jaan

nnakajima@cuecacp

AbstrctMMO is one of the important technologies in LTE ,

WiMAX and LTE-Advanced for improving spectrum eciency.

However, it is not easy to make a compact MMO antenna for

portable terminals, keeping high performance. One of the

problems is mutual coupling among the antennas. This reduces

the eciency of the antenna. In this paper, a dB hybrid is used

to cancel the mutual coupling. This idea can be applied to 2N (Nis integer) number of MMO antennas. In addition, by using

tunable impedance matching circuits, wide operational

bandwidth is available. Experiments were carried out for 2

MMO antennas at 2.4 - 2.6 GHz band.

Keywordscomonent; decouplig; celulr; LT

1. NTDUCTIN

MIMO tecoogy was aeay appie fo ireessLAN systems to eance te secum eciency. ypicay,om two to four antennas ae impemente ot in te access

points an teminas.

Regaing to te ceuar systems, suc as L E,iM a L E-Avance, MIMO technoogy is epoyein te inteationa stana an is now panne to eimlemented in eac system. Howeve, tee ae someroblems fo imlementing MIMO technology to the actuasystems. One is to esign a compact MIMO antenna foortable terminas. High pefomance must be kept uner thestrict limitation in size.

It is sai that the correlation of the receiving signalevel becomes igher when antenna sacing becomes closer.Higher correation causes MIMO capacit degraation.Furtermore, te tigt mutual couing degraes radiationeciency.

Accoing to te revious investigations, it was foun tat te muua coeation roem was not serious[].Howeve, te tigt mutua couing causes aiation oss. ocope wit tis roem, ecouing technoogies wee

eveoed [1] [][3].is pape poposes a ecouing technoogy tat uses

a 3 B hbrid. he basic structures ae shown fo , 4 and antennas MIMO. Expeiments wee caie o fo anennasMIMO in te .5 GHz ban. e moe the couping becomestight, te naowe te banwith becomes. herefore, tunable

impeance matcing stucue was eveope to exten teopeationa anwit.

11. MIMO TENA STUCTUE WITH3 B HY

Figure I sows MIMO stuctues with 3 dB bri in

te case of , 4 and antennas. Oerational rincie isexaine below in the case of antennas.In Fig., the inut wave is fe at pot I and spit to pot

3 an pot 4 wit equa ampiue. A pase of pot 4 waveeays 0 egees compaing wit te pase of pot 3. ese

waves aiate at antenna 5, 6 an coue to te opposeanteas. ese two coue waves ret to 3 B ri anspit to pot 1 an pot wit equa amitue. At po , twooutut waves ae equa amlitude but out of hase (10degrees). eefoe, tese waves ae cancee ou an thus

te couing wave oes not appea at pot . On te ote an, at pot 1, since two coue waves ae te same pase, te sum of tese waves appeas om pot 1. A coue

waves o not go to pot ut go to pot 1. If te 3 B yriis iea, te ecouing is euency inepenent aneimination is pefect. A of te eecte waves om te twoanteas go to pot . Even if te wave is fe om pot inFig. , the oeration is the same as exlained above.

Imedance matcing circuits ae attache to suressthe etue waves as shown in Fig. 1.

At

t

4 t

Fig.1 Decouling Stuctue of the MIMO Antenna wit 3 dB Hybrid

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Fig.!

8 annna MIMO

Decouping Strcture of the MTMO Antennawith 3 dB Hybrid (contied )

3 dB ybid3

HXl

t

Fig. Paths of the Couled Waves

In te case of 4 an anteas, te MIMO strcte becomes moe comlicated. Howeve, the mutual coupling between pos can be erfectly canceled as wel, if the 3B ri an te impeance matcing circuits ae iea.

I. NTENNAS AND3 DB HYBRI PRFORMNCS

In or expeiments, sma ieectic antenas wit meane ine aiation eement ae appie. e istanceetween two teas is 6 mm ( 0.05 waveengt). Poto an pefomance ae sown in Fig. 3, 4 an 5. e mutuacoupling is ve tight (- dB ).

Figure 6 and 7 show the hoto and pefomance of the3 dB brid. he equency characteristics ae almost atwithin 3 GHz.

Fig. 3 Ceramic Antenna with Meander Line Radiato

Fig Closely Packed Antennas

823=�-�-F

"'--

�--4- E .� . .

, '•••: 6 h='-_4+".- =-

9 ;.·:·I _2 / ....

/P -1

I-22A�·,..- q 8 ++- -15I-a -18I-

-124I-

2 2.2 2.4 2.6

2.

Fig.5 Antea S Paametes

Fig.6 3 dB Hybrid

Or 3

-10 --�----------- ---- ---/-----� 831 i i

841-20 : ---- ----

Q�

S11 : :

-30 ----;-- 821

-40 ----------i-------- : ---- ---- -----

2 2.2 2.4 2.6 2.

Fig.7 3 dB Hybid Performances

3

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IV XPEINT FOR EOUPLING

Fiue 8 n epeiment tutue feupi ntenn hbi n impene mtiiuit e nnete ui mi-tip tnmiin ieFiue 9 etu e f pt 11 n pt 222 In Fi 9b e ie 12 equen epne

befe eupi n i ie te epne e

eupin It n be een tt te upi i eimite b te B bi n te te te e e einee bee te uin e t te inut pt

W ·3";2 -9Q ·12� ·15( ·18

2124

V

2

Fi8 Epeiment tutue

"-- S2 ---

S11

2.2 2.4 2.6 2.8

V XPEINT FOR MPEDNE ATHING

bn ine i ue f urein te ein e n in Fi 10 Dintinit b te bn ieue eetin n te mi-tip tnmiin ine Bjutin te mpitue n pe f te eetin eti e m te ntenn n be nee e mpitue f te etuin e n te eete e t te bn u

be te me n te pe f tem u be ppite ut f pe Fm tee nitin te ent te pitin f te bn ine e eteine In te epeiment te entn te pitin f te bn ine e jute b t ne Fiue 11 te reut t te equen f 272GHz, te eui e m te ntenn i nee

Fi 1 0 Bn Line Impene Mtin iuit

W 3 6 Q 12� -15 1( 21

-24

�

/S

1 v

. .4

v

.6 .8

(a) Rt Fi Re L Pefne it Impene Mtin

Befe Oeup

m 3'_---J- -- 6p�T � 9-+-r"=�--V-

l,2 -+-

--I-/I

- 15 Afe Oeup

18 21

241

Frequency GHzb Coupling Loss

Fi9 Feqen Repne

3

VI UNABLE MPEDNCE ATCHING

tu te muu uin eiminte b te B bi bit i e n If te me te upin

beme tit te nre te bnit beme pe it ti pbem tunbe iruit eepe f teimpene mtin Fi2 i bn tuue Retie

pitin f te bn ine e eie b fi equtin

Eeti ent H / Eeti ent L = f f 1

t = Eeti ent H - Eeti ent L 2

ee t i eptin beteen t bne f ie mte equen f i ie mte eqen n

978145770787/11/$6.00 ©011 IEEE



g is aveage wavelength on the micro-stri line. Electrical

length is the phsical length divided by g. he hsicallengths ae shown in Fig. 13.

Fig. 14 shows the imedance matching circuit with thee rch lines and Fig. shows the e loss pefomances. PIN diodes o MEMS switches m ealicale to switch the opeational eqency as shown in Fig.1. In the expeiment, thin coppe stips ae sed to coectand discoect the ranch line to the mico-stip tansmissionline. Fig. 14 is the case whee the imedance is matched at.4 GHz hen the middle branch line in Fig.4 is connected to the micro-si line, the imedance is matched at .5 GHz

When the uppe branch line is connected to the micro-striline, the impedance is matched at .6 GHz

s, the expeiments show that wideand decolingis enabled by the tunable matching circuit.

Fig.1 Dal Band Impedce Matching Circit

Hybrid

MachingPoint lor

t �t__ _ ___ MachingPoint lor IL

Fig.13 Electical Length and t

Fig.14 hee Impedance Matching Banches

; h.-4l___·r'U", ::,: ,-/o X. 1- --4 :.._ "<, k-�...� � _61:- ;.- •. , . \ "/ \( .' -

9 \ / : \ !

" ,2 / I \. \ / V .f 5 f f++�'8 \!

-21+ -+- 24 V

3reuenc Gz

Fig. Retu Loss Performances with Imedance Matching

IT. ONCLUSION

Decouling fo closely acked MIMO antennas wasachieved by using 3 dB hbrid. his decouling technology

will e sel fo ortale teminal MIMO antea, ecse the mtal coling cses adiation loss and the MIMOcapacit deceases e to the SNR redction y the inceased

adiation loss.he more the coling ecomes tight, the narrower the

bandwidth becomes. o coe with this roblem, a tuableimedance matching circuit was develoed using the branchlines. Decouling equency can be conrolled by the ositionof the branch line. hus, wide band decouling erformancebecomes available by switching the branch lines that arecouled to the micro stri line at the different ositions.

Net esech taget s to deveo a smal, wdebdand low loss 3 dB hrid. Capacit mst e evalatedexpeimentally in the mlti-ath envioent fo the MIMOantenna with 3 dB hbrid. 4 and antenna MIMO with 3 dBhbrid should be develoed and tested.

FRNCS

[1] W. Ni, N. Nima, "Two Microstrip Decoupling Techniques onighly Copled Antennas for MIMO Communications, WMC'09,(Sept 2009)

[2] [2] C.Chiu, C.Cheng and C.R.Rowell, "Reduction of mutual couplingbetween closely-packed antenna elements, I Trans. On Antennasand ropagation, vol.55, pp.1732-738,(June 2007)

[3] [3] S.Chen, Y.Wang and S.Chng,"A decopling technique forincreasing the port isolation beteen to strongly coupled tennas,I Trans. On Antennas and ropagation, vol.56, pp.3650-3658,(Dec.2008)

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05940842 Lte a Compact Mimo Ant Japan