ENHANCED GAIN CYLINDRICAL DIELECTRIC RESONATO R ANTENNA BASED ON COMBINATION OF HIGHER ORDER MODES Michal Mrnka and ZbyněkRaida Department of Radio Electronics, Brno University of Te chnology Abstract: IINTROD!CTION Dielectric resonator antennas, frstly proposed by Long et al. [1], have become very popular radiating elements in micr owave and millimeter -wave reuency bands. !o their main advantages belong high radiation e"ciency, compact si#e, ease oe$citation and relativel y large impedanc e bandwidth when compar ed to other resonant antenna elements, to list a ew. %ylindrically shaped resonator, operating with the low order hybrid electromagnetic mode &'(11) placed above a su"ciently large ground plane is probably the most r euently used D* + confguration [1-]. !his mode generates broadside radiation pattern with linear polari#ation and gain about di. /everal approaches have been suggested to increase the gain othe D*+s. +rraying osingle element D*+s [0] is probably the most ver sat ile met hod in whi ch the gain val ue can be dir ect ly contr oll ed by number oelements in the array. evertheless, increased si#e, comple$ity and costs othe resultant antenna are the main disadvantages. +ltering oa single element D*+ can be used in cases, where medium gains up to around 12 di are su"cient. 3n general, two tactics to increase the gain othe single element D*+ e$ist. 4irstly, additional structures are placed in near vi cini ty othe resonator operati ng in the low order mode. !hese can represent e.g. su r ace mounted short horns [5 ], '6 structures [7] or super strat es [8]. 9a rticul arly, the rectan gular hybrid D*+ anten na described in [8] provided pea: gain o1.di and gain above 11 di in complete 3/( band at 52 6&#. ;n the other hand, the common disadvantages othe antennas based on the frst approach are again higher comple$ity and increased si#e. /econd strategy is to utili#e higher order radiating modes in single dielectric resonator. !his approach has been already adopted in both rectangular and cylindrical D*+. 9etosa and !hira:oune [8] showed the D*+ based on higher order !')1<and !')1modes in rectangular resonator can achieve gains o7.0 di and12.0 di, respectiv ely . !he struc ture operating in !')1mode [8] reuired ma$imum dimension othe resonator oabout 1.1 λ2when build rom dielectric material with relative permittivity =r> 12, where λ2is the ree space wavelength. 6uha et al. [12-10] managed to e$cite higher order &'(10)mode in cylindrical resonator by intr oducing an ai r -fll ed cavi ty in the ground pl ane below the resonator. !his way pea: gain oabout 12 di was achieved but only in relatively narrow impedance bandwidth.
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High Gain Cylindrical DRA Based on Higher Order HEM133 Mode – Kopie
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7/23/2019 High Gain Cylindrical DRA Based on Higher Order HEM133 Mode – Kopie
3n presented letter, we use e$citation o higher order hybrid
electromagnetic &'(1<< mode in single cylindrical dielectric resonator with partial
e$citation o the nearby &'(10< mode in order to accomplish considerable gain
enhancement. !hese modes do not reuire any special eeding schemes nor the
ground plane modifcations and can be e$cited similarly to the well-:nown &'( 11)
mode. !he aperture coupling eed [] is selected and optimi#ed in order to avoide$citation o unwanted !'?!( modes within the resonator. 9arametric study in
%/! (icrowave /tudio [1<] was conducted to see the behavior and to determine
the limits o the proposed D*+. !he antenna was designed to operate over
unlicensed 3/( .7 6&# band @.80 6&# - .78 6&#A, but the concept might be
more suitable at higher reuencies, where the resonatorBs si#e can be less
crucial.
!he letter is organi#ed as ollows. /ection 33 brieCy describes the antenna
concept and design process. !he '-feld distributions within and in close vicinity
o the resonator are discussed. 9arametric study, fnal dimensions and simulation
results are given in /ection 333. (anuacturing o the prototype together with
e$perimental results are summed up in /ection 3. 4inally, the letter is concluded
by short discussion in /ection .
II ANTENNA CONCE"T
!he antenna is composed o a single cylindrical dielectric resonator placed above
the ground plane o circular ootprint. !he resonator is e$cited through
rectangular slot in the ground plane o a microstrip line according 4ig 1. +perture
coupling eeding mechanism was selected in order to minimi#e e$citation o
unwanted lower-order modes in the structure. *elative permittivity o the
resonator in all simulations was 5.1. !his value was simply selected due to
availability o material with given er. /ubstrate +rlon 0 with relative
permittivity <.<7 was used in the eeding structure design.
3nitial dimensions or the resonator @height h and diameter d according to the
4igure <A were ound by magnetic wall method using %/! 'igenmode solver. +ll o
the walls were considered perect magnetic conductors and the resonatorBs
dimensions were obtained so that the resonant reuency o the both target
modes &'(1<< &'(10< lied close to the desired reuency .7 6&#. /ince the
method does not ta:e into account radiation losses o the resonator, considerablylarge inaccuracy is a result. evertheless, the method provided reasonable initial
appro$imation o the dimensions that needed to be tuned and optimi#ed
aterwards. 4ull-wave transient solver in %/! (icrowave /tudio was used or this
purpose.
7/23/2019 High Gain Cylindrical DRA Based on Higher Order HEM133 Mode – Kopie
Fig. ) *+11* ,s. freuency for se,eral diameters of the resonator
4ollowing 4igure depicts the dependency o reali#ed gain on reuency or
several diameters o the resonator as well as or several ground plane si#es @4ig.
5A. 3t was ound out that the gain was increasing with increasing the ground plane
si#e only to a certain pointI e$tending its si#e beyond this value did not bring anyurther gain improvement. &eight o the resonator h was f$ed to the value 00.2
mm in all o the plots.
Fig. Reali/ed pea0 gain in the broadside direction ,s. freuency for se,eraldiameters of the resonator
Fig. Reali/ed pea0 gain in the broadside direction ,s. freuency (ith groundplane diameter as a parameter
7/23/2019 High Gain Cylindrical DRA Based on Higher Order HEM133 Mode – Kopie
to the x a$is and the cross-polari#ation to the y a$is.
!he measured data complied reasonably well with the simulation results.
(oreover, it should be mentioned that the bac: lobe present in the simulations
was not measured accurately. 9robable reason was the nature o the anechoic
chamber in which the antenna was measured, i.e. the line o sight between the
illuminator and the +M! was obstructed by antenna scanner or corresponding
angles.
Fig. 6 +imulated and measured radiation patterns at .42 G"/% E-planecorresponds to xz plane and "-plane to yz plane
Fig. 17 Freuency response of the gain8 simulation ,s. measurement
# CONCL!SIONS
ew concept o dielectric resonator antenna based on combination o higher
order modes in simple cylindrical resonator was presented and e$perimentallyverifed by measurement. Directive radiation pattern with high gain o 11.F di
was measured and impedance bandwidth was su"cient to cover the whole .7
6&# 3/( band. *elatively high side lobe levels in the '-plane @8 d below the gain
in the broadside directionA could be considered the main disadvantage.
!he implementation o the antenna might be more convenient at higher
reuencies, where the dimensions are less crucial. /ince the structure operates
with higher order modes, the electrical si#e is increased when compared to the
operation with low order modes. 4urther miniaturi#ation might be possible using
higher permittivity materials, which was not attempted in this letter.
7/23/2019 High Gain Cylindrical DRA Based on Higher Order HEM133 Mode – Kopie