Ci a ion: Kolangiammal, S.; Balaji, L.;
Mahdal, M. Design o Compac
Plana Monopole UWB MIMO
An enna wi h Fou O hogonal
Elemen s and Tape ed Fed
Con igu a ion o Wi eless Di e si y
Applica ions. Elec onics 2022,11,
3087. h ps://doi.o g/10.3390/
elec onics11193087
Academic Edi o : Dimi a I.
Kaklamani
Recei ed: 2 Augus 2022
Accep ed: 25 Sep embe 2022
Published: 27 Sep embe 2022
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elec onics
A icle
Design o Compac Plana Monopole UWB MIMO An enna
wi h Fou O hogonal Elemen s and Tape ed Fed Con igu a ion
o Wi eless Di e si y Applica ions
Shanmugam Kolangiammal 1,2, Logana han Balaji 1and Mi osla Mahdal 3,*
1
Depa men o Elec onics and Communica ion, Vel Tech Ranga ajan D . Sagun hala R&D Ins i u e o Science
and Technology, Chennai 600062, India
2Depa men o Elec onics and Communica ion, SRM Ins i u e o Science and Technology,
Chennai 603203, India
3Depa men o Con ol Sys ems and Ins umen a ion, Facul y o Mechanical Enginee ing, VSB-Technical
Uni e si y o Os a a, 17. Lis opadu 2172/15, 70800 Os a a, Czech Republic
*Co espondence: mi osla [email p o ec ed]
Abs ac :
In his pape , we in oduce a ou -po sel -isola ed UWB MIMO an enna o di e si y
applica ions. Fi s , we ha e de eloped a basic adia ing elemen o he p oposed an enna in ou
s ages o design, whe e pa ches o geome ically di e en shapes we e added a each s age o a i e
a he inal adia o o m. The an enna was designed on an FR-4 subs a e wi h a compac size o
28 ×28 ×1.6 mm3
. A ape ed mic os ip eeding was employed o enhance he an enna’s impedance
ma ching. An o hogonal a angemen o he ou adia o s was adop ed o mi iga e he mu ual
coupling be ween hem, a oiding he use o a sepa a e isola ion s uc u e. A p o o ype was buil
and measu ed wi h a close ag eemen be ween he expe imen al and simula ed esul s. The MIMO
an enna pe o med well in he en i e equency spec um o 3.1–10.6 GHz, wi h an isola ion be e
han 20 dB. The measu ed en elope co ela ion coe icien (ECC) was less han 0.001, he di e si y
gain (DG) was g ea e han 0.99 dB, and he o al ac i e e lec ion coe icien (TARC) was less han
−
10 dB. The pe o mance o he p oposed an enna design was compa ed wi h exis ing designs.
The compa ison showed ha he p oposed quad-elemen UWB MIMO a ay is compac , has good
isola ion and di e si y pe o mance compa ed o exis ing designs, and is well-sui ed o wi eless
di e si y applica ions.
Keywo ds: mu ual coupling; di e si y; mul iple-inpu and mul iple-ou pu (MIMO); UWB
1. In oduc ion
Ul a-wideband (UWB) is a adio equency spec um wi h a ange o 3.1–10.6 GHz.
The Fede al Communica ions Commission (FCC) app o ed a 7.5 GHz bandwid h o ul a-
wideband communica ions in 2002 [
1
,
2
]. UWB is a sho - ange wi eless communica ion
p o ocol ha uses adio wa es such as Blue oo h and Wi-Fi [
3
,
4
]. In [
5
], he au ho s p o ide
a his o ical o e iew o ul a-wideband an ennas o he ea ly days and highligh a ew
no ewo hy UWB an ennas o he imes. UWB an ennas a e used wi h a high accu acy and
wi hou in e e ence issues in a ious applica ions such as wi eless senso ne wo ks [
6
],
LiDAR [
7
], cogni i e adio ne wo ks [
8
], au omo i e ada , sho - ange ada , wea able
de ices, medical imaging, ehicula communica ions, and pe sonal a ea ne wo ks a a high
ange [9].
The ul a-wideband an enna is gaining popula i y due o se e al ad an ages o e ed by
i . These ad an ages include wideband ope abili y, a high da a a e a a low spec al powe
densi y o adia ed powe , obus ness o ading, and i s capaci y o ansmi sho -du a ion
pulses o a la ge bandwid h. The UWB MIMO (mul iple-inpu and mul iple-ou pu )
an enna has a p ominen and ou s anding pe o mance among wi eless communica ion
Elec onics 2022,11, 3087. h ps://doi.o g/10.3390/elec onics11193087 h ps://www.mdpi.com/jou nal/elec onics
Elec onics 2022,11, 3087 2 o 19
echnologies, making i widely used in he pas ew yea s. The ich dispe sion se ing
allows o da a ansmission e iciency and he abili y o be imp o ed wi hou consuming
addi ional powe o bandwid h. A compac size and high bandwid h a e necessa y when
adminis e ing he MIMO an enna sys em on po able de ices. A high isola ion be ween
an enna componen s in con ined spaces is also impo an , as he mu ual coupling a ec s
bo h he co ela ion and e iciency o he an enna. Consequen ly, his p oposed wo k
ocuses on minimizing he size wi hou a ec ing necessa y pa ame e s such as S-pa ame e s
and isola ion.
Di e en echniques o UWB an ennas ha e been epo ed in he li e a u e. An
a angemen o complemen a y spli - ing esona o s (CSRRs) on he g ound plane was
p oposed in [
10
] o maximum isola ion. An an enna design wi h he an ennal elemen s
isola ed om each o he by an ex uded T-shaped s ub and enclosed by he ec angula
g ound plane was sugges ed in [
11
]. Wi h he inclusion o a ci cula me al disc in he
g ound plane, a combina ion o ou wideband an ennas was p oposed by he au ho s
o [
12
]. This disc ac s as an exis ing pool wi h a 180
◦
phase di e ence, esul ing in sepa a ion
be ween sepa a e po s. A new oc agonal UWB an enna design p oposed in [
13
] has made
he sys em in isible o enemy ada because o i s minimal ada c oss-sec ion. Only
wo ope a ing band esonances we e added due o he al e ed g ound and semi-ellip ical
pa ch in a design p oposed by he au ho s o [
14
]. A no el sepa a ion me hod based on a
ence- ype decoupling sys em was sugges ed o MIMO an ennas in [15].
De eloping o ganic o hogonal s uc u es, ou -way s ai case-shaped decoupling,
symme ical a angemen s, mul iple slo s, and mul i-sli echniques o enable minia u iza-
ion wi h high e iciency a e discussed in [
16
]. I was demons a ed in [
17
] ha by cu ing
C-shaped slo s in o he adia o po ion and e ching ec angula slo s in o he an enna’s
g ound plane, WLAN equencies can be a oided and ecip ocal coupling be ween he
elemen s can be educed. A high isola ion be ween wo po s was achie ed by leng h-
ening he s ub om he g ound and eng a ing a T-shaped slo in he adia o in [
18
].
Good isola ion can be achie ed by a anging pe pendicula adia ing elemen s and using
sel -complemen a y s uc u es wi hou equi ing a complex decoupling s uc u e. The
WLAN sys em band ejec ion can also be accomplished by eng a ing sli s in o he adia ing
elemen s [
19
]. A high isola ion wi hou a decoupling s uc u e was achie ed by he au ho s
o [
20
] using di e en an ennal elemen s. The use o me ama e ial-inspi ed isola o s was
p oposed in [21] o inc easing he isola ion and minimiza ion.
A ing-shaped b oadband esonance c ea ed by ex ending he ec angula g ound o
c ea e a monopole and i s sides was sugges ed in [
22
]. Co-plana eeds wi h asymme ic
shapes o educe he an enna size was p oposed in [
23
]. The au ho s o [
24
] claim ha a
unique C-shaped slo wi h a C-shaped adia ing ea u e and an eng a ed g ound can esul
in a compac LTE build. A simple in e ed L-shaped g ound plane s uc u e can imp o e
sha p ejec ion on he WLAN band, po isola ion, and bandwid h [
25
]. Many echniques
o imp o ing in e -elemen isola ion ha e been p oposed in he li e a u e. These include
he o hogonal a angemen o he an ennal elemen s [
26
], decoupling s uc u es [
27
], quasi-
sel -complemen a y designs [
28
], and ac al s uc u es [
29
]. The decoupling app oach
inspi ed he me asu ace p inciple by ealizing ec angula slo s in a linea and se ies
con igu a ion inco po a ed be ween he an ennas o dec ease hei in e ac ion and educe
he su ace wa es [
30
]. A su ey p esen ed in [
31
] p o ides a comp ehensi e s udy on he
in es iga ions o a ious isola ion imp o emen app oaches based on me ama e ial- and
me asu ace-inspi ed echniques o an ennal a ays. A me hod o enhancing he adia ion
gain and e iciency o me ama e ial (MTM)-inspi ed plana an ennas using subs a e-
in eg a ed wa eguide (SIW) echnology o sub-6 GHz wi eless communica ion sys ems
was p oposed in [
32
]. The me ama e ial-inspi ed s uc u e exhibi ed imp o emen s in he
isola ion. A ou -elemen MIMO dual band, dual di e si y, dipole an enna was p oposed
in [
33
] o 5G-enabled handse s. The design p oposed in [
34
] elied on space di e si y
and pa e n di e si y o p o ide an accep able MIMO pe o mance. The di e en slo s
Elec onics 2022,11, 3087 3 o 19
and s ubs we e used o imp o e he isola ion be ween he an ennal elemen s in he wo k
p esen ed by he au ho s o [35].
In his wo k, we p esen he design o a compac plana ul a-wideband MIMO
an enna wi h good isola ion o e a wide ange o equencies. A g ound plane o pe ec
elec ic conduc o (PEC) ma e ial and FR-4 lossy ma e ial subs a es we e used in he design
o a single uni cell, making ou design cos -e ec i e. The elemen s we e o hogonally
a anged o o m a quad-pa an enna ha gua an ees compac ness and good isola ion.
The di e si y gains o he MIMO an enna, ECC, and S-pa ame e s we e imp o ed o e he
b oad bandwid h, making i sui able o ealis ic MIMO sys ems.
The key bene i s o his wo k include:
•
The UWB ange, as well as o he alloca ed communica ions anges, a e occupied
by a single an enna po wi h he in oduc ion o he di e si y o e icien use o
hese bands.
•
Using o hogonal adia o s o achie e high sepa a ion wi hou employing any compli-
ca ed s uc u e o decoupling.
•
The compac size o he whole an enna design o he equency band ex ending om
3.1 o 10.6 GHz. The size o he MIMO an enna is small enough o be packaged in a
squa e case, making i use ul o po able de ices.
2. P oposed An enna Design
The p o o ypes o he UWB MIMO an enna design p oposed in his wo k ha e been
ealized on an FR4 (lossy) subs a e o size 28
×
28
×
1.6 mm
3
. The eason o choosing FR4
subs a e is ha i is economical and pe mi s he wo s -case scena io o he analysis o he
adia ion cha ac e is ics o he an enna. The p oposed an enna was designed wi h a ape ed
eed and an o hogonal a angemen o ou an ennal elemen s o a ain a s ong isola ion
o a leas 15 dB. The dis ance be ween he an ennal elemen s also pe mi s
p ope adia ion
.
2.1. Uni Cell Design
The uni cell o he p oposed an enna consis ed o a pa ial g ound plane and an
an enna adia o ha was designed in ou s eps, whe e di e en geome ical shapes
(squa e, ec angula , hexagonal, and V-shaped pa ch) we e used, inally leading o he
pa icula o m shown in Figu e 1. The compu e simula ion ool CST Mic owa e S udio
was used o he design, analysis, and op imiza ion p ocess o he p oposed an enna. The
le hal o Figu e 1illus a es he on iew ( adia ing elemen ) o he uni cell, whe eas he
igh hal illus a es he ea iew (g ound plane) o he uni cell. The op imized geome ical
dimensions o he p oposed an enna a e lis ed in Table 1.
Elec onics 2022, 11, 3087 4 o 20
Figu e 1. F on and ea iews o uni -cell an enna.
Table 1. Geome ical speci ica ions o p oposed monopole UWB uni -cell an enna.
Pa ame e
1
2
3
l1
l2
l3
l4
l5
l6
l7
l8
Uni s (mm)
1
0.9
1.5
2
4
1
9
1
2
1.5
2.5
Pa ame e
l9
lg
w1
w2
w3
w4
w5
w6
wg
W
L
Uni s (mm)
1.3
6
3
1
3
5
9.4
4.5
10
10
18
A 50 Ω mic os ip line ed he single uni cell wi h a hexagonally shaped adia o
wi h dimensions o 10 mm × 18 mm. The FR4 subs a e had a pe mi i i y alue o 4.3 and
a loss angen o 0.02. One side o he subs a e had a 0.035 mm hick g ound plane. The
design o he pa ial g ound plane played a key ole in achie ing UWB pe o mance. The
use o a pa ial plane in he subs a e educed he s o age o ene gy, which caused a de-
c ease in he quali y ac o and e en ually esul ed in an imp o ed bandwid h. Tape ed
eed lines o 9 × 3 mm2 we e used o inc ease he cu en looding nea he adia o and
achie e he equi ed impedance.
Va ious s ages o e olu ion we e ca ied ou in o de o a i e a he inal design o
he single uni -cell an enna. A e e y s age, he S pa ame e o he simula ed an ennal cell
was e alua ed and sui able modi ica ions we e inco po a ed in o he uni cell design o
imp o ing he S pa ame e . The inal design o he uni -cell an enna was achie ed o e
ou s ages o e olu ion, as shown in Figu e 2. The simula ed S pa ame e s du ing he
e olu ion s ages a e displayed in Figu e 3. The an enna designed in S ep 1 consis ed o a
low-p o ile, compac -sized mic os ip line- ed V-shaped pa ch. (Re e o S ep 1 in Figu e
2). This an enna, howe e , had a poo impedance bandwid h, as seen in he g een-colo ed
cu e in Figu e 3. In e olu ion S ep 2, a ec angle adia o and wo o a ed squa e-shaped
adia o s we e in eg a ed in o a mic os ip- ed V-shaped adia o o inc ease he imped-
ance bandwid h, as shown in S ep 2 o Figu e 2. In his modi ica ion, he uppe UWB
equencies we e co e ed, bu he lowe UWB equencies we e no co e ed well. The
hexagonal- o m adia o concep is an in elligen solu ion o compac UWB MIMO an-
ennas. In S ep 3, we added wo hexagonally shaped adia o s along wi h ano he ec an-
gula adia o o inc ease he impedance bandwid h. The esul ing impedance bandwid h
cu e is shown in blue colo . I can be seen om he cu e ha he impedance bandwid h
imp o ed. The inal e olu ion was ca ied ou o u he imp o emen by adding a ec-
angula pa ch a he op o he s uc u e, as shown in S ep 4 o Figu e 2. The co espond-
ing cu e is shown in black colo in Figu e 3. Pic u es o he ab ica ed uni -cell an enna,
along wi h a scale, a e displayed in Figu e 4.
Figu e 1. F on and ea iews o uni -cell an enna.
Elec onics 2022,11, 3087 4 o 19
Table 1. Geome ical speci ica ions o p oposed monopole UWB uni -cell an enna.
Pa ame e 1 2 3l1l2l3l4l5l6l7l8
Uni s (mm) 1 0.9 1.5 2 4 1 9 1 2 1.5 2.5
Pa ame e l9lgw1w2w3w4w5w6wgW L
Uni s (mm) 1.3 6 3 1 3 5 9.4 4.5 10 10 18
A 50
Ω
mic os ip line ed he single uni cell wi h a hexagonally shaped adia o wi h
dimensions o 10 mm
×
18 mm. The FR4 subs a e had a pe mi i i y alue o 4.3 and a loss
angen o 0.02. One side o he subs a e had a 0.035 mm hick g ound plane. The design
o he pa ial g ound plane played a key ole in achie ing UWB pe o mance. The use o a
pa ial plane in he subs a e educed he s o age o ene gy, which caused a dec ease in he
quali y ac o and e en ually esul ed in an imp o ed bandwid h. Tape ed eed lines o
9
×
3 mm
2
we e used o inc ease he cu en looding nea he adia o and achie e he
equi ed impedance.
Va ious s ages o e olu ion we e ca ied ou in o de o a i e a he inal design o
he single uni -cell an enna. A e e y s age, he S pa ame e o he simula ed an ennal cell
was e alua ed and sui able modi ica ions we e inco po a ed in o he uni cell design o
imp o ing he S pa ame e . The inal design o he uni -cell an enna was achie ed o e
ou s ages o e olu ion, as shown in Figu e 2. The simula ed S pa ame e s du ing he
e olu ion s ages a e displayed in Figu e 3. The an enna designed in S ep 1 consis ed o a
low-p o ile, compac -sized mic os ip line- ed V-shaped pa ch. (Re e o S ep 1 in Figu e 2).
This an enna, howe e , had a poo impedance bandwid h, as seen in he g een-colo ed
cu e in Figu e 3. In e olu ion S ep 2, a ec angle adia o and wo o a ed squa e-shaped
adia o s we e in eg a ed in o a mic os ip- ed V-shaped adia o o inc ease he impedance
bandwid h, as shown in S ep 2 o Figu e 2. In his modi ica ion, he uppe UWB equencies
we e co e ed, bu he lowe UWB equencies we e no co e ed well. The hexagonal- o m
adia o concep is an in elligen solu ion o compac UWB MIMO an ennas. In S ep 3,
we added wo hexagonally shaped adia o s along wi h ano he ec angula adia o o
inc ease he impedance bandwid h. The esul ing impedance bandwid h cu e is shown in
blue colo . I can be seen om he cu e ha he impedance bandwid h imp o ed. The
inal e olu ion was ca ied ou o u he imp o emen by adding a ec angula pa ch a
he op o he s uc u e, as shown in S ep 4 o Figu e 2. The co esponding cu e is shown
in black colo in Figu e 3. Pic u es o he ab ica ed uni -cell an enna, along wi h a scale,
a e displayed in Figu e 4.
2.2. Monopole UWB MIMO An enna
The ul a-wideband MIMO monopole an enna can be made using ou uni -cell an en-
nas. The uni -cell s uc u e desc ibed in he abo e sec ion was used o de elop he UWB
MIMO an enna. Fou uni -cell an ennas we e moun ed a he ou co ne s o he subs a e
o o m he p oposed an enna. The mu ual coupling and isola ion a e impo an pa ame e s
ha ha e signi ican e ec s o indi iduali y be ween he uni cells. In o de o boos he
pe o mance o he MIMO an enna, i was necessa y o achie e adequa e isola ion. Fo his
eason, he ou uni cells we e a anged o hogonally. The on and back iews o he
p oposed MIMO an enna s uc u e a e illus a ed in Figu e 5. Be e pe o mance o he
MIMO an enna can be ob ained by es ic ing he sca e ing pa ame e s below −15 dB.
Elec onics 2022,11, 3087 5 o 19
Elec onics 2022, 11, 3087 5 o 20
Figu e 2. E olu ion o monopole UWB uni -cell an enna.
Figu e 2. E olu ion o monopole UWB uni -cell an enna.

Elec onics 2022,11, 3087 6 o 19
Elec onics 2022, 11, 3087 6 o 20
Figu e 3. Simula ed S pa ame e S11 du ing e olu ion s ages.
Figu e 4. Fab ica ed uni -cell an enna.
2.2. Monopole UWB MIMO An enna
The ul a-wideband MIMO monopole an enna can be made using ou uni -cell an-
ennas. The uni -cell s uc u e desc ibed in he abo e sec ion was used o de elop he
UWB MIMO an enna. Fou uni -cell an ennas we e moun ed a he ou co ne s o he
subs a e o o m he p oposed an enna. The mu ual coupling and isola ion a e impo an
pa ame e s ha ha e signi ican e ec s o indi iduali y be ween he uni cells. In o de
o boos he pe o mance o he MIMO an enna, i was necessa y o achie e adequa e iso-
la ion. Fo his eason, he ou uni cells we e a anged o hogonally. The on and back
iews o he p oposed MIMO an enna s uc u e a e illus a ed in Figu e 5. Be e pe o -
mance o he MIMO an enna can be ob ained by es ic ing he sca e ing pa ame e s be-
low −15 dB.
Figu e 3. Simula ed S pa ame e S11 du ing e olu ion s ages.
Elec onics 2022, 11, 3087 6 o 20
Figu e 3. Simula ed S pa ame e S11 du ing e olu ion s ages.
Figu e 4. Fab ica ed uni -cell an enna.
2.2. Monopole UWB MIMO An enna
The ul a-wideband MIMO monopole an enna can be made using ou uni -cell an-
ennas. The uni -cell s uc u e desc ibed in he abo e sec ion was used o de elop he
UWB MIMO an enna. Fou uni -cell an ennas we e moun ed a he ou co ne s o he
subs a e o o m he p oposed an enna. The mu ual coupling and isola ion a e impo an
pa ame e s ha ha e signi ican e ec s o indi iduali y be ween he uni cells. In o de
o boos he pe o mance o he MIMO an enna, i was necessa y o achie e adequa e iso-
la ion. Fo his eason, he ou uni cells we e a anged o hogonally. The on and back
iews o he p oposed MIMO an enna s uc u e a e illus a ed in Figu e 5. Be e pe o -
mance o he MIMO an enna can be ob ained by es ic ing he sca e ing pa ame e s be-
low −15 dB.
Figu e 4. Fab ica ed uni -cell an enna.
Elec onics 2022, 11, 3087 7 o 20
The on and back iews o he ab ica ed MIMO an enna a e shown in Figu e 6. The
o e all size o he ou -po an enna was 28 × 28 × 1.6 mm3. Figu e 7 shows he uni -cell
an enna sca e ing pa ame e (S11) o e he a ge bandwid h. I can be seen ha he alue
o S11 is below −10 dB o e he en i e equency ange om 3.1 o 10.6 GHz.
Figu e 5. F on and ea iew o MIMO an enna s uc u e.
Figu e 6. Fab ica ed UWB MIMO an enna.
Figu e 5. F on and ea iew o MIMO an enna s uc u e.
Elec onics 2022,11, 3087 7 o 19
The on and back iews o he ab ica ed MIMO an enna a e shown in Figu e 6. The
o e all size o he ou -po an enna was 28
×
28
×
1.6 mm
3
. Figu e 7shows he uni -cell
an enna sca e ing pa ame e (S
11
) o e he a ge bandwid h. I can be seen ha he alue
o S11 is below −10 dB o e he en i e equency ange om 3.1 o 10.6 GHz.
Elec onics 2022, 11, 3087 7 o 20
The on and back iews o he ab ica ed MIMO an enna a e shown in Figu e 6. The
o e all size o he ou -po an enna was 28 × 28 × 1.6 mm3. Figu e 7 shows he uni -cell
an enna sca e ing pa ame e (S11) o e he a ge bandwid h. I can be seen ha he alue
o S11 is below −10 dB o e he en i e equency ange om 3.1 o 10.6 GHz.
Figu e 5. F on and ea iew o MIMO an enna s uc u e.
Figu e 6. Fab ica ed UWB MIMO an enna.
Figu e 6. Fab ica ed UWB MIMO an enna.
Elec onics 2022, 11, 3087 8 o 20
Figu e 7. Simula ed and measu ed S11 pa ame e s o he monopole UWB uni -cell an enna.
3. Resul s and Discussion
The ab ica ed p o o ype o he an enna was expe imen ally e alua ed and alida ed
by a compa ison o he simula ed and measu ed esul s. Measu emen s o de e mine he
an enna’s MIMO/Di e si y pa ame e s we e conduc ed using an An i su MS2703 Vec o
Ne wo k Analyze , shown in Figu e 8. The di e si y pa ame e measu emen and adia-
ion pa e n measu emen we e conduc ed using a se up in an anechoic chambe , as
shown in Figu e 9. The pe o mance compa ison o he p oposed design wi h he exis ing
designs is also p esen ed.
S-pa ame e s can be used o calcula e a ious pa ame e s o MIMO sys ems ha en-
able a quan i a i e compa ison o he MIMO sys ems. These pa ame e s include en elope
co ela ion coe icien s (ECC), di e si y gains (DG), channel capaci y losses (CCL), and
he o al ac i e e lec ion coe icien (TARC). CST Mic owa e S udio so wa e was used
o simula e and analyze he an enna’s adia ion cha ac e is ics.
Figu e 7. Simula ed and measu ed S11 pa ame e s o he monopole UWB uni -cell an enna.
Elec onics 2022,11, 3087 8 o 19
3. Resul s and Discussion
The ab ica ed p o o ype o he an enna was expe imen ally e alua ed and alida ed
by a compa ison o he simula ed and measu ed esul s. Measu emen s o de e mine he
an enna’s MIMO/Di e si y pa ame e s we e conduc ed using an An i su MS2703 Vec o
Ne wo k Analyze , shown in Figu e 8. The di e si y pa ame e measu emen and adia ion
pa e n measu emen we e conduc ed using a se up in an anechoic chambe , as shown in
Figu e 9. The pe o mance compa ison o he p oposed design wi h he exis ing designs is
also p esen ed.
Elec onics 2022, 11, 3087 9 o 20
Figu e 8. An i su MS2703 Vec o Ne wo k Analyze used o measu e MIMO pa ame e s.
Figu e 9. MIMO an enna expe imen al measu emen se up.
3.1. Mu ual Coupling
The Ul a-wideband MIMO monopole an enna was made by a anging mul iple
uni -cell an ennas o a simila shape. When mul iple uni -cell an ennas a e in eg a ed in o
a small subs a e o o m a UWB MIMO an enna, s onge mu ual coupling be ween cells
leads o an enna impedance misma ching, which ul ima ely educes he channel capaci y.
Fo a gi en uni -cell an enna i, he mu ual coupling due o he o he cell j, wi h (i ≠ j), can
be ob ained in e ms o he Sij pa ame e . The MIMO an enna’s o hogonal a angemen
educed he mu ual coupling and o e all size. The UWB MIMO monopole an enna design
should ha e a mu ual coupling o less han −20 dB o op imal pe o mance.
Figu e 10 shows he measu ed and simula ed esul s o he isola ion o he p oposed
UWB MIMO monopole an enna. I is clea om he igu e ha he p oposed UWB-MIMO
an ennal sys em p o ides a high isola ion and a mu ual coupling o less han −20 dB o e
he equency ange om 3.1 o 10.6 GHz. Be e pe o mance o he p oposed an enna in
e ms o he isola ion and mu ual coupling be ween an ennal elemen s was achie ed due
o he use o he educed g ound plane and ape ed eed in he design.
Figu e 8. An i su MS2703 Vec o Ne wo k Analyze used o measu e MIMO pa ame e s.
Elec onics 2022, 11, 3087 9 o 20
Figu e 8. An i su MS2703 Vec o Ne wo k Analyze used o measu e MIMO pa ame e s.
Figu e 9. MIMO an enna expe imen al measu emen se up.
3.1. Mu ual Coupling
The Ul a-wideband MIMO monopole an enna was made by a anging mul iple
uni -cell an ennas o a simila shape. When mul iple uni -cell an ennas a e in eg a ed in o
a small subs a e o o m a UWB MIMO an enna, s onge mu ual coupling be ween cells
leads o an enna impedance misma ching, which ul ima ely educes he channel capaci y.
Fo a gi en uni -cell an enna i, he mu ual coupling due o he o he cell j, wi h (i ≠ j), can
be ob ained in e ms o he Sij pa ame e . The MIMO an enna’s o hogonal a angemen
educed he mu ual coupling and o e all size. The UWB MIMO monopole an enna design
should ha e a mu ual coupling o less han −20 dB o op imal pe o mance.
Figu e 10 shows he measu ed and simula ed esul s o he isola ion o he p oposed
UWB MIMO monopole an enna. I is clea om he igu e ha he p oposed UWB-MIMO
an ennal sys em p o ides a high isola ion and a mu ual coupling o less han −20 dB o e
he equency ange om 3.1 o 10.6 GHz. Be e pe o mance o he p oposed an enna in
e ms o he isola ion and mu ual coupling be ween an ennal elemen s was achie ed due
o he use o he educed g ound plane and ape ed eed in he design.
Figu e 9. MIMO an enna expe imen al measu emen se up.
S-pa ame e s can be used o calcula e a ious pa ame e s o MIMO sys ems ha enable
a quan i a i e compa ison o he MIMO sys ems. These pa ame e s include en elope
co ela ion coe icien s (ECC), di e si y gains (DG), channel capaci y losses (CCL), and
he o al ac i e e lec ion coe icien (TARC). CST Mic owa e S udio so wa e was used o
simula e and analyze he an enna’s adia ion cha ac e is ics.
Elec onics 2022,11, 3087 9 o 19
3.1. Mu ual Coupling
The Ul a-wideband MIMO monopole an enna was made by a anging mul iple uni -
cell an ennas o a simila shape. When mul iple uni -cell an ennas a e in eg a ed in o a
small subs a e o o m a UWB MIMO an enna, s onge mu ual coupling be ween cells
leads o an enna impedance misma ching, which ul ima ely educes he channel capaci y.
Fo a gi en uni -cell an enna i, he mu ual coupling due o he o he cell j, wi h (i
6=
j), can
be ob ained in e ms o he S
ij
pa ame e . The MIMO an enna’s o hogonal a angemen
educed he mu ual coupling and o e all size. The UWB MIMO monopole an enna design
should ha e a mu ual coupling o less han −20 dB o op imal pe o mance.
Figu e 10 shows he measu ed and simula ed esul s o he isola ion o he p oposed
UWB MIMO monopole an enna. I is clea om he igu e ha he p oposed UWB-MIMO
an ennal sys em p o ides a high isola ion and a mu ual coupling o less han
−
20 dB o e
he equency ange om 3.1 o 10.6 GHz. Be e pe o mance o he p oposed an enna in
e ms o he isola ion and mu ual coupling be ween an ennal elemen s was achie ed due
o he use o he educed g ound plane and ape ed eed in he design.
Elec onics 2022, 11, 3087 10 o 20
Figu e 10. Simula ed and measu ed isola ion o monopole UWB MIMO an enna.
3.2. En elope Co ela ion Coe icien (ECC)
A MIMO an enna’s essen ial di e si y pa ame e is he co ela ion be ween he adi-
a ing elemen s. The en elope co ela ion coe icien e lec s how he an ennal elemen s
a e independen o each o he . I measu es he simila i y be ween he pe o mances o he
an ennas om a adia ion pa e n poin o iew. Ideally, he adia ion pa e ns o wo o
mo e an ennas should be en i ely independen o each o he . The alue o ECC can be
es ima ed by using 3D adia ion pa e ns. This alue should be 0 in he ideal case, and i
should no exceed 0.5 in any p ac ical case. Lowe alues o ECC mean ha he wo an-
ennas a e well isola ed. Al hough i is di icul o es ima e he ECC alue, i can s ill be
compu ed using he S pa ame e s. The en elope co ela ion coe icien is de e mined by
eplacing he S pa ame e s in Equa ion (1) [36,37].
𝐸𝐶𝐶𝑖𝑗=|𝑆ii∗ 𝑆ij+𝑆ji∗𝑆jj|2
(1−|𝑆ii|2 −|𝑆ij|2 )(1−|𝑆jj|2 −|𝑆ji|2 )
(1)
He e, i and j a e he po numbe s. Looking a Figu e 11, we ind ha he ECC is
much less han 0.001 be ween all he po s, which is closely equal o he ideal alue o he
en elope co ela ion coe icien .
Figu e 10. Simula ed and measu ed isola ion o monopole UWB MIMO an enna.
3.2. En elope Co ela ion Coe icien (ECC)
A MIMO an enna’s essen ial di e si y pa ame e is he co ela ion be ween he adi-
a ing elemen s. The en elope co ela ion coe icien e lec s how he an ennal elemen s
a e independen o each o he . I measu es he simila i y be ween he pe o mances o he
an ennas om a adia ion pa e n poin o iew. Ideally, he adia ion pa e ns o wo o
mo e an ennas should be en i ely independen o each o he . The alue o ECC can be
es ima ed by using 3D adia ion pa e ns. This alue should be 0 in he ideal case, and
i should no exceed 0.5 in any p ac ical case. Lowe alues o ECC mean ha he wo
an ennas a e well isola ed. Al hough i is di icul o es ima e he ECC alue, i can s ill be
Elec onics 2022,11, 3087 16 o 19
Elec onics 2022, 11, 3087 17 o 20
(g)
(h)
Figu e 17. The adia ion pa e ns o simula ion and measu emen esul s o E-plane and H-plane
o all 4 po s: (a) po 1 E-plane; (b) po 1 H-plane; (c) po 2 E-plane; (d) po 2 H-plane; (e) po 3
E-plane; ( ) po 3 H-plane; (g) po 4 E-plane; and (h) po 4 H-plane.
Table 2 p esen s a quan i a i e compa ison o he p oposed an enna design wi h he
an enna designs epo ed in he li e a u e. The compa ison was made on he basis o di -
e en ypes o s uc u es and pa ame e s, such as he design me hod, he numbe o po s,
he size o an enna, he isola ion, TARC, ECC, CCL, gain, and he ope a ing equency
ange.
Table 2.
Compa ison wi h designs in exis ing li e a u e.
Re
Po s
Applied Design Me hod
Size
(mm
2
)
Isola ion
(dB)
TARC
(dB)
ECC
CCL
(bps/Hz)
Gain
(dBi)
GHz
[15]
4
AFS minia u izing echnique
40 × 40
>17
-
<0.03
-
5
2.94–14
[16]
4
Fou -di ec ional s ai case-shaped
s uc u e
39 × 39
>22
<−10
<0.02
<0.2
1.4–4.6
2.3–13.7
[17]
4
Decoupling s uc u e
70 × 41
17
<−9
<0.012
<0.4
-
3.1–12
[18]
2
Coplana - ed
27 × 52
≥20
-
-
-
-
-
[19]
4
QSCA
40 × 40
≥20
-
<0.04
−7
3.85–4.67
2.9–12.1
[20]
2
Fence- ype decoupling s uc u e
35 × 50
>25
-
<0.004
-
-
3–11
[22]
4
Rec angula slo s in g ound
40 × 40
>20
-
-
-
-
3–11.5
[23]
4
Co adia o
40 × 40
>10
-
-
-
-
3–11
[24]
4
Quasi-sel -complemen a y
50 × 50
>20
-
<0.5
-
-
3–12
[25]
2
Ci cula coupling s uc u e
25 × 35
>18
-
<0.005
-
-
3.1–11
[45]
4
Asymme ic coplana s ip- ed
40 × 43
20
−8
<0.2
<0.3
-
3.1–10.6
[46]
4
Phase- e e sed and phase- o a ed
an ennal elemen s
68 × 98
10
-
<0.1
-
-
1.66–2.7
[47]
4
O hogonal, de ec ed g ound s uc-
u e
40 × 40
>35
-
<0.001
-
-
3.1–10.6
P oposed
4
O hogonal, ape ed eed
28 × 28
>20
<−10
<0.001
< 0.4
3
3.1–10.6
In his compa ison, i was obse ed ha he p oposed an enna was he mos compac ,
as i s size in e ms o a ea was 28 × 28 = 784 mm2, which was he smalles among all o he
an ennas. The p oposed an enna p o ided be e isola ion han ha p o ided by he o he
an ennas o a compa able size. Fu he , he design achie ed p omising esul s in e ms o
a CCL alue less han 0.4 bi s/s/Hz, a TARC alue less han −10 dB, and an ECC alue less
han 0.001.
Figu e 17.
The adia ion pa e ns o simula ion and measu emen esul s o E-plane and H-plane o
all 4 po s: (
a
) po 1 E-plane; (
b
) po 1 H-plane; (
c
) po 2 E-plane; (
d
) po 2 H-plane; (
e
) po 3
E-plane; ( ) po 3 H-plane; (g) po 4 E-plane; and (h) po 4 H-plane.
Table 2p esen s a quan i a i e compa ison o he p oposed an enna design wi h
he an enna designs epo ed in he li e a u e. The compa ison was made on he basis
o di e en ypes o s uc u es and pa ame e s, such as he design me hod, he numbe
o po s, he size o an enna, he isola ion, TARC, ECC, CCL, gain, and he ope a ing
equency ange.
Table 2. Compa ison wi h designs in exis ing li e a u e.
Re Po s Applied Design
Me hod
Size
(mm2)
Isola ion
(dB)
TARC
(dB) ECC CCL
(bps/Hz)
Gain
(dBi) GHz
[15] 4 AFS minia u izing
echnique 40 ×40 >17 - <0.03 - 5 2.94–14
[16] 4
Fou -di ec ional
s ai case-shaped
s uc u e
39 ×39 >22 <−10 <0.02 <0.2 1.4–4.6 2.3–13.7
[17] 4 Decoupling s uc u e 70 ×41 17 <−9 <0.012 <0.4 - 3.1–12
[18] 2 Coplana - ed 27 ×52 ≥20 - - - - -
[19] 4 QSCA 40 ×40 ≥20 - <0.04 −7 3.85–4.67 2.9–12.1
[20] 2 Fence- ype decoupling
s uc u e 35 ×50 >25 - <0.004 - - 3–11
[22] 4 Rec angula slo s in
g ound 40 ×40 >20 - - - - 3–11.5
[23] 4 Co adia o 40 ×40 >10 - - - - 3–11
[24] 4 Quasi-sel -
complemen a y 50 ×50 >20 - <0.5 - - 3–12
[25] 2 Ci cula coupling
s uc u e 25 ×35 >18 - <0.005 - - 3.1–11
[45] 4 Asymme ic coplana
s ip- ed 40 ×43 20 −8 <0.2 <0.3 - 3.1–10.6
[46] 4
Phase- e e sed and
phase- o a ed an ennal
elemen s
68 ×98 10 - <0.1 - - 1.66–2.7
[47] 4 O hogonal, de ec ed
g ound s uc u e 40 ×40 >35 - <0.001 - - 3.1–10.6
P oposed
4
O hogonal, ape ed eed
28 ×28 >20 <−10 <0.001 < 0.4 3 3.1–10.6
In his compa ison, i was obse ed ha he p oposed an enna was he mos compac ,
as i s size in e ms o a ea was 28
×
28 = 784 mm
2
, which was he smalles among all o he
an ennas. The p oposed an enna p o ided be e isola ion han ha p o ided by he o he

Elec onics 2022,11, 3087 17 o 19
an ennas o a compa able size. Fu he , he design achie ed p omising esul s in e ms o a
CCL alue less han 0.4 bi s/s/Hz, a TARC alue less han
−
10 dB, and an ECC alue less
han 0.001.
4. Conclusions
A design o a compac ou -po UWB MIMO an enna wi h he o e all dimensions o
28 mm
×
28 mm
×
1.6 mm is p esen ed in his pape . Pola iza ion di e si y, an o hogonal
a angemen , and a ape ed eed we e employed in he MIMO an enna o achie e a highe
isola ion. The p oposed an enna ope a ed in he en i e UWB band (3.1–10.6 GHz) wi h a
high isola ion. The an enna had an a e age gain o 3.0 dBi. The di e si y pe o mance o
he p oposed an enna was good, wi h an ECC alue less han 0.001, a DG alue g ea e han
9.90, a TARC alue less han
−
10 dB, and an isola ion g ea e han 20 dB. The measu ed
alues o e u n loss, isola ion, and he adia ion pa e n ag ee wi h he simula ed ones.
In summa y, he p oposed an enna is a p omising candida e o UWB MIMO wi eless
di e si y applica ions. One challenge hese an ennas ace is elec omagne ic in e e ence
be ween UWB and licensed equency bands. Fu u e designs should aim a he cons uc ion
o an an enna wi h no ched-band ea u es o mi iga e his issue.
Au ho Con ibu ions:
Concep ualiza ion, S.K., L.B. and M.M.; da a cu a ion, S.K.; o mal analysis,
S.K.; in es iga ion, S.K.; me hodology, S.K., L.B. and M.M.; so wa e, S.K., L.B. and M.M.; supe ision,
L.B.; w i ing—o iginal d a , S.K.; w i ing— e iew and edi ing, L.B. and M.M. All au ho s ha e ead
and ag eed o he published e sion o he manusc ip .
Funding:
This wo k was suppo ed by he p ojec SP2022/60 Applied Resea ch in he A ea o Ma-
chines and P ocess Con ol, suppo ed by he Minis y o Educa ion, You h and Spo s,
Czech Republic
.
Da a A ailabili y S a emen :
The da a p esen ed in his s udy a e a ailable h ough email upon
eques o he co esponding au ho .
Con lic s o In e es : The au ho s decla e no con lic o in e es .
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