Expe imen al Cha ac e iza ion and Empi ical Beam
S ee ing Analysis o a 28 GHz 1-Bi 8x8 RIS
Re lec a ay ia Conduc i i y Pa e n Modula ion
Vasiliki Papapos olou
School o Elec ical and Compu e Enginee ing
A is o le Uni e si y o Thessaloniki
Thessaloniki, G eece
[email p o ec ed]
Yio gos Mak is
Dep . o Elec ical and Compu e Enginee ing
Jonsson School o Enginee ing and Compu e Science
The Uni e si y o Texas a Dallas
Richa dson, USA
[email p o ec ed]
Alkis Ha zopoulos
School o Elec ical and Compu e Enginee ing
A is o le Uni e si y o Thessaloniki
Thessaloniki, G eece
[email p o ec ed]
Zaha ias D. Zaha is
School o Compu ing and Enginee ing
Uni e si y o Hudde s ield
Hudde s ield, Uni ed Kingdom
School o Elec ical and Compu e Enginee ing
A is o le Uni e si y o Thessaloniki
Thessaloniki, G eece
[email p o ec ed]
Abs ac — This wo k in es iga es he beam s ee ing
capabili ies o a small- o-medium-sized Recon igu able
In elligen Su ace (RIS) consis ing o an 8×8 a ay o simpli ied
1-bi e lec i e uni cells ope a ing a 28 GHz. Each uni cell is
composed o wo ec angula pa ches connec ed by a single PIN
diode, o ming a compac and ab ica ion- iendly design ha
omi s ias and complex bias ci cui y. The a ay is illumina ed
unde no mal incidence by a e ically o ien ed ho n an enna,
and a ious bina y ON/OFF con ol pa e ns a e applied o
modula e he e lec i i y s a es o he uni cells. The esul ing
a - ield adia ion pa e ns a e measu ed expe imen ally o
assess he ex en o which he di ec ion o he main lobe can be
s ee ed solely by modi ying he conduc i i y pa e n ac oss he
su ace. Pa icula emphasis is placed on iden i ying empi ical
ules ha ela e he spa ial geome y o he applied pa e ns o
he obse ed beam di ec ion. The esul s demons a e ha e en
modes -sized RIS a ays can achie e e ec i e beam s ee ing
h ough app op ia ely s uc u ed bina y con ol, o e ing
insigh in o low-complexi y RIS design s a egies.
Keywo ds— Recon igu able In elligen Su ace (RIS),
Re lec a ay, 28 GHz, 1-bi uni cell, beam s ee ing, pa e n
con ol
I. INTRODUCTION
Recon igu able In elligen Su aces (RIS) ha e ecen ly
eme ged as a ans o ma i e echnology o nex -gene a ion
wi eless communica ions, such as 6G and beyond. By
enabling p og ammable con ol o e he elec omagne ic
(EM) en i onmen , RIS can dynamically manipula e inciden
wa e on s o enhance signal quali y, educe in e e ence, and
imp o e co e age, all wi h minimal ene gy consump ion and
ha dwa e complexi y. Unlike adi ional ac i e beam o ming
sys ems ha ely on powe -hung y RF chains, RIS-based
sys ems u ilize passi e o semi-passi e elemen s o e lec o
edi ec incoming wa es owa d desi ed di ec ions, o e ing a
p omising solu ion o ene gy-e icien and cos -e ec i e
beam con ol [1], [2].
A key ac o in he pe o mance o a RIS lies in he design
o i s uni cells, which a e ypically s uc u ed o impa
con ollable phase shi s upon e lec ion. Among a ious
design s a egies, 1-bi uni cells—capable o swi ching
be ween wo disc e e e lec ion phase s a es ( ypically wi h a
180° di e ence)—ha e gained signi ican in e es due o hei
simplici y, educed con ol equi emen s, and ease o
ab ica ion [3]. These uni cells o en u ilize PIN diodes as
bina y swi ches o al e he conduc i e s a e o he su ace.
P io wo ks ha e explo ed mul ilaye and ia-in eg a ed
designs o implemen such con igu a ions, achie ing
wideband pe o mance and compac o m ac o s [4].
Howe e , hese implemen a ions o en inc ease
manu ac u ing complexi y and cos .
In his wo k, we p opose and expe imen ally e alua e a
simpli ied 1-bi RIS a chi ec u e composed o an 8×8 a ay o
e lec i e uni cells ope a ing a 28 GHz. Each uni cell
ollows he geome y p esen ed in [4], consis ing o wo
ec angula me allic pa ches connec ed by a single PIN diode,
bu elimina es he use o ias and mul ilaye subs a es in
a o o a single-laye dielec ic and g ound plane. The RIS is
illumina ed unde no mal incidence by a e ically o ien ed
ho n an enna, and a ious bina y ON/OFF con ol pa e ns a e
applied ac oss he a ay o examine he esul ing a - ield
adia ion pa e ns. The ull-wa e elec omagne ic simula ions
o he uni cell and a ay con igu a ions we e pe o med in
Ansys HFSS o e i y e lec ion beha io and e alua e he
expec ed beam s ee ing pe o mance. The main ocus o his
s udy is o assess he abili y o such a modes -sized RIS o
s ee he main lobe di ec ion h ough simple bina y
conduc i i y modula ion and o de i e empi ical ela ionships
linking he spa ial geome y o he applied pa e ns o he
obse ed beam s ee ing angles.
The emainde o his pape is o ganized as ollows:
Sec ion II desc ibes he design o he simpli ied uni cell and
i s implemen a ion, he RIS a ay con igu a ion and
expe imen al se up. Sec ion III p esen s and analyzes he
measu ed adia ion pa e ns unde a ious con ol pa e ns.
Finally, Sec ion IV concludes he pape and discusses u u e
esea ch di ec ions.
II. RIS ARCHITECTURE
A. Uni Cell Design
RISs ha e eme ged as a p omising echnology o
dynamic con ol o elec omagne ic wa e p opaga ion in
wi eless communica ion sys ems. Cen al o hei
unc ionali y is he design o he indi idual uni cells, which
mus balance elec omagne ic pe o mance wi h ab ica ion
complexi y and cos . In his wo k, a simpli ied 1-bi e lec i e
uni cell (Fig. 1) is employed ollowing he geome y and
design p inciples p esen ed in [4]. Each uni cell consis s o
wo ec angula me allic pa ches connec ed ia a PIN diode
(MACOM MADP-000907-14020), enabling bina y con ol o
he e lec ed phase. The diode ac s as a swi ch o al e he
su ace cu en dis ibu ion, he eby p oducing a e lec i e
phase di e ence o app oxima ely 90° be ween he ON and
OFF s a es a 28 GHz. Unlike he o iginal mul ilaye
con igu a ion p oposed in [4], he uni cell in his s udy is
ab ica ed on a single dielec ic subs a e (Roge s RO4350B)
wi h hickness 1.116 mm, equi alen o he o al hickness
used in he e e ence design. A con inuous g ound plane is
placed benea h he subs a e. The geome ical dimensions o
he uni cell a e main ained as in [4], wi h a uni cell oo p in
o 2.5 mm × 4 mm (0.23λ × 0.37λ a 28 GHz). The op laye
con ains he wo me allic pa ches, while he PIN diode is
cen ally placed o connec hem. In simula ions, he ON s a e
o he diode is modeled as a se ies LR ci cui (Ron = 4.2 Ω,
Lon = 0.05 nH), while he OFF s a e is modeled as a pa allel
RC ne wo k (Ro = 1.2 kΩ, Co = 33 F) in se ies wi h an
induc ance Lo = 62 nH, consis en wi h he equi alen ci cui
p esen ed in [4, Fig. 8] and ex ac ed om he diode's S
pa ame e s ha can be ound in he o icial websi e o he
MACOM. This simpli ied s uc u e is pa icula ly well-sui ed
o expe imen al p o o yping and low-complexi y RIS
e lec i e a ays.
Fig. 1. Geome y o he p oposed 1-bi RIS uni cell.
B. RIS A ay Con igu a ion and Exci a ion
The RIS implemen ed in his wo k consis s o an 8×8 a ay
o iden ical 1-bi e lec i e uni cells, esul ing in a o al o 64
con ollable elemen s. The uni cells a e a anged wi h a
cen e - o-cen e spacing o λ/2, whe e λ = 10.71 mm
co esponds o he ope a ing equency o 28 GHz. This
subwa eleng h spacing is chosen o minimize g a ing lobes
and ensu e cons uc i e in e e ence in he a ield.
The RIS is illumina ed by a s anda d py amidal
( ec angula ) ho n an enna ope a ing a 28 GHz wi h a
nominal gain o 12 dBi. The ho n is posi ioned di ec ly abo e
he geome ic cen e o he RIS a a e ical dis ance o 60 mm
(Fig. 2) and i s longe ape u e dimension is o ien ed pa allel
o he x-axis, as shown in he op iew o Fig. 3.
Fig. 2. Side iew wi h ho n & RIS.
Fig. 3. Top iew wi h ho n & RIS.
III. BEAM STEERING PERFORMANCE
A. Beam S ee ing Beha io unde Bina y Con ol Pa e ns
To in es iga e he beam s ee ing capabili ies o he
p oposed RIS, mul iple bina y ON/OFF con ol pa e ns we e
applied o he 8×8 a ay o uni cells. As desc ibed ea lie , he
RIS consis s o 64 con ollable e lec i e elemen s wi h a
cen e - o-cen e spacing o λ/2 (λ = 10.71 mm a 28 GHz),
illumina ed by a s anda d ec angula ho n an enna ope a ing
a 28 GHz. The ho n is posi ioned e ically and aligned wi h
he geome ic cen e o he RIS, a a dis ance o 60 mm om
i s su ace, sa is ying he F aunho e a - ield c i e ion and
ensu ing ha he a ay is illumina ed by an app oxima ely
uni o m plane wa e. All simula ions we e ca ied ou in
ANSYS HFSS unde his ixed con igu a ion. Each pa e n
co esponds o a dis inc conduc i i y dis ibu ion ac oss he
uni cells, which in u n al e s he o e all e lec ion phase
p o ile o he su ace and s ee s he main lobe o he e lec ed
adia ion. Fo each applied conduc i i y pa e n, he a - ield
adia ion was ex ac ed and ep esen ed in e ms o h ee-
dimensional pola plo s o he o al gain, allowing he main
lobe di ec ion and side-lobe dis ibu ion o be sys ema ically
obse ed. Wi h his se up, he in luence o di e en spa ial
ON/OFF pa e ns on he s ee ing o he e lec ed beam can be
clea ly assessed and compa ed.
All adia ion pa e ns p esen ed in his sec ion co espond
o a - ield 3D pola plo s o he o al gain, wi h he
co esponding ON/OFF con ol dis ibu ions shown as inse s.
We begin by examining he wo ex eme cases in which all
uni cells a e swi ched ei he o he ON s a e (Fig. 4), o o he
OFF s a e (Fig. 5). As expec ed, bo h con igu a ions yield a
b oadside e lec ion (θ = 0°), wi h no obse able beam
s ee ing. He e, θ ( he a) and φ (phi) deno e he pola and
azimu h angles, espec i ely, in he sphe ical coo dina e
sys em adop ed o he a - ield analysis. These wo e e ence
cases se e as benchma ks o subsequen compa isons.
Fig. 4. All uni cells ON, b oadside e lec ion (θ = 0°).
Fig. 5. All uni cells OFF, b oadside e lec ion (θ = 0°).
Nex , we apply linea ON/OFF dis ibu ions. In he i s
case, all uni cells in he bo om ow we e se o ON while he
es emained OFF (Fig. 6), whe eas in he second case, only
he le mos column was ON (Fig. 7). In bo h con igu a ions,
he main lobe is de lec ed by app oxima ely θ = 5° owa d he
side o he OFF elemen s—φ = 180° o he bo om- ow
exci a ion and φ = 90° o he le -column exci a ion. These
esul s indica e ha linea discon inui ies in he su ace
conduc i i y can in oduce small bu measu able s ee ing
e ec s aligned wi h he axis o asymme y.
Fig. 6. Bo om ow ON and o he s OFF, main lobe de lec ed by
app oxima ely θ = 5° owa d φ = 180°.
Fig. 7. Le mos column ON and o he s OFF, main lobe de lec ed by
app oxima ely θ = 5° owa d φ = 90°.
A diagonal (co ne -based) ON/OFF con igu a ion (Fig. 8),
was hen es ed, p oducing a s onge de lec ion o he main
beam owa d he co ne di ec ion, wi h s ee ing obse ed a φ
= 130° and θ = 30°. Addi ionally, a ci cula -inspi ed pa e n,
adap ed om [5], yielded a mo e mode a e de lec ion o θ =
7° a φ = 90° (Fig. 9). The la e sugges s ha adially shaped
dis ibu ions can bias he e lec ion owa d he di ec ion o he
pa e n’s displacemen .
Building upon he ci cula con igu a ion and ollowing he
design concep in [6], se e al modi ied pa e ns we e
in es iga ed. One a angemen p oduced a s ee ing angle o θ
= 30° a φ = 90° (Fig. 10). By o a ing he same pa e n by 90°
a ound he z-axis, he beam was edi ec ed o φ = 0° a θ = 27°
(Fig. 11). A u he a ia ion o his design yielded an
inc eased s ee ing angle o θ = 33° a φ = 90° (Fig. 12). When
his dis ibu ion was sligh ly shi ed downwa d along he x-
axis, he main lobe s ee ed owa d φ = 65° wi h θ = 33° (Fig.
13), again ollowing he di ec ion o he geome ic
displacemen .
Fig. 8. Diagonal co ne -based con igu a ion, p oducing beam s ee ing a θ =
30°, φ = 130°.
Fig. 9. Ci cula -inspi ed pa e n p oducing θ = 7° a φ = 90°.
In he same design amily, a a ian achie ed θ = 35° a φ
= 90° (Fig. 14). Among all es ed con igu a ions, he la ges
single-lobe s ee ing was ob ained wi h he pa e n in Fig. 15,
p oducing θ = 36° a φ = 90°. Finally, a ela ed a ian wi h
educed spacing be ween OFF elemen s (Fig. 16), esul ed in
wo dominan lobes, loca ed a φ = 65° and φ = 110° wi h θ ≈
42°, highligh ing a ade-o be ween la ge s ee ing angles
and single-lobe in eg i y.
Fig. 10. Modi ied ci cula pa e n (based on Fig. 9) p oducing θ = 30° a φ =
90°.
Fig. 11. Ro a ed e sion o Fig. 10, edi ec ing he beam o θ = 27° a φ = 0°.
Fig. 12. Fu he a ia ion o he Fig. 10 design, p oducing θ = 33° a φ = 90°.
Fig. 13. Downwa d-shi ed a ian o Fig. 12, s ee ing he main lobe o θ =
33° a φ = 65°.
Fig. 14. Op imized ci cula -inspi ed pa e n p oducing he la ges single-lobe
s ee ing a θ = 35°, φ = 90°.
Fig. 15. Con igu a ion achie ing maximum single-lobe s ee ing a θ = 36°,
φ = 90°.
O e all, he esul s demons a e ha he spa ial geome y
o he ON/OFF dis ibu ion c i ically de e mines bo h he
s ee ing di ec ion and he quali y o he main lobe. Linea
bounda ies in oduce small angula de ia ions, while mo e
complex and asymme ic pa e ns can p oduce signi ican ly
la ge s ee ing angles—up o θ = 36° in his s udy— hough
o en a he expense o inc eased side-lobe le els o e en beam
spli ing. These obse a ions p o ide he basis o empi ical
design ules ha link he geome y o bina y con ol pa e ns
o he esul ing beam s ee ing beha io .
Fig. 16. Va ian o Fig. 15 wi h educed OFF-elemen spacing, p oducing
wo dominan lobes a θ = 42°, φ = 65° and φ = 110°.
B. Towa d an Empi ical Beam S ee ing Rule
Beyond he analysis o indi idual ON/OFF dis ibu ions,
he simula ion esul s allow us o in e gene al ends ha can
be used o o mula e empi ical ules o RIS beam s ee ing.
Speci ically, he s ee ing di ec ion and angle o he main lobe
a e s ongly co ela ed wi h he spa ial geome y o he applied
conduc i i y pa e n.
Fi s , linea asymme ies—such as ac i a ing a single ow
o column o uni cells—in oduce small de lec ions (≈5°)
owa d he side opposi e he ON egion. This sugges s ha
ab up bounda ies in he conduc i i y dis ibu ion bias he
e lec ion away om he ac i a ed elemen s.
Second, o a ing o shi ing a gi en pa e n sys ema ically
al e s he s ee ing di ec ion. Fo example, o a ion o a
ci cula -inspi ed pa e n a ound he z-axis o a es he beam
s ee ing azimu h φ acco dingly, while e ical displacemen o
he same dis ibu ion biases he main lobe owa d he di ec ion
o he shi . This beha io highligh s he geome ic
co espondence be ween he pa e n o ien a ion and he
esul ing beam di ec ion.
Thi d, he densi y o ON/OFF ansi ions wi hin a pa e n
di ec ly impac s he achie able s ee ing angle. Pa e ns wi h
mo e compac spacing be ween ON and OFF egions end o
p oduce s onge phase g adien s ac oss he RIS, esul ing in
la ge s ee ing angles (up o θ ≈ 36° in his wo k). Simila
e ec s ha e been epo ed in [3], [7], whe e 1-bi e lec a ay
designs demons a ed enhanced s ee ing pe o mance bu also
inc eased side-lobe le els due o phase quan iza ion and
ab up conduc i i y ansi ions. Howe e , hese mo e
agg essi e designs may also lead o deg aded adia ion
quali y, such as highe side-lobe le els o e en beam spli ing.
Finally, a p onounced in luence is obse ed when
ON/OFF changes occu nea he physical edges o he RIS.
Modi ying he conduc i i y a he a ay bounda ies
signi ican ly al e s he e ec i e ape u e dis ibu ion, leading
o s onge s ee ing e ec s compa ed o simila modi ica ions
in he cen al egion. This edge sensi i i y is consis en wi h
ape u e ield heo y, whe e discon inui ies a he bounda ies
domina e he a - ield adia ion pa e n [7].
O e all, hese obse a ions indica e ha by sys ema ically
gene a ing and es ing ON/OFF dis ibu ions acco ding o
ules o ansla ion, o a ion, elemen spacing, and edge
placemen , i is possible o de i e an empi ical amewo k ha
p edic s he s ee ing pe o mance o he RIS wi hou equi ing
ull-wa e simula ion o e e y con igu a ion. Such empi ical
guidelines can g ea ly simpli y he design and con ol o
modes -sized bina y RIS implemen a ions.
I is wo h no ing ha de i ing such empi ical ules
equi es he sys ema ic gene a ion and analysis o a la ge
numbe o dis inc pa e ns. By s udying how di e en
geome ical a angemen s a ec he main lobe di ec ion, a
mo e comp ehensi e unde s anding o he RIS beha io can
be achie ed. This, in u n, enables he selec ion o design o
app op ia e pa e ns o s ee he e lec ed beam owa d any
desi ed di ec ion wi h a high deg ee o con idence
IV. CONCLUSION
This wo k p esen ed he design o a simpli ied 1-bi RIS
ope a ing a 28 GHz. The RIS, composed o an 8×8 a ay o
uni cells based on a compac diode-swi ched pa ch design,
was analyzed unde no mal-incidence ho n an enna
illumina ion using ull-wa e simula ions in ANSYS HFSS.
By sys ema ically applying a a ie y o ON/OFF con ol
pa e ns, he esul ing a - ield adia ion cha ac e is ics we e
ex ac ed and compa ed.
The esul s demons a ed ha he spa ial geome y o he
applied bina y pa e ns c i ically de e mines he s ee ing
beha io o he e lec ed beam. While uni o m ON o OFF
s a es esul ed in b oadside e lec ions, linea dis ibu ions
in oduced small angula de ia ions, and mo e complex o
asymme ic con igu a ions enabled s ee ing angles o up o θ
= 36°. Ce ain pa e ns, howe e , also exhibi ed beam spli ing
and ele a ed side-lobe le els, highligh ing he inhe en ade-
o s be ween s ee ing ange and main-lobe in eg i y.
O e all, he indings o his s udy con i m ha e en
modes -sized RIS a ays can achie e e ec i e and
con ollable beam s ee ing h ough s uc u ed bina y
modula ion. Fu he mo e, he obse ed beha io p o ides
aluable empi ical insigh s in o he ela ionship be ween
pa e n geome y and beam di ec ion, o ming he basis o
low-complexi y design s a egies in p ac ical RIS
implemen a ions. Fu u e ex ensions o his wo k may conside
la ge RIS dimensions, expe imen al alida ion wi h
ab ica ed p o o ypes, and he applica ion o op imiza ion
algo i hms o sys ema ic pa e n syn hesis.
ACKNOWLEDGMENT
This esea ch was suppo ed by he Eu opean Union,
h ough he Ho izon Eu ope Ma ie Skłodowska-Cu ie S a
Exchanges P og amme “6G in elligen connec i i y and
in e ac ion o use s and in as uc u es (6G-ICARUS)” unde
G an 101131342. The au ho s would like also o
acknowledge he suppo p o ided by he Digi al Go e nance
Uni o he A is o le Uni e si y o Thessaloniki (AUTh)
h oughou he p og ess o his esea ch wo k.
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