sensi i i y, which is de ied by he dielec ic ilm s uc u e o he
senso pad. The calcula ion is based
on
an
e ec i e index model
o he dielec ic wa eguide senso pad. Thus he expe imen al
alue is in good ag eemen wi h he heo e ically expec ed phase
shi
AQcai
=
5.05n, calcula ed o he TE, mode.
The esolu ion o he e ac ome e chip was de e mined by
measu ing he de ec o signal d i wi h he measu emen cell
placed
on
op o he Mach-Zehnde in e e ome e ba and wi h a
con inuous low o analy e
A.
Using a linea i , he phase d i
was de e mined o be 39m ad
e-’,
which co esponds o a
e ac i e index esolu ion o
1.3
x
l@5
o a measu emen pe iod
o
1min.
Cu en wo k is ocusing on he ealisa ion o
a
monoli hically
in eg a ed immunosenso chip
[6]
wi h applica ions in medical
diagnos ics, ood analysis o en i onmen al con ol. The phase-
modula o can be used o phase-shi ing in e e ome y, in ensi y
d i compensa ion o he DBR lase and de e mina ion o he sign
o e ac i e index change
[3].
Also,
mul i-senso a ays and on-
chip e e encing can be ealised wi h his monoli hically in eg a ed
op ical e ac ome e chip.
Acknowledgmen s:
The au ho s a e g a e ul o
B.
G a ,
D.
Jeggle,
R. Widme and
H.
Schu z o p ocessing assis ance, H.P. Sch-
weize o c ys al g ow h, M.T. Gale and
K.
D ans eld (Uni e -
si a Kons anz) o hei gene ous suppo .
0
IEE
1997
Elec onics Le e s Online
No:
1997061 7
B.
Maisenholde ,
H.P.
Zappe,
M.
Mose ,
P.
Riel
and
R.E.
Kunz
(Paul Sche e Ins i u e, Badene s asse 569,
8048
Zu ich, Swi ze land)
J.
Edlinge
(Balze s AG, 9596 Balze s, Liech ens ein)
21
Ma ch 1997
Re e ences
STAMM, c.,
and
LUKOSZ,
w.:
‘In eg a ed op ical di e ence
in e e ome e as e ac ome e and chemical senso ’,
Sens.
Ac ua o s
B,
1993,
11,
pp.
177-181
LECHUGA, L.M., LENFERINK,
A
T.M., KOOYMAN, R.P.H.,
and
GREVE,
J.:
‘Feasibili y
o
e anescen
wa e
in e e ome e
immunosenso s
o
pes icide
de ec ion:
chemical aspec s’,
Sens. Ac ua o s B, 1995,
24-
25,
pp.
762-765
KUNZ, R.E.:
‘To ally in eg a ed op ical measu ing senso s’,
P oc.
SPZE,
1992,
1587,
pp.
98-113
EDLINGER, J.:
‘A
GaAs/AlGaAs e ac ome e pla o m
o
in eg a ed op ical sensing applica ions’, o
be
published in
Sens.
Ac ua o s B,
1997,
3811-3
HOFSTETTER,
D., ZAPPE, H.P.,
and
EPLER,
J.E.:
‘Ridge
wa eguide
DBR
lase
wi h nonabso bing g a ing
and
anspa en in eg a ed
wa eguide’,
Elec on. Le .,
1995,
31,
pp.
980-982
MAISENHOLDER,
B.,
ZAPPE,
H.P.,
KUNZ,
R.E., RIEL,
P.,
MOSER,
M.,
and
DUVENECK,
G.L.:
‘A
GaAdAlGaAs
-
based
Mach-Zehnde
in e e ome e
as in eg a ed op ical immunosenso ’,
P oc. SPIE,
MAISENHOLDER,
B.,
ZAPPE, H.P., KUNZ, RE, RIEL,
P.,
MOSER, M.,
and
1996,
2928,
pp.
144-152
Ci cula syn he ic ape u e ada (C-SARI
sys em o g ound-based applica ions
A.
B oque as,
R.
De Po a a,
L1.
Sagu&s,
X.
Fab egas
and
L1.
Jo e
Indexing e ms: Syn he ic ape u e ada , Rada
The
au ho s
p esen
an
SAR sys em capable
o
ob aining ada
images
om
measu emen s
ca ied
ou
wi h
an ennas
ha
desc ibe a ci cula ajec o y cen ed ou side
he
a ge egion.
The analy ical o mula ion
o
he p ocesso is p esen ed
along
wi h i s g ound ange and azimu h esolu ions. Some
expe imen al esul s ob ained
in
an anechoic chambe a e also
shown.
In oduc ion:
Mos o he exis ing
SAR
sys ems a e ai bo ne o
spacebo ne. G ound-based
SAR
sys ems, howe e , a e be e
sui ed o sho - ange applica ions such as su ace sca e ing s ud-
ies o bu ied objec de ec ion whe e e y high spa ial esolu ions
a e equi ed. In con as o ai bo ne and spacebo ne
SAR,
whe ein he whole pla o m usually desc ibes a linea ajec o y,
in
uck-moun ed o owe -moun ed
SAR,
while only he an enna
mo es he es o he sys em emains s a ic. The mechanical imple-
men a ion
o
a linea ajec o y o he an enna
(L-SAR)
he e o e
becomes di icul . The C-SAR sys em p esen ed he e simpli ies his
p oblem by allowing he an enna o desc ibe a ci cula ajec o y
a ound
a
o a ing e ical mas .
Ci cula geome ies o
SAR
ha e been ex ensi ely s udied
when he a ge is in he cen e o he an enna pa h, o example
in he spo ligh and in e se
SAR
con igu a ions
[l].
Howe e
in
his case he a ge
is
ou side he an enna ajec o y, allowing an
angula
high
esolu ion scan o he su ace a ound he ada si e.
A
con inuous wa e s epped equency
scan
has been used in
o de o achie e a wide bandwid h, hus he inpu s o he C-SAR
econs uc ion algo i hm a e he cohe en measu emen s o he
sca e ed ield agains equency and azimu h angle.
=
hlcos
eele
Fig.
1
Geome y
o
imaging sys em
C-SAR
p ocesso :
The geome y o a C-SAR sys em is illus a ed
in Fig.
1
in cylind ical co-o dina es. The sca e e , loca ed a poin
S,
emains s a iona y a a posi ion
(p,
Q)
o he
xy
plane. The
an ennas a e loca ed a
(R,Qa,h)
and poin a
I,
he cen e o he
illumina ed a ea, wi h an o -nadi ele a ion angle o
Qeie .
Assum-
ing ha he a ge is o med by
a
dis ibu ion o non-di ec ional
and independen sca e e s o e lec i i y
(p,
Q),
he complex
alue o he ield sca e ed back o he ecei e will be gi en by he
cohe en addi ion o he con ibu ions associa ed wi h each sca -
e e :
whe e
dAS
=
JR2
+
p2
-
~R~cos($
-
+
h2
(2)
is he dis ance be ween he an ennas and he sca e e , and
E,
is a
cons an ha depends, among o he s,
on
pa ame e s o he sys em
such as an enna gain and ansmi ed powe . Since his cons an
will be no mally emo ed by ex e nal calib a ion using a e e ence
a ge , i
will
no hence o h be conside ed.
The objec i e o he imaging sys em will be he econs uc ion
o he e lec i i y map om
a
se o measu emen s
E3((QJ
a di -
e en equencies and angles.
In
ma hema ical e ms his can be
achie ed by applying a ocusing ope a o o he measu ed ields:
m
27T
&P’>
47
=
J’
J’J%( ,
daw,
4a,p ,
4W4ad
(3)
00
whe e
cV;Qa,p‘,
$7
is he ke nel unc ion o be ound, hence he
image
~(p’,
@?
=
~(p,
Q).
Fo
a
gi en scene poin
(p’,
Q’),
&&,,p’,
Q’)
should ‘ ocus’ all he pe o med measu emen s on his
poin by gene a ing he a gumen and ampli ude ha he wa e has
‘los ’
on
i s way o and back om he sca e e loca ed a
(p,
Q).
The p oposed solu ion is he e o e
[( ,
da,
p’,
4’)
=
e3~- /R2+p 2-2Rp‘
cos(4’-4,)+h2
X
[R2
+
p”
-
2Rp’
cos(q5’
-
&)
+
P]
(4)
988
ELECTRONICS LETTERS
22nd
May
1997
Vol.
33
No.
I
I
I
R
+
00,
eqn.
S
becomes he con en ional linea SAR econs uc-
ion implying
a
quad a ic phase wi h espec
o
he an enna dis-
placemen .
Wi h good signal
o
noise a ios
(2
20dB), he e ec s o he
adia ion diag ams o bo h ansmi e and ecei e an ennas
GAP)
and
GR(P)
can be aken in o accoun a id co ec ed in he
econs uc ion by mul iplying
E,V;Qa,p',
$')
by
1
GT(P)GR
(PI
wi hin he beamwid h o he an enna.The angle
p
is shown in Fig.
1
and can be exp essed agains geome ic pa ame e s o he sys-
em. Fo his pu pose,
GAP)
and
G,(P)
can be nodelled by using
a
Gaussian o pa abolic app oxima ion.
An ad an age o compensa ing he ampli ude e ms o he a -
ge ange and gain o an ennas in he ocusing ke nel
5
is ha he
sensi i i y becomes in a ian ac oss he image ield. The shape o
an imaged poin sca e e (poin sp ead unc ion) depends on he
a ge ange, al hough i has been ound app oxima ely in a ian
in sho ange nume ical simula ions.
Image esolu ion:
The ange esolu ion
AR
depends on he ime
pulse esolu ion
AT,
which is he in e se o he bandwid h sys em
B
=
maX- m,,
[l].
The esolu ion in slan ange
AR
and g ound
ange
4
a e gi en by [l]:
(5)
(6)
ca
AR=-=-
2
2B
C
AR,
=
2B
sin(Qele )
The azimu h esolu ion
AS
o he C-SAR sys em is de ined
as
he
abili y
o
disc imina e wo close ada a ge s which a e loca ed
a
he same a c, and i can be calcula ed om he Dopple equency
esolu ion
A&
[I]:
(7)
c
JR2
+
p2
-
2Rpcos(A8~/2)
+
h2
AS=-
4. maz
R
sin(A%a/2)
whe e
AOH
is he 3dB beamwid h o he an ennas.
I he an ennas p esen a high di ec i i y
(AOH
<
20") and
R
+
00,
he azimu h esolu ion
AS
2
112,
which is he con en ional lin-
ea
SAR
azimu h esolu ion,
1
being he dimension o he an enna.
In con as o linea SAR, he azimu h esolu ion deg ades wi h
ange because he leng h
o
he syn he ic ape u e does no
inc ease p opo ionally. The op imal ele a ion angle is ha whe e
bo h esolu ions a e equal, and i can be calcula ed by equa ing
eqns. 6 and 7:
Measu emen esul s:
Se e al mul i equency measu emen s ha e
been unde aken in he X-band a he elec omagne ic anechoic
chambe
o
he Uni e si a Poli ecnica de Ca alunya
(UF'C).
The
measu emen sys em is basically
a
ec o ne wo k analyse based
sca e ome e using wo closely spaced an ennas placed a he end
o a 0.9m me allic ba moun ed on an azimu h posi ione . The
ansmi - ecei e an ennas we e wo ec angula ho ns loca ed a
a
heigh o 1.95m, wi h an o -nadi ele a ion angle o 45". A pe -
sonal compu e con olled he sca e ome e o pe o m a e-
quency sweep o each angula sample poin .
Fig. 2
08
-20
04
nO
-30
-04
-0
8
3
n
/74212j
-40
2
Re lec i i y image
o i e
ihed als
Fig.
2
shows he econs uc ed image o ho izon ally pola ised
copola da a sampled o e 161 angula poin s measu ed om 12
o 16GHz wi h a equency in e al o 10MHz. This image co e-
sponds o i e iden ical small ihed als sp ead on he g ound o
he anechoic chambe . The quasi-space in a iancy as well
as
he
uni o m sensi i i y can be obse ed in his image.
I
im
1.
i
-54U
L
Fig.
3
Expe imen al se up
and
ob ained e lec i i y image
An
impo an po en ial applica ion o he C-SAR sys em is
bu ied objec de ec ion, such
as
o an i-pe sonnel plas ic mines.
In his case, equencies in he ange OS4GHz would be p e e ed
in o de
o
ob ain some e ain pene a ion. Howe e , a p elimi-
na y expe imen a highe equencies has been ca ied ou
o
assess he imaging capabili ies o dielec ic objec s laid on
a
g ound su ace. In his con ex , h ee plas ic mine equi alen
objec s o di e en sizes (5, 10,
20cm)
and
a
s one (1Ocm) we e
sp ead o e a la ge egion o sandy simula ed
soil
inside he ane-
choic chambe (Fig.
3).
The measu emen was ca ied ou wi h
HH pola isa ion, 161 poin s in azimu h and sweeping om 12 o
18GHz wi h a equency in e al o 15MHz. Fig.
3
shows he
econs uc ed
SAR
image. As we can see, he h ee mines a e
de ec ed abo e he g ound clu e and he s one le el and loca ed
a i s exac posi ion. No e ha he bigges mine is la ge han he
image esolu ion cell and p esen s wo dis inguishable b igh
poin s.
Conclusions:
A
ci cula syn he ic ape u e ada p ocesso has
been p esen ed and e alua ed.
This
sys em has been designed in
o de o ob ain ada images using
a
g ound-based sca e ome e
whe e only he an ennas mo e desc ibing
a
ci cula ajec o y.
Al hough he o mula ion and implemen a ion a e mo e compli-
ca ed han
a
con en ional linea SAR, he expe imen al se up is
conside ably simpli ied. The esul s show e idence o he applica-
bili y o his app oach o e y high esolu ion su ace sca e ing
analysis and bu ied objec s de ec ion.
Acknowledgmen s:
This wo k has been suppo ed by he Spanish
Commission o Science and Technology CICYT TIC 96-0879.
0
IEE
1997
Elec onics Le e s Online
No:
19970635
A.
B oque as,
R.
De
Po a a,
L1.
Sagues,
X.
Fab egas and
Ll.
Jo e
(Depa amen o Teo ia del Senyal i Comunicacions, Uni e si a
Poli dcnica de Ca alunya
(UPC),
Cumpus No d
UPC,
03,
08034,
Ba celona,
Spain)
24
Ma ch 1997
Re e ences
1
2
WEHNER, D.R.:
'High
esolu ion ada ' (A ech House, No wood,
USA,
1997)
BROQUETAS,
A.,
JOFRE, L.,
and
CARDAMA,
A.:
'A
nea
ield
sphe ical
wa e
in e se
syn he ic
ape u e
ada
echnique'.
IEEE
An ennas
and
P opaga ion
Soc.
In .
Symp
,
Chicago,
1992,
Vol.
2,
pp.
114-
117
ELECTRONICS LETTERS
22nd
May
1997
Vol.
33
No.
I
I
989