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Microwave Power ProtectorsAttenuators and Limiters
Khalifa ECHCHAKHAOUI1, Elhassane ABDELMOUNIM1, Hamid BENNIS2, MohamedLATRACH
1ASTI Laboratory, FST of Settat, Hassan 1st University, Morocco
2LITEN, FPK/FST of Settat, Hassan 1st University, Morocco
Micro!ave "ro#$ ESE% AN"E&S, France
ABSTRACT
In t'is c'a$ter, (icro!ave $o!er atten#ator an) *i(iter t'eory an) tec'no*o+ica* rea*iation are$resente)- T'e c'a$ter is )ivi)e) in t!o sections, first section is )e)icate) to atten#ator circ#its an) t'e
secon) section is )e)icate) to $o!er *i(iters circ#its-
A#t'ors )escribe, in first section, $rinci$*es c'aracteristic an) f#n)a(enta*s of atten#ator an) )etai* of
t'e (ost co((on to$o*o+ies s#c' as T.atten#ator, PI.atten#ator an) bri)+e).atten#ator- After a
$resentation of i($ortant e#ations nee)e) to ca*c#*ate atten#ation rate $rovi)e) by eac' of t'ese
$revio#s cite) to$o*o+ies, a#t'ors $resent t'e variab*e atten#ator base) on active co($onent 0PIN )io)e,
Transistors-
In secon) section, a#t'ors $resent $o!er *i(iter c'aracteristic an) f#n)a(enta*s- After!ar), t'ey $resent
a state of arts of tec'no*o+ica* so*#tion to )esi+n $o!er *i(iter base) on so*i) state co($onents s#c' asPIN )io)e an) Sc'otty )io)es-
Ke!"o#ds$ A%%en&a%o#, Limi%e#, mi'#os%#i(, )IN diode, S'ho%%*! diode, a%%en&a%ion #a%e, limi%in+ #a%e, Tee
a%%en&a%o#, )Ia%%en&a%o#, inse#%ion loss, impedance characteristic.
INTRODUCTION
Sin'e %he a((ea#an'e of R- . mi'#o"a/e s!s%ems, %he flo" of ele'%#oma+ne%i' "a/es of hi+h (o"e#
(#esen%s a se#io&s %h#ea% %o sensi%i/e ele'%#oni' 'om(onen%s s&'h as lo" noise am(lifie#s 0LNA, #ada# and
s(a'e 'omm&ni'a%ions 0D Shiffle#, 2334 Belo", fe" e5am(les of dama+in+ effe'%s of hi+h (o"e#
mi'#o"a/e flo"s$
Destruction of electronic components$ LNA 0Lo" Noise Am(lifie# 'om(onen%s a#e
sensi%i/e %o hi+h (o"e# mi'#o"a/e -aile %o 'on%#ol %he #e'e(%ion 'hain ma! dama+e %hese
'om(onen%s (e#manen%l!
Saturation of radio-receiving elements$ in %he 'ase "he#e %he #e'ei/ed (o"e# e5'eeds %he
sensi%i/i%! %h#eshold of %he #e'ei/e#s, %he (e#fo#man'e of #adio #e'ei/e#s is no% linea# and%he#efo#e, %hese #e'ei/e#s 'anno% fil%e# %he &sef&l si+nal
Generation of interference$ mo6ile 'ell&la# %ele'omm&ni'a%ions s!s%ems s&'h as CDMA,
7CDMA and LTE s!s%ems a#e 6ased on %he (o"e# 'on%#ol si+nals %o (#e/en% m&%&al
in%e#fe#en'e 6e%"een diffe#en% mo6ile de/i'es 'o/e#ed 6! %he same 'ells Mo6ile de/i'es
a#o&nd %he #adio 'ell m&s% #ed&'e %hei# emission (o"e# in o#de# %o %#ansmi% lo" (o"e# si+nals
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'om(a#ed "i%h %he (o"e#s of si+nals %o 6e emi%%ed 6! de/i'es lo'a%ed in a #emo%e a#ea of %he
'ell
The#efo#e, %he#e is a (e#manen% in%e#es% %o in%e+#a%e in%o %he R- #e'ei/e# 'hains )o"e# 'on%#ol 'i#'&i%, in
o#de# %o a/oid e8&i(men% malf&n'%ion o# des%#&'%ion of %he sensi%i/e elemen%s of %he #e'ei/in+ 'hain
In li%e#a%e, %he mi'#o"a/e de/i'e (#o%e'%ion a+ains% hi+h (o"e# si+nal is (#o/ided 6! %"o *inds of
'i#'&i%s$ )o"e# a%%en&a%o# 0S&n, Choi, . 7eide, 9UNE 2334 and (o"e# limi%e# 'i#'&i%s 0Malo#a%s*!,233: The main diffe#en'e 6e%"een %he %"o 'i#'&i%s lies in %he fa'% %ha% %he a%%en&a%o# #ed&'es %he (o"e#
si+nal 6! a (#ede%e#mined #a%io "hile %he (o"e# limi%e# %ends 'li((in+ in'iden% si+nal 6elo" a %h#eshold
(o"e#
This Cha(%e# is di/ided on %"o se'%ions -i#s% se'%ion is dedi'a%ed %o a%%en&a%o# 'i#'&i%s and se'ond se'%ion
is dedi'a%ed %o )o"e# limi%e# 'i#'&i%s In ea'h se'%ion a&%ho#s (#esen% ne'essa#! defini%ion of (o"e#
'on%#ol 'i#'&i%s and %he main 'on'e#ns a6o&% desi+n and 'on'e(%ion of %hese 'i#'&i%s A% %he end of ea'h
se'%ion, e5am(les a#e (#esen%ed and dis'&ssed %o (oin% o&% 6es% (#a'%i'e %o desi+n and o(%imi;e (o"e#a%%en&a%o# and limi%e# 'i#'&i%s
SECTION I: ATTENUATORS
Attenuators are equipment and circuits introduced between electrical andmicrowave power source and receiver or load in order to reduce the signal power by
a predetermined ratio (Sundararajn & Peterson, 1!. "he attenuation ratio is
e#pressed in decibels by the ratio o$ the output power (Pout! to the incident power
(Pin! as shown in equation below%
Attenuation 1' log1'(Pin Pout!.
"he attenuator should not introduce re)ection to the power source. *onsequently
the attenuator input impedance and output impedance must be matched on the
main line.
Attenuators are designed with lumped circuit and distributed circuits. "hey may be
in the $orm o$ transmission line, microstrip, stripline, waveguide component. "he
most used method to introduce attenuation on a transmission line is to place
resistors in the electric +eld centre. "hans to the electric +eld, there is an induced
current causing a loss o$ power on the line (Sundararajn & Peterson, 1!.
"here are several circumstances where it is necessary to insert an attenuator to
reduce the power and the level o$ signals (current and voltage! as%
- educe the signal level to avoid saturation o$ the systems.- /n order to adapt the output o$ a circuit to the impedance o$ the load.
- "o measure the gain or loss o$ two ports.- "o provide isolation between components o$ a circuit.- "o e#tend the power range capacity o$ equipment0s such as measurement
instruments. or e#ample, i$ a measurement device supports only 1''mw, it
is possible to measure the power level o$ 2'' m3 i$ an attenuator 4d5 or
more is inserted at the input o$ the this device.- "o balance the power received $rom several sources
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"he attenuators can be classi+ed into di6erent types according to the nature o$ the
circuits used, the con+guration and method o$ attenuation. "hus there are%
- Passive and active attenuators- e)ective and absorptive attenuators- 7ariable and +#ed attenuators
ATTENUATORS CHARACTERISTICS
"he attenuators are designed according to the speci+cations required by their
use. 8i6erent parameters are considered in the design o$ attenuator
(Sundararajn & Peterson, 1!, namely%
- Attenuation rate range% it is the ratio o$ output power and input power.
According to this $eature, there are variable attenuators and +#ed
attenuators.- re!uenc" #and% "he attenuation rate is more accurate in the operating
$requency band o$ the attenuator.- re!uenc" Sensitivit"% it is the ma#imum variation (pea to pea! o$ the
attenuation rates across the $requency band.- Power range% this is the ma#imum power supported by the attenuator
without compromising its $unctionality and per$ormance.- Power sensitivit"% this characteristic represents the variation o$ attenuation
rate as a $unction o$ power. "his variation can be measured by d5 3.- O$erating tem$erature% the temperature range in which the attenuator
operates in $ull power.- Tem$erature sensitivit"% the variation o$ the attenuation as a $unction o$
the temperature d5 (d5# 9 *!.
- In$ut Re%ection rate% this is the level o$ signal re)ected bac to the sourcewhen the load impedance is matched to the source.
- Out$ut Re%ection rate% the level o$ the re)ected signal to the load whenthe load impedance is matched to the source.
PASSI&E ATTENUATORS
At low $requency, Passive attenuators are made o$ pure resistances. "he
arrangement o$ resistances between them and their values are determined
according to the desired attenuation and the circuit topology. /n high $requency,
:icrostrip attenuators are implemented using resisting layers, which are made
by etching thin;+lm resistive coating on an isolating substrate (oshin, ateev, & Popov, 2'12!. /n the literature, there are
several attenuator topologies nown according to the arrangement o$
resistances. "he most popular $ormats are% P/, ", ";bridged, ? topology,
rectangular (:ice, 1'! and cruci$orm (ournier & 5oillot, 2''@!, interdigitated
structure (7eteran, 11!.
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T attenuator:
"his con+guration is consisting o$ three resistors in " $ormat as drawn in the
+gure below. "his attenuator can be symmetric i$ 1 2 or asymmetrical in the
general case (ie 1 2!. 3here 1 2, the ";attenuator will serve also $or
matching impedances between the source and the load.
igure ': T(attenuator to$o)og"
*alculation o$ 1, 2 and 4 resistance values
/$ we set the attenuation Pin Pout, the $ollowing equations give the values o$
1, 2 and 4%
1Zink+1
k12
ZinZoutkk1 (1!
2Zoutk+1
k12
ZinZoutkk1 (2!
4 2ZinZoutk
k1 (4!
Im$ortant s$ecia) cases:
Symmetrical T-attenuator/$ the input impedance and the output impedance o$ the circuit are equal, then
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et 42B
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3e replace /?with 2 B Pout
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igure + PI(attenuator
*alculation o$ resistance values 1, 2 and 4
"he values o$ 1, 2 and 4 are given by the $ollowing $ormulas%
R 1= Zink1
k+12k Zin
Zout
(1C!
R3= Zoutk1
k+12k Zin
Zout (1D!
R2=(k1)ZinZout
2k (1G!
3here K= Pin
Pout
/mportant special case
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et R2=Z(k1)2k (1H!
*alculation o$ the power dissipated in a symmetrical P/Rattenuator *ircuit
4et
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"he table below shows the values o$ the resistors according to the desired
attenuation rate ( Pin Pout! $or three attenuator $ormat, the characteristic
impedance at the input and output is considered at the value
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&ARIA-LE ATTENUATOR:
7ariable attenuators are used to adjust the attenuation level according to the needs.
7ariable attenuator are use$ul in automatic gain control (A>*! circuits and power
leveling applications KGM
"hus, the design o$ variable attenuator consists o$ using attenuator resistive circuitand replacing +#ed resistor with active component having the ability to change its
resistance with a control input (current or voltage control! such as P/ diode. "he
variable attenuator design will be simple i$ there is no need $or a matched
attenuator circuit (the re)ection signal to the source is tolerated!. Towever,
elaborated and more comple# circuits are designed $or matched variable attenuator.
7ariable attenuators can present continuous attenuation rate or discrete reduction
rate (step by step!.
1. Ste$ #" ste$ attenuation% "o construct discrete attenuator, a series o$
+#ed attenuators are arranged to provide mechanically variable attenuationrate step by step. or each level o$ attenuation, a switch is used to select the
appropriate attenuator. "his arrangement allows discrete attenuation values
in each position. esistive attenuators networs provide a theoretically
unlimited bandwidth (resistor characteristics limit in reality this assumption!,
but require many attenuator stage to provide desired attenuation while the
aggregation o$ several stages will present insertion loss and re)ection due to
mismatch impedance. /n addition, switchs may introduce noise and distortion
K1M.
2. Continuous attenuation% "he attenuation rate can also be controlled by a
current or voltage and automatically adjusted according to the needs usingactive components such as Pin 8iode, :FSF" transistors.
PIN .IO.E ATTENUATOR
P/ 8iode Attenuators are a subset o$ variable attenuators and are use$ul $or
circuits requiring continuously changing attenuation levels K1M.
Pin diodes are used in many microwave communication systems because o$ their
high breadown voltages, $ast switching characteristics, and their variable
resistance characteristics with bias. "hey provide circuit $unctions in antenna
switches, phase shi$ters and attenuators $or automatic gain control (A?*! or level control applicationsKM.
P/ diode attenuators can tae many $orms% $rom a simple diode connected in
series or parallel, acting as a lossy re)ection device, to more comple# structures
that maintain a mached input impedance over the $ull attenuation rate capacity
o$ the attenuatorKFmmanuel >atardM.
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3hen the P/ diode is used in the attenuator, the attenuation characteristics are
controlled by the $orward bias current through the P/ diode. "his is compatible
with the $act that the resistance o$ the P/ diode is determined by the $orward
bias currentKM.
PIN diode characteristics
A P/ diode is a semiconductor device $ormed o$ o$ three layers%
- positively doped layer P L
- lightly doped intrinsic layer and very small width 3- negatively doped layer L
igure /: PIN diode )a"er $resentation
Forward bias operation :
At low $requencies, the P/ diode behaves as an ordinary P junction diode, but
at high $requencies it behaves as a resistor whose value can be controlled by
current. ig. D shows a P/ diode high $requency equivalent linear model where%
- */% is the constant capacitance, 3hich depends on the geometry o$ the
intrinsic layer.- /is the variable resistance which depends on $orward current passing
through the diode.- ?p and p represent parasitic pacaging inductance and resistance.
igure 0: Linear E!uiva)ent Circuit Mode) 1or PIN diode
"he equivalent impedance o$ P/ diode is calculated $rom its equivalent circuit as
R
1+jRiCiW . 3hen the current through the diode is below a threshold value,
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the diode acts as a capacitor o$ low value and a high resistanceU 3hen the
current e#ceeds the threshold (the threshold o$ the diode is de+ned by the width
o$ the intrinsic region and the doping o$ the P L layer and L!, electrical
charges (electrons and holes! are pushed toward the intrinsic region and
there$ore the diode becomes equivalent to a low resistance value. /n a low
$requency, /$ the reactance value o$ */ is much larger than variable resistance,the P/ diode can be considered as a pure resistor (when the parasitic pacage
inductance and resistance will be ignored!.
"he variable resistance o$ P/ diode depends on bias current according to the
$ollowing equationKCM %
Rs= W
2
(p+n)If
3here %
- % "he resistance characteristic o$ a P/ diode- 3% the /;region width- V % carrier li$etime- Wp, Wn% the hole and electron mobility respectively
"his equation is valid $or $requencies higher than the transit time o$ the /;region% $ X
14'' 32 ($ in :TY and 3 in microns!KDM.
or a P/ diode with an /;region width o$ typically 2D' Wm, carrier li$etime o$ C Ws,
and Wn o$ '.14 m2s, Wp o$ '.'D m2s, igure 4 shows the esistance vs current
characteristic. At '.'1mA, the resistance is about H.GOZ . "his resistance $all to CZat /$2'mA.
igure 2: T"$ica) .iode Resistance vs3 orward Current
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PIN .IO.E ATTENUATOR TOPOLO45
"he main use o$ P/ diode in attenuator circuit is to provide a tool to control
attenuation rate with a current signal taing in consideration the
resistance$orwarding current characteristic.
T(attenuator designed wit6 two PIN diode:/n ig @. ";attenuator is designed using two P/ diodes. According to equation
presented in table 1%
Attenuation 2'Blog(
R+Z0
Z0R
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load
Source
V+DC supply
Pin_Diode2Pin_Diode1
C2 C3
L2 L1
P_nTonePORT1
CC1
C=100.0 p
R2
DC_!loc"
DC_!loc"2Ter#
Ter#2
$=$l O%#
&u#=2
DC_!loc"
DC_!loc"1
igure 7:T(attenuator wit6 PIN diode
T(#ridged attenuator designed wit6 PIN diodes
"he most appropriate $or matched broadband attenuator applications, especiallythose in the bands $rom T 5and through JT 5and, are the 5ridged "FF & P/
circuits.
/n ig H. ";bridegd attenuator is designed using two P/ diodes. According to
equation presented in table 1%
Attenuation2'Blog(1L R 1
R2 !
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igure 8: T(#ridged attenuator designed wit6 two PIN diodes
PI attenuator designed wit6 PIN diodes
/n ig . Presents a P/ attenuator designed with three P/ diodes. the biasing circuit
involved with this design is unbalanced. ay 3augh designed a blanced P/attenuator using $our P/ diode as presented in ig 1'.
V+
R
R3R='.(1"O%#
LL1
R=
L=1.0 n)
DC_!loc"DC_!loc"1
DC_!loc"
DC_!loc"2
DC_!loc"DC_!loc"*
P&_diodePinDiode1
P&_diode
PinDiode3P&_diodePinDiode2
Ter#
Ter#2
$=*0O%#&u#=2
Ter#Ter#1
$=*0 O%#&u#=1
DC_!loc"DC_!loc",
DC_!loc"
DC_!loc"3
R
R2
R=1.-,"O%#RR1R=-*0 O%#
igure '9: PI attenuator designed wit6 t6ree PIN diodes
/$ 82 is replaced by two diodes, as shown in ig 1', several bene+ts result%
- Since the ma#imum isolation o$ the networ is set by the capacitive
reactance o$ the series diode(s!, the use o$ two diodes in place o$ one will
increase the ma#imum attenuation or double the upper $requency limit $or a
given value o$ attenuation.- "he twin diodes which occupy the position o$ the series resistor are physically
set up 1H'9 out o$ phase, resulting in the cancellation o$ even order distortionproducts.
- "he resulting attenuator networ is symmetrical and the bias networ is
substantially simpli+ed.
Conrol_curren
DC_supply
P&_diodePinDiode1
RR*
R=-*0O%#
RR1
R=-*0O%#
DC_!loc"
DC_!loc"*
R
R-R=1.-,"O %#
Ter#Ter#1
$=*0O%#&u#=1
R
R3R='.(1"O%#
LL1
R=
L=1.0n)
DC_!loc"
DC_!loc"1
P&_diode
PinDiode-
P&_diode
PinDiode2
DC_!loc"DC_!loc"2
P&_diodePinDiode3 Ter#
Ter#2
$=*0O%#
&u#=2
DC_!loc"
DC_!loc",
DC_!loc"
DC_!loc"3
RR2
R=1.-,"O%#
igure '': PI attenuator designed wit6 1our PINdiodes
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SECTION II: POER LIMITER
A power limiter is a power attenuation device inserted between the source andreceiver to prevent incidents signals above a ma#imum power to pass to the
receiver while allowing signals below a given threshold to pass to the receiver withminimum loss. Powers attenuators induce attenuation independently o$ receivingpower signal value.
Jsually, power limiters e#ploit the $unctionality o$ the impedance variation o$ acomponent according to the incident signal. "hus, the component used to limitpower is inserted in the circuit in anti;parallel $orm shunted between thetransmission line and the common ground. 3hen the power increases, thecomponent impedance decreases, and starts to absorb some o$ the received power.
Solid state Power limiters based on semiconductor components are mainly based onthe re)ection and absorption o$ a portion o$ the stream o$ a transmission line byusing many topologies. Among these topologies, we +nd the topology presented inig.1, the diode used to limit the power level is inserted in the circuit in anti;parallelposition (shunted between the transmission line and the common ground!. 3henthe power increases, the diode impedance decreases, and starts to absorb some o$the received power and a rest o$ the power will be re)ected.
R +& R Ou.
DC_/loc"2
D1
DC_!loc"1
+& O0TTL2TL1
igure '*: C)assic Power Limiter To$)og"
According to current supply o$ the circuit, power limiter can be distinguished in twotypes% active power limiters that require e#ternal current to operate and passivepower limiters that don0t demand any bias. /n addition to these two modes limiters(re)ective and absorbing limiter!, there is a third mode o$ operation where thee#cess power is redirected to a dedicated circuit $or analysis ($or militaryapplications, $or e#ample!.
;E5 PARAMETERS O A POER LIMITER
?imiters are speci+ed by a number o$ Oey Parameters%
Power range
perating $requency band. ?ow insertion loss in the power range o$ the protected circuit
?imiting rate $or signals that e#ceed the per$ormance limit tolerated by thecircuit to be protected.
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esponse time (on the order o$ nanoseconds! upon arrival signals e#ceedingthe threshold power limit.
ecovery time to normal operation as soon as the incident power is belowaccepted threshold.
oise and distortion induced by the limiter and attenuator
8issipation o$ temperature. Powers limiters operating con+guration.
Power range
Power range is the most important characteristic that impact the choice o$ asolution to limit or attenuate :icrowave Power. or power limiter, we distinguishthree thresholds%
Activation o$ limiting mode% signal having power under this threshold arecalled small signal. /n this case, the power limiter must introduce aminimum insertion loss. Signal having power above this threshold are
called large signal. Power limiting capacity% i$ the incident power e#ceeds the capacity o$ thelimiter, the limiter cannot continue to clip the signal. A portion o$ thesource power is transmitted to the load.
:a#imal power supported by the limiter% the power threshold o$ the limiterwithout damaging its active components
O$erating 1re!uenc" #and:
"he ideal Power ?imiter or attenuator must have same behaviour in all $requencybands. Towever this ind o$ power limiter doesn0t e#ist and the choice o$ activecomponent and circuit design depends on operating $requency band.
or high $requency, the component chosen to operate as Power limiter must have asmall capacity. /$ this condition cannot be met, the circuit will e#hibit low impedanceand will present a high insertion loss. 7aractor are made $rom materials that changetheir dielectric according to power signal applied to it. 5ut this component is notesuitable $or high $requency because o$ the presence o$ the capacity.
/n semiconductor component, P/ diode present two equivalent circuits dependingon operating $requency KApplications o$ P/ diode (A22!, ovember 1M. /n$requency is below $\'.1B$c, the P/ diode acts as a simple diode P, but in$requency $E1'B$c, P/ diodes acts as variable resistance.
/n very high $requency, intelligent materials such as 8io#ide 7anadium are moresuitable $or power limiter.
Insertion )oss:
"his parameter de+nes the small signal throughput loss (S21! o$ the ?imiter./nsertion loss is de+ned over a dynamic range up to the input limiting range. "oavoid signal distortion, ?imiter should e#hibit a constant insertion loss over theoperating $requency band.
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Limiting rate
"he ratio o$ di6erence o$ output power to di6erence o$ input power over the limiting
input power range.
Res$onse and recover" Time
Power limiters are required to respond quicly to large signals and to recover quicly$rom limiting events to get bac on line (ns requirement! (1'' ; 4D'' ns $or P/
diode limiters!. "his is a pulsed condition and is de+ned as the time between the
D'] point o$ the trailing edge o$ the high power pulse to the time where the output
reaches '] o$ the +nal small signal level.K22M
Noise and distortion
?imiter must not introduce noise or distortion to incident signal in operating
$requency range. "hus, the insertion loss and the limiting rate should be identical
$or the $requency range.
Tem$erature dissi$ationAs the limiter absorbs a portion o$ incident signal power, the limiter design must
implement solutions to handle temperature dissipation. Also the behaviour o$ the
limiter must remain constant over the temperature range
O$erating con
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< ?arge signal% $orward power e#ceeds the dynamic threshold o$ the limiter. /nthis case, the output power tends to remain constant with increase o$ inputpower.
< 7ery large signals% $orward power e#ceeds the capacity o$ the limiter. "helimiter cannot continue to clip the incident power. Part o$ the power source istransmitted to the load.
An ideal limiter is assumed to operate in two states%
< Small signal% no insertion loss< ?arge signal% the power is clipped regardless o$ the incident power
"he below +gure illustrate the three state operating modes o$ an ideal limiter and apractical limiter%
igure '+: o$erating mode o1 $ower )imiter
TECHNOLO4ICAL SOLUTIONS TO ACHIE&E POER LIMITERS:
Several technological solutions have been used to mae limiter circuits and powerattenuators. 5elow is a summary o$ these solutions with their ey $eatures
Semiconductor(#ased )imiters =so)id state )imiter>
"hese limiters are most prevalent in domestic telecommunications systems (mobilephones! and are made primarily based on P/ diodes, Schotty diodes, :FSF"transistors.
8i6erent topologies are cited in state;o$;art literature to per$orm power limiterbased on semiconductor components mounted in microstrip circuit and inmonolithic technology. 5elow some technical realiYations are given as illustration%
"he ?imiter design incorporate a networ o$ P/ or Shotty diode mountedacross a planar D'Z transmission line as described by ?eo >. :aloratsy in^Passive &:icrowave integrated circuits_, ewnes, 2''C, Flsevier /nc
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5y using a microstrip lines coupled with a resonator circuit as proposed byiolai 7. 8roYdovsi&?ioudmila :. 8roYdovsaia in ^:icrostrip andwaveguide passive power limiters with simpli+ed construction_, [ournal o$:icrowaves and ptoelectronics, 7ol. 1, o. D, 8ecember 1
Power limiter based on :FSF" mounted across the lines transmission as
proposed by iolai 7. 8roYdovsi in ^:icrowave passive power limiters basedon :FSF"s_, [ournal o$ :icrowaves and ptoelectronics, 7ol. 1, o. 2, April1H.
a
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possibility o$ varying the capacitance o$ the component as a $unction o$ thereceived power.
erroe)ectric materia)
"he $erroelectric material has the property o$ having a permittivity which depends
on the electric +eld. As the value o$ the capacity depends on the permittivity o$ amedium, these materials can be used to mismatch a transmission line and get thepower limiter $unction.
"his type o$ power limitation has high threshold power (1'' 3!. "here$ore they arenot suitable $or use in telecommunications systems. /n addition, and given thecapacity utiliYation, this type limiter will present in high $requency a signi+cantinsertion loss even in low power.
erromagnetic materia)3
Some materials (eg =ttrium /ron >arnet, lithium $errite! are saturated in the
presence o$ a magnetic +eld. "his property is e#ploited to design power limiterbased on these materials. 3hen the incident power is su`ciently high, themagnetic +eld causes the saturation o$ the material and e#cess power is dissipatedby the material in the $orm o$ heat. "hese limiters also have limitations in terms o$$requency bandwidth (a $ew :TY!, low power handling and a high response time.
Power)imiters#asedongas?$)asmas$ar@3
"he power limiters based >as discharge tubes are designed $or protectionapplications against high electrical powers (lightning arrestor $or e#ample!. "hebasic principle is based on the ioniYation o$ a gas between two metal plates where ahigh electric +eld is applied to these plates. "he spar plasma;based power limiters
e#ploit the same plasma ioniYation phenomenon but the powers involved arerelatively low KC@ d5mM compared to gas discharge. 7acuum diode based powerlimiters e#ploiting the phenomenon o$ electron emission $rom a metal in vacuum inthe presence o$ an electric +eld.
Com$arison wit6 state(o1(art tec6ni!ue
The table below presents comparisons between some implementation solutions cited in the scientific literature of
power limiters.
Ta#)e +3 Com$arison o1 microwave $ower )imiter3
Design Insertion
loss(S21)
Frequency
range
Limiting rate Reference
Microstrip Passive limiters
using discrete Schottky diodes
0.9 dB 2.45 Ghz 20 dB
Passive limiters using PIN
diode and detector diode
0.8 dB 7 Ghz 12 dB [8]
Planar Schottky diode 1 dB 1 Ghz 20 dB [10]
Planar Schottky diode and
MESFET based limiter
1 dB 1 Ghz 15 dB [10]
Passive limiters using Discrete
MESFET and Schottky diode
0.9 dB 7 Ghz 15 dB [13]
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Design Insertion
loss(S21)
Frequency
range
Limiting rate Reference
EAMPLES O SOLI. STATE POER LIMITER .ESI4N
Solid state Power limiters (PL) are mainly based on the reflection and absorption of a portion of the stream of atransmission line by using many topologies [3-11]. Among these topologies, we find the topology presented in
Fig.12, the diode used to limit the power level is inserted in the circuit in anti-parallel position (shunted between the
transmission line and the common ground). When the power increases, the diode impedance decreases, and starts to
absorb some of the received power and a rest of the power will be reflected [2].
According to current supply of the circuit, Power limiter can be distinguished in two types: active power limiters
that require external current to operate and passive power limiters that dont necessitate any current supply.
The presented design is a passive power limiter based on two microstrip lines. One of them is a linear line that
transmits the main signal and the second line is equipped by two Schottky diodes which are used to divert a portion
of incident signal when the amplitude of the signal reaches the threshold of the diodes. The two Schottky diodes
operate as voltage controlled attenuator and amplitude detector.
igure ',: t6e structure o1 microstri$ $ower )imiter #ased on ring )ine
In low signals, the characteristic impedance of the diodes is high. Consequently, the signal cannot pass through the
bypass second line. The main line transmits the signal to the output with a low insertion loss generated mainly by
the tangential line losses and capacities of Schottky diodes junction.
In high signals, the received power exceeds the detection threshold of the Schottky diode. It follows that the
impedance of Schottky diode falls and the RF signal starts to spread on the bypass line. Since the difference between
the electrical length of the bypass line and the main line is equal to /2, the signals propagating between the two
lines will have a phase shift of . Consequently, the power of the resulting signal is reduced.
In high power, Schottky Diode will generate a DC rectified current. Therefore, an anti-parallel stub connected to the
common ground is inserted to the main transmission line to assure the DC return path. The stub must have a quarter
wavelengths ( /4) in order to provide an open circuit for high frequency and short circuit for DC current.
To improve the performance of this design in terms of limiting rate and insertion loss, the final design will be
composed of two stages:
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igure '/3 Microstri$ Power )imiter #ased on Sc6ott@" diode
The simulation results of this circuit by using ADS (Advanced Design System) from Agilent technologies are
presented below in Fig. 17. The circuit provides less 1dB of insertion loss at low signal over 1Ghz bandwidth, and
up to 20 dB of limiting power rate with a wide operating frequency band.
igure '03 S($arameters resu)ts versus 1re!uenc" and Out$ut Power versus in$ut $ower at*3'B *3,/B *30 and *38 4H
UTURE RESEARCH .IRECTIONS
"echnological developments tend towards miniaturiYation o$ devices and integrationo$ several $unctions in one equipment. /n this trend, recent research concerns theuse o$ ::/* and *:S technologies to improve insertion loss and e#tend thesupported $requency band o$ microwave limiter and attenuator. /n this trends
Peregrine has announced in April 2'1C the introduction o$ a new limiters based onultra*:S technologie. According to Peregrine0s press release, the new powerlimiters provide a 1';1'' improvement in response and recovery timeU and delivergreater than C' d5 improvement in linearity (/P4!U o6er a 2' improvement in FS8(electrostatic discharge! protection K2'M.
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igure '2: PeregrineDs U)traCMOS $ower )imiter =rig6t> re$)aces discrete 4aAs PIN diodecircuits =)e1t>
Another technology trend concerns the development o$ power limiters $or protectionagainst high;power microwave signals. /n this category, solutions based on vacuumdiodes and microplasma are proposed to limit the high power microwave signals.
CONCLUSION
:icrowave attenuator and limiter are presented in this chapter. "he target is tomae this chapter a re$erence manual $or microwave power attenuator and limiterdevices. Principles *haracteristics and ey parameters o$ limiters and attenuator arepresented and $ully e#plained.
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introduces;ultracmos;r$;power;limiters;the;industry;s;+rst;monolithic;
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ote_24.:ini;*ircuits Application ote, ^Tigh Power ?imiter :odules_, A;C2;''1
ev.% :12C'4' ('H2@'!.
2C.S&nda#a#a=n, R, )e%e#son, E . No"lin, R 1>>> A%%en&a%o#s 7ile! En'!'lo(edia ofEle'%#i'al and Ele'%#oni's En+inee#in+
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dans les diodes p;i;n % *ontribution la modlisation lectrothermique
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