Microwave Attenuator

7/24/2019 Microwave Attenuator

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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.


24/25

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.

REFERENCES

1. 8. Shier, ".O. Statom, ".3. Tussey, .. Tiller, 8esign with P/ diodes_ :A;*: Application ote A>412. . 8. [oos, ^Selection o$ P/ 8iodes in 8esigning :atched 5ridge "FF

Attenuators $or ?ow requency 8istortion_, :icrosemi *orp. :P8 1'4, 1


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1'.3augh, . 3., A Low Cost Surface Surface Mount PIN Diode PI

Attenuator, :icrowave [ournal, vol. 4D, no. D, :ay 12, pp 2H';2HC.11.5. :. *oaer, adar receiver protection technology,0 :icrowave [ournal%

:ilitary :icrowaves Suppliment, August 2''@, pp. H;1C.12.5. :. *oaer, 8. :. 8owthwaite and . F. Priestley, Tigh;Power multi;

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technology o$ monolithic >aAs pRiRn diode limiters $or the millimeter

wavelength range_ "F*T/*A? PT=S/*S ?F""F 7ol. 41 o. @, 2''D.1C.8. [. Seymour, 8. 8. Teston, and . F. ?ehmann ^;5and and Oa;5and

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:icrowave [ournal, 7ol. 4C, o. 2, ebruary 11, pp. 121R12D.1G.iolai 7. 8roYdovsi & ?ioudmila :. 8roYdovsaia ^:icrostrip and

waveguide passive power limiters whith simpli+ed construction_, [ournal o$:icrowaves and ptoelectronics, 7ol. 1, o. D, 8ecember 1.

[email protected] /.[., ^1'3 *3 broadband balanced limiter?A $abricated using :SA>

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Aided Fngineering, vol. 14, /ssue 2, pp. 11HR12@, :arch 2''4.1H.iolai 7. 8roYdovsi :icrowave passive power limiters based on

:FSF"s_, [ournal o$ :icrowaves and ptoelectronics, 7ol. 1, o. 2, April

1H.1.Sandeep *haturvedi, >. Sai Saravanan, :ahadeva 5hat O., Sangam 5hale

:FSF" process based planar Schotty diode and its application to

passive power limiters @H;1;C@;2D'1;H1441.'' f2'14 /FFF.

2'.5era, S., 5asa, O., [ain, 7., Singh, ., and >arg, 7.% Schotty diode basedmicrowave limiter with adjustable threshold power level0, :icrow. pt.

"echnol. ?ett., 2'1', D2, pp. 1G@[email protected] press release 5F/[/> R F8/ * R April @, 2'1C

^http%www.psemi.comnewsroompress;releases@@2@1@;peregrine;

introduces;ultracmos;r$;power;limiters;the;industry;s;+rst;monolithic;

alternative;to;discrete;pin;diode;limiters_22.arda :icrowave;Fast company ^Pin diode control product Application

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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+

2D.Fmmanuel >A"A8, doctoral thesis Analyse des phnomnes physiques

dans les diodes p;i;n % *ontribution la modlisation lectrothermique

pour les applications de puissance et hyper$rquences_ 2''G,

J/7FS/"F 8F ?/:>FS

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