Three different types of p-i-n diode, reflective CPW switches are presented. The first two switches are the series and the shunt mounted diode switches. Each has achieved greater than 15 dB of isolation over a broad bandwidth. The third switch is a narrow band, high isolation switched filter which has achieved 19 dB of isolation. Equivalent circuits and measured performance for each switch is presented

Ponchak, G. E.

Simons, R. N.

English

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NASA Technical Memorandum 102289
Channelized Coplanar Waveguide
Pin-Diode Switches
G.E. Ponchak
Lewis Research Center
Cleveland, Ohio
and
R.N. Simons
Case Western Reserve University
Cleveland, Ohio
November 1989
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https://ntrs.nasa.gov/search.jsp?R=19900002627 2020-03-20T00:48:45+00:00Z

CHANNELIZED COPLANAR NAVEGUIDE PIN-DIODE SNITCHES
G.E. Ponchak
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
and
R.N. Simons*
Case Nestern Reserve University
Cleveland, Ohio 44106
"T
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C_
I
1,1
SUMMARY
Three different types of p-i-n diode, reflective CPW switches are pre-
sented. The first two switches are the series and the shunt mounted diode
switches. Each has achieved greater than 15 dB of isolation over a broad band-
width. The third switch is a narrow band, high isolation switched filter which
has achieved 19 dB of isolation. Equivalent circuits and measured performance
for each switch is presented.
INTRODUCTION
Coplanar waveguide, CPW, on a dielectric substrate consists of a center
strip conductor with semi-infinite ground planes on either side (ref. I).
Channelized coplanar waveguide, CCPW, consists of CPW transmission llne placed
in a metal enclosure (ref. 2). Because the ground planes and the center con-
ductor are on the same side of the substrate, shunt as well as series mounting
of circuit components can be done without the need for wraparounds or via-
holes. The improvements in circuit yield and the reduction in inductance for
ground paths over microstrip based circuits should permit microwave integrated
circuits, MlC's, to be fabricated at higher frequencies and less expensively.
However, the extent of applications of CPW circuits is limited due to the
unavailability of circuit elements and models which can be incorporated into
CAD programs.
Microwave switches are a basic circuit element for phase shifters and
radiometers. A CPW switchable attenuating medium propagation, SAMP, switch
has been demonstrated by Fleming et al. (ref. 3). This device is useful for
GaAs MMIC circuits but it is not easily incorporated into MIC's on oassive sub-
strates such as alumina or duroid. P-i-n diodes are good microwave switches
since the impedance of the diode can be changed from a very high value to
nearly zero in a short time (refs. 4 and 5).
This paper presents for the first time CPW D-i-n diode, reflective
switches. Three basic switches are oresented. The first is a shunt mounted
diode switch. This switch is similar to fin line shunt mounted diode switches
(ref. 4). The second switch is a series mounted diode across a gap in the cen-
ter strip conductor. The last switch is a novel design which converts a CPW
interdigital coupler with bandpass filter characteristics into a spurline,
bandstop filter.
*NASA Resident Research Associate at Lewis Research Center.
The three swltches have been fabricated on CCPWtransmission llnes. All
of the circuits have been fabricated on RT/Duroid 5880 substrates w_th Metellcs
Corporation beamlead diodes, MBP-IO30-BII. Figure I is the equlvalent clrcuit
7
REVER FORWARD
BIAS yK-" BIAS p
TCj IrF 
TYPICAL VALUES
SUPPLIED BY
MEIELICS
Rs O,2fl
RI 6.011
Lp O.I nH
CT:Cj_ Cp O.03pF
FIGURE I. - P-I-N DIODE EQUIVALENT CIRCUIT AND TYPICAL CIRCUIT
ELEMENT VALUES.
of the diode with the circuit element values supplied by Metelics. Although no
tuning to resonate off the diode parasitlcs was done, the CPW slots were made
equal to the length of the packaged diode to minimize the package inductance,
Lp. Testlng of the switches has been done on an HP 8510 automatlc network ana-
lyzer with bias tees to supply the dc bias to the diodes. The test fixture is
comprised of a 2 in. length of CCPW with a 0.045 In. center strip and 0.010 in.
slot. Connectlon to 3.5 mm coax cables is made through a pair of coaxial con-
nectors. Tuning notches in the ground plane have been used to improve the
coax-to-CCPW characterlstlcs over selected frequency bands. The test fixture
has a total Insertlon loss of 0.5 dB and a return loss greater than 15 dB for
the frequencles reported In this paper.
P-I-N DIODE SHUNT SWITCH
In a shunt mounted configuration, a pair of diodes are placed In parallel
across the slots of the CCPW transmission llne (fig. 2). When the diodes are
1.... _,glq--- "I
FIGURE 2. - SCIIEMATICAND EQUIVALENT CIRCUIT OF CPW P-I-N
DIODE SIIUNISWITCII.
forward biased, each slot Is loaded by the forward blas impedance of the diode;
at ]0 GHz, the impedance across the slot is approximated by Rf + jeLp = 8.7
<< Zo. The shunt impedance for CPN, with two parallel slots, is therefore
4.35 Q. This low impedance loading the slot reflects the propagating wave.
Hhen the diode is reverse biased, each slot is loaded by an impedance approxi-
mated by I/(juCt) = 530 _ >> Zo. This is an equivalent shunt impedance of
265 Q for CPH. This load results in a small attenuation. Using expressions by
Natson (ref. 6) modified for two parallel shunt elements, an isolation of 16 dB
and an insertion loss of 0.04 dB is predicted.
S 2 :]. Iog MAG
REF 0. @ dB
10. @ riB/
C +--_ ..... i
........ 1
(a) MEASURED INSERTION LOSS AND ISOLATION.
$11 Io 9 MAG
REF 0.0 dB
10.0 _B/
,Prn-ei_eEpHuszr_w__eH-PC t! ...............i -_
= r-................ T- t.... ; ........f......... ? ---
' ' 4
L ........... ! ! +--i ..............i .. 4
i = ; i ____£ .........
_-----; .... SwITCH-0FFL - I _
I_T----,-/ -7 _ 1
, , + I i ',E SWITCH-ON r
t-----'-__}x-, (0.0 MA) 'r ............. ---;-.......... '----' --_
;........ __ ..... _.. :...... •....... : ..... t..... i--
START 8. 0000000_D GHz
STOP II.0_0000000 GHz
(b) MEASURED RETURN LOSS.
FIGURE 3. --CPW P-I-N DIODE SHUNT SWITCH WITH TWO PAIRS OF
DIODES.
3
An insertion loss less than I dB and an isolation of 15 dB has been meas-
ured over the frequency band of 8 to 11GHz. The return loss was less than
10 dB across the band. By incorporating more than one pair of diodes across
the slots with a _g/4 separation, higher isolation can be achieved. Typi-
cally, two pairs of diodes have resulted in an Isolation of 30 dB over the 8 to
11GHz frequency band with little Increase In insertion loss, this is shown in
figure 3(a). Figure 3(b) shows the return loss which is less than I0 dB across
the band.
P-I-N DIODE SERIES SWITCH
In the series mounted diode conflguration, a diode is mounted across an
0.008 in. gap in the center strip conductor of the CCPN line (fig. 4). The
J
c, Tc,
FIGURE 4. - SCtlEPLATICAND EQUIVLENT CIRCUIT OF CPWP-I-N I)IOI)E
SERIES SWITCtl.
center strip has been tapered to the width of the beam lead diode to provide a
better match to the width of the diode package. The gap appears as an equiva-
lent capacitive _ network (ref. 7). Nhen the diode is forward biased, the
coupling capacitance is shorted by the low diode impedance and the wave is
transmitted. Reverse biasing the diode results in an impedance across the gap
which can be approximated by I/[jm(Ct + Cc)] >> Zo at I0 GHz. Therefore, the
propagating signal is reflected as if from an open circuit. A measured inser-
tion loss of I dB and an isolation of 15 dB has been obtained from 0.045 to
8 GHz (fig. 5(a)). The return loss over this band is less than 10 dB
(fig. 5(b)). The gap impedance is not large enough at higher frequencies to
provide good isolation. The gap can be lengthened to decrease Cc but the
increase in inductance from the longer diode leads will ultimately limit the
gap separation. Resonating out these reactances is required for higher fre-
quency operation (ref. 6).
4
$21
REF 0.0 dE)
10. @ dE)/
_IN
7
i_ i =-- r
__SWITCH-OfF
Iog NAG
rODE SERIE_ SWl rCH
I./ r
(a) I_I_ASURED INSERTION LOSS AND ISOLATION.
_____ SWITCH-ON_ __
(0.7 MA)--\ / -INSERTION LOSS--J,, )
I't
-- ISOLATION --
S11
REF 0.0 dB
5.0 d8/
_IN D
Iog MAG
[ODE ERIE _ SWI
=SWITCH-OFFJ____
// (0.0 _)
d t
I
F SWITCH_ON
,_x0'7 _)
/ -
START 0.045000000 GHz
STOP 8.000000000 GHz
(b) _ASURED RETURN LOSS.
FIGURE 5. - CPW P-I-N DIODE SERIES SWITCH.
P-I-N DIODE SPDT SNITCH
To realize a SPDT switch, a CCPN Tee-junction with gaps in the center
strip conductor at the junction was formed (fig. 6). Diodes were mounted
across the gaps in parallel. As shown in figure 7, the measured insertion loss
is l dB and the isolation is greater than 15 dB over the octave bandwidth of
2.25 to 5.5 GHz. The return loss was less than lO dB.
PORI #2
_ PORT It_
PORT 111
FIGURE G, - SCIIEMMIC AND EQUIVALEN1 CIRCUIT
OF SERIES MOUNTED P-I-N DIODE CPW SPDT
SWI TCII.
c
$21 I o g HAG
RE_" 6'. 0 dB
5.0 dB/
SWITCH-ON
----(0.7 MA)_-_ _INSErTION lOSS ..... I---
START 2. 250@0000@ GHz
STOP 5. 580®_@®8_ GHz
FIGURE 7. - EASURED INSERTION LOSS AND ISOtATION OF SERIES
MOUNTED PIN DIODE CPW SPD[ SWITCH.
P-I-N DIODE SWITCHED-SERIES-STUB SWITCH
A diode Is mounted across the open end of a Xgl4 stub which is in series
with the center strip conductor of the CCPW as shown in figure 8, When the
diode is unbiased, the stub Is terminated in an effective open clrcuit and
therefore appears as a series short circuit. Hence, the wave propagates with
negllglble attenuation. This is the on-state of the switch. When the diode
is forward biased, the stub is terminated in an effective short circuit which
[ ;: J
F
I)IODE UNBIASED DIODE FORWARD BIASED
FIGURE 8. - SCHEMMIC AND EQUIVALENT
CIRCUIT OF CPW P-I-N DIODE SWITCIIED-
SERIES-STUB SWITCH.
therefore appears as a series open circuit. The wave is therefore reflected;
this is the off-state of the switch. The diode reactances result in an effec-
tive lengthening of the stub and can easily be compensated for. A measured
insertion loss of 1.0 dB and an isolation of 19 dB has been obtained at 9 GHz
(fig. 9(a)). Figure 9(b) shows the return loss.
1;
14
S21 log MAG
REF 0.0 dB
5.0 dB/
IN DIODE _WlTCHi
i
I [SWITCH-ON
[-(o.o _>_--
I
I-INSERTION LOSS
7 /! !
---- --ISOLATION
SWITCHIOFF ____/
(0.7 jMA)_' I
(a) MEASUREDINSERTION LOSS AND ISOLATION,
SII log MAG
J
START 8.000000000 OHz
STOP 10.000000000 GHz
(b) MEASURED RETURN LOSS.
FIGURE 9. - CPW P-I-N DIODE SWITCHED-SERIES-STUB SWITCH.
CONCLUS IONS
P-I-N diode reflective switches are easily realizable on CCPW transmission
line and therefore CPN transmission line. Each of the three type of switches
presented are practical for specific applications. The performance of the
switches could be improved through typlcal tuning of the diode reactances once
the necessary CPWcircuit models becomeavailable.
REFERENCES
1. Wen, C.P., "Coplanar Waveguide, A Surface Strip Transmission Line Suitable
for Nonreciprocal Gyromagnetic Device Applications," 1969, IEEE Trans.
Microwave Theory Tech., vol. MTT-17, pp. 1087-1090.
2. Simons, R.N., Ponchak, G.E., Martzaklis, K.S., and Romanofsky, R.R.,
'IChanne]ized Coplanar _aveguide: Discontinuities, Junctions, and
Propagation Characteristics,: 1989, IEEE MTT-S International Microwave
Symposium Digest, IEEE, Piscataway, NJ, pp. 915-918.
3. Fleming, P.L., Smith, T., Carlson, H.E., and Cox, W.A., "GaAs SAMP Device
for Ku-Band Switchlng," 1979, IEEE Trans. Microwave Theory Tech.,
vol. MTT-27, pp. 1032-1035.
4. Bhat, B., and Koul, S.K., Analysis, Design and Applications of Fin Lines,
Artech House, Norwood, MA, 1987.
5. White, J.F., Microwave Semiconductor Enqineering, Van Nostrand Reinhold
Co., New York, 1982.
6. Watson, H.A., Microwave Semiconductor Devices and Their Circuit
Applications, McGraw-Hill Book Company, New York, 1969.
7. Slmons, R.N., and Ponchak, G.E., "Modeling of Some Coplanar Waveguide
Discontinuities," IEEE Trans. 1988, Microwave Theory Tech., vo1. MTT-36,
pp. 1796-1803.
Report Documentation PageNalional Aeronauhcs and
Space Administration
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
NASA TM- 102289
4. Title and Subtitle
Channelized Coplanar Waveguide Pin-Diode Switches
7. Author(s)
G.E. Ponchak and R.N. Simons
9. Performing Organization Name and Address
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
2. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
5. Report Date
November 1989
6. Performing Organization Code
8. Performing Organization Report No.
E-4959
10, Work Unit No.
506-44-2C
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
This report is an expanded version of material presented at the European Microwave Conference cosponsored
by the IEEE, IEE, URSI, and EUREL, London, England, September 8, 1989. G.E. Ponchak, NASA Lewis
Research Center; R.N. Simons, NASA Resident Research Associate from Case Western Reserve University,
Cleveland, Ohio 44106.
16. Abstract
Three different types of p-i-n diode, reflective CPW switches are presented. The first two switches are the series
and the shunt mounted diode switches. Each has achieved greater than 15 dB of isolation over a broad
bandwidth. The third switch is a narrow band, high isolation switched filter which has achieved 19 dB of
isolation. Equivalent circuits and measured performance for each switch is presented.
17. Key Words (Suggested by Author(s))
Microwave transmission lines
Diodes
Coplanar transmission line
18. Distribution Statement
Unclassified - Unlimited
Subject Category 33
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