A full wave space domain integral equation (SDIE) analysis of coplanar waveguide (CPW) two port discontinuities is presented. An experimental setup to measure the S-parameters of such discontinuities is described. Experimental and theoretical results for CPW realizations of pass-band and stop-band filters are presented. The S-parameters of such structures are plotted in the frequency range 5 to 25 GHz

Dib, N. I.

Katehi, P. B.

Ponchak, George E.

Simons, Rainee N.

English

NASA Technical Reports Server

NASA Technical Memorandum 102534
w .... =. : _ : .... -_ _
- Coplanar WaWg_de Discontinuities -::-
for P-I-N Diode Switches and
= Filter Applications
N.I. Dib and P.B. Katehi
University of Michigan
Ann Arbor, Michigan
G.E. Ponchak
Lewis Research Center
Cleveland, Ohio
R.N. Simons
Case Western Reserve University _
Cleveland, Ohio ....................
i
Prepared for the
- 1990 IEEE MTT'S Internation/il Microwave Symposium
Dallas, Texas, May 8-10, 1990
i:
• (_A_A-TM-102534) C_PLAMA_ WAVEGUIOE NQ0-21278
OISCONTINUITI_S FOR P-I-N GIODE SWITCHES AND
_, FILTER APPLICATIONS (NASA) 20 p CSCL O9C
Unclas
G3/_3 0275339
https://ntrs.nasa.gov/search.jsp?R=19900011962 2020-03-19T23:18:08+00:00Z
_ 41r
COPLANAR WAVEGUIDE DISCONTINUITIES FOR P-I-N DIODE SWITCHES
AND FILTER APPLICATIONS
N.I. D1b and P.B. Katehl
Radiation Laboratory
University of Michigan
Ann Arbor, Michigan 48109
G.E. Ponchak
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohlo 44135
R.N. Slmons*
Case Western Reserve University
Cleveland, Ohio 44106
I
i,t
SUMMARY
A full wave space domain integral equatlon (SDIE) analysis of coplanar
waveguide (CPW) two port dlscontlnuitles is presented. An experimental setup
to measure the S-parameters of such dlscontlnuitles is described. Experimen-
tal and theoretlcal results for CPW realizations of pass-band and stop-band
filters are presented. The S-parameters of such structures are plotted in the
frequency range 5 to 25 GHz.
INTRODUCTION
The coplanar wavegulde (CPW) was introduced for the first time in 1969 by
C.P. Wen (ref. l) as an appropriate transmission llne for nonreciprocal gyro-
magnetic device applications. Recently, with the push to high frequencies and
monolithic technology, CPW's have experienced a growing demand due to their
appealing properties (refs. 2 and 3). However, the extent of applications of
CPW circuits is limited due to the unavailability of circuit element models
which can be incorporated into CAD programs. Houdart (ref. 2) proposed several
configurations using the coplanar llne technique in order to realize basic
types of elements required in MIC's.
Microwave switches are circuit elements widely used in phase shifters and
radiometers. A CPW switchable attenuating medium propagation, SAMP, switch has
been demonstrated by Fleming et al. (ref. 4). This device is useful for GaAs
MMIC circuits but it is not easily incorporated into MIC's on passive sub-
strates such as alumina or durold. P-1-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. Recently, CPW p-i-n diode switches were proposed
and fabricated (ref. 6). Figure l shows a switch where a diode is mounted
across the open end of a quarter wavelength stub which is in series with the
*NASA Resldent Research Associate at Lewls Research Center; present
address: Sverdrup Technology, Inc., NASA Lewis Research Center Group,
Cleveland, Ohio 44135.
center strip conductor of the CPW. The two states of the switch, ON and OFF,
can be realized separately by appropriate CPN discontinuities which in turn
can be used to build pass-band and stop-band filters respectively (refs. 2, 7
and 8).
In this paper, the space domain integral equation (SDIE) method, presented
in reference 5 is extended to analyze the S-parameters of the CPW realization
of the above switches, figure 2. Experlmenta] results are compared to theoret-
ical data and a good agreement is achieved. The experimenta] setup, measure-
ment technique and the sources of error are described. As a next step, the
study of the switches will be completed by Including the diode as a lumped ele-
ment in the method of moments solution. Thus, the ON and OFF states of the
switch wlll be predicted from the same structure without having to go to dif-
ferent CPN discontinuities for realization of these states.
THEORY
The coplanar line under consideration is shown in flgure 3. The measure-
ments were performed using an open CPN structure. However, in the theoretical
analysis the CPN is assumed to be inside a rectangular cavity of perfectly con-
ducting walls as opposed to experiments where open structures were measured.
The cavity dimensions were chosen such that the CPW fundamental mode is not
affectedby hlgher order cavity resonances.
The original boundary problem is split into two simpler ones by introduc-
ing an eqOivalent magnetic current Ms, on the slot aperture. This surface mag-
netic current radiates an electromagnetic field in the two waveguide regions
(above and below the slot) so that the continuity of the electric field on the
surface of the slots is satisfled. The remaining boundary condition to be
applied is the continuity of the tangential magnetlc field on the surface of
the slot apertures which leads to the following integral equation
_
n x s - • (g')ds' = is' (I)
=h
where GI, 2 are the magnetic dyadic Green's functions In the two waveguide
regions (ref. 5) and Js denotes the ideal current source feeding the CPN,
(gap generator model).
The integral equation (I) is solved using the method of moments where the
unknown magnetic current is expanded In terms of rooftop basis functions.
Then, GaIerKin's method is applied to reduce the above equation to a linear
system of equations
Yyy Yzy_ Vy
(2)
where YIj(i : y,z; j : y,z) represent blocks of the admittance matrix,
= (ref. 5) V1 is the vector of unknown y and z magnetic current amplitudes,
and I_ Is the excitation vector which is identically zero everywhere except
at the-position of the sources. Finally, the equivalent magnetic current dis-
tribution and consequently the electric fleld in the slots are obtalned by
matrix inversion.
Away from the discontinuity, the slots fields form standing waves of the
fundamental CPW propagating mode. Uslng the derived electric field, an ideal
transmission line method as described in reference 9 is applled to determine
the scattering parameters of the two port discontinuity.
R
EXPERIMENT
The circuits were fabricated using a liftoff procedure. A 2.8 _m gold
layer was electron beam evaporated onto a 25 mil thick polished alumina sub-
strate ((r = 9.9). The alumina substrate was placed on a 125 mil thick 5880
RT/Durold (cr = 2.2) substrate with copper cladding on one side to serve as
the bottom ground plane.
The RF measurements were performed using HP8510ANA and a probe statlon
with design techniques DC - 26 GHz probes. In order to measure the circuit
elements, an LRL calibration (ref. lO) was performed to remove the effects of
the system to the reference plane PP' (fig. 4) using E-Esof ANACAT software
(ref. ll). The calibration standards shown in figure 5 were fabricated on the
same substrate as the circuits.
g+
RESULTS AND DISCUSSION
For the solution of reference 2, most of the computation effort Is spent
on the evaluation of the elements of the admlttance submatrlces. These elements
Involve double summations in their computation which are inherently slowly con-
vergent. Detalls on the numerical evaluation of these summatlons may be found
in reference 2. Extensive numerical experiments were performed on the conver-
gence of the S-parameters with respect to the above summations and the number
of basis functions used in the expansion of the slot field. Both were chosen
such that at least 2 percent accuracy Is achieved.
Figure 6 shows the scatterlng parameters for the short circuit CPW stub
(SC-CPW stub) of length 500 pm. It can be seen that the agreement between the
theoretical and experimental results is very good. The differences can be due
to conduction losses and radiation losses since an open structure was used in
the measurements. Figure 7 shows the scattering parameters for the SC-CPW stub
of length 1500 pm. From these results it can be observed that a resonance
occurs when the stub length is slightly less than a quarter wavelength (_g ~
6.14 mm at f = 21GHz). This Is due to the inductive reactance which exists
at the end of the stub as a result of the end effect. A stop-band filter can
be realized by cascading several SC-CPW stubs in series.
Figures 8 and 9 show the scattering parameters for the open circuit CPW
stub (OC-CPN stub) of length 500 pm and 1500 pm respectively. It can be seen
from figure 9 that Sll (Sl2) has its minimum (maximum) value at f = 19 GHz at
which xq/4 ~ 1.7 mm. This is due to the capacitive end effect of the stub.
Such strOctures operate as pass-band filters. The agreement between the theo-
retlcal and experimental results Is very good.
The errors associated with the measured data are nonrepeatability In probe
placement and pressure and circuit fabrlcatlon tolerances. The circuit dimen-
sion variations across the 2 in. by 2 in. alumina substrate were negllglble as
was the variation In the gold thickness. The circuit dimensions varied by, at
most, l percent compared to the designed dimensions. The probe placement was
repeatable to 5 pm. The probe pressure created the largest uncertainty in the
measurements since it changed the contact between the alumina and the duroid
substrates. One further consideration is that the spacing between circuits on
the substrate was approximately (S + 2N)/2 which resulted in a finite size
ground planes.
CONCLUSIONS
The space domaln Integral equation method solved by the method of moments
(Galerkin's technique) In conjunction with simple transmission llne theory was
applied to analyze CPN realizations of pass-band and stop-band filters. An
e×perlmental setup to measure the S-parameters of those structures has been
described and the various sources of error were discussed. The agreement
between the theoretical data and the experlmenta] measurements was very good,
thus, the validity of both results is verified.
ACKNONLEDGMENT
The theoretical part of this paper was supported by the National Science
Foundation under contract ECS-8657951.
REFERENCES
I. C.P. Wen, "Coplanar Naveguide- A Surface Strip Transmission Line
Suitable for Nonreciprocal Gyromagnetic Device Applications," IEEE Trans.
Microwave Theor_ Tech., vol. MTT-17, pp. I087-I090, 1969.
2. M. Houdard, "Coplanar Lines" Application to Broadband Microwave
Integrated Circuits," 6th European Mlcrowave Conference, Microwave
Exhibitions and Publishers, England, pp. 49-53, 1976.
,
,
.
,
,
K.C. Gupta, R. Garge, and l.J. Bahl, Microstrlp Lines and Slotlines,
Dedham, MA" Artech House, 1979.
P.L. Fleming, T. Smith, H.E. Carlson, and N.A. Cox, "GaAs SAMP Device for
Ku-Band Switching," IEEE Trans. Microwave Theory Techniques, vo]. MTT-27,
pp. 1032-1035, 1979.
N.I. Dib and P.B. Katehi, "Modeling of Shlelded CPN Discontinuities Using
the Space Domain Integral Equation Method (SDIE)," submitted to the
Journal of Electromagnetic Naves and Applications, Special Issue on
Electromagnetism and Semiconductors.
G.E. Ponchack and R.N. Slmons, "Channelized Coplanar Naveguide PIN-Diode
Switches," 19th European Microwave Symposium Digest, Microwave Exhibl-
tlons and Publishers, England, pp. 489-494, 1989 <Also, NASA TM-I02289).
R.N. Bates, "Deslgn of Microstrip Spur-Line Band-Stop Filters," IEE J.
Microwave, Optics Acoustics, vol. I, pp. 209-214, 1977.
.o
10.
D.F. Willlams and S.. Schwarz, "Deslgn and Performance of Coplanar Wave-
guide Bandpass Filters," IEEE Trans. Microwave Theory Techniques,
vol. MTT-31, pp. 558-566, 1983.
P.B. Katehi, "A Generallzed Method for the Evaluation of Mutual Coupllng
In Microstrip Arrays," IEEE Trans. Antennas Propagat., vo1. AP-35,
pp. 125-133, 1987.
P.R. Pantoja, M.J. Howes, J.R. Richardson, and R.D. Pollard, "Improved
Calibratlon and Measurement of the Scattering Parameters of Microwave
Integrated Circuits," IEEE Trans. Microwave Theory Techniques,
vol. MTT-37, pp. 1675-1680, 1989.
Anacat User's Manual, E-Esof Inc.
L.P. Dunleavy and P.B. Katehi, "A Generalized Method for Analyzing
Shielded Thln Microstrlp Dlscontinulties," IEEE Trans. Microwave Theory
Techniques, vol. MTT-36, pp. 1758-1766, 1988.
i!iiii!i!iiii iiii!iiiiiiiiiiiiiiiiiii!iii 
;'":':','-'.'.'," '.'." " "I I: ............... ': ....... : ........ ":"
::::::::::::::::::::::::::::: .:,:, • .:.:.:, ,:- • .:.:.:,:,:
 ii!iiiiiiiiii!ii!iiiiiii!ii!iiiii iiiiiiiii 
FIGURE I. - SCHEMATIC DIAGRAM OF CPW P-I-N DIODE SWITCHED SERIES-
STUB SWITCH.
P P
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I!i!_!_i_!iiiiiiii_i_i_!_ii`_?_:_:_:i_i_i!i!i!iii!_!_!iiiiii_i_i!i_!iI
.................. j ........ [ ...........................
I 1
p) p1
P P
  ii!iiiiiiiiiiiii!!iiiii! ! ii iiiiiilililiiiiiiiiiiiil
iiili ii!il iil !:_"_! i !iii_iii!iiii_ii!_i_i_i!_
I'!iii..............................i iii;iiiiiii!iii?i?iiiii?iiiililli: !}i :: iilliiilliiii'!! ! ':iiii
I 1
p_ p_
FIGURE 2. - CPW REALIZATIONS OF STOP-BAND AND BAND-PASS FILTERS.
_0
__.._.¢{¢._._.,._._. ,._._._._. ._._..
_._._....,.__Y#_._#_.
FIGURE 3. - COPLANAR WAVEGUIDE INSIDE A CAVITY,
Coex I
referencel---- _ _ ....
plane '
aI
I I
Circuit
reference
planes
v" \
_ discontinuity
FIGURE 4, - BASIC CONCEPT OF DE-EMBEDDING,
Coax
refeFence
plane
(a) DELAY OF LENGTH LI.
_J
____'/////////////_/////////////
p,
(b) DELAY OF LENGTH L2.
///////////I//
I _/_/_/_ / Open c,rcuit
(C) REFLECTION OF ARBITRARY MAGNITUDE.
FIGURE 5. - CPW STANDARDS FOR LRL CALIBRATION.
_J_._ ....
__ [.w,_2....__
0._
-4. 04)0
o O_l
_s
ooo I_ oO
THEORETICAL
_r._,_.,_-;,
+ OB[S_!
NEAS
1
I
0.11011
FIGURE 6. - S-PAR/V_ETERSFOR SC-CPW STUB WITH L = 500 pro.
DI = 25 MIL, D2 = 125 MIL, Erl = 9.9, {r2 = 2.2.
a OB(S_,I + 0B(Stl]
ME_ MEAS
o._ _ _ _-_--.._ ,_ ._
-30.O0 _ ........
]_ 00 FI_EQ-GHZ
FIGURE 7. - S-PARAMETERSFOR SC-CPWSTUB WITH L
OTHERDIMENSIONS ARE THE SAMEAS IN FIG. G.
i THEORETICAL
= 1500 pro.
7
7s_. Wd225 P"
75Fq
o _sa] + o_sil]
_EAS
!
g
--&000 _
-.t6.00 _
-- THEORETICAL
....... _T O.000
-EO_
....... -'IE00
FIGURE 8. - S-PARAMETERS FOR OC-CPW STUB WITH L =
500 pm. D I = 25 MIL, D2 = 125 MIL, Erl = 9.9,
Er2 = 2.2.
O.(_)0
-B. 000
--iE O0
MF.AS
_J
.... i
ooo
+ 0B[SI|] _ THEORETICAL
MEAS
...... --t6.00
llOO F_ 25.0O
FIGI]RE9. - S-PARAMETERS FOR O£-CPW STUB WITH L
1500 pm, OTHER DIMENSIONS ARE THE SAME AS IN
FIB. 8,
8
Report Documentation PageNational Aeronauticsand
Space Administration
1. Report No. 2. Government Accession No.
NASA TM-102534
4. Title and Subtitle
Coplanar Waveguide Discontinuities for P-I-N
Diode Switches and Filter Applications
7. Author(s)
N.I. Dib, P.B. Katehi, 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
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
3. Recipient's Catalog No.
5. Report Date
6. Performing Organization Code
8. Performing Organization Report No.
E-5343
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
Prepared for the 1990 IEEE MTT-S International Microwave Symposium, Dallas, Texas, May 8-10, 1990. N.I. Dib
and P.B. Katehi, Radiation Lab, University of Michigan, Ann Arbor, Michigan 48109. G.E. Ponchak, NASA Lewis
Research Center. R.N. Simons, Case Western Reserve University, Cleveland, Ohio 44106 and NASA Resident
Research Associate at Lewis Research Center; present address: Sverdrup Technology, Inc. NASA Lewis Research
Center Group, Cleveland, Ohio 44135.
16. Abstract
A full wave space domain integral equation (SDIE) analysis of coplanar waveguide (CPW) two port discontinuities
is presented. An experimental setup to measure the S-parameters of such discontinuities is described. Experimental
and theoretical results for CPW realizations of pass-band and stop-band filters are presented. The S-parameters of
such structures are plotted in the frequency range 5]25 GHz.
17. Key Words (Suggested by Author(s))
Coplanar waveguide
P-I-N diodes
Switches
Filter
19. Security Classif, (of this report)
Unclassified
18. Distribution Statement
Unclassified- Unlimited
Subject Category 33
20. Security Classif. (of this page)
Unclassified
21. No. of pages
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22. Price*
A02
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Coplanar waveguide discontinuities for P-I-N diode switches and filter applications

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