Figure 6 Dark soliton damping at an instant of time due toexponential and exponential and algebraic dampings

erated through an existing method. Furthermore, simultane-ous effects of the exponential and algebraic dampings on thebright and dark solitons are given.

REFERENCES

1. D. J. Kamp and A. C. Newell, ‘‘Solitons as Particles, Oscillators,and in Slowly Changing Media: A Singular Perturbation Theory,’’Proc. R. Soc. Lond., Vol. 361, 1978, pp. 361]532.

2. N. N. Akhmediev and A. V. Buryak, ‘‘Soliton State and Bifurca-tion Phenomena in Three-Core Nonlinear Fiber Couplers,’’ J. Opt.Soc. Amer. B, Vol. 11, 1994, pp. 804]809.

3. N. Akhmediev and A. Ankiewicz, ‘‘Novel Soliton State and Bifur-cation Phenomena in Nonlinear Fiber Couples,’’ Phys. Re¨. Lett.,Vol. 70, 1993, pp. 2395]2398.

4. F. Ahmad and M. Razzaghi, ‘‘An Approximate Solution to theEnvelope of a Pulse Propagating in a Nonlinear Optical Fiber,’’Proc. Inst. Elect. Eng., OptoElectron., Vol. 143, 1996, pp. 200]204.

5. B. Malomed, ‘‘Soliton Stability in a Bimodal Optical Fiber inthe Presence of the Raman Effect,’’ Phys. Re¨. E, Vol. 50, 1994,pp. 5142]5144.

6. K. Hizanidis and D. Frantzeskakis, ‘‘Reductive Perturbation Anal-ysis of Short Pulse Propagation in a Nonlinear Dielectric Slab:The Role of Material Dispersion in Bright-to-Dark Solution Tran-sitions,’’ IEEE J. Quantum Electron., Vol. 29, 1993, pp. 286]295.

7. T. Yamada and K. Nozaki, ‘‘Effects of Dissipative Perturbation onBound-State Solitons of Nonlinear Schrodinger Equation,’’ J. Phys.¨Soc. Jpn., Vol. 58, 1992, pp. 1944]1947.

8. J. Giannini and R. Joseph, ‘‘The Propagation of Bright and DarkSolitons in Lossy Optical Fiber,’’ IEEE J. Quantum Electron., Vol.26, 1990, pp. 2109]2114.

9. M. Lisak, D. Anderson, and B. Malomed, ‘‘Dissipative Dampingof Dark Solitons in Optical Fibers,’’ Opt. Lett., Vol. 16, 1991,pp. 1936]1937.

Q 1997 John Wiley & Sons, Inc.CCC 0895-2477r97

WAVEGUIDE FILTERS WITH PLANARCIRCUIT INSERTS SUITABLE FORINTEGRATION OF ACTIVE DEVICESPatrick Morin,1 Ke Wu,1* and Jifu Huang21 Poly-Grames Research Center

´Departement de Genie Electrique et de Genie Informatique´ ´Ecole PolytechniqueC.P. 6079, Montreal, P.Q. H3C 3A7, Canada´2 Harris-Farinon, Canada

Recei ed 29 April 1997

* On leave at the Telecommunication Research Center, City University ofHong Kong, Kowloon, Hong Kong.

ABSTRACT: This paper presents a class of wa¨eguide bandpass filterswith conformal iris patterns made of planar circuits suitable for integra-tion of acti e de¨ices. Multiple planar inserts are located along thepropagation path with specially designated spacing between two adjacentplanar inserts on which the iris patterns are etched. The electricalperformance of such no¨el filters with the enclosure of a circularwa¨eguide is demonstrated by the field-theoretical design and experimen-tal characterization of a three-pole Tschebyscheff-type filter. Results ofthis type of planar-insert-based wa¨eguide filter is compared with itscon¨entional all-metallic iris counterpart designed at the same centerfrequency, showing nearly an identical frequency response between thetwo different topologies. Q 1997 John Wiley & Sons, Inc. MicrowaveOpt Technol Lett 16: 77]80, 1997.

Key words: wa¨eguide filters; planar circuits; bandpass filters

INTRODUCTION

Iris-coupled bandpass waveguide filters have been extensivelystudied over decades for high-performance microwave and

w xmillimeter-wave circuits and systems 1, 2 . These iris patternsare always formed on a number of metallic building blockshaving a high-Q property and high-power-handling capacity.

wThese filters, loaded with a series of all-metallic iris as anŽ .xexample, the circular waveguide shown in Figure 1 a , have

w xbeen designed and used for a wide range of applications 3 .It has been recognized, on the other hand, that planar

Ž .structures such as M H MICs offers unparalleled advantagesand flexibility, compared with the metallic waveguide technol-ogy, in the design and fabrication of microwave and millime-ter-wave circuits and systems. However, it is certainly difficultto use the planar circuit in designing a high-Q bandpass filterwith sharp out-of-band rejection. This is mainly due to thefact that the signal path of the planar circuit is very lossy, andbecomes much more pronounced at higher frequencies. Andalso, the planar circuit cannot usually support high-powerapplications.

It is obvious that complete metallic structures such asŽ .described in Figure 1 a are not compatible with the integra-

tion of active devices, and therefore find limited applicationswhich are essentially of a passive nature. Nevertheless, it isreasonable to be affirmative that an appropriate use of com-bining the planar and metallic waveguide techniques within asingle building block presents an attractive compromise for

Ž .realizing high-Q, high or medium -power applications. Thiscan be done by integrating or inserting active devices into themetallic waveguide. The well-established finline technologymay be considered as a typical example. Unfortunately, thesignal path of a finline is still very lossy because it is based onthe planar transmission line whose electrical field is made tobe matched with the E-plane of its enclosed metallic wave-guide, although a number of advantages have been obtainedw x4 .

In this work, we propose an alternative topology, as de-Ž .picted in Figure 1 b , which may illustrate potential interests

for applications exploring and combining the advantages of aplanar structure and metallic waveguide such as an electroni-cally tunable high-Q filter. The technical merits of using thishybrid technique are experimentally demonstrated throughthe design and measurement of a class of circular bandpassfilters with all-metallic iris and planar inserts having irismetallic pattern. Results obtained by using the proposedtechnique of planar circuit inserts and the conventional ap-proach indicate that comparable electrical performance canbe achieved for the new structure while the potential integra-

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 16, No. 2, October 5 1997 77

Ž . Ž .Figure 1 Illustration of a class of circular waveguide filters a with the classical all-metallic iris, b with the proposed printed iris.Geometrical parameters are fixed in our case study with D s 38.10 mm, t s 4.00 mm, t s 1.25 mm. Other physical parameters are1 2subject to design requirement

tion of active devices is readily attainable for generating newapplications.

DESIGN PROCEDURE

To illustrate this attempt, we have designed two waveguidebandpass filters based on the two different topologies shown

Ž . Ž .in Figure 1 a and b , namely, the classical all-metallic irisand the proposed planar inserts with iris etches. Obviously,they are both housed in a circular waveguide in our casestudy, which can be extended into other waveguide structuressuch as a rectangular waveguide. Such a geometrical arrange-ment using planar inserts with particular etched patterns canbe used to integrate active devices inside the waveguide, andelectronic tuning is therefore easily done. In addition, thehigh-Q features of the signal path and radiationless charac-teristics of the waveguide housing remain intact. Further, it ispossible to design a class of planar inserts such that appropri-ate mode coupling and field polarization control can be easilyachieved through the connection of a diode or transistor onthe planar inserts. This may be useful in the design of activewaveguide devices such as a high-Q and high-power active

Ž .filter, a tunable dual-mode or multimode filter, and anelectronically controlled field polarizer.

To demonstrate the advantages of the proposed hybridtechnique, the design of two different circular waveguidefilters should be made for the same center frequency andfrequency response so that the electrical performance can bemeasured and compared between them. To do so, we makeuse of field-theoretical modeling techniques to determinecircuit parameters in conjunction with the classical filterdesign, considering the fact that the planar circuit inserts

present a layered inhomogeneous structure. Obviously, thegeometrical parameters of the two topologies also should bedifferent to achieve the design goal of centering the sameoperating frequency.

To begin with, the two structures are modeled by anequivalent inverter prototype filter as shown in Figure 2,allowing for the choice of a set of consistent relevant circuitparameters which are valid for the two different techniquesin obtaining the same center frequency. Our designated spec-ifications of a three-pole bandpass filter are defined and givenin Table 1. The consideration of selecting a third-orderTschebyscheff filtering response leads to the expected proto-type filter parameters which are found in Table 2 with adefined number of corresponding K inverter values calcu-i j

w xlated from 3 . Both filters operate in the TE mode.11Now, in order to determine the iris diameters d andi

spacing L as defined in Figure 1 for the two filter structuresibased on the obtained K inverter models, two field-theo-i jretical modeling and analysis tools are used simultaneously tocalculate the S-parameters for the two types of iris disconti-nuities. The inverters are spaced by l r2 as shown in Figureg2 for the prototype of the filters. The modeling and analysistools are based on the engine of a three-dimensional method

Ž . w x Ž .of lines MoL 5 and of a transmission line matrix TLMw xmethod 6 , which are both developed in cylindrical coordi-

nates. The inverter model can be associated with the S-parameters calculated by our modeling tools. Considering thecenter frequency and bandwidth of the expected filters aswell as our available planar circuit substrate, the thicknessesof the two iris discontinuities are determined prior to thedesign of the iris diameters and the spacing between two

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 16, No. 2, October 5 199778

Ž . Ž .Figure 2 Prototype design of the two filters with a equivalent circuit for a generalized iris and b K inverter model of a completefilter

adjacent discontinuities. Note that the use of the two model-ing and analysis tools aims at validating the accuracy of ourdesign and results through a comparison of the modelingresults obtained from them. An excellent agreement of theresults between the two tools is obtained, with the details

w xpresented in 5 which are beyond the scope of this work andare omitted in the paper.

Since it is impractical to use these modeling tools directlyin the design of such filters, we have to set up a lookup tableor a design chart which relates the complex value of a Ki jinverter to the physical dimensions of both an all-metallicand a printed planar iris. In our work, a simple design chartin the form of a set of curves is used, and also the choice ofthe predesignated geometrical parameters such as the thick-ness should be made to allow the inverter values to fall intothe design objective for both structures. In this way, we areable to use the designed chart to identify the inverter valueŽ . Ž .K d and its electrical length f d through these curves for

both types of iris, as shown in Figure 3; the details related tow xthis design also have been described in 5 . With the Ki j

Ž .values given in Table 2, we can interpolate K d curves toobtain d values which are subsequently used to interpolatei

TABLE 1

Central Frequency 5.5 GHzBandwidth 5%Ripple 1 dBSelectivity Tschebyscheff, Third Order

TABLE 2 Third-Order Tschebyscheff Filter

g ??? g K ??? K0 Nq1 01 N , Nq1

1.0000 0.27862.0236 0.11070.9941 0.11072.0236 0.27861.0000

Ž .the corresponding f d curves to obtain all f values neces-iw xsary to calculate L 3 . Of course, the same circular wave-i

guide enclosure is used for both types of filter. This designprocedure allows us to build two different filters having thesame frequency response with a set of different physicaldimensions that are summarized in Table 3.

RESULT DISCUSSION

Experimental results for the two designed filters are pre-sented in Figure 4 for the return and insertion losses indecibels. The measurements are made with an HP8510Cnetwork analyzer which is calibrated with a TRL technique.This TRL calibration kit is fabricated and used with a coax-ial-to-circular waveguide TE mode launcher such that the11transitions effect can be effectively removed. In addition, alimited number of tuning screws are used to obtain better

Figure 3 Design chart using a set of K inverter values for bothtypes of filters calculated from the TLM and MoL modeling tech-niques. Note that the results obtained by the two numerical tech-niques are quasi-identical, and therefore are not indicated in thefigure

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 16, No. 2, October 5 1997 79

TABLE 3

Metallic Iris Printed Iris

d ??? d f ??? f L ??? L d ??? d f ??? f L ??? L1 N 1 N 1 N 1 N 1 N 1 NŽ . Ž . Ž . Ž . Ž . Ž .mm rad mm mm rad mm

23.81 y0.6797 40.80 20.52 y0.7804 38.7819.58 y0.3177 43.59 18.09 y0.4824 41.0919.58 y0.3177 40.80 18.09 y0.4824 38.7823.81 y0.6797 20.52 y0.7804

inputroutput impedance matching, and are inserted essen-tially between the filters and the coaxial-to-waveguide transi-tions. Such a tuning is essential because the effect of higherorder modes susceptibly generated by all the irises of thefilters is not taken into account in the design. The compari-son made between them indicates that a nearly identicalfrequency response is obtained between the two differentdesign schemes. And also, the design expectation is consis-tent with the experimental results with the same centerfrequency of 5.5 GHz and less than 1 dB in-band ripple.These results suggest that electrical performance is similarfor the all-metal and printed iris. Both filters present lessthan 1 dB of insertion loss and roughly 20 dB of return lossover the designed bandpass. It is expected and confirmed thatthe insertion loss of the filter made with the planar inserts isslightly higher than its all-metallic counterpart. This is due tothe higher ohmic loss of the planar printed iris. Nevertheless,the lower side of the out-of-band for the planar printed irisfilter is better rejected than for the all-metallic filter, while itsupper side presents the opposite characteristics.

In our experiments, deteriorated electrical performancefor the upper out-of-band is observed in Figure 4, which maybe attributed to the problem of positioning the planar inserts.Nevertheless, we can claim that the planar insert techniquepresents similar electrical performance to its all-metalliccounterpart.

CONCLUSION

We report a hybrid technique in the design of a waveguidefilter using planar circuit inserts suitable for the integrationof active devices. An application example is demonstrated forthe proposed technique through the design of two compara-

Figure 4 Measured frequency response of the two designed filtersfor insertion and return losses using the all-metallic and printedplanar iris techniques

tive three-pole bandpass filters based on the all-metallic irisand the planar printed iris with the enclosure of a circularwaveguide. The design is made in such a way that the samefrequency and bandwidth of the two different filters arerespected. Two field-theoretical modeling and analysis toolsare used in this work to determine a set of physical dimen-sions for the two dissimilar structures. Experimental resultsare very consistent with the design objective, and a nearlyidentical frequency response is obtained for the two differenttechniques. Therefore, this experimental study indicates thatthe proposed hybrid technique is useful for designing high-Q

Ž .and high medium -power active circuits and devices.

ACKNOWLEDGMENT

This work was supported by the Natural Sciences and Engi-Ž .neering Research Council NSERC of Canada under a

strategic grant. The technical assistance of Jules Gauthier onthis work is very much appreciated.

REFERENCES

1. L. Young, ‘‘Direct-Coupled-Cavity Filters for Wide and NarrowBandwidths,’’ IEEE Trans. Microwa e Theory Tech., Vol. MTT-11,May 1963, pp. 162]178.

2. R. Levy, ‘‘Theory of Direct-Coupled-Cavity Filters,’’ IEEE Trans.Microwa e Theory Tech., Vol. MTT-15, June 1967, pp. 340]348.

3. P. Pramanick and P. Bhartia, ‘‘A New Efficient CAD Techniquefor Inductive Reactance Coupled Waveguide Bandpass Filters,’’Int. J. MIMICAE, Vol. 3, No. 2, 1993, pp. 134]142.

4. T. Itoh, Ed., Planar Transmission Line Structures, IEEE Press, NewYork, 1987.

5. P. Morin, ‘‘Analyse de Structures Resonantes Micro-Ondes a´ `´Geometrie Cylindrique,’’ Master’s thesis, Ecole Polytechnique,´ ´

Ž .Mar. 1996 in French .6. J. Huang, R. Vahldieck, and H. Jin, ‘‘Fast Frequency-Domain

TLM Analysis of 3-D Circuits Discontinuity,’’ 9th Annu. Re¨.Progr. Appl. Computational Electromagn., Mar. 1993.

Q 1997 John Wiley & Sons, Inc.CCC 0895-2477r97

NONDESTRUCTIVE DETECTION OFDELAMINATIONS IN MULTILAYERCERAMIC CAPACITORS USINGIMPROVED DIGITAL SPECKLECORRELATION METHODY. C. Chan,1 X. Dai,1 G. C. Jin,1 N. K. Bao,1 and P. S. Chung11 Department of Electronic EngineeringCity University of Hong KongKowloon, Hong Kong

Recei ed 4 April 1997; re¨ised 9 May 1997

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 16, No. 2, October 5 199780