COMPARISON OF WIPL-D MICROWAVE AND MICROWAVE OFFICE SOFTWARE

Milka Potrebić, Dejan V. Tošić, School of Electrical Engineering, University of Belgrade

Abstract – We present a comparison of two software tools for microwave circuit simulation from the educational view point. We highlight salient features of the tools and their relevance and suitability for undergraduate teaching process. The accompanying 3D EM simulation functionality, provided by the tools, is considered as the mean for better understanding circuit models and their limitations as taught in microwave engineering curricula.

1. INTRODUCTION

As we move towards a learner-oriented, self-paced, asynchronous system for higher and continuing education, the traditional course-based curriculum structure must be examined for its efficiency [1].

Courses can be restructured into primary concept modules that are interlinked to reflect the logical development of knowledge in the domain of the discipline being studied [2].

With the wireless revolution, brought on mostly by cellular radio technologies, microwave applications have come to dominate the industry. Cost, time to market, and manufacturing capacity are much stronger influences within the microwave engineering. Cost versus performance will always be a trade-off within any engineering project. However, the weighting coefficients have shifted [3].

Software tools are indispensable in microwave engineering, so the corresponding courses should always address computer aided design and simulation in the teaching process [4].

In this paper we compare two software tools for microwave circuit simulation that can be used for microwave engineering curricula. First, we consider AWR Microwave Office (MWO) [5]. Next, we present WIPL-D Microwave [6], a recently released tool. Both environments are evaluated from the educational viewpoint. Software tools are treated as supplements to microwave courses covered by standard textbooks, such as [7, 8].

Section 2 presents the MWO environment and section 3 describes WIPL-D Microwave. Section 4 presents simulations in MWO and WIPL-D Microwave. Section 5 presents the comparison of salient features of the tools from the educational view point. Section 6 gives a conclusion about this comparison from the teaching view point.

2. MICROWAVE OFFICE

One of the most popular microwave software environments, in both academia and industry, is AWR Microwave Office (MWO). However, a professional tool like MWO can be over-sophisticated for teaching, so it might be desirable to deploy a more compact software solution instead.

MWO is the linear and nonlinear solution for microwave hybrid, module and monolithic microwave integrated circuit (MMIC) design. It includes linear, harmonic-balance, time-domain, electromagnetic (EM) simulation, and physical

layout. It includes linear and nonlinear noise analysis [5]. MWO is, essentially, a frequency domain simulator.

EM simulation is not based on the full-wave analysis (3D solver), but relies on a so called 2.5D solver that is suitable for layered structures, such as microstrip filters and antennas. It has predefined objects, such as rectangle, polygon, path, ellipse, drill hole, edge port, via, and so on. The 2.5D solver has only automatic meshing (subdividing structure into smaller parts for better accuracy) in three levels.

MWO can generate layout (implementation) view from the schematic. The layout view represents the structure that can be analyzed by the 2.5D EM solver. This is important for microwave structures when the circuit model does not take into account mutual couplings, parasitics, and discontinuities. The layout view has many properties and options, so it might be over-sophisticated for introductory microwave courses.

MWO cannot optimize physical structures, but it has a powerful optimizer for circuit model parameters.

Manual optimization, referred to as tuning, is provided so parameter values can be changed interactively while observing the resulting response.

3. WIPL-D MICROWAVE

WIPL-D Microwave is a new design and simulation tool for microwave projects involving microwave circuits, components, and antennas. It has a full-wave 3D EM solver.

Except predefined circuit components, arbitrary composite metallic and dielectric structures can be built interactively. Whenever circuit level simulations are performed, the circuit parameters of the included 3D EM components are computed on-the-fly.

WIPL-D Microwave is intended for a large audience: engineers, practitioners, researchers, academia, and as a teaching tool for microwave engineering curricula.

Unique feature of this tool is the advanced modeling that includes:

1) Defining of structures by means of grids 2) Using symmetry to facilitate analysis 3) Modeling of the end effect and feed area for thick wires 4) Coaxial line excitation 5) Taking the edge effects into account 6) Modeling of layered structures 7) Refining the analysis 8) De-embedding of circuit parameters from the 3D EM

analysis.

WIPL-D Microwave features self-explanatory component palettes. Ideal palette, Fig. 1, contains all basic components relevant for introductory microwave courses, such as short-circuited end, open-circuited end, amplifier, ideal transformer, circulator, symmetric power splitter, and quadrature hybrid coupler. The student can easily build idealized microwave circuits and networks and demonstrate the principal operation of basic microwave devices.

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Technology-related components are grouped in four palettes: microstrip, coaxial, rectangular, and transitions.

Fig. 1. Ideal components palette

WIPL-D Microwave has some microstrip components which are not available in MWO, such as double step, and patch antenna, Fig. 2.

Fig. 2. Microstrip components palette

Unique feature of WIPL-D Microwave is its coaxial palette with components, such as coaxial taper, band, step, gap, T-junction, and cross, Fig. 3.

Fig. 3. Coaxial components palette

Rectangular waveguide components palette contains: E- and H-post, E- and H-band, ET- and HT-junction, E- and H- coupled waveguides, rectangular horn antenna, and magic tee junction, Fig. 4.

Fig. 4. Rectangular components palette

Transitions between different technologies are grouped into a special palette. This palette has transitions from coaxial to rectangular or microstrip technology, Fig. 5.

Fig. 5. Transitions components palette

Transitions palette makes students better understand interfacing microwave components implemented in different technologies.

Ports of each component can be electrically extended, that is, equivalent transmission lines can be added to ports. Consequently, the student can build schematics with fewer elements. In addition, the student can experiment with shifting of reference planes which define component ports.

Another unique feature of WIPL-D Microwave is the possibility to specify symbolic parameters of geometrical structures and to optimize the 3D EM model by varying these parameters.

Moreover, this 3D EM modeling provides predefined objects, such as wires, plates, dielectric domains, sphere, circle, reflector, and body of revolution (a transition between two coaxial cables, a half-sphere with a hole, a ring with circular cross, a ring with a square cross sections).

Students can make their own 3D EM models when the component parameters are out of the range over which the analytical model is valid, or when complex models are not available in the component library.

Full wave 3D EM analysis enables students to explore differences between the results generated by analytical closed-form equations and accurate EM numerical simulations.

In some cases, as microstrip filters and antennas, the edge effect substantially affects the global solution. This effect is taken into account by subdivision of plates in the

vicinity of their edges into narrow strips, which is referred to as edging. Edging can be done manually, or automatically. Edging control is suitable for better teaching on parasitics and fringing effects.

This software is provided with multiple component characterization so the student can specify a component as ideal or analytical or 3D electromagnetic. This kind of characterization enables students to make only one circuit schematic with different realization aspects. Overlaying the results of all characterizations, students can observe differences between ideal, analytical, and EM models.

4. A SIMULATION EXAMPLE

A typical textbook example [9] is used to demonstrate simulation in the two software tools. Consider a lowpass filter with the following specification: cutoff frequency

GHz1c =f , passband ripple dB1.0 , and source/load impedance Ω= 500Z .

MLINID=TL2W=Wl mmL=13.32 mm

MLINID=TL3W=Wl mmL=15.09 mm

MSUBEr=10.8H=1.27 mmT=0.036 mmRho=3Tand=0ErNom=10.8Name=SUB1

1 2

3

MTEE$ID=TL4

MLEFID=TL1W=Wc mmL=5.86 mm

1 2

3

MTEE$ID=TL5

1 2

3

MTEE$ID=TL6

MLINID=TL7W=Wl mmL=13.32 mm

1 2

3

MTEE$ID=TL9

MLEFID=TL10W=Wc mmL=9.54 mm

MLEFID=TL11W=Wc mmL=9.54 mm

MLEFID=TL12W=Wc mmL=5.86 mm

MLINID=TL8W=1.126 mmL=13.88 mm

MLINID=TL13W=1.126 mmL=13.88 mm

PORTP=1Z=50 Ohm

PORTP=2Z=50 Ohm

Wc=5

Wl=0.1

Fig. 6. Schematic of the lowpass filter in MWO

1 21 2

Fig. 7. 2.5D model of the schematic from Fig.6

The filter is realized as a seven-pole microstrip lowpass filter with the Chebyshev response. It is fabricated on a substrate with a relative dielectric constant 8.10r =ε and a thickness mm27.1=h without losses. Open-circuited stubs implementation is chosen with high-impedance lines as

Ω=1100LZ and a line width mm1.0=LW . Open-circited stub has a line width mm5=CW on the used substrate. The relevant design parameters of microstrip lines, are

mm86.571 == ll , mm32.1362 == ll , mm54.953 == ll , mm09.154 =l .

Fig. 8. Schematic of the lowpass filter in WIPL-D Microwave

An important teaching issue is to demonstrate differences between various simulation models: analytical, 2.5D EM (MWO), and 3D EM (WIPL-D Microwave).

Figures 6 and 8 present the schematic of the filter in MWO and WIPL-D Microwave, respectively. The corresponding EM models are shown in Figs. 7,9. The simulation results are shown in Fig. 10. FSV Tool software is

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used to quantify differences between the response curves, Fig. 11 [10].

Fig.9. 3D model of the schematic from Fig.8

0.1 0.6 1.1 1.6 2.1 2.6 3Frequency (GHz)

S21dB

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20DB(|S(1,2)|)2_5D EM _ MWO

DB(|S(1,2)|)Analytical _ MWO

DB(|S(1,2)|)Analytical _ WIPL_D

DB(|S(1,2)|)Full 3D_WIPL_D

Fig. 10. Frequency response of the filters from Figs. 6,7,8,9

5. COMPARISON OF THE TWO TOOLS

Modern microwave engineering education has many specific issues. Generally, a lot of material should be presented in the teaching process, in one-semester courses. Consequently, appropriate software tools should be used to illustrate microwave circuit simulation as easier as possible.

In addition, students should be encouraged to practice computer simulations in their homeworks or projects. Often, students prefer to use their own computers and personalized copies of the target software.

WIPL-D Microwave is a candidate tool for implementing efficient microwave education. From the teaching view point, it has the following benefits:

1) Contains all components and microwave circuit models needed for undergraduate microwave courses

2) Ideal microwave elements are grouped into a separate toolbar, so the student easily builds idealized microwave circuits

3) Numerous teaching examples are available and are based on the widely used textbooks [7] adopted in many microwave courses

4) Comprehensive review of microwave circuit basics is provided, so students can quickly review the scattering matrix properties, element definitions, and other background lessons

5) Full wave 3D EM analysis is available so the student can compare the results generated by analytical closed-form equations and accurate EM numerical simulations

6) Multiple component characterization is provided so the student can specify a component as ideal or analytical or 3D electromagnetic

7) Technology-related components have integrated parameters and technology descriptors

8) Arbitrary metallic-dielectric structures can be characterized by, for example, scattering parameters and incorporated into the schematic when the components

parameters are out of the range over which the analytical model is valid

Fig. 11. Amplitude difference measure of the frequency response

Table 1. Comparison of the two environments

Feature MWO WIPL-D

Full 3D simulation No Yes

Predefined object Basic Basic & Complex

Uniform/Non-uniform grid (EM model) Uniform

Uniform & Non-uniform

Symbolic variables No Yes

Optimization No Yes

Symmetry planes No Yes

Automatic check Yes Yes

De-embedding Yes Yes

2.5D

or

3D

Edging Automatic Automatic & Manual

Nonlinear components Yes No

Transitions Only ideal Yes

Symbolic variable Yes Yes

Circuit optimization Yes Yes

Layout (implementation) view Yes No

Cir

cuits

& S

yste

ms

Functional blocks (systems) Yes No

S, Y, Z, G, H, ABCD

V, I, P Yes

Not all, such as: G,H, ABCD

Near/Far field radiation Far Near & Far

Mea

sure

s

Time domain reflectometry Yes No

Cos

t

Price Very high Low

9) WIPL-D optimizer can optimize all schematic parameters including the parameters of the embedded 3D EM models

10) Ports consist of transmission lines with adjustable length that can be set to an arbitrary value, so a schematic can be built with fewer elements

11) WIPL-D is affordable for students because of its low price.

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Here are potential disadvantages of this environment:

1) Time response can not be computed 2) Nonlinear circuits can not be simulated 3) Subcircuit (hierarchical decomposition) is not available 4) Graphical presentation of the simulation results by default

smoothes data (fitting tool) that might lead to unexpected curves (peaks); this might confuse students and cause them to misinterpret the results.

Fig. 12. Frequency response of the filter from Fig. 9 with/without

fitting (interpolation) process

MWO is a professional tool for advanced users. Its main features from the teaching view point are:

1) Provides nonlinear microwave circuits and systems 2) Physical layout representation is assigned to each

component in a schematic, but this option does not always give correct layout

3) Arbitrary 2.5 D EM multi-layer structures can be incorporated into the schematic

4) MWO can not optimize physical structure, but it has a powerful manual and automatic optimizer for circuit model parameters

5) Subcircuits can be used in the schematic realization 6) Computes the time-domain response.

Here are some potential disadvantages of MWO:

1) Numerous components and their grouping sometimes might be confusing for undergraduate students

2) Layered EM structures can be modeled but cannot be optimized

3) Abundant advanced examples may not be suitable for undergraduate teaching process

4) MWO is not so affordable for students because of its high price.

6. CONCLUSION

In the modern microwave engineering education software tools should be used to illustrate microwave circuit operation as easier as possible.

WIPL-D Microwave is a candidate tool for implementing efficient microwave teaching. The main benefits of WIPL-D Microwave are: numerous teaching examples, multiple component characterization, suitable grouping of components into palettes, full wave 3D EM analysis, low price, and simple definition of complex electromagnetic structures. Potential disadvantages of this environment are lack of time response computation, nonlinear circuit models, and lack of hierarchical decomposition.

MWO is a professional tool and it can be over-sophisticated for undergraduate teaching process. From the teaching view point, it has the following benefits: provides both linear and nonlinear microwave circuits, physical layout representation, manual and automatic optimizer for circuit model parameters, subcircuits, and time-domain response computation. Its potential disadvantages are: high price, lack of appropriate teaching examples, and lack of multiple component characterizations (ideal, analytical or 3D EM models).

ACKNOWLEDGEMENT

We thank Ministry of Science and Environmental Protection of the Republic of Serbia for partial support of our research on this topic (Project No. TR-6154).

REFERENCES

[1] K. C. Gupta, “Concept maps and modules for microwave education,” IEEE Microwave Magazine, vol. 1, no. 3, pp. 56–63, Sept. 2000.

[2] K. C. Gupta, R. Ramadoss, and H. Zhang, “RF and Microwave Network Characterization – A Tutorial,” University of Colorado at Boulder, USA, Concept-Modules LLC, Boulder, CO, USA. [Online] http://www.eng.auburn.edu/~ramadra/elec6340/S4-4/Article2/Module-2-with-Voice/Tutorial/index_tutorial.htm

[3] J. S. Kenney, “Challenges and opportunities in microwave education,” IEEE Microwave Magazine, vol. 5, no. 2, pp. 102–103, June 2004.

[4] M. S. Gupta, “Curricular implications of trends in RF and microwave industry,” IEEE Microwave Magazine, vol. 6, no. 4, pp. 58–70, Dec. 2005.

[5] Microwave Office 2004, Applied Wave Research, USA, 2004. www.appwave.com

[6] B. M. Kolundžija, J. S. Ognjanović, T. K. Sarkar, D. S. Šumić, M. M. Paramentić, B. B. Janjić, D. I. Olćan, D. V. Tošić, M. S. Tasić, WIPL-D Microwave – Software and User’s Manual, Artech House, USA, 2005.

[7] D. M. Pozar, Microwave Engineering, 3rd ed. John Wiley&Sons, 2005.

[8] A. R. Đorđević, D. V. Tošić, Microwave Engineering, Academic Mind, 2005. (in Serbian)

[9] Jia-Shen G. Hong, M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, John Wiley&Sons, 2001.

[10] Feature Selective Validation (FSV) Tool, UAq EMC Laboratory, Italy, 2005. [Online] http://ing.univaq.it/uaqemc/public_html

Sažetak – Porede se dva simulatora mikrotalasnih kola sa gledišta izvođenja nastave iz mikrotalasne tehnike. Navode se glavna svojstva ovih alata i njihova podesnost pri izvođenju nastave na osnovnim studijama. Razmatrani alati se odlikuju mogućnošću 3D EM simulacije što se analizira kao sredstvo za bolje razumevanje kola i njihovih ograničenja shodno programu predmeta iz mikrotalasne tehnike.

POREĐENJE SOFTVERSKIH ALATA WIPL-D MICROWAVE I MICROWAVE OFFICE

Milka Potrebić, Dejan V. Tošić

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