This paper describes a software package for the design, analysis, and simulation of microwave radio systems. This article is mainly directed to engineering education. The software can also be used to aid in the Hybrid Microwave Integrated Circuit Design needs in industry. Different Design procedures for various types of microwave circuit are used. Special emphasis is given in the progressive use of simulation techniques to stimulate learner activity and overcome some difficulties inherent to the experimental subject and theoretical results. The developed tool has been used in the Microwave Circuits discipline for the graduation course in electric engineering of the University of Brasilia, Brazil

Abdalla Júnior, Humberto

Bermudez, Luciana

Carvalho, Paulo de

Evangelista, Carlos

Molinaro, Luis Fernando Ramos

Repositório Institucional da Universidade de Brasília

Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739926TOOLS FOR MICROWAVE RADIOCOMMUNICATIONS SYSTEM DESIGNH. Abdalla Jr, Paulo Carvalho, Luis. F. Molinaro, Carlos Evangelista, L BermudezDepartamento de Engenharia Elétrica – Universidade de Brasília – UnBP.O. Box 04386, Zip Postal: 70.919-970, Brasília – DF – BrasilPhone: (55 61) 273 5977, Fax: (55 61) 274 6651, abdalla@ene.unb.brAbstractThis paper describes a software package for the design, analysis, andsimulation of microwave radio systems. This article is mainly directed toengineering education. The software can also be used to aid in the HybridMicrowave Integrated Circuit Design needs in industry. Different Designprocedures for various types of microwave circuit are used. Special emphasis isgiven in the progressive use of simulation techniques to stimulate learner activityand overcome some difficulties inherent to the experimental subject andtheoretical results. The developed tool has been used in the Microwave Circuitsdiscipline for the graduation course in electric engineering of the University ofBrasilia, Brazil.1. INTRODUCTIONMicrowaves are generally described as waves with frequencies that range from approximately 500MHz to 300 GHz or more. Microwave radios propagate signals through Earth’s atmospherebetween transmitters and receivers often located on top of towers spaced about 90Km to 180 kmapart. Therefore, microwave radio systems have the obvious advantage of having the capacity tocarry thousands of individual information channels between two points without the need forphysical facilities such as coaxial cables or optical fibers. The main advantages of microwaveradio systems are:• Due to their operating frequencies, microwave radio systems can carry large quantities ofinformation;• High frequencies mean short wavelengths which require relatively small antennas;• Minimum delay times are introduced;• Minimal crosstalk exists between voice channels;Microwave radio systems capacities range from less than 12 voice-band channels to more than22,000 channels. Early microwave systems carried frequency-division-multiplexed voice-bandcircuits and used conventional, noncoherent frequency modulation techniques. Most recentdeveloped microwave systems carry pulse-code time-division-multiplexed voice-circuits and usemore modern digital modulation techniques, such as phase shift keying (PSK) or quadratureamplitude modulation (QAM).Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-7399272. MICROWAVE RADIO SYSTEMIn essence, electronic communication is the transmission, reception, and processing ofinformation with the use of electronic circuits. Information is defined as knowledge orintelligence communicated or received. Fig. 1 shows a simplified block diagram of an electroniccommunication system, which comprises three primary sections: a source, a destination, and atransmission medium.Fig.1. Simplified block diagram for an electronic communication system.In our case the transmission medium is radio frequency, specifically the microwave. Theblock diagram of a microwave radio system is show in Fig.2.Fig2. Simplified block diagram of a microwave radio system: transmitter and receiver.In following are the software, which allows each device project and the microwave linkanalysis – Fig.3.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739928Fig3. Software package for the design, analysis, and simulation of microwave radio system.3. MICROWAVE LINK SIMULATORThe Microwave Link Simulator is a software developed in Visual Delphi Environment formicrowave point-to-point links. This software has two main parts: one dedicated to tower calculuswhere the tranceptors systems should be installed and the other dedicated to system analyses ofpower balance throughout the links.From position data of the tranceptors systems and the obstacle, main frequency of systemoperation, system dimensions, and atmosphere parameters the software calculates to the usertower heights for a Fresnel first zone visibility system, Fig. 4.The software allows equally observation of the various Fresnel zones obstruction, illustratedin Fig. 4. The user can move the obstacle along the line between the origin and destination points.This allows the observation of the non-obstruction Fresnel zones on the entire link. To refresh thevalues or make new tests, the user can alternate between the windows Model and Diagram.In Fig. 5 it is shown the developed environment for system analysis of power balance. In thisenvironment, the user can arrange the desired system from basic elements like: origin anddestination tranceptors (  and ), active and passive repeaters (  and ) andobstacles ( ). When this happens, it is only needed to point the mouse and click on the iconwhich represents the desired system element and drag to the project area.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739929Fig. 4. Tower heights calculus.When the mouse button is released a dialog box opens to enter the data referred to theelement, such as: antenna gain, output power, transmission rate, distance and heights, diversity(spatial and frequencial), etc. The user can insert the amount and variety of elements to build thepoint-to-point system.Fig. 5. (a) Link calculus and (b) power balance.As soon as the system is assembled the user may simulate a link and get the power balance.Power gain and lost values are indicated in each point of the system. The final result is shown intable and graphic, as shown in Fig. 5.b. From these values the user may modify the systemparameters and proceed a new analysis till the desired behavior is obtained.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-7399304. THE MICROWAVE DIODE FREQUENCY MULTIPLIERSThe CAD of Microwave Diode Frequency Multipliers, called MultFreq, has the followingfeatures.• Calculus of project parameters such as efficiency output power, bias voltage, and inputand output diode’s impedance.• Design of the necessary filters for the isolation of the multiplier ports: low-pass and band-pass filters of Chebyshev and Butterworth kinds in distributed and lumped parameters.• Impedance matching networks using series and parallel stubs.• Design of λ/4 transformers of Chebyshev and Butterworth providing dimensions andimpedance characteristics of each section.• Multiplier layout in distributed parameters, including all calculated dimensions.• Simulation in frequency of each project block: insertion and return losses.• Poles and zeros analysis of filters.As an example, a step–by-step design procedure of a varactor frequency multiplier usingMultFreq is outlined below.1) Give the diode’s specifications and the drive level, as illustrated in Fig.6.2) Based on Burkhardt method and from initial specifications, all project parameters arecalculated. These parameters are: efficiency (r), input power (Pin), output power (Pout), biasvoltage (Vdc), input (Rin+jXin) and output (Rout+jXout) diode’s impedance at input andoutput frequencies. The Burkhardt’s results and the block scheme of the multiplier areshown in another screen, Fig.7. From this block scheme it is possible to access theMultFreq’s functionalities that allow the multiplier implementation in distributedparameters.3) Finally, with all blocks already calculated, it is possible to view the multiplier layout andto verify the dimensions of all circuit sections, Fig.8.Fig. 6. Screen of varactor’s input parameters.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739931Fig. 7. Burkhardt’s results and exit to subsequent project sections.Fig. 8. Reactive multiplier layout.5. THE MICROWAVE FILTERThe CAD for Filter design is composed of two independent modules that execute the followsfunctions:• Construction module of the transfer function filter with frequency response of Chebychevor Butterworth. This module also contains a dedicated graphic interface that permits thevisualization of the frequency response before of the filter synthesis.• Synthesis module of the filter in lumped parameters and distributed parameters. Thismodule provides the layout filter, including all calculated dimensions, taking into accountthe chosen fabrication technology.A step–by-step design procedure using the software developed is outlined below:1) Select the kind of frequency response and the structure of the desired transmission.Complete the filter specifications and the basic parameters of the transmission structurebased at Fig. 9.2) With the specifications, it is possible to access the analysis and syntheses modules of thecomputer program.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739932These modules allow the construction of the circuit using all necessary data. The Fig. 10shows a typical output of the frequency response module, in which it is possible to see theinsertion loss and the return loss. In the synthesis module, it is possible to obtain the project inlumped and distributed parameters distinctly. The screen with the layout of the tappedminiaturized hairpin line resonator filter is shown in Fig. 11.Fig. 9. Main screen of the softwareFig.10. Frequency responses of the filterFig.11. Miniatured Hairpin line resonator Filter designJournal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-7399336. THE CAD FOR MULTIPLEXERThe software of complementary Diplexer and Triplexer design is composed of the analysis andsynthesis modules. The analysis module contains a dedicated graphic interface that permits thevisualization of the frequency response and input admittances of each filter. Fig. 12 shows atypical output of the frequency response module, in which it is possible to see the admittancescurves, attenuation and the return losses for each filter.Fig.12. Frequency responses and admittance filters.The synthesis module provides the layout of the filter, including all calculated dimensions,taking into account the chosen fabrication technology In the synthesis module, it is possible toobtain the project in lumped and distributed parameters. In the program, the distributedparameters design initiates calculating the isolated filters, and in sequence it calculates theinterconnection network. The screen with the layout of the stripline triplexer is shown in Fig. 13.Fig.13. Stipline Triplexer designJournal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-7399347. THE CAD FOR OSCILLATORIn this section we present the developed software operation structure to be used in the computer-supported project to microwave oscillators called Oscillator Designer.In Fig. 14 are the elements from which the program is made of. Each of these blocksrepresents a step, which can be analyzed individually or together.Fig. 14. Basic scheme for an oscillator.Two types of transistor may be worked on by the oscillator designer: bipolar and FET. Theyare characterized by their spread parameters, [S], which are available in their manuals or in *s2pfiles, supplied by the manufacturers.The software allows the user to choose an existing file or access a transistor editor. It is alsopossible to simulate every S parameter and line input and output impedance of the device.The use of transistors implies in an adequate study of the polarization because [S] parameterssupplied by the manufacturers are valid only to a single polarization. So the Oscillator Designerallows a DC and a RF analysis, i.e., the user may choose structures that guarantee the operationpoint of the transistor and also structures that protect the RF signal DC source.Chosen the active element and the adequate topology of polarization, the next step is thefeedback structure. An example of this structure proposed by the Oscillator Designer is shown inFig. 15.Fig.15. Feedback Network Screen.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739935Then maximum power should be supplied to the output of the device. This target is reached inthe Oscillator Designer through the impedance match using open or shortcut stubs.A structure that supplies the desired frequency is chosen after completed all the steps above:active element, polarization circuit, feedback circuit and match circuit. The resonator is thepassive element responsible for determining the oscillation frequency. Among the existingtopologies, a microstrip that supplies a unitary reflection coefficient and opposite phase to thereflection coefficient in the active device gate was chosen. The Oscillator Designer allows theuser to choose the optimum values for the length and width of the resonator.The Smith Chart is one of the most used graphic tools that support spread parameters in circuitproject. That is why this chart was incorporated in the Oscillator Designer. In every stepdescribed previously circuits can be simulated and circuit stability may be analyzed by [S]parameters, through what is called stability circles, as shown in Fig. 16. The completeconfiguration of the oscillator is shown in Fig. 17.Fig. 16 – Stability circles analysis.Fig. 17. Designed microwave oscillator topology.8. THE CAD FOR AMPLIFIERMr. Smith! is a software to design microwave amplifiers. Its friendly interfaces allow from datainput, building a library of transistors and amplifiers, to the access of its several functions.The following steps are the ones to project a single stage microwave amplifier:Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-7399361. First the transistor to be used in the project is chosen.2. Then an input/output adaptation network is defined for a previously determined powergain and frequency or operational frequency range.3. Chosen the impedances to be synthesized to promote a certain gain, it is time to defineinput/output adaptation networks.4. Finally, a polarization network can be defined.Besides supplying a library with unnumbered transistors the software allows the inclusion of otherdata-sheets. The transistor is chosen in the standard ‘open’ window of the Microsoft Windows,Fig. 18.Fig. 18 – Input data.A system benchmark analysis can be made using the Mr. Smith! simulation tools. Thesoftware presents a power gain analysis as a function of frequency: the user enters the regionswhere the transistor is unconditionally stable and also where the transistor can present powerinstabilities. Having this analysis as a basis the user may study a unique or multiple frequencies.Fig. 19 illustrates the analysis for the multiple frequencies case. In this case besides allowing astudy to several frequencies in an amplifier operational band and to every match, Mr. Smith!displays to the designer the impedance, norm and phase profile that will be synthesized to theproject of an amplifier with constant gain in a specific frequency band.Fig. 19 – Multiple frequencies analysis.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739937After the impedance profile has been defined, which will allow the choice of an amplifier to aspecific frequency; it is time to adjust the matching structures. Figure 20 illustrates a tool to alocalized matching structures project.Fig. 20 – Adaptation network in localized technology.Figure 21 shows an adaptation structures project in distributed technology: stripline andmicrostrip. Again every adaptation procedure is presented in Smith abacus.Fig. 21 – Adaptation networks in distributed technology.Mr. Smith! presents to the user an auxiliary tool to the transistor polarization networkproject as shown in figure 22.Journal of Microwaves and Optoelectronics, Vol. 3, N.o 1, April  2003.Copyright SBMO                                                                                                                                   ISSN 1516-739938Fig. 22 – Polarization network.9. CONCLUSIONThe final product of this work is characterized as a software package for the design, analysis, andsimulation, consecrated to the teaching and application of Microwave Circuits. The developedtool has been used in the discipline of Microwave Circuits of the degree course in electricengineering of the University of Brasilia. The positive reactions to this experiment areencouraging us for continuing the development of this type of approach.It is thus possible to build up a complete, coherent, and stimulating tool that relieves the userof the computation development and lets them concentrate on the application they are interestedin. This attractive tool makes learning more efficient when used in conjunction with a textbook.REFERENCES[1] Wayne Tomasi, “Advanced Electronic Communications Systems”, fifth edition, 2001,Prentice Hall[2] H. Abdalla Jr et al, “Ambiente Multimídia Como Suporte para o Processo EducacionalInterativo”, I Congreso International “Retos de la Alfabetization Tecnológica en un Mundo enRed”, november 2000, Extremadura, Espanha.[3] Inder Bahl, Prakash Bhartia, “Microwave Solid State Circuit Design, 1988, Wiley-Interscience[4] M.F. Iskander, “Development of Multimedia Modules for Education”, Comput. Appl. Eng.Educ., vol. 3, No 2, 1995, pp.97-110.[5] B.P. Lathi, “Modern Digital and Analog Communication Systems, third edition, 1998, OxfordUniversity Press, Inc.[6] Marek T. Faber, Jerzy Chramiec, Miroslaw E. Adamski. Microwave and Millimeter-WaveDiode Frequency Multipliers”. ”. Artech House, Inc. USA, 1995.[7] Gabor C. Temes, Sanjit K. Mitra, “Modern Filter Theory and Design”, John Wiley & Sons,Inc, 1973, pp. 48-53.[8] Bermúdez, Luís Afonso. Osciladores de Microondas. Universidade de Brasília. Departamentode Engenharia Elétrica. Julho, 1990.[9] Sweet, Allen. MIC & MIC Amplifier and Oscillator Circuit Design. Artech House, 1990.

Tools for microwave radio communications system design

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Tools for microwave radio communications system design

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