SIMULATION AND DESIGNING TOOLS FOR HIGH FREQUENCY BANDS

1Niraj Ada, 2A.A.Daiya, 3 V. M .Dabhi, 4Jagdish M. Rathod,B.V.M.Engg. College, B.V.M.Engg. College ICCT, B.V.M.Engg. College,V. V.Nagar-Gujarat V. V.nagar-Gujarat New V.V.Nagar V. V.nagar-Gujarat

Email: 1niraj_ada@yahoo.co.in , 4 jmr.bvm@gmail.com

Abstract

One of the most critical issues in high frequency electronics and communication university courses is the availability of inexpensive or free software that demonstrates major circuit analysis and design considerations necessary for laboratory, homework, and projects. The most recent technological developments in communication circuit design have created a necessity for introduction of newexperiments and associated software to demonstrate applications of very complex methods of high frequency circuit design that include scattering matrix parameters, stability tests, distributed and lumpedparameters, and circuit nonlinearities. This paper has been written to share our interesting experiences using both free and inexpensive, circuit level software, such as PSPICE, PUFF, APPCAD and RFToolbox in a course High Frequency Electronics

1. INTRODUCTION

Academic courses related to wireless, radio, and high frequency systems and circuits have become much more popular over the last few years than before. The major reason for such proliferation has been the booming interest in high-speed personal and office communication systems, which incorporate a large number of electronic technologies, especially microwaves, integrated circuits,electromagnetic compatibility, software Embedded systems, and quite a few others. One of the most difficult problems related to development of such courses is

accessibility to inexpensive or free software support. We have prepared a large number of software examples based on free demonstration versions of software, and also on other inexpensive software packages. The software introduced throughout the course includes PSPICE of Microsim (currently CADENCE), PUFF of CALTECH, APPCAD of Agilent Technologies, RF Toolbox of Black Cat Systems Thepackage of MATLAB (education version) supports additional calculations and data processing. The examples presented here constitute only a small fraction of all examples available and used throughout the course but they demonstrate the extent of software support and its flexibility. One of the examples described as per below and is also practically implemented in a larger measurement system. The intent of the paper is to show how the students can benefit from availability of highly economical software in processes of learning high frequency electronics.

2. DESCRIPTION

a. PSPICE Examples

The PSPICE is a classical circuit analysis program, which includes nonlinear models of electronic devices but it does not have a direct link to high frequency parameters such as S-matrix parameters. Figure 1 shows the circuits assembled to determine the S-parameters for the MRF501 bipolar transistor of Motorola. The upper circuit extracts S11 and S21, while the lower circuit extracts S22 and S12 [3]. The linear S-

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Parameters are determined from Gummel-Poon PSPICE nonlinear model at the DC operating point defined by the supply current (I = 5mA). The S parameters dependence upon frequency is shown in Figure 2. The S-parameters can be later used to design HF amplifiers or generators.

Figure 1: S-parameter extraction circuits.

Figure 2: Magnitude and phase versus frequency of s11, s22, s12, and s2.

b. PUFF ExamplesThe PUFF is a DOS based program that helps analyze the HF circuits whose topologies can be drawn the way they are finally implemented in practice. The circuit layout shown in Figure 5 is an HF

amplifier whose S-parameters are determined during simulation. The transistor, represented by component a, isconnected to several lumped and distributed components, which shape the frequency response [5]. The centerfrequency of operation is set to 6GHz where the amplifier delivers about 8dB of the gain and has very low reflection coefficients. The transistor S-parameters can be entered directly from the device specifications or from PSPICE extraction schemes. See in Figure (3)

Figure 3: HF amplifier analysis using PUFF

c. APPCAD Examples

The APPCAD is an excellent example of free software package that provides educators with a suite of HF analysis and design tools. Computerized Application Notes support many designs. The most typical modules allow calculating parameters of various configurations of transmission lines, simple amplifiers, and some nonlinear circuits, such as mixers and detectors [4]. The examples shown here include an amplifier designed to satisfy the power gain of 17dB (Figure 4)

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and two structures of the transmission lines (Figures 5).

Figure 4: Amplifier design for the nominal gain of 17dB and the bandwidth of about

2200MHz.

Figure 5: Design of the 50-ohm Microstriptransmission line.

The amplifier software calculates component values for the bias circuit when the gain and bandwidth are given. as shown in Figure 7. The preloaded data include parameters of an Agilent MGA-85563 low noise integrated circuit. The transmission line calculator computes the characteristic impedance of the line when line geometry and dielectric parameters are known or it calculates dimensions for a given value of the impedance.

d. RF Toolbox:

RF Toolbox is a program that allows you to quickly design antennas, as well as perform many useful RF, electronics, and electrical calculations. You select the type of antenna and the desired characteristics, and RF Toolbox gives you the suggested design for the described antenna. You can design several types of antennas. These types include. Dipole, Fat Dipole, Yagi,J-Pole,Super J-Pole, Log Periodic, CubicQuad, Vertical (over a ground plane),Helical [2].You can also perform the following additional calculations: LC calculations - by entering two of the following: L, C, frequency, the third is calculated. Coil design - by entering three of the following: L, diameter, length, number of turns, the fourth is calculated Transmission line loss - given the type of cable, length, and band, computes the loss in dB, also computes the additional loss caused by SWR.L Network - L matching network, Pi Network - Pi matching network, Impedance - Calculate the impedance of a capacitor or inductor at a given frequency, Wire inductance -Calculate the inductance of a straight piece of wire, Wire resistance - Calculate the resistance of a length of wire, as well asthe voltage drop Transmission Line Calculator - Handles many transmission line related calculations, including SWR and impedance transformations.db Calculator - Convert between dB and voltage/power ratios. Resistor Color Code Calculator - Determine the color code for resistor [1] .This software is useful for Transmission line of calculation and Yagi-Uda kind of basic antenna’s problems. Seein Figure (6) and Figure (7) in which we have tried to mentioned the Yagi-Uda antenna and its calculation and Transmission line problem with respectively Transmission

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Figure 6: Yagi Antenna Calculator

Figure 7: Transmission Line Calculator

This calculator allows you to compute several parameters for a transmission line installation. Select the cable type from the popup menu. The impedance and velocity factor are automatically set; you can change them if you wish. Then select the frequency, either directly in MHz, or by selecting the appropriate ham band. Enter the length of the cable run, and select the units of feet or meters. The attenuation and electrical length are computed. Enter the load resistance and reactance and check the Load radio button, or enter the values as seen at the input end

of the cable and select the Input radio button. The Input and Load resistance, reactance, impedance, and SWR are calculated, as well as the extra loss due to SWR. Enter the input power in watts, and the loss in watts is also calculated.

3. Conclusions

All demonstrated software can be an extremely effective pedagogical tool applied in teaching high frequency electronics. Collecting the software to support their courses, the authors of the paper prepared initially a broad selection of examples limited only to applications of PSPICE and PUFF [3]. Later in this process, the authors expanded their search thanks to the efforts of various companies, which decided to make many of their software packages available either on Internet, or as the demonstration samples. The use of instructor-devised sets of examples for high frequency electronics related courses greatly extends students’ interest, understanding and design capabilities in studying wireless technologies at an extremely low cost.

References

[1] Behzad Razavi, RF Microelectronics, Prentice Hall 1997.[2] S-Parameter Design, HP Application Note 154.[3] A.Rusek, B. Oakley, Pspice Applications in the Teaching of Wireless and High Frequency Electronics,Proceedings of the 2001 American Society for Engineering Education Annual Conference &Exposition.[4] AppCAD2.0, Agilent Technologies, www.agilent.com/view/rf [5] S. W. Wedge, R. Compton, D. Rutlege, PUFF, Computer Aided Design for Microwave Integrated Circuits, Version 2.0, CALTEC, 1991

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National Conference on Recent Trends in Engineering & Technology