A Low-Cost Hands-On Laboratory for anUndergraduate Microwave Course

S. V. Hum and M. Okoniewski

Department of Electrical and Computer EngineeringUniversity of Calgary, Alberta, Canada

E-mail: svhum@ieee.org

Abstract

A low-operating-cost microwave laboratory for undergraduate students is presented, which emphasizes fundamentalconcepts while enabling students to gain practical experience with the design and measurement of microwave circuits. Bytraining the students in the proper use of modern microwave test equipment, students are able to test hand-built circuits,made of adhesive copper tape, using modern vector network analyzers. Additional experiments with waveguides, and severalsystems applications, such as radar experiments, provide students with an exciting laboratory experience.

Keywords: Microwave circuits; microwave measurements; electrical engineering education; microstrip circuits; radar

1. Introduction

Introductory RF/microwave engineering courses are taught in thevast majority of university-level electrical engineering programs

worldwide. Such courses usually follow one or two semesters ofelectromagnetics or electrodynamics, and may be taught over oneor two semesters themselves. Students often find basic microwavecourses challenging, as the syllabus focuses on material that is fun-damentally different and, for most, unintuitive. The last decade has

seen the introduction of advanced computer tools that were devel-oped to alleviate some of those difficulties (e.g. [1], or for moreadvanced courses, [2]). There even was a trend to replace labora-tory experiments with virtual experiments that take advantage ofthe phenomenal development of computers and electromagneticmodeling software [3]. Computer experiments are appealing, asthey can provide insight into the physics of the phenomena thatwould be difficult to achieve with a lab-bench approach, and,moreover, dramatically lower the cost of running hardware labs.However, we believe that while virtual experiments have theirplace in teaching, they cannot replace the hands-on experience ofbuilding circuits and performing advanced measurements.

At the University of Calgary, we have found that electromag-netic software can indeed play an invaluable role as a tool used forillustrating concepts during lectures. Virtual, lecture-time Mefisto'

[3] experiments provide unprecedented insight into concepts suchas partial standing waves, modes, matching or directional couplers,to name a few, with which students traditionally struggle. How-ever, using microwave simulation software during labs usuallyleads to student fascination in the virtual at the expense of thepractical. When faced with the design of an introductory but hands-on microwave laboratory experiment, instructors are tomn betweenthe teaching of fundamental concepts, such as standing-wave phe-nomena, and modem, practical topics, such as couplers or splittersin microstrip technology. The former are best taught using tradi-

IEEE Antennas and Propagation Magazine. Vol. 49. No. 3, June 2007

tional slotted-line and waveguide-based hardware; the latter, with avector network analyzer (VNA) and etched, RF-quality printed cir-cuit boards (PCl~s). A further dilemma is created by the fact that avery effective, inexpensive, and instructive lab can be built usingold, waveguide/slotted-line-based technology. However, the draw-back of such an approach is that students find it unappealing andremoved from industrial reality. Furthermore, it fails to provide

students with the training in modem microwave-measurementtechnology that many employers would expect the students to beable to use right after starting their new jobs. On the other hand,many vector network analyzer/microstrip labs can automateexperiments to a degree that the practical and hands-on experienceis lost, and, instead, students spend time scripting GPITB or Lab-View" control algorithms. Recognizing this issue, educatorsreported attempts to find the right balance (see, e.g., [4]).

The introductory microwave laboratory at the University ofCalgary Schulich School of Engineering, ENEL575, has beendesigned with the fundamental goal of providing students withhands-on experience that should lead to the development of somedegree of intuition about modem RF hardware testing and design.We kept the following goals in mind:

-Illustrate and expand concepts taught in class withexperiments

" Provide hands-on experience with modem testing andmeasurement instruments

" Provide design experience

" Provide sustainable, low-cost experiments withmodem circuits

" Rely on modem equipment, but use traditionalequipment when best-suited for illustrating concepts

175

We decided to base the laboratory on microstrip circuits andvector network analyzers, but however to use slotted-line andwaveguides in the introductory experiments that are best performedusing that technology. The workhorse of the lab is high-qualitycopper tape and reusable "connectorized" RF-quality circuitboards. There were some attempts to use copper tape in selectedexperiments in the laboratory in the past [5, 6], but never to thesame extent. We use a combination of pre-cut tape, correspondingto selected impedances, and sheets that students can cut to requiredshapes. The tape allows for quick construction and modification ofa wide variety of circuits. Student feedback is excellent, with mostsaying that the RF lab experience provides very high educationalvalue.

The paper is organized as follows. In Section 2, we present anoverview of the laboratory requirements and the laboratory itself.The experiments are outlined in Section 3. Section 4 presents theindividual experiments in detail. Section 5 provides and discussesan example of results generated by students. Prior to concluding,we discuss the costs associated with running the lab in Section 6.

2. The Undergraduate Microwave LabProgram at the University of Calgary

The general characteristics of the laboratory program inENEL575 are as follows:

" Students are provided with a lab manual outlining allof the experiments for the semester.

" The lab consists of a three-hour period every otherweek.

" The lab meets the Canadian Engineering AccreditationBoard (CEAB) requirements for a designcomponent in the course.

" Students are required to submit lab reports within oneweek of completing the lab, noting theirobservations.

" All laboratories generally consist of a pre-lab exercise(sometimes consisting of electromagneticsimulations) and/or an assignment related to thelab.

" Lab supervision is conducted by the instructor and twoteaching assistants.

Laboratory experiments are completed in a new undergradu-ate microwave laboratory, recently constructed at the University ofCalgary as a part of the ongoing expansion of the Electrical andComputing Engineering Department. As part of the expansion,large donations were acquired from a number of local telecommu-nications companies. A large donation from Telus hinc. in particularenabled the microwave lab to be fitted with the latest in microwavetesting equipment. Most of the equipment was sourced fromAgilent, who provided a sizable educational discount for theexpansion, as well as a donation of useful items, such as calibrationkits and adaptors. A subset list of the major pieces of test equip-ment in the undergraduate microwave lab is provided in Table 1.

For the microwave course, the lab is configured into four sta-tions, each equipped with a vector network analyzer, power supply,RF power meter, oscilloscope, RF signal source, and multi-meter.In principle, eight laboratory groups can be working in the lab andaccessing the four measurement stations. In addition to the equip-mernt already described, each station also includes a soldering sta-tion for constructing circuits, and an assortment of tools to aid thestudents in circuit construction.

The vector network analyzer is at the core of most of theexperiments performed by the students. One of the major goals ofthe laboratory is to familiarize students with the proper usage ofthis important piece of microwave testing equipment. In manymicrowave education programs, measurements on the vector net-work analyzer are often conducted by an instructor or qualifiedteaching assistant, due to the limited number of vector networkanalyzers available in most laboratories, their high cost, their ratherinvolved calibration procedure, and the high replacement cost ofcalibration standards for this instrument, which tend to be quitefragile. With four vector network analyzers available in the under-graduate microwave lab, there is the potential to produce a fullyhands-on experience in the laboratory. We believe that developingthe skill in using such an instrument is invaluable for trainingundergraduates for industry, and provides them with a much morehands-on experience in the laboratory. Toward this end, the net-work analyzers in the lab were "hardened" to some extent byattaching adaptors to protect the ports, and by replacing the expen-sive testing cables with inexpensive SMA cables, which suffice forthe frequency range utilized in the laboratory. Additionally, a low-cost calibration kit was developed that replaces the expensive3.5 mm calibration kit that is normally used to calibrate the instru-ment. The short-open-load-through (SOLT) standards werereplaced with low-cost SMA parts sourced from various vendors.The parameters of these standards were subsequently characterizedand stored as a separate calibration kit on each vector networkanalyzer. In this way, experiments can be carried out on vector

Table 1. A list of test equipment in the undergraduate laboratory.

Equipment Description _ Number Experiment

Agilent 8719ES 50 MLHz - 13 GHz vector network analyzer 4 1-5Agilent E4433B 100 MHz -4 GHz synthesized source 8 5Agilent 53149A RF power meter!/ frequency counter 8 1,5Agilent E4419B dual channel RF power meter 1 5Agilent 83640B synthesized sweeper 1 5Agilent 8560EC spectrum analyzer 1 3,5Agilent 54615B 100 MHz digital sampling oscilloscope 4 5Agilent E363 1lA power supply 16 1,5Agilent 85052D 3.5mm calibration kit 4 1-5Agilent 3440 1A multi-meter 8 2-5

176 IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007176

network analyzers by students with a minimum risk to the health of

the instrument.

The test equipment is connected to computers, primarily for

data-capture purposes, facilitating report generation. It is worth

noting that for experiments where the circuit must be optimized,

this capability allows for easy comparison between design itera-

tions.

3. Overview of Experiments

The laboratory for ENEL575 is organized into a series of five

experiments. The first experiment consists of measuring various

transmission lines, and is primarily analytical. It is designed to

assist students in familiarizing themselves with the equipment in

the lab and making basic measurements. Transmission-line

experiments are used to reinforce basic concepts that have already

been introduced in the lectures, such as group and phase velocities.

The second, third, and fourth experiments are design labs, whereby

the students are given a design specification and asked to synthe-

size several microwave circuits. The transmission-line technology

chosen for these experiments was microstrip, because of its prolific

use in industry and its ease of construction in the lab environment.

A number of laboratory programs employing microstrip cir-

cuits have been proposed in the literature [7-91. Unfortunately, fab-

ricating the circuits can take a significant amount of time. Tradi-

tional lithography techniques are very time consuming, although

some novel approaches have reduced this time considerably [10].

However, even if rapid-prototyping techniques, based on circuit-

board milling machines, are used, as proposed in [ 11, 121, there is

still some delay in preparing the boards for students. Additionally,

the final board is inflexible in that it cannot be easily modified to

explore the behavior of the circuit. Ideally, it would be preferable

to implement a technique that provides students with design feed-

back as quickly as possible.

To address these issues, a number of authors have proposed

microstrip laboratories based on building the circuits from adhe-

sive copper tape [5, 6, 13]. The laboratory experiments in

ENEL575 were based on this approach. Students are provided with

a microwave laminate that already has SMA connectors and 50 C1

microstrip "pigtails" printed on the board, which can be easily con-

nected to the tape-based circuit by soldering the pigtails directly to

the copper tape. The layout of the prototyping board is shown in

Figure 1Ia. The network analyzer on which students verify their

designs is easily connected to the circuits under test via the SMA

connectors on the board.

A GIL, GML1000 laminate (1.5 mm height, v, =3.05) was

previously used for the test boards. The board material is no longer

available, and the labs now use a Taconic substrate of similar prop-

erties. Various pigtails were printed on all sides of the board,

allowing it to be reused in subsequent years by simply de-soldermng

the SMA connectors, and placing them on the pigtails on the fresh

edges of the board, as necessary. The board is mounted on a large

piece of wood to provide it with structural strength. The original

boards have been in successful use for five years thus far.

The fifth and last experiment in the laboratory program is a

system laboratory, where students have the opportunity to experi-

ment with several microwave systems built from components in

the lab, and even some of the components they have built in previ-

IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007

111111

Figure 1 a. The prototyping board.

ous experiments. The systems include a scalar network analyzerand several radar systems.

The details of each of the laboratory experiments are now

expanded upon in the following sections.

4. Laboratory Experiments

4.1 Lab "0"

Prior to their first session in the laboratory, the students are

given a short seminar during the lecture and in the lab on the

microwave laboratory itself. Most students have not encountered

microwave testing equipment in their earlier courses, and it is help-

ful to introduce them to these instruments, due to their more fragile

and expensive nature. Students are introduced to each of the pieces

of equipment shown in Table 1. Particular attention is given to the

different types of connectors on the equipment, and to the other

components they will encounter in the lab. Proper connector care is

emphasized, since it is often the connectors that get abused the

most in the laboratory. Students are also introduced to other dan-

gers in the lab, such as electrostatic discharge (ESD) and RE power

levels associated with the equipment.

During Lab 0, the students are also introduced to the calibra-

tion procedure for the vector network analyzer. A great deal of

attention is given to this procedure, because of the degree of care

that must be exercised when executing it. A proper calibration pro-

cedure is vital to producing accurate, repeatable measurements, as

well as to developing habits for caring for the instrument and the

delicate calibration standards normally used with it.

In the final part of Lab 0, a technician provides a tutorial for

students in the proper assembly and soldering of microwave cir-

cuits. The construction of microwave circuits is usually unlike any

other circuit-building techniques they have attempted in other

courses, especially with odd materials such as copper tape and

177

M M==._

Wo

scalpels. Tips for constructing the circuits are provided to mini-mize parasitics in the resulting circuits.

4.2 Lab I

The first laboratory focuses on the study of transmission linesand reflections. It consists of two distinct experiments, designed toprovide students with physical insight into the operation of trans-mission lines, using the knowledge they have gained in the lecturesin this area. This introductory laboratory is also designed to famil-iarize the students with several instruments and components in thelaboratory, which will be important to future experiments.

The first experiment is a classical slotted-line experiment,using WR-90 waveguide components. This experiment has beenretained despite the fact that a modem network analyzer providesthe same information, because students can observe an actualphysical standing wave using this setup. Through connecting dif-ferent loads to the slotted line, students can work out the imped-ance of the load using classic techniques taught in class. Throughusing this apparatus, students also gain a better appreciation ofmodem network analyzers, which perform the same measurementinstantly. This experiment has also been retained because it illus-trates useful principles with rectangular waveguide, a transmissionline students study in the course. Indeed, one of the most interest-ing things students witness in the experiment is the existence of asuperlurninal phase velocity in the wavegnide, which is a phe-nomenon that is easily demonstrated with a slotted-line setup.

Students are also introduced to some of the test gear in thisexperiment. The detector is replaced with a more modem RFpower meter, providing students with hands-on experience with thecalibration procedure and usage of this commonly used instrument.The source used in the experiment is a Gunn-diode source, a devicethat students will leamn more about in the latter half of the course,and a component that they will use again in Lab 5.

The second experiment introduces students to the vector net-work analyzer. Students gain experience calibrating the instrumentusing the modified calibration kit discussed earlier, and performphysical measurements on two transmission lines: a length ofcoaxial cable, and a section of WR-90 waveguide. For the coaxialcable, students are asked to measure the amplitude and phase ofS2 1 . Usually, students expect higher losses at higher frequencies,which is something easily confirmed on the instrument. Measure-ment of the phase response is a good exercise for students becauseit familiarizes them with the phase "wrapping" that occurs on vec-tor network analyzer displays, so that they know how to interpret itproperly. From their phase measurements, students are asked tomanually determine the phase velocity and delay through the cable.They then can compare it with the delay calculated by the vectornetwork analyzer, which is essentially worked out intemnally usinga similar procedure, providing students with an appreciation of thesome of the functionality provided by the vector network analyzer.

Another important experiment performed with the coaxialline is terminating it in open and short circuits. Through using theelectrical delay option on the vector network analyzer, studentslearn how to move the electrical reference plane on the vector net-work analyzer. This is a procedure that is very important in futurelabs when students design circuits and must know the scatteringparameters of a circuit at an exact position in their circuit.

178

The coaxial line also provides students with a transverse elec-tromagnetic (TEM) line for comparison with a non-TEM line, suchas a wavegnide. Following the measurement of the coaxial line,students are asked to measure a section of wavegnide (TE mode)and compare it to results generated with the TEM line. Thisexperiment illustrates to students the existence of a cutoff fre-quency inside the waveguide, as well as dispersion, which is easilymeasured using the delay feature on the vector network analyzer.The existence of the nonlinear phase response is confirmed, aswell. The experiments also allow students to experimentally verifythe differences between group and phase velocities: a concept withwhich many students struggle. This is accomplished utilizingphase- and group-delay measurements on the vector network ana-lyzer.

4.3 Lab 2

The second laboratory is the students' first introduction tomicrostrip circuits. Students are asked to design two differentmicrostrip matching circuits: a quarter-wave transformer, and asingle-stub tuner, which are illustrated in Figures lb and Ic. Stu-dents have already been exposed to these circuits in the lecture, andhave completed assignments on these circuits prior to the lab, sothat they are familiar with their design. Mefistotm [3] is used to cal-culate the parameters of the microstrip line for the laboratory.

Students have access to a number of copper strips that havebeen milled to various widths by an LPKF circuit-board plotter,and, more recently, a lathe. This way, students do not need to con-cern themselves with the difficult procedure of accurately cuttingmicrostrip widths, and can instead focus on cutting them to th~eappropriate length for the circuit being built.

For both matching circuits, students are asked to match to aknown resistive load that has been integrated into the test boardstudents use in the experiments. For the single-stub matching cir-cuit, students choose an arbitrary point along the transmission lineto match to, as shown in Fignre lb. They use an open-circuitedmicrostrip line parallel to the feed line to act as an open-circuit ref-erence for moving the measurement plane, so that they know theinput impedance of the load at a precise location. They can thenproceed to design the single-stub matching circuit at the location,confirming movement of the reflection coefficient on the Smithchart display of the vector network analyzer as they proceedthrough the design process. Usually, through the process studentsdiscover multiple solutions to the stub problem, and the keen oneswill recognize that minimizing the distance between the stub andthe load will yield a match with the most bandwidth.

Simple design specifications are provided for the students.They are given a design frequency, and it is also required that thereturn loss be 20 dB or better at the design frequency. This labtends to be a lot of fun for students because they compete with eachother to produce the best design in terms of retumn loss, center fre-quency, and bandwidth. Generally, students who take a lot of carein assembling the circuit obtain the highest amount of retumn loss.They also learn just how tedious the matching process can be (par-ticularly with the stub), and gain an appreciate for manual tuning,which is still performed in industry, today. They also start devel-oping an intuition with microstrip circuits, such as learning howobjects (notably, fingers) placed close to a microstrip line canchange the circuit's response significantly.

IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007

transformer designed by students

R1EFERNCPLANE

0ZHFigure 1c. A single-stub tunerdesign labs.

designed by students in the

4.4 Lab 3

In Lab 3, students are exposed to some additional microstripcircuits. The first of these is a microstrip resonator. By this point inthe semester, students have covered resonators in class, and stu-dents are capable of simulating them in Mefisto"- using equivalentparallel-plate waveguide circuits. For this circuit, students areasked to build a microstrip resonator coupled on two sides by gapcouplers, as shown in Figure id. By varying the gap width on thecouplers, students can illustrate all three coupling cases for a reso-nator (under-coupling, over-coupling, and critical coupling). Addi-tionally, students can experiment with varying the coupling by

IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007

HUH

IL H W

Figure Id. A gap-coupled resonator designed by students in thedesign labs.

H HH H

H9 1 f HFigure le. A patch antenna designed by students in the designlabs.

179

placing dielectrics and metallic objects near the gap coupler tochange its capacitance. It is usually a very insightful lab, and dem-onstrates to students how they can make a very simple microwavefilter.

As an alternative to the microstrip resonator, the students alsobuild a microstrip-patch antenna from sheets of copper tape. Stu-dents often express an interest in antennas, which are not coveredin great detail in this particular course, so this experiment providesthem with some experience with this commonly used antenna. Astandard inset feed is used to allow the students to easily changethe feed point on the antenna and to achieve an impedance match,as shown in Figure le. Matching of the patch antenna is performed

Figure lb. A quarter-wavein the design labs.

REHERENH

PLAHNE

==:30

by manual trimming the inset feed to the 50 f0 point of the antenna, _as shown in Figure 1le. Again, groups are often fascinated by this 11experiment, and compete with each other to get the best match andthe correct resonant frequency. At the end of the lab, we pair theantennas up to demonstrate transmission, using vector networkanalyzers and data-transmission equipment.

In the second experiment, students build a microstrip L-bend,as shown in Figure If. Though this is a seemingly simple circuit to --- -build, circuits such as this one often leave a lasting impression onstudents, because it does not behave as expected at high frequen-cies when the corner is left un-mitered. By manually optimizing(trimming) the miter, students are able to improve the performanceof the bend. This experiment introduces them to equivalent-circuitmodels used for microstrip discontinuities, which they may see inmore advanced courses on electromagnetics.

4.5 Lab 4 _______________

The focus of the fourth laboratory is designing microstripcouplers. Two couplers are studied in detail: the 900 hybrid cou- Figure 1g. A 900 hybrid coupler designed by students in thepler, and the directional coupler, both shown in Figures I g and Ilh. design labs.The former is easily designed by hand and analyzed by transmis-sion-line methods, and therefore can be designed as an exerciseprior to the laboratory. The hybrid tends to be somewhat more dif- Ificult to construct physically, since particular attention must be fIHpaid to feeding the coupler symmetrically with equal-length lines, Lso that the phase difference between ports can be accurately meas-

ured.

The directional coupler is provided as a "canned" design,since to go into the design procedure for coupled lines is beyondthe scope of the course. A basic introduction to the coupler hasbeen provided in the lectures. Students realize the coupler by usingtwo proximal 50 n2 lines. A detailed design involving even- andodd-mode impedances is not pursued in order to illustrate to stu-dents that the presence of a second line near a matched line actu-ally serves to degrade the reflection characteristics of the line. The

Figure lh. A directional coupler designed by students in thedesign labs.

design is also not very sensitive to the spacing between the lines,so provided that it is close to the specified gap width, students usu-ally obtain similar values for coupling and isolation. Students areasked to measure these quantities. After the lab is over, the direc-tional couplers constructed by the students are kept for the finallaboratory, two weeks later, where they will use them to construct asimple scalar network analyzer.

LI LI4.6 Lab 5The last laboratory in ENEL575 is structured as more of an

Figure if. An L-bend designed by students in the design labs, applications laboratory, where students have an opportunity to see

180 IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007180

how several microwave systems work. Student learn how a con-

ventional network analyzer works by constructing a scalar version

from the coupler they created in Lab 4. They also investigate two

radar systems, based on active devices that they have been intro-

duced to in the last part of the course.

The scalar network analyzer experiment encourages students

to use what they have learned about the directional coupler to cre-

ate a system capable of separating forward- and reverse-traveling

waves at the ports of a two-port device. Using the microstrip direc-

tional couplers they have constructed in Lab 4, a scalar network

analyzer is constructed, and several one- and two-port devices are

characterized. Measurements obtained are then compared to meas-

urements performed on an actual vector network analyzer instru-

ment, and to an additional scalar network analyzer built by the stu-

dents based on laboratory-grade directional couplers. Through the

process, students discover that their couplers generally lack the

directivity to adequately resolve IS, I and I S221I for some devices

under test (DUTs). They gain an appreciation of both the complex-

ity of designing good couplers, and the internal operation of the

network analyzer instrument.

The radar experiments are subdivided into three compact

experiments. Most of the experiments are based on an inexpensive

Gunn-diode oscillator, available from MIACOM, which integrates

a Gunn diode, a tuning varactor diode, and a Schottky detection

diode into a WVR-90 package. Students learn how this component

can be used to build a radar system though several systems that

have been set up for the students.

4.6.1 Gunn Diode Characterization

In this brief experiment, students investigate the operation of

a Gunn-diode source used to generate the RF chirps for the static

radar systems. Students have learned about this type of oscillator in

the lectures, and understand how it can be tuned through a varactor

diode integrated with the source. They characterize the source's

oscillation frequency as a function of varactor bias voltage, so that

they better understand how the oscillator can be used as a source of

RF chirps.

4.6.2 Doppler Radar Experiment

This experiment is used to measure the speed of an object

using the Gunn-diode source operating at a single frequency (CW

operation), connected to a 10 GHz horn antenna. Reflections from

moving objects Doppler shift the received signal, which is mixed

with the outgoing signal in the Schottky diode in the source mod-

ule. Students are able to directly observe the resulting signal and

the Doppler frequency on a digital oscilloscope. The output of the

Schottky diode can also be connected to an audio amplifier tc

directly listen to the Doppler frequency. By observing unprocesse(c

signals on the oscilloscope, students gain an appreciation for th(

underlying physics of the problem. This experiment helps reinforce

concepts about mixers that students have learned about in class. A

the same time, the experiment tends to be a lot of fun for students

as they compete to generate the highest Doppler frequency possi

ble. In recent years, a toy race track with "RCS-enhanced" rac,

cars has been used in the experiment, as shown in Figure 2, whic]

adds an additional element of fun.

IEEE Antennas and Propagation Magazine. Vol. 49, No. 3, June 2007

4.6.3 Static Radar Experiment

This experiment realizes a simple version of a radar range

finder. ideally, the setup was to employ the Gunn-diode modules to

generate the chirp signals used for this experiment, but it was

found that they lacked the sensitivity to reliably detect distant

objects. Therefore, the experimental setup shown in Figure 3 was

used instead. The synthesized sweeper was used to generate the

chirp signals and gain introduced into the receiving path to

improve the range of the setup. Originally using X-band WR-90

equipment', more recently the experiment was moved to Ka band

using WR-28 components, as shown in the figure.

Students are able to directly observe the down-converted sig-

nal (as well as other intermodulation products) on the oscilloscope.

The oscilloscope performs a fast Fourier transform (F'FT) of the

input signal. By isolating the frequency component of interest in

the frequency domain, students are able to determine the range to

the object, and compare it with physical measurements. Students

move the target around and repeat the procedure. They are usually

amazed to see how accurate the setup is, and enjoy being able to

see the signals change in real time as the object is moved about the

lab. Students comment on sources of error in their reports. A photo

of some students engaged in radar measurements is shown in Fig-

ure 4.

Figure 2. A photograph of the Doppler radar experiment.

f, =20 GHzf2, 24 GHz7 = 10s

Figure 3. The experimental setup used for the static radar

experiment.181

TARGET

Figure 4. Students experimenting with an older WR-90 versionof the radar range finder.

0S41

-30Z 5 1 . 2.5 3 3.5 4 4.5

Fm c(GHZ)

150 Figure 6b. The completed hybrid coupler.

100 5. Example Measurements~ 50 To illustrate the performance of the prototyping techniques

used by the students in the lab, results for a student-built 9000 ~hybrid coupler are shown in Figure 5. The log-magnitude responses0.5 1.5 F Z~ 5 3 as of the circuit are shown in the upper plot, illustrating excellentoperation of the circuit at the specified design frequency of 2 GHz.

Figure 5. Measurements of a student-built 900 hybrid coupler. The return loss and isolation exceeded 20 dB, and a 3.6 dB powersplit was achieved between the two output ports. The lower plotshows the phase difference between the output ports, which is 90'over a 200 MHz band centered at 2 GHz.

These results illustrate how both the prototyping techniqueand the use of inexpensive calibration standards achieve an accept-able level of quality for the purposes of the laboratory. It has beenfound that above 5-6 GHz, the use of copper tape affects the per-formance of the circuits significantly. Additionally, parasitics inthe inexpensive cahibration standards must be included in the stan-dard definitions on the network analyzer if they are to be usedbeyond this frequency.

A photograph of students engaged in the design of the cou-pler is shown in Figure 6a. A close-up of the complete coupler isshown in the photo in Figure 6b.

6. Laboratory Costs

One of the goals in developing the laboratory was to make itFigure 6a. The design process: assembling and testing a 900 as economical to operate as possible. With this goal in mind, labhybrid coupler. costs were minimized through the use of the following measures:

182IEEVE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007

Table 2. Costs associated with operating the undergraduate

microwave laboratory.

*The use of an inexpensive circuit prototype system,

based on copper tape and simple tools that

students can use to assemble circuits;

" The development of a reusable microwave laminate so

that the same prototyping system can be used for

several years;

" Arrangements for the donation of microwave

laminates to eliminate costs in this area, while

providing the benefit to manufacturers of

spreading their name among undergraduates;

*The use of low-cost, easily replaceable SMA

standards for the network analyzer to save on

replacement and certification costs for the actual

Agilent standards.

The costs associated with operating the laboratory are

summarized in Table 2. This summarizes most of the components

in the lab that need to be replaced on a regular basis, or that have

aided us in producing a more cost-effective laboratory program.

Costs shown are in US dollars.

7. Conclusions

We have described the University of Calgary's Microwave

Circuit undergraduate laboratory in this paper. The lab has been

designed to develop basic RE intuition in students, and to provide

them with hands-on experience in the use of the state-of-the-art

equipment. The lab evolves around simple design experiments. To

spark additional enthusiasm, groups compete with each other for an

award (usually a gift certificate to a student pub on campus) given

at the and of semester to the best team. The equipment in the lab

has been purchased through a generous industrial donation, and the

lab has been designed to have low operational cost. Students at the

University of Calgary carry out course evaluations towards the end

of each semester. The evaluations are anonymous and performed

by university personnel from outside the faculty. We have received

very positive feedback, with students typically writing that the

microwave lab was the most instructive and most interesting lab in

the program.

IEEE Antennas and Propagationl Magazine, Vol. 49, No. 3, June 2007

8. Acknowledgemenlts

The authors would like to extend their appreciation to John

helley, the laboratory technician, for his assistance in developing

ie laboratory program with the authors. The authors would also

ke to thank Rob Randall, who supervised and taught the labora-

ory with the authors, for his contribution to the lab program.

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183

Introducing the Authors

Sean Victor Hum was born in Calgary, Alberta, Canada. Hereceived his BSc, MSc, and PhD degrees from the University ofCalgary in 1999, 2001, and 2006, respectively. While he was agraduate student, he assisted in developing the new microwavelaboratory described in this paper. In late 2006, he joined theEdward S. Rogers Sr. Department of Electrical and ComputerEngineering, where he currently serves as an Assistant Professor.His research interests lie in the areas of reconfigurable RF antennasand systems, spacecraft antennas, and microwave photonics.

Michal Okoniewski is a Professor in the Department ofElectrical and Computer Engineering, University of Calgary. Heholds an endowed Alvin Libin Ingenuity Chair in biomedical engi-neering and a Canada Research Chair in applied electromagnetics.He is also affiliated with TRLabs Calgary.

Dr. Okoniewski is heading the Applied ElectromagneticsGroup at the University of Calgary. He is interested in manyaspects of applied electromagnetics, ranging from computationalelectrodynamics to refiectarrays, RIF MEMS and RF micro-machined devices, as well as development of computational hard-ware for electromnagnetics applications. He is also actively involvedin bioelectromagnetics, where he works on tissue spectroscopy,cancer detection, and novel cell-level micro-imaging methods.

In 2004, he co-funded Acceleware Inc., a public companydeveloping acceleration hardware for simulation software. Dr.Okoniewski is a Senior Member of the IEEE and an AssociateEditor of the IEEE Transactions~ on Antennas and Propagation.

184IEEE Antennas and Propagation Magazine, Vol. 49, No. 3, June 2007