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The Design of an Economical Antenna Gain andRadiation Pattern Measurement System

Brandon C. Brown, Frederic G. Goora and Chris D. RouseUniversity of New Brunswick

Dept. of Electrical and Computer Engineering

Fredericton, New Brunswick, Canada

{brandon.brown, f.goora, chris.rouse}@unb.ca

AbstractThe design of a system capable of making an-tenna gain and radiation pattern measurements at 2.4 GHz ispresented. System performance based on component specifica-tions is summarized and compared to measured data. Antennameasurements taken using the system are compared to thoseobtained using commercially available test equipment in ananechoic test chamber. The accuracy of the system is found tobe 0.5 dB within a dynamic range of 13 dB plus the gainsof the antennas in use. The system is shown to be capable of

making high quality antenna radiation pattern measurements inan anechoic test chamber. For a total cost of less than $1 300, thesystem presents an economical alternative to more sophisticatedmicrowave measurement systems, and is well suited for use in alearning environment.

I. INTRODUCTION

Developing an understanding of antenna properties is es-

sential for anyone hoping to pursue a career in wireless

systems. Perhaps the most important property is antenna gain

as it strongly impacts the range of a wireless link. Antenna

gain is achieved by directing radio frequency (RF) energy

more favorably in some directions than others. Consequently,an antenna gain specification is often accompanied by a

radiation pattern. Due to the prohibitive costs associated with

commercial antenna test equipment, it is impractical for large

groups of students to gain handson experience in making

antenna measurements. This motivates the development of a

system which is capable of making such measurements with

an accuracy of0.5 dB and which can be easily reproducedfor less than $1 500 in cost.

This paper presents the design of a system which is capable

of measuring the gain and radiation pattern of an antenna

in accordance with these specifications. Commercial off the

shelf (COTS) components have been specified such that the

system can be easily reproduced. The antenna radiation patternmeasurement is fully automated and antenna gain is measured

using the three antenna method [1]. A graphical user interface

(GUI) accessed on a laptop provides user control over the

system.

The system is used to characterize a set of COTS antennas,

as well as an antenna which has been custom-built using a

Pringles can. This form of antenna is colloquially referred to

as a cantenna and is reported to exhibit upwards of 12 dBi

of gain [2].

II. SYSTEM OVERVIEW

A block diagram of the antenna measurement system is

shown in Fig. 1. The RF source consists of a dual-output

frequency synthesizer. One of the outputs is connected directly

to a transmit (Tx) antenna; filtering is not required since the

transmit antenna is assumed to be narrowband and designed

for operation at 2.4 GHz. The other output is passed to the

detector in the receiver stage via fixed RF attenuation.The signal received by the antenna under test (AUT) is

amplified by a low noise amplifier (LNA) and is band-pass

filtered (BPF). Signal detection is achieved using a gain

detector. This device generates an analog voltage proportional

to the gain in dB of the signals present at its two inputs.

The voltage output of the detector is digitized by a micro-

controller for processing. The microcontroller provides a GUI

which can be accessed via Ethernet connection to a laptop.

In response to user commands, the microcontroller exercises

control of the RF source and a stepper motor which is used

to rotate the AUT by means of a belt drive assembly.

Detector

Attenuator

Microcontroller

Laptop

LNA BPFRF Source

Gain

Frequency Control

Stepper

Motor

AUTTx

Fig. 1. System block diagram

III. HARDWARE DESCRIPTION

A photograph depicting the hardware associated with the

system is shown in Fig. 2. The following subsections describe

the RF and electrical details associated with each hardware

component.


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Fig. 2. System hardware as mounted on 12x20 MDF board.

A. RF Source

The RF source consists of the Analog Devices ADF4360-

0 evaluation board. The ADF4360-0 is an integrated frequency

synthesizer and voltagecontrolled oscillator, capable of gen-

erating crystalreferenced complementary microwave signalsover a frequency range of 2.4 GHz to 2.725 GHz [3]. Both the

frequency and power level of the 50 outputs are adjusted

by updating control registers serially from the microcontroller.

Upon startup, the frequency is set to 2.4 GHz and the power

level is set to -3 dBm. During a measurement, the frequency

is swept from 2.4 GHz to 2.45 GHz in ten discrete steps; see

Section III-G1 for details.

B. Transmit Antenna

One of the outputs of the ADF4360-0 is fed to the transmit

antenna via 2.8 m of RG-316 coaxial cable. The loss associated

with this length of cable is approximately 4 dB. Consequently,

the transmitted power is -7 dBm. The antenna is mounted0.9 m above the table top on a fixed wooden stand to mini-

mize perturbation of the electromagnetic fields. The transmit

antenna should exhibit an input VSWR of 2:1 or less from

2.4 GHz to 2.45 GHz. It should also exhibit exhibit 5 dBi-

10dBi of gain in order to improve the dynamic range of the

detector.

C. Antenna Under Test (AUT)

The AUT is mounted 0.9 m above the table top on the

antenna positioning system. In order to ensure that all mea-

surements are made in the far field, the AUT is placed at least

1.25 m from the transmit antenna. The associated free-space

path loss is approximately 42 dB. Neglecting antenna gains,

the received power is -49 dBm. The AUT should exhibit an

input VSWR of 2:1 or less from 2.4 GHz to 2.45 GHz.

D. Low Noise Amplifier (LNA)

The output of the AUT is fed to the LNA via 2 m of RG-

316 coaxial cable which results in a loss of approximately

3 dB. The MiniCircuits ZX60-272LN+ LNA operates from

2.3 GHz to 2.7 GHz and provides a gain of 14 dB. Conse-

quently, the output power of the amplifier is approximately

-38 dBm with 0 dBi antennas.

E. Band-Pass Filter (BPF)

The input to the BPF is connected directly to the output of

the LNA. The MiniCircuits VBF-2435+ BPF operates with

a center frequency of 2435 MHz and a bandwidth of 190 MHz.

The insertion loss at 2.4 GHz is approximately 2 dB, resulting

in an output power level of approximately -40 dBm with 0 dBi

antennas. The output of the BPF is fed to one input of the gain

detector through a short length of coaxial cable.

F. Attenuator

The other output of the ADF4360-0 is connected to an

attenuation stage through a short cable exhibiting 0.5 dB

of loss. The attenuation stage consists of a 6 dB attenuator

(MiniCircuits VAT-6+) followed by a 20 dB attenuator

(MiniCircuits VAT-20+). As a result, a -29.5 dBm signal

is fed to the other input of the gain detector.

G. Detector

The detector consists of the Analog Devices AD8302

evaluation board. The AD8302 is an RF/IF Gain and Phase

detector which is capable of operating up to 2.7 GHz and offersa nominal gain sensitivity of 30 mV/dB [4]. Note that the gain

is measured between inputs INPA and INPB. The power at

INPB acts as the reference level for the gain calculation. The

device responds to signals between 0 dBm and 60 dBm,consequently the optimal reference power level at INPB is

30 dBm which coincides with the 29.5 dBm deliveredfrom the attenuation stage. The linearity error at 2.2 GHz

is specified as 0.5 dB for a dynamic range of 51 dB [4].Consequently, the power level appearing at INPA should range

between -4 dBm and -55 dBm. For antennas with 0 dBi

of gain, the power level at INPA is -40 dBm, setting the

minimum dynamic range at 15 dB. Choosing a relatively high-

gain transmit antenna results in a flexible system capable ofmeasuring many different types of AUTs with accuracy.

The output voltage of the AD8302 is fed to a 10-bit analog

to digital converter (ADC) on the microcontroller. Since the

ADC uses a 3.3 V reference voltage, the expected equation

relating the gain between INPA and INPB and the ADC result

is shown in Equation 1, where D is the value reported by

the ADC between 0 and 1023, and G is the gain measured

between INPA and INPB in dB.

G = 0.1075D 30 (1)

1) Phase Sensitivity: Gain measurements made by the

AD8302 are highly phasesensitive. Since the ADF4360-0produces phasecoherent and frequencylocked signals, the

detector output fluctuates sinusoidally about the true gain

measurement as a function of the electrical path length dif-

ference between signals fed to INPA and INPB. Therefore,

the frequency of the ADF4360-0 is swept from 2.4 GHz

to 2.45 GHz in ten discrete steps during a measurement,

effectively sweeping the electrical path length difference.

Averaging the set of results suppresses the phase-sensitivity

of the detector and yields a proper gain measurement.


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H. Microcontroller

The microcontroller consists of the Making Things Make

Controller Kit (MCK). The MCK features a 10-bit ADC with

a 3.3 V reference which is used to digitize the output voltage

from the AD8302. There are 8 high-current digital outputs:

four outputs are configured to drive the stepper motor in a

bipolar configuration, three outputs are used to communicate

serially with the ADF4360-0, and one remains as a spare. TheMCK also features both mini-USB and Ethernet interfaces.

An Ethernet cable is connected from the Ethernet port on the

MCK to the laptop to enable GUI access.

I. Stepper Motor

The Portescap 42L048D1U stepper motor is used to drive

the antenna positioning system. The motor is powered by

5 V and features an angular resolution of 7.5. An external

gear ratio of 7.5 increases torque and results in an angular

resolution of 1. Although the motor is unipolar, it is driven

by the microcontroller in a bipolar configuration to reduce

current requirements.

J. Power Considerations

The Power One MPB125-4350G switching power supply

provides power to the system. The supply is rated for 125 W

and offers a variety of DC voltage outputs: 3.3 V, 5 V and

12 V. The 5 V line powers the LNA, microcontroller andgain detector, while the RF source is powered by the 12 V

line. The other lines are available for future expansion.

The power supply requires a minimum load of 5 W in

order to achieve proper load regulation. While a simple power

resistor would be sufficient, a small light bulb was chosen for

both aesthetic and practical reasons; anechoic test chambers

tend to be poorly lit and the light bulb proved helpful when

making measurements.1) Powering the Microcontroller: Both the stepper motor

and the microcontroller run from the same power source. The

stepper motor is intended to be driven with 5 V, however the

first stage of regulation on the MCK specifies an input voltage

of 6 V to 24 V to operate properly. In order to power both

devices from the regulated 5 V output of the power supply,

the first regulation stage is bypassed by directly connecting

the power supply lines to the power pins of the miniUSB

interface on the MCK. Refer to Section VI-E for details.

IV. SOFTWARE DESCRIPTION

The MCK is open source and has the ability to run freeR-

TOS, which is an open source realtime operating system. Thefollowing subsections summarize software development. Refer

to the documented code listing for additional details.

A. Development Environment

The mcbuilder integrated development environment (IDE)

is freely available and used for compiling and uploading the

project to the MCK. The MCK uses the C programming

language. All of the code required to compile the freeRTOS

is hidden to simplify software development.

B. Graphical User Interface (GUI)

Since the operating system includes an Internet Protocol

(IP) stack, the MCK has the ability to send data over any IP

based network. With the functionality of a simple web server

provided by Making Things, a web page was created and is

stored on the microcontroller. The MCK serves the web page

to a laptop or webenabled device upon request.

Although the controller is programmed in C, the web pageis written using the JavaScript, CSS and HTML program-

ming languages. A website was chosen over a dedicated

application as websites have better portability across many

operating systems. By using Asynchronous JavaScript and

XML (AJAX), data is able to be loaded in the background

without causing a page reload which results in a user interface

with the feel of an application. In addition, the use of the

experimental HTML5 specification allows the radiation pattern

to be generated algorithmically using JavaScript.Upon request by the webenabled device, the web server

on the microcontroller responds by transmitting a character

array containing the web page. Due to the limited resources

of the microcontroller, the number of characters used toimplement the website was minimized. The user can begin

taking measurements once the web page is displayed. When

a button is pressed on the website, a special function makes a

background request for other web pages. The microcontroller

will take action based on which background web page was

requested. When the controller closes the connection after

transmitting the requested data, the web client detects that

the transfer is complete. Actions such as displaying data,

performing calculations or drawing the radiation pattern are

then completed by the web client. An example of the user

interface after a full set of measurements is shown in Fig. 3.

C. Functional DescriptionUpon startup, the MCK programs the synthesizer to produce

a 2.4 GHz tone using a customized serial communication

protocol. The web server routes corresponding to the various

user input commands are then defined. Each route defines an

action that the MCK is required to take. Once initialization

is complete, the microcontroller enters its normal mode of

operation and waits for a page request. When the user accesses

the GUI, the MCK will respond by sending a large static

character array which holds all the required information. When

a measurement is requested by the user, the web server

determines which function handler to call. The following

subsections discuss the web server route function handlers.

1) WebsiteHandler(.. . ): When called, this function simplyreturns a static character array containing the website. The

MCK no longer takes any action, the GUI is initialized and

rendered by the webenabled device.2) dataQuery(. . . ): When a gain measurement is requested,

the MCK initiates a sweep of the synthesizer output frequency.

At each discrete frequency point, 32 ADC readings are aver-

aged. The resulting ten measurement results are then averaged

to produce the phaseinsensitive result. Refer to Section III-G1

for further details. The measurement result is converted to a


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Fig. 3. A screen shot of the user interface showing a complete set ofmeasurements.

gain value in accordance with Equation 2 and is returned to

the GUI. The GUI is responsible for any further calculations,

such as compensating for freespace path loss and computing

antenna gains.

3) reCalibrate(. . . ): Pressing the calibrate button on the

GUI will trigger this function. The MCK assumes a 20 dB

attenuator is connected between the antenna feed cables and

adjusts the offset term in Equation 2 accordingly.4) radiationTest(. . . ): This function is similar to data-

Query(...) with the addition of triggering the stepper motor

between each successive measurement. Data is returned to

the GUI as it is taken, which eliminates the need for a large

storage array in the MCK and ensures continuous data transfer.

Once the MCK has completed the tests, the socket connection

to the user is closed, which indicates to the GUI that the

measurement has finished. The GUI then displays the radiation

pattern while the MCK rotates the antenna positioning system

in reverse to unwind the antenna feed cable.

5) moveHandler(.. . ): A web route has been defined which

accepts an argument that allows the user to specify how

many degrees (and in which direction) the antenna positioning

system is to be rotated. See Section VII-F for operation

instructions.

V. ANTENNA POSITIONING SYSTEM

The primary considerations associated with the design of

the positioner were: ease of manufacturing, assembly and

integration with a motor and belt drive assembly, minimal

impact on the quality of RF measurements, and low cost.

Based on these criteria, a positioning system of primarily

wooden construction was selected.

The positioner requires a turntable such that the base re-

mains static while the platform above it is capable of rotation.

This was accomplished through the use of a Lazy Susan

bearing (LS). A threaded rod shaft is fixed to the upper

platform and extends through the middle of the LS and the

lower platform. A large timing pulley is fixed to the end of theshaft allowing the turntable to be driven by a stepper motor via

a belt drive assembly (BDA). A photograph of the completed

BDA installed on the underside of the lower platform is shown

in Fig. 4.

Fig. 4. A photo of the underside of the lower platform.

The BDA uses a single timing belt to couple the threaded

rod shaft to the small timing pulley on the motor shaft. Due

to challenges associated with attaching the drive shaft to the

upper platform at its exact center of rotation, a tension assem-

bly was required. The belt drive tension assembly (BDTA)

ensures that sufficient tension is applied to the timing belt

which mitigates slip in the BDA. The entire assembly is

mounted underneath the lower platform. Refer to Section VI

for assembly instructions.Due to variations in antenna geometries a universal mount-

ing solution is not practical. A slot was cut into the tops of

the antenna stands to permit insertion of PCBtype antennas.

Other antennas may be mounted through the use of clamps

and/or non-metallic adhesive tape. Note that the antennas must

not be so large or heavy that the antenna positioning system

is overloaded. Due to the dynamic nature of the positioner,

the user must not permit the antenna feed cable to become

snagged by the rotating platform.


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VI . ASSEMBLY

For practical reasons, all structural dimensions in this sec-

tion are given in imperial units.

A. Antenna Positioning System

The antenna positioning system is comprised of a static

lower assembly and rotating upper platform assembly. A LS

is used as the rotary joint between the two platforms.1) Upper Platform: A 1x1x1 piece of wood forms the

base of the upper platform. Note that the use of a drill press for

all required drilling is recommended to ensure that holes are

square to the assembly. Drill the holes as indicated in Fig. 5.

Note that the middle 3/8 hole is at the center of the base.

Fig. 5. Drill hole locations for upper platform

Cut a 1/4 threaded rod to a length of approximately 3-1/2.

Screw a nut to one end of the rod. Place a washer on the center

hole on the base and feed the threaded rod through it. Install

a washer and two nuts on the bottom of the base. Tighten the

first nut against the base then tighten the second nut against

it. This ensures that the first nut will not loosen during use.Cut a piece of 2x3 to approximately 31-1/2 in length.

Using the dimensions shown in Fig. 5, drill 5/8 holes as

opposed to those indicated. Drill to a depth of approximately

3/4. In each of the two outer holes, screw in a 1/4 plain insert

nut. The purpose of the center hole is to provide clearance such

that the nut holding the top of the threaded rod does not foulon the bottom of the 2x3 post.

Install washers on two 1/4 hex bolts and insert them

through the bottom of the base. Secure the 2x3 post to the

base by threading the hex bolts into the corresponding plain

insert nuts.The upper platform is now assembled.2) Lower Platform: Bore a 3-1/2 hole through the center

of a 1x1x1 piece of wood. This forms the base of the lower

platform. Drill a 1-3/4 diameter hole to a depth of 3/4 at

the location indicated in Fig. 6. The stepper motor will be

installed in this location. Drill a 3/8 hole through the side of

the base adjacent to the 1-3/4 stepper motor hole to permit

wiring of the stepper motor to the MCK. Secure the steppermotor to the base using two #4x1/2 wood screws.

Cut four pieces of 2x2 wood to lengths of 1 each with

45 degree mitred edges. These four pieces of wood are used

to frame the base and elevate it from the table or support

structure that the positioner will rest on. Notch two of these

pieces such that when they are installed they do not interfere

with the stepper motor. Affix the mitred edges to the bottom

platform using two 1-3/4 wood screws per edge. Refer to

Fig. 4 and Fig. 6 for guidance.

Fig. 6. Bottom platform showing mitred edges, stepper motor notch, andeyelet screw location.

Use a hacksaw to increase the gap on a 1/4 eyelet screw

(near the end of the eyelet). Install the eyelet on the inside of

the mitred edge as shown in Fig. 6.

Install four 1/2 rubber feet on the bottom of the mitred

edges as shown in Fig. 4.

The lower platform is now assembled.

3) Positioner Assembly: Center the LS on the base of the

lower platform and mark the mounting holes. Drill these

mounting holes using a 1/8 drill bit.

Center the LS on the bottom of the upper platform and

secure it using four #4x1/2 wood screws.Install wood screws through each of the pre-drilled mount-

ing holes on the lower platform and secure it to the LS. The

upper and lower platforms are now connected through the LS.

Using a clamp, glue, or a set screw, install the small timing

pulley onto the shaft of the stepper motor. Install two nuts,

a washer, and the large timing pulley onto the threaded rod.

Position the two bottom nuts and washer such that the large

timing pulley is at the same height as the motor shaft timing

pulley. Tighten the two nuts in place when the correct position

is obtained. Place a washer above the timing pulley and tighten

the assembly with another nut.

Cut a piece of 1/8 thick aluminum into a rectangle of

approximately 2-1/2 by 3/4. Drill a 1/2 hole centered1/2 from each end of the aluminum rectangle. Drill a 1/4

hole in the center of the rectangle. Fold the rectangle into a

channel such that the edge with the 1/4 hole is centered and

is approximately 1/2 long. Refer to Fig. 7 for a graphical

representation of the channel which is used for the belt drive

tension assembly.

Connect a 1 spring to a 1 machine screw eyelet. Thread

a nut onto the eyelet and insert the threaded portion into the

end of the assembly shown in Fig. 7. Secure the eyelet to


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Fig. 7. Belt drive tension assembly timing pulley channel.

the channel with another nut and tighten the assembly. Install

a timing belt onto a medium sized timing pulley. Place a

washer onto the 1/4x1-1/2 bolt and insert it through one

end of the channel, through the medium timing pulley, andthrough the opposite end of the channel. Install a washer and

secure loosely into place with a nut. Wrap the belt around the

small and large timing pulleys. Connect the opposite end of

the spring to the eyelet screw as installed previously (refer to

Fig. 6). The result should resemble Fig. 4.

The antenna positioner is now complete.

B. Transmitting Antenna Stand

Drill two holes through a 1x1x1 piece of wood in

accordance with the outer holes depicted in Fig. 5.

Cut a 2x3 piece of wood to 35 in length. Drill 5/8 holes

to a depth of 5/8 into one end of the 2x3 using the outerholes shown in Fig. 5. Install 1/4 plain insert nuts into these

drilled holes. Install washers onto the 1-1/4 hex bolts, insert

them through the platform into the plain insert nuts installed

into the 2x3. Secure both bolts and install four 1/2 rubber

feet to the four corners of the bottom of the platform.

The transmitting antenna stand assembly is now complete.

C. Pringles Cantenna

The Pringles cantenna was built using instructions avail-

able on the Internet [2]. Note that the length of the antenna

feed was adjusted until an input VSWR of less than 2:1 from

2.4 GHz to 2.45 GHz was obtained.

D. System Mounting

All individual system components were installed onto a 1/2

thick piece of wood that was cut to 12x20. The components,

as shown in Fig. 2 were raised on hex standoffs and installed

using machine screws. The placements shown in Fig. 2 are

not critical and may modified as required. The terminal block

for mounting the light bulb was installed using hot glue. A

custom aluminum platform was fabricated to mount the LNA.

E. Electrical Interconnections

A detailed diagram showing all of the required power

connections is shown in Fig. 8. The light bulb and stepper

motor connections were completed used 20 American Wire

Gauge (AWG) wire. All other connections were completed

using 24 AWG wire.

As shown in Fig. 8, 5 V is applied to the MCK through the

DC plug mounted on the board. As stated in Section III-J1, acustom connection between the input voltage pads to the mini-

USB connector is required on the MCK. This is accomplished

through the modification of a mini-USB cable in accordance

with the electrical connections shown in Fig. 8.

Power

Supply

1

23

J1GND

N

L

1

23

J3

1

23

4

56

7

89

10

111213

14

J3RF Source

1

2

P1

LNA+

-

Detector

1

23

P1

+ -

DC Plug

1 2 3 4 5

Mini-USB

X1-1

X1-2Make

Microcontroller

Fig. 8. Power system interconnection diagram.

The MCK provides screw terminals that are used to connect

the MCK to the stepper motor. Using these screw terminals,

connect output 0 and 1 to one of the coils of the stepper motor

and the connect outputs 2 and 3 to the other coil of the steppermotor. The center taps of each coil are not connected and must

be electrically isolated from all other connections.

The MCK is also used to program the ADF4360-0 over a

custom serial interface. Note that 5.1 k resistors are required

on the communication lines. Refer to Fig. 9 for a detailed

diagram outlining the electrical connections between the MCK

and both the frequency source and the stepper motor.

Connect an SMA cable to the GAIN output of the detector.

The opposite end of the cable must be cut such that the inner

conductor is exposed and the outer shield is grouped into a

pigtail connection. Connect the shield and inner conductor

to the pins labelled GND and AIN0 on the MCK board,

respectively.The light bulb terminal block is connected to the 5 V power

supply output as shown in Fig. 8. Stranded wire was soldered

to the terminal block and covered with heat shrink tubing.

The terminal block was hot glued to a convenient location on

the 12x20 wood. A light bulb was installed into the screw

terminals such that the bulb can be easily replaced in the event

of a filament failure.

From the ADF4360-0: connect RFOUT to the transmit

antenna using a 2.8 m length RG-316 coaxial cable and


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Make

Microcontroller

Out 7

Out 6

Out 5

Out 4

GND

Vout

RF

Source

DB-9

Out 3

Out 2

Out 1

Out 0

GND

Vout

1

9

5.1k

5.1k

5.1k

Coil A

Coil B

Stepper

Motor

Fig. 9. Microcontroller to RF source and stepper motor interface

connect RFOUT directly to the VAT-6+. Connect the VAT-

6+ to the VAT-20+ using a 0.3 m length of coaxial cable.

Connect the VAT-20+ directly to INPB on the AD8302.

Connect the AUT to the input of the ZX60-272LN+ using a2 m length of coaxial cable. Connect the VBF2435+ directly

to the output of the ZX60-272LN+. Connect the VBF2435+

to INPA on the AD8302 using a 0.3 m length of coaxial cable.

VII. OPERATION

A. Basic Setup

Connect an Ethernet cable from the MCK to a computer

with a wired Ethernet connection. Modify the computer net-

work settings as follows: set the IP address to a static address

of 192.168.0.210, with a subnet mask of 255.255.255.0. The

default gateway does not need to be specified.

Open a web browser and navigate to URL

http://192.168.0.200. The browser will now display the

GUI as per Fig. 3. It should be noted that the web browser

needs to have the latest HTML5 specification implemented.

As of version 8, Microsoft Internet Explorer is incapable of

rendering the full GUI; a browser such as Mozilla Firefox

is preferable.

B. Calibration

To calibrate the system, connect a 20 dB attenuator between

the antenna feed cables. Click the Calibrate button. A

message will be displayed indicating that calibration was

successfully completed. The system can be recalibrated by

repeating this procedure however note that the only way to

clear the calibration is to power cycle the MCK.

C. Antenna Gain Measurements

Antenna gain measurements are accomplished using the

three antenna method. Identify three suitable antennas and

designate them as number 1, 2 and 3. In accordance with

the Gain Measurement block featured in the GUI, mount

antenna 1 on the transmit antenna stand and connect the

appropriate coaxial cable. Mount antenna 2 on the antenna

positioning system and connect the appropriate coaxial cable.

Ensure that the antennas are pointing directly at one another

and that they are polarization aligned. Measure the distance

between the two antennas and enter the value in meters in the

appropriate field. Note that for best results, it is recommended

that the antennas be at least 1.25 m apart. Click the Capture

button. A number which reflects the sum of the two antenna

gains in dB should appear in the Result field.

Repeat this procedure for the two remaining antenna com-

binations. Once all three measurements have been completed,

the individual antenna gains will be displayed in dBi in the

Gain Results block.

D. Radiation Pattern Measurements

Mount an antenna with 5 dBi-10 dBi of gain on the

transmit antenna stand and connect the appropriate coaxial

cable. Mount the AUT on the antenna positioning system

and connect the appropriate coaxial cable. Ensure polariza-

tion alignment between the two antennas and an appropriate

separation distance for far field measurements. In the Ra-

diation Pattern block, click the Measure Pattern button.

The antenna positioning system should begin to rotate theAUT. Ensure that the coaxial cable feeding the AUT does not

interfere with the operation of the antenna positioning system.

The radiation pattern will be displayed once a full rotation has

been completed. The antenna positioning system will execute

a full reverse rotation to unwrap the coaxial feed cable.

The raw measurement data can be accessed by clicking the

Show raw data link. This data can be selected and copied

from the browser window for use in an external application.

A copy of the radiation pattern may also be saved as an image

in the Portable Network Graphics (PNG) format by clicking

the Save Graph link.

E. Optional Network ModeThe firmware on the MCK sets the default IP address to

192.168.0.200 but can be dynamically reassigned should the

user decide to connect the device to a network which has

DHCP enabled. A limitation of the device is that there is no

feedback to indicate the assigned IP address; it is left to the

user to determine.

F. Additional Functionality

To determine the calibration value used by the MCK, the

user can navigate their webclient to the /recal subdirectory,

which will trigger a recalibration and will display the value of

the variable cal; this variable modifies the offset of Equation 2.

The user can manually rotate the antenna positioning sys-tem, by navigating to the /m?m= directory and appending

the number of degrees of rotation to the address of the GUI.

This argument can be negative. Note that a leading zero is

required for rotations of less than 10.

VIII. SYSTEM EVALUATION

The complete system, set-up for measurements in the ane-

choic test chamber, is shown in Fig. 10. The following sections

evaluate the performance of the system.


8/10

Fig. 10. Complete system setup for measurements in the anechoic chamber.

A. Gain Measurement AccuracyThe ability of the system hardware to accurately measure

the gain between the antenna feed cables was tested using an

Sband variable attenuator. The performance of the attenuator

was characterized in 5 dB steps from approximately -10 dB

to -60 dB using a calibrated Agilent performance network

analyzer (PNA). The attenuator was then connected between

the antenna feed cables and the ADC outputs were recorded as

a function of attenuation. The relationship between gain and

ADC output was determined using linear regression and is

shown in Equation 2 where G is the gain between the antenna

feed cables in dB and D is ADC output.

G = 0.1117D 67 (2)

In Section III-G, the nominal slope relating the gain between

INPA and INPB to the ADC result was determined to be

0.1075. The experimental slope is 0.1117, representing a 4 %

relative error. The offset has changed since the gain is no

longer being measured between INPA and INPB.The linearity performance of the system is depicted in

Fig. 11. Specifically, the linearity error associated with Equa-

tion 2 is presented. Based on the accuracy specification of

0.5 dB, the dynamic range performance of the system can bedetermined. The absolute error remains below 0.5 dB for gain

values between -13 dB and -55 dB, resulting in a maximum

dynamic range of 42 dB. For a freespace path loss of 42 dBand 0 dBi antennas, the minimum dynamic range is 13 dB.

These results show that the complete system has reduced

dynamic range performance relative to the AD8302. This is

expected, as additional linearity error is introduced by each

hardware component in the system, coupled with quantization

errors introduced by the ADC and subsequent microcontroller

calculations. As mentioned in Section III-B, it is recommended

that the transmit antenna exhibit 5 dBi-10 dBi of gain in order

to improve dynamic range performance.

100 150 200 250 300 350 400 450 50060

50

40

30

20

10

0

ADC Value ()

Gain(dB)

100 150 200 250 300 350 400 450 5000

1

2

3

Absolu

teError(dB)

Linear Fit

Measured Data

Linearity Error

Fig. 11. System linearity performance.

TABLE IANTENNA GAI N MEASUREMENTS

PNA Results IsoTropic Thunder Absolute Error(dBi) Results (dBi) (dB)

Yagi 5.6 5.4 0.2Monopole 0.3 0.2 0.1

LPD 4.7 4.6 0.1

B. Antenna Gain Measurements

Three COTS antennas were acquired in order to evaluate

the performance of the system prior to characterizing the

cantenna. A 2.4 GHz monopole antenna was purchased due

to its relatively constant H-plane radiation pattern. A 2.4 GHz

printed circuit board (PCB) Yagi antenna was purchased due to

its relatively high forward gain, and a PCB logperiodic dipole

(LPD) antenna, which operates over 900 MHz to 2600 MHz,

was borrowed from UNB for testing purposes. The input

VSWR of each of these antennas was confirmed to be less

than 2:1 between 2.4 GHz and 2.45 GHz using the PNA.

The three antenna method was carried out for the COTS

antennas inside an anechoic test chamber using both the

system and the PNA. The results are summarized in Table I.

The system is confirmed to meet accuracy specifications, as the

absolute error associated with the antenna gain measurements

is less than 0.5 dB.

The three antenna method was repeated using the Yagi,monopole, and cantenna. The antenna gains were measured

to be 5.6 dBi, 0.2 dBi, and 5.5 dBi, respectively. Despite

a somewhat legendary status among RF hobbyists on the

Internet, the Pringles cantenna falls short in its promise of

providing upwards of 12 dBi of antenna gain. However, at

a cost of less than $15 in parts, the cantenna offers 5.5 dBi

of gain which rivals the gain offered by a COTS PCB Yagi

antenna sold at over double the price. Also, unlike the Yagi,

the Pringles cantenna includes a delicious snack.


9/10

C. Antenna Radiation Pattern Measurements

H-plane radiation pattern measurements were made for

the Yagi and monopole antennas using the system inside an

anechoic test chamber and were compared to results obtained

using the UNB Antenna Positioning System with the PNA.

Fig. 12 and Fig. 13 show the results. Note that the angular

resolution for each measurement is 1 and the data is normal-

ized such that the pattern maximum is 0 dB.

35

35

30

30

25

25

20

20

15

15

10

10

5

5

0 dB

0 dB

90o

60o

30o

0o

30o

60o

90o

120

o

150o

180o

150o

120

o

PNA Pattern

IsoTropic Thunder Pattern

Fig. 12. Yagi antenna radiation pattern measurements.

35

35

30

30

25

25

20

20

15

15

10

10

5

5

0 dB

0 dB

90o

60o

30o

0o

30o

60o

90o

120o

150o

180o

150o

120o

PNA PatternIsoTropic Thunder Pattern

Fig. 13. Monopole antenna radiation pattern measurements.

While the UNB system has greater accuracy and dynamic

range performance, there is strong agreement between the pat-

tern results. As the measurements were taken using different

measurement hardware and with different feed cable arrange-

ments, some variation in the measured patterns is expected.

Nevertheless, it is clear that the system is capable of making

high quality automated radiation pattern measurements.

The H-plane radiation pattern of the Pringles cantenna was

measured using the validated system and is shown in Fig. 14.

As expected, the cantenna pattern is qualitatively similar to

that of a Yagi antenna, with a fronttoback ratio of approxi-

mately 11 dB. It should be noted that since the cantenna feed is

unbalanced and lacks a proper ground connection, the radiation

pattern results are very sensitive to feed cable orientation.

35

35

30

30

25

25

20

20

15

15

10

10

5

5

0 dB

0 dB

90o

60o

30o

0o

30o

60o

90o

120o

150o

180o

150o

120o

Fig. 14. Cantenna radiation pattern measurements.

D. Budgetary Considerations

A bill of materials is included in the Appendix. The total

cost to reproduce the system is $1 240.64 (CAD), which is in

compliance with the maximum specified budget of $1 500.

I X. CONCLUSION

The motivation for this project was to design and build a

system capable of making antenna gain and radiation pattern

measurements with an accuracy of 0.5 dB for less than$1500 in cost. Due to the fact that many of the specified

components are COTS, the system presented here can be

easily reproduced, and meets budgetary constraints at a cost of

$1 240.64. It has been shown to achieve a gain measurement

accuracy 0.5 dB over a dynamic range of 13 dB plus the

combined gains of the two antennas in use. Antenna gainand radiation pattern measurements made inside an anechoic

test chamber were validated through comparison with results

obtained using a commercial PNA and the UNB antenna

positioning system. The flexible nature of the GUI allows for

system access and control independent of operating system or

hardware platform.

The system has been used to measure the gain and radiation

pattern of a homemade Pringles cantenna. Despite claims

from Internet RF hobbyists that the cantenna is capable of


10/10

achieving a gain of 12 dBi, measurements made by the system

indicate a gain of 5.5 dBi.

In summary, the system presented here is accurate, econom-

ical, robust and easily reproducible. With minor enhancements,

the system would be suitable for use in a learning environment

such as an undergraduate laboratory.

APPENDIX

The bill of materials is summarized in Table II. Note thatall prices are in Canadian dollars.

ACKNOWLEDGMENTS

The authors would like to thank Dr. Bruce Colpitts, Dr.

Brent Petersen, Ryan Jennings, Michael Wylie and Lars Wood-

house for their support and guidance throughout the course of

the project.

REFERENCES

[1] C. A. Balanis, Antenna Theory: Analysis and Design, 3rd ed. Hoboken,New Jersey: John Wiley & Sons, Inc., 2005.

[2] R. Flickenger. (2001, July) Antenna on the cheap (er, chip). [Online].Available: http://www.oreillynet.com/cs/weblog/view/wlg/448

[3] ADF4360-0 Datasheet Rev. A, Analog Devices, Norwood, MA, 2004.[4] AD8302 Datasheet Rev. A, Analog Devices, Norwood, MA, 2002.

Brandon C. Brown was born in Kitchener, Ontarioin 1983. He received a Bachelor of Applied Science(Computer Engineering) from Queens University in2006. After spending a short time working in indus-try, he enrolled at the University of New Brunswick(UNB) and received his masters in 2007. Currently,he is enrolled at UNB and is working toward aPh.D. degree. His research interests include wirelesssystems, signal propagation and various aspects ofnetworking.

Frederic G. Goora was born in Sydney, NovaScotia in 1977. He received a Bachelor of Science inEngineering (Electrical Engineering) and a Master ofScience in Electrical Engineering from the Univer-sity of New Brunswick (UNB) in 2000 and 2003,respectively. After more than 6 years of industrialexperience, he returned to UNB and is currentlypursuing a Ph.D. degree in Electrical Engineering.His research interests include magnetic resonanceimaging and microwave systems. He is registeredas a Professional Engineer in New Brunswick.

Chris D. Rouse was born in Halifax, Nova Sco-tia in 1986. He received a Bachelor of Sciencein Engineering (Electrical Engineering) from theUniversity of New Brunswick (UNB) in 2009, andis currently pursuing a Ph.D. degree in ElectricalEngineering at UNB. His research interests includewireless systems, communications, and fiber optics.

TABLE IITHE BILL OF MATERIALS FOR CONSTRUCTION OF THIS PROJECT.

Part Quantity Cost ($) Vendor

AD8302 Evaluation Board 1 212.99 Analog DevicesADF4360-0 1 121.44 Analog Devices2 m SMA cable 1 26.70 Assemble / Digikey2.5 m SMA cable 1 30.33 Assemble / Digikey

0.3 m SMA cable 5 53.05 Digikey2 Position Terminal Block 1 0.32 Digikey42L048D1U 1 24.00 Digikey9 V Battery Snap Connec-tor

1 0.35 Digikey

DB9 Female 1 3.94 DigikeyEthernet Cable 1 3.50 DigikeyHeat Shrink 1 6.00 DigikeyMolex Headers and Pins 1 5.00 DigikeyMonopole Antenna 1 5.19 DigikeyPower Cord (5.2mm bar-rel jack)

1 2.37 Digikey

Power Cord (AC withGround)

1 5.00 Digikey

Power Supply 1 94.51 DigikeyResistors 3 1.00 DigikeyRing Connector 1 0.35 Digikey

SMA Barrels 3 14.13 DigikeyStandoffs 20 5.00 DigikeyUSB A to mini B Cable 1 4.13 DigikeyWire, 20 AWG 1 25.70 DigikeyWire, 24 AWG 2 34.80 DigikeyCantenna Parts 1 15.00 Grocery / Hardware StoreBelt Drive Tension Parts 1 8.50 Hardware Store1/4x1-1/2 Hex Bolts 4 2.00 Hardware Store2x2x8 Wood Stud 1 1.50 Hardware Store2x3x8 Wood Stud 1 2.50 Hardware StoreDowel (3/8O.D.x4) 1 3.48 Hardware StoreLarge Lazy Susan 1 6.19 Hardware StoreLight bulb 1 1.50 Hardware StoreMDF (1 x 4) 1 5.00 Hardware StoreNuts (#8) 12 1.80 Hardware StoreNuts (3/8) 6 1.50 Hardware StorePlain Insert Nut 4 2.50 Hardware Store

1 O.D. Screwin RubberFeet 12 12.00 Hardware Store

Scrap Aluminum 1 5.00 Hardware StoreScrews (#4) 36 3.00 Hardware StoreScrews (#8) 12 2.79 Hardware Store1 Thick Wood 1 10.00 Hardware StoreThreaded Rod (3/8) 1 12.00 Hardware StoreWashers (#4) 26 1.82 Hardware StoreWashers (#8) 12 1.08 Hardware StoreWashers (3/8) 6 2.00 Hardware StoreWire Clamps 14 5.00 Hardware StoreWood Screws (pack) 1 3.18 Hardware StoreMake Microcontroller 1 120.00 M akingThingsVAT-20+ 2 29.60 Mini CircuitsVAT-6+ 3 14.80 Mini CircuitsVBF2435+ 1 43.06 Mini CircuitsZX60-272LN+ 1 49.95 Mini Circuits

Yagi Antenna 1 32.95 Ramsey ElectronicsBelt (A 6B 6M193060) 1 4.47 Stock Drive ProductsTiming Pulley(A 6M 6M10DF06003)

1 3.27 Stock Drive Products

Timing Pulley(A 6M 6M25DF06008)


Timing Pulley(A 6M 6M75DF06008)


Tax $142.74Total (CAD) $1240.64
http://www.oreillynet.com/cs/weblog/view/wlg/448http://www.oreillynet.com/cs/weblog/view/wlg/448

diseño de una antena económica

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