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Antenna Design First Semester Report

Fall 2011

By:

Nate Hufnagel

John James

Prabhat Lamsal

Prepared to partially fulfill the requirements for ECE 401

Department of Electrical and Computer Engineering

Colorado State University

Fort Collins, CO 80523

Project Advisors: Dr. Branislav Notaros, Olivera Notaros, Nada Sekeljic

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ABSTRACT

In order to effectively test any antenna in the Antenna Test Range, multiple families of

horn antennas will be needed. The design and fabrication of these antennas has been

addressed this semester by our group with the aid of WIPL-D software.

Standard gain horn antennas can be used effectively for applications within the test

range because of their inherent characteristics, simple design and acceptable size. As opposed

to other types of horn antennas, it has been found that standard gain horn antennas operate

over narrow frequency ranges, can attain a low VSWR, and can attain a high gain.

The program WIPL-D makes design and optimization of antennas possible through the

use of its parametric sweep function and numerical analysis. WIPL-D has been used effectively

in this project to design antennas that meet or exceed the constraints imposed on their design

and operation by Dr. Branislav Notaros.

The findings of this project include a full design of a standard gain horn antenna that is

able to operate at over 20 dB over the frequency range of 8-12GHz. This design also meets the

desired VSWR by maintaining a value under 2 for the entire operational frequency range.

Future work related to further developing this project will include fabrication with Aluminum

and completing a design and fabrication of a double ridge horn antenna that can theoretically

provide over 20dB gain over the frequency range of 1-18GHz.

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Contents Antenna Design ....................................................................................................................................... 1

ABSTRACT ............................................................................................................................................... 2

Table of Figures ....................................................................................................................................... 4

I. INTRODUCTION............................................................................................................................... 5

II. Background and Theory ...................................................................................................................... 5

A. Radiation Pattern ......................................................................................................................... 7

III. Antenna Simulation and Design ....................................................................................................... 11

A. WIPL-D Simulations ...................................................................................................................... 11

B. WIPL-D Results ............................................................................................................................. 18

C. Final Results .................................................................................................................................. 19

IV. Future Work and Conclusions .......................................................................................................... 22

A. Continuation of Antenna Design ................................................................................................ 22

B. Antenna Testing ......................................................................................................................... 22

C. Conclusions ................................................................................................................................ 23

References ........................................................................................................................................ 24

Appendix A – Budget ......................................................................................................................... 25

Appendix B – Acknowledgments ........................................................................................................ 26

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Table of Figures

Figure 1: E-plane horn [1] ........................................................................................................................ 6

Figure 2: H-plane horn [1] ........................................................................................................................ 6

Figure 3: Rectangular horn [1] ................................................................................................................. 6

Figure 4: Normalized field pattern of the directional antenna [4] ............................................................. 8

Figure 5: 2-Dimensional cut in phi plane [4] ............................................................................................. 8

Figure 6: Radiation of rectangular waveguide [5] ..................................................................................... 9

Figure 7: Monopole feed into waveguide [5] ........................................................................................... 9

Figure 8: Annotated Horn as seen in WIPL-D program ........................................................................... 11

Figure 9: Gain plotted from 8 – 14 GHz with minimum swept aperture size. .......................................... 12

Figure 10: Gain plotted from 8 – 14 GHz with B dimension increased by 7.6mm. ................................... 12

Figure 11: Gain plotted from 8 – 14 GHz with B dimension increased by 19mm. .................................... 13

Figure 12: Gain plotted from 8 – 14 GHz with B dimension at original 40mm and A increased by 10.8mm.

.............................................................................................................................................................. 13

Figure 13: Gain plotted from 8 – 14 GHz with B dimension increased by 7.6mm and A increased by

10.8mm. ................................................................................................................................................ 14

Figure 14: Gain plotted from 8 – 14 GHz with B dimension increased by 11.4mm and A increased by

18mm. ................................................................................................................................................... 14

Figure 15: Gain plotted from 8 – 14 GHz with B dimension increased by 19mm and A increased by

10.8mm. ................................................................................................................................................ 15

Figure 16: Gain plotted from 8 – 14 GHz with B dimension increased by 19mm and A increased by

18mm. This is the larges aperture tested. ............................................................................................ 15

Figure 17: Gain plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located

10.7mm from the back of the waveguide. ............................................................................................. 16

Figure 18: VSWR plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located

10.7mm from the back of the waveguide. ............................................................................................. 16


8.62mm from the back of the waveguide .............................................................................................. 17


8.62mm from the back of the waveguide .............................................................................................. 17

Figure 21: Final dimensions of all parameters, Initial dimensions were the basis for initially drawing horn

in WIPL-D .............................................................................................................................................. 18

Figure 22: Gain plot with Mid-band frequency (10GHz) annotated. ....................................................... 19

Figure 23: Final VSWR plot with maximum value annotated. ................................................................. 19

Figure 24: 3-D radiation pattern and Phi cut showing HPBW of 13.08 degrees at 8GHz. ......................... 20

Figure 25: 3-D radiation pattern and Phi cut showing HPBW of 10.24 degrees at 10GHz. ....................... 20



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I. INTRODUCTION In today’s technological world, wireless communication has become an important part of our

lives. We use all kinds of wireless devices such as radios, cell phones, wireless internet, and

satellite dish antennas just to name a few. Cell phones and wireless devices communicate with

each other by transmitting and receiving electromagnetic waves. An antenna is an electrical

device which converts electric currents into radio waves, and vice versa. To transmit the signal a

transmitter applies an oscillating radio frequency electric signal to the antenna’s terminals, and

the antenna radiates the energy in the form of electromagnetic waves. Similarly, when

receiving, an antenna receives a radio frequency wave which produces a small voltage in the

conductor which is then transmitted through the conductor. [1]

Horn antennas are characterized using several parameters like gain, voltage standing wave ratio

(VSWR), geometry, half-power beam width, frequency of operation, and polarization. Our

senior design team is designing and fabricating a series of horn antennas, waveguides and

monopole feeds. There are several constraints that apply to our design. Our antenna is

required to operate within a frequency range of 1 to 20 GHz, attain a gain of 20 dB, maintain a

voltage standing wave ratio (VSWR) of 2 or below, and maintain a half-power beam width of

less than 20 degrees. The first part of the design year, we have designed an X-band standard

gain horn antenna that operates in the frequency range of 8 to 12 GHZ. This paper includes the

design process which was accomplished using WIPL-D software. Fabrication of our first

standard gain horn antenna is in progress right now and we are aiming for its completion by the

end of the semester.

II. Background and Theory

Horn antennas are used for receiving and transmitting RF signals. Horn antennas are simply

elongated structure of rectangular waveguide. The waveguide structure is open out or flared,

launching the signal towards the receiving antenna. Since horn antennas are used in VHF (very

high frequency) their application is in microwave and radar communication. There are

numerous companies designing and manufacturing this type of horn antenna and they are very

costly because their design and fabrication requires professionals to accomplish.

There are three types of rectangular horn antennas, H-plane sectoral horn, E-plane sectoral

horn and rectangular horn which can be seen in the figures below:

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Figure 1: E-plane horn [1]

Figure 2: H-plane horn [1]

Figure 3: Rectangular horn [1]

After considerable research regarding horn antennas our group decided to design rectangular

horn antennas because of their directional radiation pattern, ability to achieve high gain and

directivity, slowly varying input impedance, and their ease of fabrication. The horn antenna we

designed was subject to the following constraints:

• Operating frequency around 10 GHZ

• Maintain a gain of 20 dB over the entire operating frequency range

• Maintain voltage standing wave ratio (VSWR) of 2 or less over the entire operating

frequency range

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• Maintain a half-power beam width (HPBW) that is below 20 degrees over the entire

operating frequency range

Voltage standing wave ratio (VSWR) is a function of the reflection coefficient, which describes

the power reflected from the antenna. The smaller the VSWR is, the better the antenna is

matched to the transmission line and more power is delivered to the antenna [2]. For this

project we had to keep our VSWR below 2, which we did successfully in simulation. The other

parameter is gain, which is related to directivity. High directivity leads to high gain. We were

able to meet the antenna gain constraint which required that we maintain 20 dB across our

complete operating frequency. The antenna aperture which is the area of the opening part of

the horn influences the gain of the antenna. We noted through simulation that increasing

aperture size also increases the gain of the antenna. During our simulations we did numerous

parametric sweeps to tailor the aperture so that we could meet all of our constraints. The final

parameter we designed for is half-power beam width which is defined as the angular

separation in which the magnitude of the radiation pattern decrease by (-3 dB) from the peak

of the main beam [1]. As an example in our simulation the half-power beam width at 10 GHZ

was found to be 10.24 degree.

The program we used to design horn antenna is WIPL-D. It is 3-D electromagnetic solver. We

can model any type of structure in this program and we can parametric sweep the dimension to

get the optimum gain for the particular antenna. The applications of this software include 3-D

modeling of antennas, microwave circuit design, scattering problems, EMC, prediction of

radiation hazards to human health, and simulation of all kinds of antennas [3].

A. Radiation Pattern

There are four different patterns that antenna radiate in:

Isotropic Pattern: This pattern is uniformly radiated along all the directions.

Directional Pattern: Is a pattern characterized by more efficient radiation in one direction than

the other.

Omni directional Pattern: A pattern which is uniform in a given plane.

Principal Plane Pattern: These are the E-field and H-field of a linearly polarized antenna. Our

horn antenna is linearly polarized on both fields.

Radiation patterns are characterized by their lobes. The various lobe definitions are below.

Radiation Lobe: Is a peak in the radiation intensity surrounded by the weaker intensity.

Main Lobe: Radiation lobe with a maximum radiation.

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Side lobe: A radiation lobe in any direction except the main lobe.

Back Lobe: Is a Lobe opposite to the main lobe.

HPBW (half-power beam width): The angular width of the main beam at the half-power point.

We were able to achieve a half-power beam width around 11 degrees.

Figure 4: Normalized field pattern of the directional antenna [4]

Figure 5: 2-Dimensional cut in phi plane [4]

Waveguide: Waveguides are rectangular shaped tubes. They are used for energy and

information transfer in electromagnetic systems. Electromagnetic waves travel along

waveguides by means of multiple reflections from the metallic walls, through the dielectric tube

so the waves are guided by the tube conductor. Generally metallic waveguides have one

conductor and operate at frequencies above 1 GHz. Metallic waveguides and cavity resonators

are important components of many technologies with practical applications such as radar

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antenna feeds, circuitry, waveguide slot antenna arrays, horn antennas, microwave filters and

other various other circuit component. The size of waveguide depends on the frequency you

want to pass through it. Large frequencies have smaller wave guide. Because our design covers

the frequency range of 8 - 12 GHZ, the waveguide dimensions we designed for are 59 × 22.46 x

10.16 mm.

Figure 6: Radiation of rectangular waveguide [5]

Figure 7: Monopole feed into waveguide [5]

Antenna Aperture & Body: The antenna body is an extension of the waveguide. The length of

an antenna is proportional to its gain. As length increases the gain of antenna increases, but

other characteristics such as VSWR can also be affected positively or negatively by length

increases. Another physical parameter is the antennas effective aperture. It is defined as the

ratio of the power received by the load at the antenna terminals and the surface power density

of the incoming electromagnetic wave. The aperture of horn antenna is directly related to the

gain of the antenna, which is given by the formula,

��

4 � Π

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Where, G is the gain of an antenna and � is the wavelength.

The above equation concludes that as aperture increase so does the gain of an antenna but it

might have significant effect on the VSWR and beam width. In our project we did several

simulations to get the optimized aperture to meet our constraints.

Antenna Feed: The waveguide of a horn antenna is fed with a monopole to transmit

electromagnetic radiation. The most frequently used monopole antenna is quarter-wave

vertical wire monopole i.e. h =�/4. In our design the monopole is fed with the outer connecter

connected to the waveguide. The height of the monopole affects the gain and VSWR of any

antenna. We parametrically swept to obtain a 6.48 mm, which was good enough to meet our

constraints. We are also using a 2.4 mm connecter to feed our standard gain horn antenna due

to the dimensions of our waveguide.

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III. Antenna Simulation and Design

A. WIPL-D Simulations

The basis for this given design was to implement an X-Band (10 GHz) Standard Gain horn

antenna using WIPL-D software. This design, shown below, was tested over the frequency

range of 8-14Ghz while parametrically sweeping various parameters and outputting the gain,

VSWR, and 3dB beam-width to find the optimized dimensions. In order to effectively

implement into WIPL-D and be centered at the origin, the parameters of the horn aperture and

the waveguide aperture needed to be represented as in the figure below. Dimensions A and B

are the aperture width and height of the horn, D and E are the width and height of the

waveguide, F is the waveguide length and L is the overall length of the antenna.

Figure 8: Annotated Horn as seen in WIPL-D program

Z1: Distance of the monopole to the back of the waveguide.

Y1 = -5.08mm: Position of the monopole contact inside the waveguide.

Y2 = 1.4mm: Height of the monopole (2/3) height of waveguide (2E).

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The following figures show the Gain of the antenna with the corresponding dimensions

of A, B, and z1. These dimensions of the horn were all parametrically swept together with 6

points each. The final length of the antenna was determined to be best at 345mm through

simple trial and error. The waveguide dimensions remained at those of the commonly used

WR-90 waveguide that can be found on the market. Because the waveguide aperture

dimensions are directly set based on frequency, there was no need to sweep these parameters.

A=60mm B=40mm z1=5.5mm

Figure 9: Gain plotted from 8 – 14 GHz with minimum swept aperture size.

The following plots indicate how gain is affected as aperture size increases.

A=60mm B=47.6mm z1=5.5mm

Figure 10: Gain plotted from 8 – 14 GHz with B dimension increased by 7.6mm.

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Figure 11: Gain plotted from 8 – 14 GHz with B dimension increased by 19mm.

A=70.8mm B=40mm z1=5.5mm

Figure 12: Gain plotted from 8 – 14 GHz with B dimension at original 40mm and A increased by 10.8mm.

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A=70.8mm B=47.6mm z1=5.5mm

Figure 13: Gain plotted from 8 – 14 GHz with B dimension increased by 7.6mm and A increased by 10.8mm.

A=78mm B=51.4mm z1=5.5mm

Figure 14: Gain plotted from 8 – 14 GHz with B dimension increased by 11.4mm and A increased by 18mm.

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A=70.8mm B=59mm z1=5.5mm

Figure 15: Gain plotted from 8 – 14 GHz with B dimension increased by 19mm and A increased by 10.8mm.

The plot below shows gain over our frequency range with the largest aperture that was

swept. This and all of the above plots indicate that a better gain is achieved as aperture size

increases.


Figure 16: Gain plotted from 8 – 14 GHz with B dimension increased by 19mm and A increased by 18mm. This is the largest

aperture tested.

The plot below shows the effect of increasing the distance of our monopole (z1) from

the back of the waveguide while using our maximum aperture size. Again, the ideal location for

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the monopole from the back of the waveguide is λ 4� so the distance was swept over the range

between the highest and lowest frequency to determine the ideal location. Gain increased at

some frequencies and decreased at others. Overall, this didn’t affect gain significantly.

A=78mm B=59mm z1=10.7mm

Figure 17: Gain plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located 10.7mm from the back of

the waveguide.

While moving the monopole away from the back of the waveguide didn’t affect gain

much, it did ruin our VSWR as can be seen in the following figure.

A=78mm B=59mm z1=10.7mm

Figure 18: VSWR plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located 10.7mm from the back of

the waveguide.

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As the distance of the monopole from the back of the waveguide decreased, there was a

consistent decrease in the VSWR.

A=78mm B=59mm z1=8.62mm


the waveguide

Placing the monopole 5.5mm from the back of the waveguide, while retaining maximum

aperture dimensions, lowered the VSWR substantially. It can be concluded from these plots

that the slight gain increases that are obtained by moving the monopole are not worth the

VSWR degradation.



the waveguide

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B. WIPL-D Results

What can be concluded:

1. Bigger is better. It is already known that increasing the length of our aperture would

help increase gain so it wasn’t necessary to sweep this parameter because there is

limited time and processing power when parametrically sweeping more variables. It’s

now known that as the dimensions of the aperture increase, the gain increases as well.

• Now we have to find the happy medium between size, which will

influence our cost and the specs that are desired.

2. Distance of our monopole from the back of the waveguide can lead to gain increases. It

also leads to unacceptable VSWR in this case.

Final concluded Dimensions:

Figure 21: Final dimensions of all parameters, Initial dimensions were the basis for initially drawing horn in WIPL-D

A B D E F L Z1 Y1 Y2Length (mm) Initial 61.845 45.97 11.43 5.08 70.35 325.85 N/A N/A N/A

Optimized 78 59 11.43 5.08 59 345 5.5 -5.08 1.4

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C. Final Results

Now that the dimensions of the horn have been concluded, a much larger sweep

including 100 frequencies was run to make sure that there were no discrepancies throughout

the range. A maximum gain of 22.31dB at 10 GHz was achieved, and the gain maintained over

20dB for the entire range. VSWR was also under 2 for the 8-12 GHz range but slightly increased

over 2 past 12 GHz.


Figure 22: Gain plot with Mid-band frequency (10GHz) annotated.

Figure 23: Final VSWR plot with maximum value annotated.

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The following pictures and plots show the radiation representation that’s modeled in

WIPL-D. The Phi cut graphs are used to determine the HPBW. As can be seen from the

annotated angles in the graphs, the HPBW remained well under 20 degrees.

8 GHz 3D plot and Phi cut:

Figure 24: 3-D radiation pattern and Phi cut showing HPBW of 13.08 degrees at 8GHz.



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IV. Future Work and Conclusions

A. Continuation of Antenna Design

As fabrication of our first standard gain horn antenna’s continues, our group will focus our

attention on new antenna designs. We intend to explore double-ridged horn antenna design

and optimization in the immediate future. Just like standard gain horn antennas, double-ridged

horn antennas have a directional radiation pattern which we can control to some extent

through our design specifications. Their directional radiation pattern makes it possible to

achieve high gain. Horn antennas of all kinds have very little loss, so their gain is very close to

their directivity. Their input impedance varies slowly over a large frequency range, and this

allows us to guarantee that sufficient power will be delivered to the antenna over a large

frequency range. The benefit of the double-ridged horn antenna is its operational frequency

range. There are multiple companies advertising double-ridged horn antennas that maintain a

gain of 20 dB and VSWR of less than 2 over the frequency range of 1 – 18 GHz.

Our groups most basic goal for the semester was to design, optimize, and fabricate a family of

horn antennas, waveguides, and coaxial to monopole feeds that effectively cover the

microwave spectrum of 1 – 20 GHz. The design of an effective double-ridged horn antenna

would be a realization of that goal. If we attempted to cover 1 – 20 GHz with standard gain

horn antennas, we would be required to design and fabricate 5 to 7 sets of transmitting and

receiving antennas. The double-ridged horn antenna will save our group money, and allow us

more time to focus on quality fabrication of the antenna instead of quantity fabrication of many

antennas.

B. Antenna Testing

In the near future and in conjunction with the Antenna Test Range senior design team, we will

begin testing our first operational standard gain horn antennas. To decrease noise and losses

from our coaxial cable, our transmitting and receiving antennas will be operated in Dr. Notaros’

anechoic chamber. A network analyzer will be used during this testing process to characterize

our antennas gain and VSWR.

After fabrication of our double-ridged horn antenna is complete, we will apply the same testing

process to it. If time allows, we intend to compare our testing results to those observed by

Christian Bruns, Pascal Leuchtmann, and Ruediger Vahldieck in their paper, “Analysis and

Simulation of a 1-18 GHz Broadband Double-Ridged Horn Antenna”. They found that at their

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upper frequency ranges, the performance of double-ridged horn antennas degrades because of

their inability to suppress higher order mode propagation [5].

C. Conclusions

For the Antenna Design team, this semester has been successful one. There are still a few

issues regarding our coaxial to monopole feed that need to be resolved, but as a whole the

project has gone well.

At the beginning of the semester, our project required that we research horn antennas and

their components. We required a much better understanding of the geometries and

electromagnetics that dictate the functionality of horn antennas. Both our research and ECE

444-Antennas and Radiation have increased our understanding of our project and knowledge

regarding antennas.

We later learned WIPL-D software. Learning to use engineering software is always tedious, but

we felt comfortable with our understanding of WIPL-D software and our ability to use it to its

potential by mid-semester. WIPL-D allowed us to both design and optimize our first standard

gain horn antennas. This was accomplished through the use of WIPL-D’s batch file and

parametric sweep function. The parametric sweeps we performed applied to all dimensions of

our antenna, waveguide, and monopole. One particular sweep required five days to complete.

The results of these sweeps made it possible for our group to meet and exceed the constraints

imposed on our antennas functionality and operation. Currently, Steve Johnson, a Mechanical

Engineering student at Colorado State University is fabricating our first set of optimized

waveguides and standard gain horn antennas.

At semesters end, we’re still trying to resolve how we will feed our antennas. With the help of

Steve Johnson, we will attempt to fabricate an acceptable 2.4 mm connector and monopole. If

this is unsuccessful, we will be forced to purchase these items. Due to our budget, and the high

cost of 2.4 mm connectors and monopoles, our group considers fabrication of our own a

priority.

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References

[1] Introduction to antennas [online]. Available: http://www.antenna-

theory.com/intro/main.html

[2] Antenna theory [online]. Available: http://www.antenna-theory.com/definitions/vswr.php

[3] WIPL-D [online]. Available: http://www.wipl-d.com/quicktour/who.php

[4] Branislav M. Notaros, Antenna characteristic radiation function and radiation patterns ,in

Electromagnetics,1st

edition, Upper Saddle River,

NewJersey,USA:Pearson,2011,chp14,sec14.5,page 737 [online] Available:

http://view.ebookplus.pearsoncmg.com/ebook/launcheText.do?values=bookID::3953::invokeT

ype::lms::launchState::goToEBook::scenarioid::scenario5::logoutplatform::1027::platform::1027

::scenario::5::globalBookID::CM39946096::userID::1540208::hsid::d5f247464d18f83e8fc6a9bf3

7c8704a

[5] Branislav M. Notaros, Waveguide Coupler ,in Electromagnetics,1st

edition, Upper Saddle

River, NewJersey,USA:Pearson,2011,chp13,sec13.14,page 694 [online] Available:

http://view.ebookplus.pearsoncmg.com/ebook/launcheText.do?values=bookID::3953::invokeT

ype::lms::launchState::goToEBook::scenarioid::scenario5::logoutplatform::1027::platform::1027

::scenario::5::globalBookID::CM39946096::userID::1540208::hsid::d5f247464d18f83e8fc6a9bf3

7c8704a

[6] C. Bruns, “Analysis and Simulation of a 1 – 18 GHz Broadband Double-Ridged Horn Antenna,” IEEE

TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, February 2003.

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Appendix A – Budget

Our group has been allotted $300.00 by Colorado State University. It is still unknown how

much of that we will spend. Up to this date, we have spent a total of $9.83.

Thickness(Inch) Area(Feet) Quantity Metal Estimated Cost Total Cost

1/32 4×1 1 Aluminum $9.83 $9.83

1/4 59×12 mm 2 Aluminum $0 $0

N/A 2.4 mm 2 Aluminum

Connecter

$202.90 $0

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Appendix B – Acknowledgments

We would like to thank Dr. Branislav Notaros for creating a senior design project that will allow

our group to design and produce something tangible. Education in this field is for the most part

very theoretical. We learn about design in many of our classes, but we rarely have the

opportunity to fabricate our designs. This project allows our group to apply our education just

as we will when we become part of industry.

We would also like to thank Olivera Notaros and Nada Sekiljic for all of the project guidance,

support and extra presentation preparation that you had to put up with.

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