Intro Background Waveguide Horn Antenna Basics H-Plane Horn E-Plane Horn Pyramidal Horn ECSE:593 Graduate Lectures: Rectangular Horn Antennas Adam Santorelli Why are we interested in Rectangular Antennas? Popularity Easy to Understand Think of EM wave like a sound wave

Much like a megaphone amplifies sound waves, a horn antenna amplifies the input EM waves Rectangular Horns Fed by a rectangular waveguidge

This is the source of the EM wave

Horn reduces reflections from the open end of waveguide Reflections are reduced

Better transmission Horn is created by flaring edges of waveguide

This tapered angle allows for impedance matching image taken from [1] image taken from [2] Design Concerns Operation Frequency

Desired Gain

Aperture Size

Horn Length High gain

Ease of construction

Well behaved

Work over wide Frequency Range

Commonly used as feed for Reflector Antennas Motivation Horn antenna increases fields from waveguide like a horn amplifies sound Development of horn antenna is intuitive

Once we realize that EM radiation travels as waves Acoustic wave knowledge known for long time... The First Horn Antenna Apply this expertise to EM! 1897- Sir Jagadish Chandra Bose

operated in mm range

demonstrated radiation of waves by: ringing bells

exploding gun powder Image taken from [4] Image taken from [3] Ignored for so long... Not used until 1930s Gained popularity during WW2

Increased interest in microwave applications

Became very popular with ascent of reflector antennas Image taken from [5] EM waves confined by TIR

Wave propagates within the structure

Fields are zero at boundary surfaces Rectangular waveguide

Confinement in both x and y

Many modes can be excited at a given frequnecy

Physical size will play a role Dominant mode is TE

It is possible to excite only this mode:

Operate below cutoff frequency to ensure this criteria

Image taken from [6] Single Mode Operation Cutoff frequency is dependant on waveguide dimensions! Similar Analysis to H-plane horn

Assumed TE mode operation Rectangular Horn Defined by a rectangular aperture

Other shapers possible... Three types

H-plane

E-plane

Pyramidal Popular use in microwave range

Commonly above 1GHz Directivity Simple Concepts Governed by frequency and Aperture size: Outside our chosen design point behaviour will not be ideal Half-Power beamwidth can also be used to determine directivity Gain Related to directivity Efficiency is characterized by aperture efficiency Aperture taper efficiency, ε

Antenna efficiency, ε

Phase efficiency, ε Aperture Taper Efficiency Loss due to amplitude distribution of aperture

Defined by waveguide

Set to be 0.81 for rectangular waveguide

Antenna efficiency

About 1 for horn antennas Phase efficiency Discussed later!

Varies based on horn design t r ph Assume TE operation: 10 H-plane is along broadwall dimension x-axis

Taper waveguide along this dimension Phase Variation In H-plane aperture is larger than waveguide

waves are no longer in phase

waves arriving at edges have travelled further than those at center Phase varies exponentially: Define a factor t:

Represents phase error

Increasing phase error affects the gain Increasing factor t Increased side Lobes Decreased Directivity Increasing phase error Directivity Depends on aperture size as well... Variance in gain for specific horn length

Optimum value for A dimension for a given horn length This optimal value is given by: Can then determine optimal value for phase parameter t:

Optimal t=0.375 How does this make sense? Why is some phase error optimal?? Balance between gain from increasing aperture size and phase mismatch! Waveguide is flared along dimension in the E-plane (y-axis) Phase variation Phase errors across aperture

Quadratic phase variation Introduce phase factor s: Similar antenna behaviour for varying s Directivity Observe similar behaviour to

H-plane, but.... Note that maximum directivity for a given horn length will now occur at a different aperture size: Thus the optimal value for the phase factor is changed. Here optimal value for s=0.25 Design Options A Case Study The best of both worlds... Flare the waveguide in both planes Creates a narrow BW in both directions

Analysis is caried out by combining results Phase Variation Aperture size is larger in both x and y directions:

Phase error along both axis Directivity Aperture distribution can be considered separable: Antenna Efficiency Overall directivty is a function of corresponding directivty of E-plane and H-plane models Antenna efficiency is a function of taper and phase efficiency: Phase efficiency can be broken down into efficiency for each plane. Phase efficiency along each axis is a function of phase error parameters s and t respectively For optimum operation (s=0.25 & t=0.375), phase efficiency is 0.80 and 0.79 respectively Taper efficiency is dependant on waveguide aperture

Always using rectangular waveguide

Fixed value of 0.81 Overall antenna efficiency:

ε = 0.51 ap Develop procedure to design horn antenna to meet design requirements Requirements:

Connecting waveguide dimensions are known

Set phase error to be optimal values Why?

Want a physically realizable horn

Setting s & t to optimum values obtains shortest horn length to meet desired gain The all powerful equation.... Design steps 1. Specify desired Gain, operating wavelength and waveguide structure to be used

2. Solve for A

3. Find B. Can then solve for horn length and other horn dimensions

4. Verification Drawbacks... Performance is optimized for a single wavelength

Outside this frequency the antenna will not behave as designed

Difficult to determine behaviour Balance between effects of varying wavelength and change in phase error in aperture Design Problem Want:

G=21.75dB

f= 8.75GHz Given:

a=2.29cm

b=1.02cm Find the optimal Horn! Use the "all powerful" equation:

Solve for A first

Our design:

A=18.61cm

B=14.75cm

G=21.8 Results Solve for half-power beam width HP=12.4 HP=14.2 E H References 1. www.1389blg.com

2.http://www.q-par.com/products/horn-antennas/standard-gain-horns

3. http://amrabangalee.org/page3.html

4. http://www.setileague.org/photos/wghorn.htm

5. http://www.interfacebus.com/Electronic_Dictionary_Radar_Terms_F.html

6. http://depts.washington.edu/cmditr/mediawiki/index.php?title=Planar_Dielectric_Waveguides

7. http://www.rfcafe.com/references/electrical/rectangular-waveguide-modes.htm

8. Microwave-induced acoustic imaging of biological tissues Lihong V. Wang, Xuemei Zhao, Haitao Sun, and Geng Ku, Rev. Sci. Instrum. 70, 3744 (1999), DOI:10.1063/1.1149986

9. Fear, E.C.; Sill, J.; Stuchly, M.A.; , "Experimental feasibility study of confocal microwave imaging for breast tumor detection," Microwave Theory and Techniques, IEEE Transactions on , vol.51, no.3, pp. 887- 892, Mar 2003doi: 10.1109/TMTT.2003.808630 URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1191744&isnumber=26710 Applications Microwave induced thermoacoustic Imaging Biomed Applications Illumination of human anatomy for Imaging Communications? Military? MITAS Confocal Microwave Imaging Confocal Microwave Imaging Ridged Pyramidal Horn Antenna

Radiation of short microwave pulses Illuminate the breast with microwave radiation

Absorbed energy causes thermal expansion

Acoustic pressure wave generated Operate at 9.4GHz

Gain = 16DB

Aperture Size = 55mmx74mm

10KW of radiating Power! Image taken from [8] Used as feed for reflector antennas Image taken from [9] Antenna Parameters:

Width = 24.4cm

Height = 27.9cm

Length = 15.9cm

Weight = 1.8kg Purpose

Test experimental setup

Compare monopole and horn antenna to detect tumor in phantom models

Use EMCO model 3115 horn antenna Horn antenna is used to illuminate the breast with microwave pulse

Records reflected signal Improved performance with horn antenna vs. monopole A double ridged-pyramidal horn Questions?

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# ECSE-593: Horn Antennas

Rectangular Horn Antenna Presentation

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