Antenna Design Second Semester Report Spring 2012

Antenna Design Second Semester Report Spring 2012 By: Nate Hufnagel John James Prabhat Lamsal Prepared to partially fulfill the requirements for ECE...
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Antenna Design Second Semester Report Spring 2012

By: Nate Hufnagel John James Prabhat Lamsal

Prepared to partially fulfill the requirements for ECE 402

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 and our Mechanical Engineering consultant, Steve Johnson. 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. Research and simulation have also been done regarding Double-Ridge horn antennas which increase bandwidth at the expense of simplicity. 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 when simulated in WIPL-D. Fabrication of our Standard gain horn was achieved by Steve Johnson and included the horn and waveguide made from Aluminum, and the coaxial connector made from Teflon and Copper. The findings of the Double-Ridge horn research and simulation concluded that the majority of claims regarding performance were inaccurate and further research and design is required to develop a satisfactory Double-Ridge horn antenna. Future work regarding the Standard gain includes fixing flaws on the Standard gain antenna caused from the manufacturing process while constructing the second identical antenna required for full testing in the Anechoic chamber. Further research into Double-Ridge antennas will also take place in preparation for designing a new set of functional antennas.

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Contents Antenna Design............................................................................................................................................. 1 ABSTRACT.................................................................................................................................................. 2 Table of Figures ............................................................................................................................................. 4 I. Introduction .............................................................................................................................................. 6 II. Background and Theory ........................................................................................................................... 6 A.

Radiation Pattern ............................................................................................................................... 8

III. Summary of Previous Work................................................................................................................. 11 A. WIPL-D Simulations......................................................................................................................... 11 B. WIPL-D Results ................................................................................................................................ 18 C. Final WIPL-D Simulation Results .................................................................................................... 18 D. Double-Ridged Horn Antenna Design .............................................................................................. 21 E. Design and Simulation of the Double-Ridged Rectangular Waveguide ............................................ 22 F. Simulation results ............................................................................................................................... 24 G. Fabrication ........................................................................................................................................ 25 IV. Conclusions and Future Work .............................................................................................................. 27 A.

Conclusions ..................................................................................................................................... 27

B.

Recommendation for Continuation ................................................................................................. 28

References ............................................................................................................................................... 29 Appendix A – Abbreviations .................................................................................................................... 30 Appendix B - Budget ............................................................................................................................... 31 Appendix C – Acknowledgments ............................................................................................................ 32

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Table of Figures Figure 1: E-plane horn [1] ............................................................................................................................. 7 Figure 2: H-plane horn [1] ............................................................................................................................. 7 Figure 3: Rectangular horn [1] ...................................................................................................................... 7 Figure 4: Normalized field pattern of the directional antenna [4] ............................................................... 9 Figure 5: 2-Dimensional cut in phi plane [4] ................................................................................................. 9 Figure 6: Radiation of rectangular waveguide [5]....................................................................................... 10 Figure 7: Monopole feed into waveguide [5] ............................................................................................. 10 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 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 largest 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 Figure 19: VSWR plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located 8.62mm from the back of the waveguide................................................................................................... 17 Figure 20: VSWR plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located 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. .......................................................... 18 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. .......................... 19 Figure 25: 3-D radiation pattern and Phi cut showing HPBW of 10.24 degrees at 10GHz. ........................ 20 Figure 26: 3-D radiation pattern and Phi cut showing HPBW of 7.76 degrees at 12GHz. .......................... 20 Figure 27: 3-D radiation pattern and Phi cut showing HPBW of 7.76 degrees at 14GHz. .......................... 21 Figure 28: Initial Dimensions of DRH .......................................................................................................... 22 Figure 29: Initial Dimensions of DRH with Cavity Back ............................................................................... 23 Figure 30: Traditional DRH .......................................................................................................................... 23 Figure 31: VSWR for 10 Frequencies........................................................................................................... 24 4

Figure 32: Final Assembled Antenna (Side View) ....................................................................................... 25 Figure 33: Final Assembled Antenna (Front View)...................................................................................... 26 Figure 34: View of Antenna Interior (Copper Monopole in Background)................................................... 26 Figure 35: Coaxial Connector ...................................................................................................................... 27

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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. Throughout the year, we have designed, optimized and fabricated an X-band standard gain horn antenna that will ideally operate in the frequency range of 8 to 12 GHZ. This paper includes the design process and physical fabrication which was accomplished using WIPL-D software and help from Mechanical Engineering student, Steve Johnson.

II. Background and Theory Horn antennas are used for receiving and transmitting RF signals. Horn antennas are simply an elongated structure of rectangular waveguide. The waveguide structure is open or flared out, 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 Maintain a half-power beam width (HPBW) that is below 20 degrees over the entire operating frequency range

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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 a 3-D electromagnetic solver. We can model any type of structure in this program and we can parametrically 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. 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.

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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 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.

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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,  

 4Π

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 10

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.

III. Summary of Previous Work 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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A=60mm B=59mm z1=5.5mm

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 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.

A=78mm B=59mm z1=5.5mm

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 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. 15

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.

As the distance of the monopole from the back of the waveguide decreased, there was a consistent decrease in the VSWR.

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

Figure 19: VSWR plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located 8.62mm from the back of 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.

A=78mm B=59mm z1=5.5mm

Figure 20: VSWR plotted from 8 – 14 GHz with maximum aperture dimensions and monopole located 8.62mm from the back of 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

Length (mm)

Initial Optimized

A 61.845 78

B 45.97 59

D 11.43 11.43

E 5.08 5.08

F 70.35 59

L 325.85 345

Z1 N/A 5.5

Y1 N/A -5.08

Y2 N/A 1.4

C. Final WIPL-D Simulation 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.

A=78mm B=59mm z1=5.5mm

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

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Figure 23: Final VSWR plot with maximum value annotated.

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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10 GHz 3D plot and Phi cut:

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

12 GHz 3D plot and Phi cut:

Figure 26: 3-D radiation pattern and Phi cut showing HPBW of 7.76 degrees at 12GHz.

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14 GHz 3D plot and Phi cut:

Figure 27: 3-D radiation pattern and Phi cut showing HPBW of 7.76 degrees at 14GHz.

D. Double-Ridged Horn Antenna Design The main reason to use a double-ridged horn antenna (DRH) is because of their ability to cover a frequency range of 1 to 20 GHZ using a single antenna. DRH’s are also linearly polarized and small in size. We would have had to design multiple standard gain horn antennas to cover a frequency range that large. We first looked at designs that operate over a frequency range of 8 to 18 GHZ and implemented them in WIPL-D software. DRH antennas are used in different fields like radar communication, electronic warfare, detection system, EMC testing, satellite communication system, ground penetrating radar system, etc. Each member of our group simulated a unique DRH that operated over a frequency range of 8 to 18 GHz. To familiarize ourselves with DRH design, we researched journal papers that contained DRH designs, simulations and measurements. Our first goal was to implement their design in WIPL-D and run simulations which we would then compare to the data contained in their papers. One of the DRH designs we simulated came from a research paper from A.R. Mallahzadeh and A. Imani, department of EE, Iran [7]. In their paper they claimed that their design maintained a VSWR under 2, and a gain ranging from 14 to 19 dB.

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E. Design and Simulation of the Double-Ridged Rectangular Waveguide The initial design of the rectangular waveguide was adopted from the research paper but after the design was completed in WIPL-D software, we optimized to meet our constraints. In this design they adopted the cavity back, but in one of our design we included a flat back waveguide as well as a cavity back waveguide. The impedance is being matched with 50 Ω from connecter to the coaxial. The impedance matching is very crucial to maintain the return loss from the antenna. In order to achieve low VSWR, the distance between the starting of ridges in antenna and probe spacing were optimized. The spacing has to be optimized because it affects the gain of an antenna. The initial dimension of the horn designed in WIPL-D is in the figure below. The dimension “L” is the length of tapered part of an antenna, W is the width of the tapered part, “Lw” is the length of the waveguide from the back of the cavity, “A” is the width of the rectangular double ridge waveguide.

Figure 28: Initial Dimensions of DRH

The second design included the back cavity on the waveguide. The back cavity on the waveguide helps maintain a low VSWR at the lower frequencies of operation. The shape of the cavity is pyramidal. The cavity dimensions later were optimized in an attempt to keep VSWR below 2. The parameters of the DRH with cavity back are shown in the figure below.

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Figure 29: Initial Dimensions of DRH with Cavity Back

The dimension “L” is the length of the tapered section of DRH, “Lw” is the length of waveguide, “Lb” is the length of the back cavity, “Lc” is the length of pyramidal side of back cavity and “Ld” is the width of the extended back cavity. The third design we implemented was a traditional DRH. The parameters of the traditional DRH are shown in the figure below [8].

Figure 30: Traditional DRH

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The dimension “L” is the axis of the antenna opening from the waveguide, “la” is the length of the waveguide, “lb” is the length of the back cavity extension, “b” is the height of the waveguide, “a” is the width of the waveguide, “b’” is the height of the height of the horn aperture, “a’” is the width of horn antenna. As, in the previous model the waveguide is extended back in order to achieve the desired VSWR. The paper talks about constructing a polarizer layer in front of DRH antenna results in lowering the VSWR below 2. But we did not use this technique because the program we were using does not have this option.

F. Simulation results All three DRH antenna designs were implemented in WIPL-D. 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 also known that as the dimensions of the aperture increase, the gain increases as well. Distance of the monopole from the back of the waveguide was swept in an attempt to obtain a desirable VSWR. Increasing the diameter of the monopole led to a significant decrease of VSWR for all cases we studied. After performing numerous simulations and sweeps we were never able to validate the claims about the antenna characteristics documented in the papers we used as reference. With the optimized dimensions, we came up with 5.26 VSWR, and around 10 dB of gain along the entire frequency range of 8 to 18 GHZ.

Figure 31: VSWR for 10 Frequencies

There are various reasons why we were not able to match the simulation results presented in the papers we referenced. We are not using the same software and we are still working with different 24

monopole lengths. The results we obtained do deserve further study due to their extreme difference from those documented in the papers.

G. Fabrication After obtaining the final results from WIPL-D, we began fabrication in collaboration with Steve Johnson from the Mechanical Engineering department. After a few trial prototypes the following physical model was obtained. The horn was constructed with four, thin Aluminum sheets bolted at the edges and the waveguide was fabricated using ¼” Aluminum. The coaxial connector attached to the waveguide was made using Teflon for the dielectric and Copper for the inner conductor which extends into the waveguide as the exciting monopole. Due to time constraints and availability of machines necessary for fabrication, the final details and flaws of the Standard gain horn have yet to be addressed. This includes connecting the necessary outer conductor of the coaxial connector to the waveguide and polishing of the interior surfaces of the entire antenna.

Final Fabrication Results: The following two figures shows the final assembled antenna after fabrication. In order to secure our antennas to the testing equipment in the Anechoic chamber the rear of the antenna is attached to a pre-fabricated gear mount that will allow the antenna to rotate while testing.

Figure 32: Final Assembled Antenna (Side View)

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The coaxial connector can also be seen here attached to the waveguide. Our connector which was fabricated from Teflon and Copper was designed so that the height of the inner conductor (exciting monopole) can be adjusted.

Figure 33: Final Assembled Antenna (Front View)

The following figure shows the interior of the antenna with the waveguide at the exterior. The exciting, copper monopole can clearly be seen here protruding from the waveguide wall. This monopole, which is attached to the inner conductor of the coaxial connector, has adjustable height to allow for better impedance matching.

Figure 34: View of Antenna Interior (Copper Monopole in Background)

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Figure 35: Coaxial Connector

IV. Conclusions and Future Work A. Conclusions For the Antenna Design team, this yeah has been somewhat successful. 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 and we have learned a lot about antenna design. At the beginning of the yeah, 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. Steve Johnson, a Mechanical Engineering student at Colorado State University fabricated our first standard gain horn prototype. Initial measurements with a network analyzer show that VSWR stays below 3 for the frequency range it was designed for. We believe that with a few minor mechanical changes we will come very close to matching our simulation results.

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B. Recommendation for Continuation The Antenna Design project is unique because of its focus on electromagnetic theory. It requires a group that has a desire to study antenna theory, simulation and fabrication. If the goal of this project is to fabricate antennas, this project should either include a mechanical engineering student or be discontinued. Steve Johnson, a mechanical engineering student at CSU was nice enough to donate some of his free time to our group, but in the end it was only enough to get one standard gain horn antenna prototype built. If the goal of this project doesn’t involve fabrication of antennas, then this project should be continued by students that are interested in electromagnetics, antenna theory and simulation. The skills learned during the course of this project could be valuable for students who seek employment in the RF industry. If this project is continued without a full time mechanical engineering student, the project goals will have to be redefined. The best course of action for a group in this case would be to ignore standard gain horn antennas and delve into double ridged horn antenna research and design. Our group attempted to simulate three double ridge horn antenna designs that were presented in papers and we were unable to replicate the simulation data presented in those papers. We also attempted our own double ridged horn antenna designs and were unable to design any double ridged horn antennas with satisfactory characteristics. A future group could definitely expand upon our double ridged horn design and simulation results. They could also investigate claims made in papers regarding double ridged horn antennas through simulation in WIPL-D software. If this project is continued with a full time mechanical engineering student the group should maintain the project goals that were established this year. It would be best if they design and fabricate a standard gain horn antenna first. The standard gain horn is the best antenna to start with because of their relatively simple geometry, which makes them the easiest to optimize and fabricate. The group could then choose to design either standard gain horn antennas or double ridged horn antennas. The benefit of going with double ridged horn antennas is that the group can cover a much wider frequency range with a fewer amount of antennas. This will save the group money because fewer materials would be required during fabrication. If the group took this route, they would see their most significant savings in connector costs. If the group decided to go with standard gain horn antennas, the cost of building multiple sets may be too much. It would require around 7 different standard gain horn designs to cover the 1 GHz to 20 GHz frequency range but it would require only 2 different double ridged horn designs to cover that same frequency range. If money isn’t a concern then the group should come up with desired gain, VSWR, and HPBW characteristics that would then dictate whether they design standard gain or double ridged horn antennas.

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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::invokeTyp e::lms::launchState::goToEBook::scenarioid::scenario5::logoutplatform::1027::platform::1027::s cenario::5::globalBookID::CM39946096::userID::1540208::hsid::d5f247464d18f83e8fc6a9bf37 c8704a

[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::invokeTyp e::lms::launchState::goToEBook::scenarioid::scenario5::logoutplatform::1027::platform::1027::s cenario::5::globalBookID::CM39946096::userID::1540208::hsid::d5f247464d18f83e8fc6a9bf37 c8704a [6] C. Bruns, “Analysis and Simulation of a 1 – 18 GHz Broadband Double-Ridged Horn Antenna,” IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, February 2003. [7] A.R. Mallahzadeh & A. Imani, Double-ridged Antenna for Wideband Applications, no. 91, pp. 273–285, 2009. [Online]. Available: http://www.jpier.org/PIER/pier91/17.09022104.pdf. [Accessed Apr.29, 2012]. [8] A.R. Mallahzadeh, A.A. Dastranj & H.R. Hassani, A Novel Dual-polarized Double-ridged Horn Antenna for Wide Band Applications, no. 1, pp. 67–80, 2008. [Online]. Available: http://electronix.ru/forum/index.php?act=attach&type=post&id=15463. [Accessed Apr. 29, 2012].

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Appendix A – Abbreviations Double-Ridged Horn = DRH Half-Power Beamwidth = HPBW Super High Frequency = SHF Voltage Standing Wave Ratio = VSWR

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Appendix B - 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 $52.18. Thickness(Inch)

Dimensions

Quantity

Material

Total Cost

1/32

4 ft. x 3 ft.

1

Aluminum

$29.83

1/4

59×12 mm

2

Aluminum

$0

1/4

5 in. x 5 in.

1

Teflon

$22.35

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Appendix C – Acknowledgments First and foremost we would like to thank Steve Johnson for donating his free time and expertise. He is responsible for the quality of our prototype. We would like to thank Dr. Branislav Notaros for creating a senior design project that allowed 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 allowed 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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