V

|Team 4: Adam Winterstrom | |
|Cheng-yu Chang | |
|Thuan Dinh |EE175WS00-4 |
| |June 14,2000 |

Quarter Wavelength Microstrip Antenna for Communication between Vehicles

Final Report

Technical Advisor: Alex Balandin

Project Advisor: Barry Todd

Table of Contents

Executive Summary………………………………………………………………..3

Keywords……………………………………………………………………………3

Introduction………………………………………………………………………….4-6

Problem Statement…………………………………………………………………6

Possible Solutions…………………………………………………………………..7-8

Solution……………………………………………………………………………….9-13

Engineering Analysis………………………………………………………………..14-15

Discussion of Results………………………………………………………………..16-25

Conclusions and Recommendations……………………………………………….22-23

References……………………………………………………………………………25-26

Appendix………………………………………………………………………………26-46

Executive Summary:

A low profile, omni-directional, car-mounted antenna that can withstand harsh road and weather conditions is needed for communication between vehicles at 469.2 MHz. A new state-of-the-art printed circuit antenna is proposed that can actually be integrated into the vehicle body during production and become invisible. This low cost antenna is only 8 x 10 centimeters in area and less than a half centimeter thick. A standard BNC connector is used for easy receiver connection with coaxial cable. The microstrip antenna, made of common copper plated FR4 substrate, was modeled and designed using transmission-line analysis [3]. The normally half-wavelength patch antenna was modified using copper-shorting pins to cut the size of the antenna in half, making it a quarter-wavelength patch antenna. The antenna was tested in a large grass field using a MOTOROLA transmitter passing a 469.2Mhz signal to an ICOM communications receiver (IC-R8500). The small antenna (10x10x.41 cm) under test exhibited an omni-directional far-field radiation pattern in the H-plane with only a +/- 2.5 dB variations. The over-all gain of the antenna was -12dB over an isotropic radiator.

Keywords:

▪ Microstrip

▪ Patch

▪ Resonator

▪ Quarter-wave

▪ Small antenna

▪ Omni microstrip antenna (OMA)

▪ Dielectric substrate

▪ Omni-directional

▪ Transmission line model

▪ Conformal

▪ Low profile

▪ Electrically short antenna

▪ Strip line

▪ Shorting pins

▪ Probe-fed

▪ Printed circuit antenna

▪ Low-gain-antenna

Introduction:

Summary of the problem

There is a consumer demand for a small, omni-directional, low profile, antenna that needs to be able to with stand off-road vehicle use; in other words virtually any imaginable environment. Especially important is the durability since it will encounter very high vibration levels and lots of scrapping from trees and bushes. Since the antenna application is for short-range (less than 1km) communication between vehicles, a narrow bandwidth (around 10MHz), low gain and mediocre efficiency can be tolerated.

History of the Problem

Presently CB radios (28Mhz) are being used for off-road vehicles. The antennas for these radios are very long and unattractive. They have a tendency to get pulled off or bent by low hanging trees and garage doors. At a higher frequency of 469.2 MHz a microstrip antenna can be used. This type of antenna is very low profile, conformal, and rugged, which makes it attractive for off-road applications. So far the only microstrip antennas used for vehicles (that we have knowledge of) is a conformal antenna that was used on armored vehicles for military satellite communication [2].

History of Microstrip Antennas

Microstrip lines were first proposed in 1952 but it wasn’t until 1974 that microstrip antennas got a lot of attention and began being used for military applications. So far these antennas have mainly been used on aircraft, missiles, and rockets. Just recently they have been expanded to commercial areas such as mobile satellite communications, the direct broadcast satellite (DBS), and the global positioning system (GPS) [1].

Motivation and Goals

Coming into this project we knew virtually nothing about antennas except that they were used in wireless communication. We wanted to know more about the field of antenna engineering. How they related to what we had been learning in the University, how they worked, why there were so many different types of antennas, and why the shapes and sizes of antennas varied so much. Our goal was to be able to design, build and understand simple antennas for various applications. We learned the importance of antennas in a Webster’s dictionary definition; antenna- one of the sensory appendages on the heads of insects and most other anthropoids. That definition says it all, just as our senses; hearing, seeing, feeling, smelling, and tasting, are important to us so is the antenna important to wireless communication. Without the antennas wireless communication would not be possible.

A Forecast of Results

We believe our design will meet all of the desired specs needed for the vehicle antennas. We expect the customer and consumer will be pleased with the outcome, and a demand for microstrip antennas in other consumer markets will result. Although efficiency and bandwidth test cannot be performed due to a lack in testing equipment, an accurate estimation will be calculated.
What the Reader Will Find in the Report. This document provides the detailed design, testing results and analysis of a small (10x10cm) quarter-wave antenna. The antenna was designed slightly above the specification size but it is predicted that a production model could be manufactured at 8x10 cm with better results if an alternate substrate is used. The contents of this report include: an overview of microstrip antenna design parameters including the function of each component, the design of four patch antennas (one designed to meet the specs and the others used for comparison and analysis); detailed test procedures including drawings of the test set-up; test results of the far field E and H planes; polar plots of the E and H planes that show the gain of the antenna compared to a reference dipole antenna; a discussion of how to improve the prototype; solution methods and derivations; computer programs and printouts with descriptions; hardware details; and a bibliography.

Problem Statement:

One of the hottest vehicles on the market today is the Sports Utility Vehicle (SUV), these vehicles are built for off-road, rugged terrain. Though they are made for hard-core four-wheel drive use, it is not smart to go four-wheel driving alone. Most people go in teams that way when someone gets stuck or breaks a part they have other people who can get them UN-stuck or tow them if necessary. Communication between cars is necessary; this is why most 4-wheelers have Citizens Band (CB) radios. The problem with these radios is their conversation can be heard by anyone who wants to listen, and require very long wire antennas. These antennas are often bent or ripped of the vehicles when going through tight spots with low hanging branches from trees and bushes. This has created a demand for a new antenna. The four wheelers need a small, Omni-directional, small range, low profile, economical, rugged, efficient, and easy to mount antenna. It should have a gain of at least 1db, a rather narrow bandwidth, and operate in some frequency higher than 28MHz but less than 2GHz.

Possible Solutions:

The problem is for a mobile, Omni-directional, small range, low profile, rugged, efficient, inexpensive, easy to mount antenna, that has a gain of 1db and operates in the specified frequency range. With these factors in mind, we first looked at many of the different types of antennas that exist. Then we threw out all of the ones that could not possibly work because of certain factors such as being too big, too directive, and too expensive. Then, we narrowed our possible solutions down to the three antennas that we felt could meet our specifications with the best results and lowest cost (This process can be seen on our analysis of possible solutions). The antennas that we considered are: ▪ A reduced height helical whip antenna, which would be approximately 2" in length have a flexible shaft, and would be damage resistant and fully weatherized. ▪ A phasing coil whip antenna, which would create great efficiency at a low cost by essentially creating two antennas. ▪ A microstrip antenna, which would be very small, low profile, could be conformed to the shape of the car and would be the cheapest to manufacture. Any one of these solutions would be a great choice and it would be impossible to argue one of them as the best choice since it really depends on consumer's preference. However, we choose to go with the microstrip antenna.

|Solution |Feasibility |Mounting |Cost |Arrow Dyn. |Directivity |Time |Comment |
|Microstrip Antenna |Very possible |Very easy, |Definitely |Very good |Flexible |Possible to |Low weight, low |
| | |could be |very low cost | | |Finish with |profile with |
| | |attach to | | | |Time limit |conformability, and |
| | |anywhere | | | | |low manufacturing |
| | | | | | | |cost |
|Slot Antenna |Very Possible |Not easy |Low cost |Good |Flexible |Possible to |Low gain, not |
| | | | | | |Finish with |practical, require to|
| | | | | | |Time limit |input slot in the car|
|Horn Antenna |Very Possible |Very hard |Expensive |Bad |Highly |Long |Very directive, not |
| | |Too big | | |directive | |good for |
| | | | | | | |omni-directional |
|Wire Antenna |Very Possible |Easy |Very low cost |Ok |Omni |Short |Very common and |
| | | | | |directional | |practical. |
| | | | | | | |Not challenging |
| | | | | | | |Too long for specs |
|Dipole Antenna |Very Possible |Easy |Low cost |Ok |omni- |Short |Possibility, |
| | | | | |directional | |Not challenging |
| | | | | | | |Too long for specs |
|Helices Antenna |Possible | need to be |Very low cost |Bad |Highly |Short |Narrow Bandwidth, |
| | |mounted to PCB| | |directive | |Rugged construction.|
| | | | | |Need | |Not enough work |
| | | | | |omni-directiona| | |
| | | | | |l | | |
|Parabolic Reflector |Possible |Very hard and |Too expansive |Very Bad |Highly |Long |Not practical |
| | |not practical | | |directive | |Too big |
|Phase Coil Antenna |Possible |Very easy and |Low cost |Very Good |Omni- |Possible to | practical choice, |
| | |most common | | |directional |Finish with |but too common. We |
| | | | | | |Time limit |want a new design |
|Reduce Height |Very Possible |Very easy |Very low cost |Very Good |Omni- |Possible to |Omni-direction, |
|helical whip | | | | |directional |Finish with |Flexible shaft, |
| | | | | | |Time limit |looks good for this |
| | | | | | | |problem |

Table 1 This table shows various different types of antennas and eliminates ones that would not be suitable for the problem at hand. The most suitable antennas are Microstrip,Phase Coil, Reduced whip

Solution:

[pic]Fig. 1 Basic Model of Microstrip Antenna. Shows the fringing electric fields at the two ends due to the dicontinuites of the patch
Overview of the Design Solution The solution chosen for this problem is a rectangular quarter-wave microstrip patch antenna that can be mounted to any side of a vehicle depending on user preference. The Microstrip patch is modeled as a transmission line that radiates from its ends Fig1. The antenna is fed with a coaxial cable via a BNC connector. A small ground plane gives the antenna its omnidirectional pattern in the H-plane. The structure of the patch antenna is very simple. The complexity in design comes in the equations modeling the antenna (see Apendix E). Once the antenna is modeled it is easy to change the various parameters to get the desired characteristics. The characteristics of the rectangular patch antenna that can be adjusted or changed to achieve the desired specifications are: length of patch, width of patch, thickness of the patch, height of substrate, dielectric constant of the substrate, loss tangent of the substrate, feed type, feed point, conductivity of patch, and the size of the ground plane. The important properties of interest that the features above control are: impedance, resonant frequency, bandwidth, efficiency, beamwidth, directivity, gain, and polarization.

Impedance and Resonant Frequency

The input impedance of any antenna is very important. For maximum efficiency the input impedance must match the feed-line impedance, which is 50ohms in most cases. When the length of the antenna is approximately a half-wavelength the impedance of the antenna becomes entirely real. Since the wavelength is directly related to the frequency (E.1) the patch is said to be at resonant at this frequency [1]. The impedance of a half -wave microstrip patch is zero in the center of the patch and becomes maximum at the edges of the patch length. Therefore impedance matching can easily be accomplished by insetting the feed point of the patch at the point of desired impedance (E.5). The feed inset can be done in several ways; the two most common methods are microstrip fed and probe fed patches. Probe fed patches tend to produce less cross-polarization at the feed point making them more efficient [8].

Bandwidth

The major limitation to microstrip antennas are there narrow bandwidths [10]. The bandwidth is defined as the frequency range over a certain Voltage Standing Wave Ratio (VSWR) (E.8). Since the bandwidth is a function of the tolerable mismatch, it can very depending upon the application. For our application a VSWR of 2.5:1 will be tolerated. The VSWR was not mentioned in the original specifications, but it is one of the most important parameters in antenna design. The bandwidth of a patch is increased by increasing the size of the antenna. The length of the patch is determined by the resonant frequency and dielectric constant (E.4). Since the frequency is usually predetermined, using a substrate of lower dielectric constant would be the only way to increase the length and consequently the bandwidth. Of course from E.22 there is also the width and height of the patch that can be increased for better bandwidth. In fact when designing a microstrip patch you always want the width to be as wide as possible, the thickness as thick as possible (without exciting higher-order modes E.7) and the dielectric constant and loss tangent as low as possible [3]. If the Bandwidth is still not large enough a multilayer patch also known as multi-band patch can be constructed. Multi-layered patches are discussed in detail in [1,] and [14].

Efficiency

The total efficiency of the antenna (E.20) is affected by the resistively of the patch, loss tangent, height, width and the feed matching network. To get the most radiation efficiency out of your antenna you want the lowest loss tangent and the lowest receptivity that is available in materials [3]. You also want the width and height as large as possible. The over-all efficiency of your antenna is very much depending on the feed matching network. In fact most of the efficiency in microstrip antennas is lost in the feed network [1]. One of the on-going researches in patch antennas is impedance-matching technique for increasing bandwidth and efficiency [10].

Beamwidth, directivity, and Gain

Microstrip antennas are low-gain antennas. This is due to the wide beamwidth of the antennas. The beamwidth is what characterizes the directivity an antenna [1]. Microstrip radiation patterns are slow functions of the patch dimensions and substrate properties. The factors that effect the patterns are the patch width, substrate dielectric constant, and, to a lesser degree substrate height. The antenna polarization is linear with the E-field parallel the patch length. Therefore the E-field lies along the length while the H-plane is parallel to the width [1]. The wider the width the more narrow the beamwidth in H-plane (E.12). The H-plane radiation is a result of fringing fields at the two edges along the length. As the width increases the edges get further apart. The radiation from these fields adds up to produce a far-field pattern with a maximum broadside to the patch [1]. The same thing happens for the E-field, but the E-field is changed by varying the dielectric constant (E.11). Most microstrip patch patterns have the same general shape if you assume an infinite ground plane and no higher order modes are excited (E.7). Of course there is no such thing as an infinite ground plane, and other factors such as ridges and bumps will play a roll in the actual pattern. For finite ground plane patches the energy that radiates along the ground plane can be scattered in many directions by the edges. It then combines with the direct radiation from the patch [1]. For very small ground planes (less than a wavelength), ripples are introduced into the pattern over a wide range of angles and a lot of radiation spills onto the backside of the ground plane. The effect of a finite ground plane is presented in [5] where a good agreement between theory and measurement was predicted using Geometrical Theory of Diffraction.
Quarter-wave Microstrip The above discussion applies for both half-wave and quarter-wave patches with a few small exceptions. A quarter-wave patch is possible since the electric field under the patch is oriented vertically between the patch and ground plane and has an approximate co sinusoidal variation with the maximum values at the edges and the center being zero [1]. Since the electric fields are zero at the center a short circuit can be placed at the center, and the basic operation will not be affected. These patches are used insinuations where there is not enough room for a full sized patch. These patches also have a broader E-plane pattern since the patch now only has one radiating edge along the length. Being smaller than the normal patch, the short-circuited patch bandwidth is only about 80% of that of the half-wave patch [1]. The short circuit can be accomplished using shorting pins that connect the radiating patch and ground plane. The size and number of pins is determined by E.9. This equation also shows that pins have some effect on the patch length.

Designing the Prototype

From the above discussion it is clear that to get the most out of your design at a particular frequency the patch should be as wide as possible, substrate as thick as possible, and dielectric constant and loss tangent as low as possible. However in our case the antenna element is constrained to be mounted within a small volume and yet the antenna gain is desired to be as high as possible. This case calls for compromises to be made within the bounds of the design while maximizing the bandwidth and efficiency. The biggest challenge in this problem is the 10x8 cm size constraint and the 1dB gain requirement. We were not able to design a half-wave patch to meet the size specification so our first compromise was to design a quarter-wave patch. The next compromise was the choice of FR4 substrate. We choose to use FR4 substrate because of its availability and the short time schedule we were under. Although the FR4 dielectric constant (er=4.7) was suitable for our needs the loss tangent (loss=. 01) was not. We expected a very low efficiency (E.20) in our prototype but we knew that it could be greatly improved in production by using a substrate of lower loss tangent that is available from various companies. With the dielectric constant and loss tangent chosen the only other parameters that we could vary were the width and thickness. Using the equations and concepts discussed in the design solution a quarter-wave patch using shorting pins was designed. The equations were implemented in a Matlab program (Appendix F) that was organized in a systematic fashion to help the user design a patch antenna to meet certain size constraints. To insure that the antenna would not excite higher order modes, our thickness was limited to E.7. The width of the prototype is the maximum width 8cm if the ground plane is trimmed. Trimming the ground plane would not have much effect on the radiation pattern of the already very small ground plane. The feed point of the antenna was determined from E.5

Engineering Analysis:

[pic] Fig. 2 This block diagram describes our approach to designing and implementing a microstrip antenna to meet the specs of the problem.

Antenna Design (Pre-Software Stage) ▪ Basic Antenna parameters [1]. ▪ Microstrip special parameters (substrate dielectric constant and loss tangent, patch shape and dimensions, substrate height, conductor conductivity, feed location, input acceptable “vswr” for Bandwidth calculation) [3].
Antenna Design (Software Stage) ▪ Microstrip antenna parameter equations [3] . ▪ Write programs to implement equations and plot results. ▪ Make sure programs meet spec requirements ▪ Mechanical Design using Protel.

Antenna Design (Hardware) ▪ Prototype fabrication of Mechanical design

Antenna Testing

▪ Test antenna using test procedures ▪ Record all data and plot results. ▪ Record all unacceptable errors

Antenna Final Design

▪ Revise software to account for error ▪ Fabricate revised design if there is time. ▪ Test new design (continue until results are exceptable).

Fig. 3 The picture below shows all of the components of a quarter-wave microstrip patch. The feed method shown is slightly different than our prototype. This picture actually shows how we feed the larger ground plane antennas in Appendix C. Notice the three layers of substrate used to achieve a thicker patch. There is shorting pins that are soldered to the patch and ground plane. The center conducting wire of the BNC connector is connected to the patch and the nut used fasten BNC connector is used for the ground connection.

Discussion of Results: evaluation of Design

Prototype Relative to the Production Model

The size of the prototype (10 x 10 x 0.41 cm) is slightly larger than the production model (10 x 8 x 0.41). For production the shorting-pins and probe-feed could actually be etched, adding to the efficiency of the antenna. The original model also uses three layers of substrate to achieve a thickness of .41cm, during production a single thick layer should be used to reduce the losses due to the glue used to hold the substrate together. Also during production a cover-layer can be placed over the patch for added protection. For the prototype FR4 substrate (er=4.7, loss tangent = .01) was used because of the availability and cost. For large-scale production it is suggested that a substrate of lower loss tangent be used. A good alternative would be RO3006 (er=6.15, loss tangent =. 0013) from Rogers Corporation (See appendix G). Although the dielectric constant is slightly larger, the loss tangent is much smaller than that of FR4. This change would actually decrease the length of the antenna by approximately 1 centimeter and increase the efficiency by 30%. The increase in substrate cost would be a small price to pay for the added efficiency. Depending on the receiving device being used for communication, a different connector may be used instead of a BNC-Female. If all of the changes above are incorporated into the production models a significant increase in efficiency would be made, and the antenna gain would begin to approach zero.

Table 2. Below are the prototype characteristics using FR4 and the changes that would result from using RO3006. The dimensions were calculated using the Matlab program in Appendix F.

|Parameters |FR4 |RO3006 |
| | | |
|Dielectric Constant |4.7 |6.15 |
|Loss Tangent |0.01 |0.0013 |
|Patch width (cm) |8.2 |8.2 |
|Patch Length (cm) |7.654 |6.15 |
|Patch thickness (cm) |0.0035 |0.0035 |
|Antenna Length (cm) |10 |8 |
|Antenna width (cm) |10 |10 |
|Antenna thickness (cm) |0.41 |0.41 |
|Efficiency (%) |52.7 |81.22 |
|Bandwidth (MHz) |7.86 |4.47 |

Results

Fig 4 The polar plot below shows the measured E and H plane radiation patterns that resulted from the prototype antenna. Notice how close the H-plane pattern is to an Omni-directional pattern. This is the result of a very small ground plane. See Appendix D for an analysis of the effects of a small ground plane.
The null that results in the E-plane is also an expected result due to a small ground plane [5]. Both planes have there maximum gains in the front broadside to the patch at around zero degrees. The numbers on the plot correspond to the difference between the minimum and maximum gain, not the actual gain. The maximum gain in the plot is –12dB.
Table 3. This table shows the gain of the prototype over an isotropic radiator (reference dipole). The maximum gain of –12 dB in the H-plane corresponds to the maximum point in Fig 4, and the minimum gain of –37 in the E-plane corresponds to the Minimum point in Fig.4.

|Degree |E-plane Gain db |H-plane Gain db |
|0 |-17 |-12 |
|10 |-17 |-12 |
|20 |-17 |-12 |
|30 |-17 |-12 |
|40 |-17 |-12 |
|50 |-16 |-12 |
|60 |-16 |-12 |
|70 |-16 |-13 |
|80 |-16 |-13 |
|90 |-15 |-13 |
|100 |-15 |-13 |
|110 |-15 |-14 |
|120 |-15 |-14 |
|130 |-15 |-16 |
|140 |-15 |-16 |
|150 |-15 |-16 |
|160 |-18 |-16 |
|170 |-18 |-17 |
|180 |-21 |-17 |
|190 |-23 |-17 |
|200 |-28 |-17 |
|210 |-37 |-17 |
|220 |-31 |-17 |
|230 |-22 |-17 |
|240 |-20 |-17 |
|250 |-18 |-17 |
|260 |-18 |-16 |
|270 |-18 |-16 |
|280 |-18 |-16 |
|290 |-19 |-16 |
|300 |-19 |-15 |
|310 |-19 |-15 |
|320 |-19 |-15 |
|330 |-18 |-15 |
|340 |-18 |-14 |
|350 |-18 |-14 |
|360 |-17 |-13 |

Strengths and Weaknesses

The strengths of this antenna are its durability, small size, low profile, conformability and low cost. The small size and low profile make the antenna aesthetically pleasing to consumers. Being conformable would also allow car manufactures to implement the antennas into their automobiles body structure making them invisible and less prone to vandalism or damage from off-road use. The durability of the antennas makes them suitable for extreme situations, including vibrations, wind, rain, snow, and temperature. All this features are at a very low cost. The antenna does have its weaknesses however. The small bandwidth and low efficiency of the antenna are not desired features. Although the bandwidth can be increased if needed, it will consequently increase the thickness of the antenna. The original specifications for problem don’t indicate a specific efficiency, but it is always desired to have as much efficiency as possible.

Table 4. Prototype Comparison to specifications

| |Specs |Theoretical |Prototype |
|Frequency |469.2 MHz |469.2 MHz |469.2 MHz |
|Pattern |Omni |Broad beamwidth |Omni |
|Dimensions |10x8x5 cm |10x10x.41 cm |10x10x.41 |
|weight |.5 kg max |******* |0.091 Kg |
|mounting |Adhesive |******* |Adhesive |
|Range |1km |******* |******* |
|impedance |50 ohms |50 ohms |******* |
|Bandwidth |10 MHz |7.65 MHz |******* |
|Gain |1.0 dB |******** |~12dB |
|Temp |-32 to 110 |******** |Yes |
|Wind Survival |150 mph |******** |Yes |
|Humidity |95% |******** |Yes |
|Connection |Comp. W/ Receiver |******** |BNC |
|Radiation Efficiency |Non spec |52.7% |******** |
|VSWR |Non spec |2.5:1 |******** |
|Patch Q |Non spec |59.68 |******** |

Specifications not met by prototype

Their where two specifications that we did not meet with our prototype: size and gain. Their where also three specifications that we were not able to measure: range, input impedance and bandwidth. Three other parameters that where not motioned in the original specifications but are very important in any antenna design are also not measured: Overall efficiency, the total patch Q, and VSWR. Of the two specifications that where not met only one is unattainable. The size is not a problem and it was already mentioned that by trimming the edges or by using a different substrate, RO3006, our size would meet the specs. The gain however is not a realistic parameter. The only way to get a gain above 0dB for a microstrip patch antenna is to construct an array of antennas [12]. This would type of antenna would not meet our size specs. We can improve our gain though, so that it would approach zero dB, by increasing the efficiency of the antenna, which can be accomplished by using a more efficient substrate (RO3006). The three specifications that we were not able to measure: range, input impedance, and bandwidth, can all be calculated theoretically using the equations in Appendix A. The range was not calculated because it depends on the power being transmitted by the transmitter, which we do not know. The input impedance and bandwidth where calculated and are shown in table 4. The input impedance was attained by insetting the feed point at the point of 50 ohms (E..5). The bandwidth was calculated to be only 7.65 MHz (when VSWR = 2.5) and even lower 4.4 MHz if RO3006 substrate is used. This is not a problem though because the bandwidth can be increased by constructing a multi-layered patch [1]. We did not attempt to do this with the prototype because we did not have the equipment to measure the bandwidth. The overall efficiency, the total patch Q and the VSWR are all very important antenna design parameters that where left out of the original specifications because of our lack of antenna knowledge at the beginning of this design project. We later defined the VSWR to be 2.5:1. We where able to calculate the efficiency and Q-factor values theoretically using the equations in Appendix E, but we where not able to measure the actual values because of a lack of testing equipment. It can be seen in table 4 that our efficiency is very low (52.7%) but table 3 shows that if we use RO3006 substrate we can increase our efficiency by almost 30%. If all these changes are incorporated into a production model the only specification that could not be met is the gain of 1db. However a gain of 1db is not needed for this application nor would be possible with our solution.

Conclusions and Recommendations

This new antenna may have a profound affect to the sport of off-road driving. With an antenna designed specially for their passion, off-roaders now have a long awaited alternative to the unpleasant CB antennas at a low cost. The next step is a compact, low cost receiving and transmitting device for 469.2 MHz that would allow for the switch to the new antenna. At this point the new microstrip antenna has only been built on an FR4 dielectric substrate at the frequency of 469.2 MHz. This is actually a low frequency when it comes to microstrip antennas. Usually microstrip antennas are built for frequencies in the GHz range due to the large size considerations at low frequencies. The results of the FR4 substrate were mediocre and it was suggested that a different substrate, RO3006, be used for better efficiency. There is however another alternative that we would have liked to pursue had we had the time that involves the use of a Ferrite substrate. The ferromagnetic substrates in [6] and [7] posses both dielectric and magnetic properties adding to the complexity of analysis but reducing the size of the patch by a factor of 3 and increasing the bandwidth by over 2 percent (a typical patch has a 1% bandwidth). The goals of this project were achieved. We all learned a lot about antennas and how to design them for different applications. We understand the importance of antennas in the field of engineering. Although our antenna was not as elaborate or as efficient as we had dreamed from the beginning, it was a groundbreaking point for us and for UCR. We are proud to have laid the foundation for antenna research at UCR and we hope that it will continue in the following years with larger and more complex projects.

Recommendations for Future Antenna Projects

Although the University was very generous in providing us with expensive equipment, we were still very limited to what we could test. It is our suggestion that the University invest even more into test equipment to provide the following: A variable frequency transmitter so that bandwidth characteristics and resonant frequency can be tested, and A VSWR meter (The allowable VSWR of an antenna is one of the most important design parameters),

Equipment Setup Procedure:

1. Connect 12V DC Battery to Receiver. 2. Once the Transmitter has power, it continuously sends out a signal of 469.2 MHz. 3. Place the Transmitter on a step latter to reduce interference. 4. Connect Receiver with 12V DC Battery and press power button. 5. Set the frequency to 469.2 MHz on the Transmitter. 6. Connect the output end of Attenuator to the Receiver. 7. Record the internal attenuator settings of the receiver. 8. Connect input end of Attenuator to RG58 cable. 9. Connect RG58 cable to the antenna under test. 10. Mount the antenna to the angle varying testing apparatus. 11. Separate the transmitter and receiver approximately 50 feet apart. 12. Ready to test.
Fig 5. Test equipment set up. [pic]
Test Procedure: 1. Align the test antenna to read 0degrees on the protractor, when the antennas zero degree point is pointed directly at the transmitter (Broadside for Microstrip antennas). 2. Continuously adjust the Attenuator until it reads your chosen reference point on the receiver’s analog meter (we used 5dB as our reference point). 3. Record the attenuator readings at every 10-degree turn of the antenna (Use smaller steps for better-defined pattern). 4. Actual gain will be the reference antenna readings subtracted from the antenna under test. 5. Measure both the E and H planes. 6. All testing people should duck below the height of antenna. 7. Do more than one trial and average out all the trials for best results.

Note. It helps to have at least two people to do the measurements. One person adjusts the Attenuator and reads the receiver, and the other person adjusting the antenna. For best results a large wide-open field should be used.

References:

[1] Robert A. Sainati, “CAD of Microstrip Antennas for Wireless Appliccations,” 1996

[2] K. Fjuimoto, A. Henderson, K. Hirasawa, J. R. James, “Small Antennas, “ 1995, pp. 242.

[3] A. D. Krall, J. M. McCorkle, John F. Scarzello, A. M. Syeles, “The omni microstrip antenna: A new small antenna,” IEEE Trans. Antenna and Propagation, vol. AP-27, No. 4, pp. 85-853, November 1979.

[4] J. Watkins, “Radiation loss from open circuited dielectric Resonators,” IEEE Trans. Microwave Theory Tech., pp. 637-639, Oct. 1973.

[5] John Huang, “The finite ground plane effect on the micrstrip antenna radiation patterns,” IEEE Trans. Antenna and Propagation, vol. AP-31, No. 4, pp. 649-653, July 1983.

[6] Srin. Das, Santosh K. Chowdhury, “Rectangular microstrip Antenna on a Ferrite Substrate,” IEEE Trans. Antenna and propagation, vol. AP-30, No. 3, pp. 499-502, May 1982.

[7] Robert A. Pucel, Daniel J. Masse, “Microstrip Propagation on Magnetic Substrates,” IEEE Trans. Microwave Theory and Tech., vol. MTT-20, No. 5, pp. 305-307, May 1972.

[8] Jian-Xiong Zheng, David C. Chang, “End-Correction Network of a Coaxial probe for Microstrip Patch Antennas, “ IEEE Trans. Antenna and Propagation, vol. 39, No 1, pp. 115-119, Jan. 1991.

[9] David R. Jackson, Nicolasos G. Alexopoulos, “Gain Enhancement Method for Printed Circuit Antennas,” IEEE Trans. Antenna and Propagation, vol. AP-33, No. 9, pp. 977-987, Sep. 1985.

[10] Hugo F. Pues, Antonine R. Van De Capelle, “An Impedance-Matching Technique for Increasing the Bandwidth of Microstrip Antenna,” IEEE Trans. Antenna and Propagation, vol. 37, No. 11, pp. 1345-1349, Nov. 1989.

[11] John Q. Howell, “Microstrip Antenna,” IEEE Trans. Antenna and propagation, pp. 90-93, Jan. 1976.

[12] W. S. Gregorwich, “An Electronically Despun Array Flush-Mounted on a Cylindrical Spacecraft,” IEEE Trans. Antenna and Propagation, vol. AP-22, No. 1, pp. 71-73, Jan. 1974.

[13] Robert E. Munson, “Conformal Microstrip Antennas and Microstrip Phased Arrays,” IEEE Trans. Antenna and Propagation, pp. 74-79, Jan. 1974.

[14] Savacina, J., “Analysis of Multilayer Microstrip Lines by a Conformal Mapping Method,” IEEE Trans. On Microwave Theory and Techniques, Vol. 40, No. 11, Nov. 1992, pp. 2116.

Appendix:

Appendix A: Definitions

Antenna: "That part of a transmitting or receiving system which is designed to radiate or to receive electromagnetic waves". An antenna can also be viewed as a transitional structure (transducer) between free-space and a transmission line (such as a coaxial line). An important property of an antenna is the ability to focus and shape the radiated power in space e.g.: it enhances the power in some wanted directions and suppresses the power in other directions. Antenna directivity: The directivity of an antenna is given by the ratio of the maximum radiation intensity (power per unit solid angle) to the average radiation intensity (averaged over a sphere). The directivity of any source, other than isotropic, is always greater than unity. Antenna efficiency: The total antenna efficiency accounts for the following losses: (1) reflection because of mismatch between the feeding transmission line and the antenna and (2) the conductor and dielectric losses. Antenna gain: The maximum gain of an antenna is simply defined as the product of the directivity by efficiency. If the efficiency is not 100 percent, the gain is less than the directivity. When the reference is a loss less isotropic antenna, the gain is expressed in dBi. When the reference is a half wave dipole antenna, the gain is expressed in dBd (1 dBd = 2.15 dBi). Antenna pattern: The antenna pattern is a graphical representation in three dimensions of the radiation of the antenna as a function of angular direction. Antenna radiation performance is usually measured and recorded in two orthogonal principal planes (such as E-Plane and H-plane or vertical and horizontal planes). The pattern is usually plotted either in polar or rectangular coordinates. The pattern of most base station antennas contains a main lobe and several minor lobes, termed side lobes. A side lobe occurring in space in the direction opposite to the main lobe is called back lobe. Normalized pattern: Normalizing the power/field with respect to its maximum value yields a normalized power/field pattern with a maximum value of unity (or 0 dB). Antenna polarization: "In a specified direction from an antenna and at a point in its far field, is the polarization of the (locally) plane wave which is used to represent the radiated wave at that point". "At any point in the far-field of an antenna the radiated wave can be represented by a plane wave whose electric field strength is the same as that of the wave and whose direction of propagation is in the radial direction from the antenna. As the radial distance approaches infinity, the radius of curvature of the radiated wave's phase front also approaches infinity and thus in any specified direction the wave appears locally a plane wave". In practice, polarization of the radiated energy varies with the direction from the center of the antenna so that different parts of the pattern and different side lobes sometimes have different polarization. The polarization of a radiated wave can be linear or elliptical (with circular being a special case). E-plane: "For a linearly polarized antenna, the plane containing the electric field vector and the direction of maximum radiation". For base station antenna, the E-plane usually coincides with the vertical plane. Effective radiated power (ERP): "In a given direction, the relative gain of a transmitting antenna with respect to the maximum directivity of a half-wave dipole multiplied by the net power accepted by the antenna from the connected transmitter". Far-field region: "That region of the field of an antenna where the angular field distribution is essentially independent of the distance from a specified point in the antenna region". The radiation pattern is measured in the far field. Frequency bandwidth: "The range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard". VSWR of an antenna is the main bandwidth limiting factor. Gain pattern: Normalizing the power/field to that of a reference antenna yields a gain pattern. When the reference is an isotropic antenna, the gain is expressed in dBi. When the reference is a half-wave dipole in free space, the gain is expressed in dBd. H-plane: "For a linearly polarized antenna, the plane containing the magnetic field vector and the direction of maximum radiation". For base station antenna, the H-plane usually coincides with the horizontal plane. Half-power beamwidth: " In a radiation pattern cut containing the direction of the maximum of a lobe, the angle between the two directions in which the radiation intensity is one-half the maximum value".

Half-power beamwidth is also commonly referred to as the 3-dB beamwidth.

Input impedance: " The impedance presented by an antenna at its terminals". The input impedance is a complex function of frequency with real and imaginary parts. The input impedance is graphically displayed using a Smith chart.

Isotropic radiator: "A hypothetical, loss less antenna having equal radiation intensity in all direction". For based station antenna, the gain in dBi is referenced to that of an isotropic antenna (which is 0 dB). Radiation efficiency: "The ratio of the total power radiated by an antenna to the net power accepted by the antenna from the connected transmitter". Reflection coefficient: The ratio of the voltages corresponding to the reflected and incident waves at the antenna's input terminal (normalized to some impedance Z0). The return loss is related to the input impedance Zin and the characteristic impedance Z0 of the connecting feed line by: Gin = (Zin - Z0) / (Zin+Z0). Microstrip antenna: "An antenna which consists of a thin metallic conductor bonded to a thin grounded dielectric substrate". An example of such antennas is the microstrip patch. Omnidirectional antenna: "An antenna having an essentially non-directional pattern in a given plane of the antenna and a directional pattern in any orthogonal plane". For base station antennas, the omnidirectional plane is the horizontal plane. Voltage standing wave ratio (VSWR): The ratio of the maximum/minimum values of standing wave pattern along a transmission line to which a load is connected. VSWR value ranges from 1 (matched load) to infinity for a short or an open load. For most base station antennas the maximum acceptable value of VSWR is 1.5. VSWR is related to the reflection coefficient Gin by: VSWR= (1+|Gin|)/(1-| Gin |).

Appendix B: Yagi Antenna Result

|Angle |Gain (dB) |Gain - Reference |Angle |Gain (dB) |Gain - Reference |
|10 |46 |15 |190 |31 |0 |
|20 |46 |15 |200 |28 |-3 |
|30 |40 |9 |210 |21 |-10 |
|40 |33 |2 |220 |13 |-18 |
|50 |28 |-3 |230 |26 |-5 |
|60 |31 |0 |240 |28 |-3 |
|70 |31 |0 |250 |27 |-4 |
|80 |32 |1 |260 |34 |3 |
|90 |26 |-5 |270 |33 |2 |
|100 |32 |1 |280 |21 |-10 |
|110 |33 |2 |290 |31 |0 |
|120 |25 |-6 |300 |25 |-6 |
|130 |21 |-10 |310 |32 |1 |
|140 |23 |-8 |320 |31 |0 |
|150 |20 |-11 |330 |34 |3 |
|160 |21 |-10 |340 |40 |9 |
|170 |28 |-3 |350 |45 |14 |
|180 |30 |-1 |360 |46 |15 |

Appendix C: Microstrip Antenna Dimensions
[pic]
[pic]

[pic]

[pic]

Appendix D: Ground Plane Radiation Analysis
This section shows the results of four different microstrip antennas that where built and tested. There are two quarter wave patches (one with very small ground plane and one with a larger ground plane) that where designed using the program in Appendix F. There are also two half wave patches (a very small and a lager ground plane antenna) that where designed using a program included in [1]. Both of these antennas are considered small ground plane antennas but it can be seen from the drawings in Appendix C that two of the antennas have larger ground planes. To be considered a large ground plane it needs to be around 3 times the wavelength. The results of a small ground plane antenna can be accurately predicted using the Geometrical theory of diffraction [5]. We did not attempt to calculate the predicted patterns for this report because of the time constraint.

Table D.1 Patch antenna gains over an isotropic radiator (reference dipole antenna)

| |½ Wavelength |¼ Wavelength |½ Wavelength |¼ Wavelength |
| |With |With |With |With |
| |Large Ground |Large Ground |Small Ground |Small Ground Gain (dB) |
| |Gain (dB) |Gain (dB) |Gain (dB) | |
|Angle |E | H |E | H |E | H |E | H |
|0 |-25 | -13 |-26 | -13 |-16 | -12 |-17 | -12 |
|10 |-27 | -13 |-26 | -13 |-18 | -12 |-17 | -12 |
|20 |-28 | -13 |-27 | -14 |-18 | -12 |-17 | -12 |
|30 |-28 | -14 |-28 | -14 |-17 | -12 |-17 | -12 |
|40 |-29 | -15 |-29 | -15 |-17 | -12 |-17 | -12 |
|50 |-30 | -16 |-30 | -16 |-16 | -13 |-16 | -12 |
|60 |-35 | -17 |-31 | -18 |-18 | -13 |-16 | -12 |
|70 |-36 | -18 |-36 | -19 |-17 | -13 |-16 | -13 |
|80 |-38 | -19 |-38 | -20 |-17 | -13 |-16 | -13 |
|90 |-41 | -21 |-41 | -21 |-18 | -13 |-15 | -13 |
|100 |-42 | -22 |-42 | -23 |-19 | -13 |-15 | -13 |
|110 |-42 | -24 |-42 | -24 |-20 | -14 |-15 | -14 |
|120 |-42 | -26 |-42 | -25 |-23 | -15 |-15 | -14 |
|130 |-40 | -27 |-40 | -26 |-24 | -16 |-15 | -16 |
|140 |-40 | -27 |-40 | -26 |-25 | -16 |-15 | -16 |
|150 |-40 | -27 |-38 | -26 |-30 | -16 |-15 | -16 |
|160 |-41 | -27 |-38 | -26 |-31 | -17 |-18 | -16 |
|170 |-42 | -28 |-39 | -26 |-35 | -17 |-18 | -17 |
|180 |-43 | -28 |-40 | -26 |-37 | -17 |-21 | -17 |
|190 |-46 | -29 |-44 | -27 |-45 | -17 |-23 | -17 |
|200 |-43 | -30 |-51 | -26 |-42 | -17 |-28 | -17 |
|210 |-41 | -31 |-51 | -28 | -40 | -17 |-37 | -17 |
|220 |-36 | -30 |-43 | -28 |-38 | -16 |-31 | -17 |
|230 |-34 | -28 |-40 | -28 |-30 | -16 |-22 | -17 |
|240 |-31 | -26 |-36 | -27 |-27 | -16 |-20 | -17 |
|250 |-30 | -23 |-35 | -27 |-23 | -16 |-18 | -17 |
|260 |-30 | -22 |-34 | -25 |-20 | -16 |-18 | -16 |
|270 |-26 | -20 |-33 | -23 |-19 | -16 |-18 | -16 |
|280 |-26 | -18 |-32 | -21 |-20 | -16 |-18 | -16 |
|290 |-26 | -16 |-31 | -20 |-18 | -16 |-19 | -16 |
|300 |-25 | -16 |-30 | -18 |-17 | -15 |-19 | -15 |
|310 |-25 | -15 |-30 | -17 |-19 | -15 |-19 | -15 |
|320 |-25 | -15 |-30 | -15 |-17 | -14 |-19 | -15 |
|330 |-25 | -14 |-26 | -14 |-18 | -14 |-18 | -15 |
|340 |-25 | -13 |-26 | -13 |-17 | -14 |-18 | -14 |
|350 |-25 | -13 |-26 | -13 |-16 | -14 |-18 | -14 |
|360 |-25 | -13 |-26 | -13 |-16 | -13 |-17 | -13 |

*Note the plots below do not show the actual gain but rather the difference between the maximum and minimum gain. The actual gain of the antennas can be obtained from Table D.1.

Figure D.1 This plot compares the E-plane patterns of the prototype antenna (very small ground) to a quarter-wave patch with a larger ground plane. It is clear that the larger ground plane antenna had a lower overall gain. This was not expected but we believe the reason for it is due to the different feed method used. Besides the over all gain this plot gives us some good insight. Notice that the larger ground plane antenna has a narrower beamwidth, this is because less radiation is allowed to spill to the back-side of the ground plane The smaller the ground plane gets the more radiation spills to the back-side of the antenna creating an almost omni directional antenna.

Figure D2 This plot compares the H-plane pattern s of the quarter and Half-wave patches with larger ground palnes. Notice that the two plots are almost Identical. This is because the width of the quarter and half-wave patch remains the same so the distances between the two radiating edges of the H-plane remain the same and a simular pattern results.

Figure D3. This plot the E-planes of the half-wave and quarter-wave larger ground plane antennas. Since in a quarter-wave patch there is only one radiating edge in the E-plane because of the short circuit, we expect the quarter-wave antenna to have a broader beamwidth than the Half wave. In reality however there is radiation coming from the shorted-side and the result is a pattern that is very simular to the half-wave pathc.

Figure D4 and Dd These two plots show the E and H planes of the the quarter and half-wave patches with very small ground planes. It can be seen tha t H-planes are almost Identical for both and the E-plane of the quarter-wave is broader than the half-wave which is what is expexted. [pic]

[pic]

Appendix E: Equations for Analysis of the Quarter-wave Resonator

These equations came from [1], [2] and [3].

Wavelength in free space
E1
Where c is the speed of light and f is the resonant frequency.
The microstrip wavelength is given by
E2

er’ is the effective dielectric constant, which is related to er the dielectric constant by

E3

Where ( and h are the width and height (or thickness) of the patch.

As an antenna, the (g/4 shorted resonator will lose energy to three main sinks: The radiation into space, the resistive loss of the conductive currents flowing in the metal strips, and the dielectric loss of the displacement currents through the substrate.

Conductor loss Qc is given by

E4

Z0 is the characteristic impedance of the feed, and p is the receptivity of the resonator conductor (ohms-m)

E5
The dielectric loss Qd is given by
E6
Where tan( is the loss tangent of the dielectric substrate and q is given by
E7

We obtain a term for the over all loss material by combining (4) and (6) to give us
E8

The radiation from the microstrip resonator QR is given by
E9
The fractional power radiated by the antenna is the antenna efficiency:
E10

The total Q governs the bandwidth (BW).

E11
Therefore the fractional bandwidth is
E12

From this equation it can be seen that decreasing the values of tan( and p (which increase efficiency) will decrease the bandwidth.

Since the bandwidth and efficiency are both functions of common factors we see that

E13
This is also known as the figure of merit.
In any design (13) along with (2) should be considered. Equation (1) allows the antenna to be small by increasing e, but from (13) this will simultaneously decrease the figure of merit.
E14

Eeff- dielectric constant h-height of substrate
E15

Appendix F: Computer Programs and Sample Radiation Patterns

%Quater wavelength patch program.

%Calculates demensions and feed point for a rectangular quarter-wave %short circuited patch. %Calculates efficiency, Bandwidth, Quality Factor clear all Er=input('Enter dielectric constant: '); loss=input('dielectric loss tangent: '); w=input('Enter patch width(cm): '); t=input('Enter thickness of the substrate (cm): '); Fr=input('Enter operation frequency (MHz): ');

%unit conversions w=w*10^-2; t=t*10^-2; Fr=Fr*10^6;

%Ee = effective dielectric constant. Ee=.5*(Er+1+(Er-1)*(1+10*t/w)^(-.5));

%wl = wavelenght in the substrate wavelength=3*10^8/Fr WAVELENGTHinFREESPACE=wavelength*10^2 wl=wavelength/(Ee^.5); WAVELENGTHinSUBSTRTE=wl*10^2

%Calculating Length of 1/4-patch lb=(3*10^8/(4*Fr*sqrt(Ee))) - (0*w); lb1=lb*10^2; patchlength=lb1

%Z=6*t; %Z1=Z*10^2

%la=L-(lb + (2*Z)); %la1=la*10^2

ue=1; A=(1+1.735*Er^(-.0724)*(w/t)^(-.836)) input('is 1