MICROSTRIP AND PRINTED ANTENNA DESIGN PDF
PDF | On Apr 4, , K. Siakavara and others published Methods to Design Conventional microstrip antennas have a conducting patch printed on a. PDF | A microstrip antenna design is discussed he designed using microstrip line feed model a IE3D software. A Microstrip patch antenna consists o on one side of a dielectric substrate which on the other side as shown .. polarized Printed. The approach in this book is historical and practical. It covers basic designs in more detail than other microstrip antenna books that tend to skip important.
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Buy e-book PDF. $ (plus tax if applicable). Add to cart. Buy print edition. image of Microstrip and Printed Antenna Design. Author(s): Randy Bancroft. Conformal microstrip printed antenna K. Elleithy H. Bajwa A. Elrashidi Conformal antennas are A better method for creating uniform cylindrical structures. Microstrip and Printed Antenna - Ebook download as PDF File .pdf), Text File . txt) or Numerous books have been published about microstrip antenna design.
Skip to main content. Log In Sign Up. Conformal microstrip printed antenna. Khaled Elleithy. Hassan Bajwa. Conformal microstrip printed antenna K.
Microstrip antenna patch on conical and spherical surfaces is studied. Some new flexible antenna is given for different Because of the advantages of conformal antennas, it is very frequencies. Finally, simulation software is used to study the popular in the different flight aircrafts . Microstrip antenna, conformal antenna, Printed 1. The dielectric material will undergo stretching and antenna, resonance frequency, curvature, input impedance, compression along the inner and outer surfaces, return loss, and voltage standing wave ratio.
Stretching of copper traces will result in phase, impedance, and resonance frequency 1. Introduction error. Shaping the material can also result in a change in Microstrip antennas have been widely studied in recent both the dielectric constant and material thickness. The main reasons are due to a plethora of reasons, The thickness is an easily measured parameter, and such as low profile, lightweight, low cost, high gain and measuring the dielectric constant of a cylindrical conformability to curved surfaces .
Planner microstrip shaped substrate can be done using the two antennas have been extensively studied and the models used microstrip line method . Dielectric materials will suffer from cracking due maturity. Conformal antennas are A better method for creating uniform cylindrical structures mainly the following advantages over the planer microstrip would be to roll the material into a cylindrical shape while antennas : Conformal antennas can be used to simplify the antenna installation under the conditions of 2.
Cylindrical-Rectangular Patch Antenna assuring the performance of the antenna. Conformal antennas can eliminate or reduce the Cylindrical-rectangular patch is the most famous and error caused by radome.
The radome does not need popular conformal antenna. The manufacture of this antenna to install; even if the radome is installed, as the is very easy with respect to spherical and conical antenna microstrip antenna and its close proximity, especially in the military field. So the research in this type distortion of the antenna is greatly reduced . Also, for much small thickness than a wavelength and the radius of curvature, only TM modes are assumed to exist.
The input impedance and Q factors are also calculated under the same conditions. Geometry of cylindrical-rectangular patch antenna Based on cavity model, microstrip conformal antenna on a projectile for GPS Global Positioning System devise is Clifford M. Krowne  calculated the resonance frequency designed and implemented by using perturbation theory is fr for a cylindrical-rectangular patch and he made a introduced by Sun L.
The The designed antenna is emulated and analyzed by IE3D field distribution within the antenna has been determined software. The emulated results showed that the antenna using a cavity model for TEmn transverse electric and could provide excellent circular hemisphere beam, better TMmn transverse magnetic , where m and n are the modes wide-angle circular polarization and better impedance match of operations and indicated that only discrete solutions for peculiarity.
The resonance frequency is given by : A cavity model and transmission line model are used to find the initial 1 dimensions of the antenna and then electromagnetic simulation of the antenna model using software called Where 2b is a length of the patch antenna, a is a radius of FEKO is applied.
An approach to the microstrip antennas on cylindrical bodies is presented by Joseph A. In this paper, the 3. Conformal microstrip antenna array printed radiator is replaced by assumed surface current distribution, and the fields are solved taking into account the Conformal microstrip arrays are used to increase the presence of the dielectric layer around the cylindrical body. So, we get a better performance using arrays.
The then used to get the radiation patterns of the wraparound radiation pattern will significantly be affected by putting antenna. The assumption is valid as long as the radiation is arrays on a conformal surface to appear as omni-directional small compared to the stored energy. Kwai et al. The effect of curvature on the characteristics pattern of array of 64 elements are given by Mao K.
Xue M. The coupling between elements is not They first obtained the electric field under the curved patch considered in this paper. In this paper, they calculated the using the cavity model and then they calculated the far field total electric field strength for an array of N elements using by considering the equivalent magnetic current radiating in the equation: Uou, W.
Hwang amd M.
Tentzeris designed and flexible materials, while substrate is of a polymer. AgHT-8 fabricated a composite antenna array conformed around material has less impact on performance with bending and cylindrical structures .
The experimental results showed consequently improves the performance. The effect of that the radiation pattern is strongly dependent on the bending was also studied for different radius of curvatures cylindrical curvature for the transverse radiation pattern, and they noted that the 10 dB bandwidth reduced as the while the array also exhibits high side-lobes and wider curvature increased.
The performance of flexible printed radio frequency Problems associated with Ultra Wide Band UWB antennas identification tags affixed onto cylindrical containers was as phased array elements discussed by Altan M. Ferendeci measured by S. Leung and D. Lam . Conductive . In this paper, he introduced various wide bandwidth polymeric coil antennas were screen printed onto flexible arrays of antennas that can be conformed and also, problems substrates, and the coil resistance, the inductances, and the that arise depending on the physical separation of antennas S-parameters of the antenna coils were measured and are discussed.
For conformal placement of an antenna either analyzed. The results in this paper showed that the coil as an individual antenna or as in an array configuration on inductance decreases slowly with increasing curvature, and any arbitrary surface may require very thin antenna. They the maximum read range of the tag reduced by increasing should be processed preferably on flexible substrates so that curvature.
Bayram et al  presented a conformal and lightweight antenna technology based on E-textile conductors and 4. Conformal Microstrip antenna patch on conical polymer-ceramic composites. E-textile conductors are and spherical surfaces fabricated with single wall carbon nanotube and Ag coated textile.
They demonstrate good structural integrity with Single and dual patch antenna conformed on a conical polymer composites due to their mechanical compatibility. Gomes and A. Giarola , . Experiments suggested that the sample patch The input impedance for this case is also calculated. Peng, L. Chaowei and W. Qiang .
The return loss and voltage A microstrip antenna on liquid crystal polymer multilayer standing wave ratio for flat rectangular patch and on a cone technology of dual frequency 14 and 35 GHz was were discussed in this paper. Also, the same software was presented for the first time by G. Dejena et al . A liquid used to design a microstrip antenna array.
The designed antenna The effects of spherical conformity on a wideband circular exhibits a return loss of better than 15 dB in both frequency patch antenna described by B. Piper and N. Shuley . The bands. But in this paper, the measured cross-polarizations theoretical design of a wideband circular patch antenna of levels are higher than the predicted ones so they suggested a 2.
The effect of distortion on the spherical polarization. So, they used the air Two dimensional curved electromagnetic bandgap dielectric to overcome the problems come from dielectric structures were designed, according to the reflection cracking. The return loss was measured for a flat antenna condition of optics Bragg, by L. Tao, C. Xiangyu, Z. Guang and then for spherical antenna for different radii and the and Y. Zhoawei . They applied this structure to the result showed the effect of the conformal antenna on the cylindrical conformal microstrip antenna.
The simulation performance. Flexible microstrip antenna comparing with the normal cylindrical microstrip patch antenna without electromagnetic bandgap.
The majority of WLANs use the unlicensed 2. The system has strict radiation pattern requirements which have been met with a combination of a printed monopole and a TM21 mode annular microstrip antenna that has been altered with notches to produce left-hand circular polarization at 2. Omnidirectional microstrip antennas are also of utility for many WiMax applications 2. March Microstrip Antennas 7 In other applications.
References  Grieg.. The use of transmission line. October 18— The advantages of using antennas in communication systems will continue to generate new applications which require their use. University of Illinois. Antennas have the advantage of mobility without any required physical connection.
September Microstrip fed printed slot antennas have proven useful to provide vertical polarization and integrate well into laptop computers Chapter 7 for WLAN. April June Advances in Computational Electrodynamics: Williamsburg Virginia. January Computational Electrodynamics: December Artech House.
October Artech House.. ISSN February New York: McGraw Hill. Modern Antenna Design. ED Online ID Microstrip Antennas 9  Licul. Patent No. Numerous full-wave analysis methods have been devised for the rectangular microstrip antenna. The two edges along the sides of length L are often referred to as nonradiating edges. The two analysis methods for rectangular microstrip antennas which are most popular for CAD implementation are the transmission line model and the cavity model.
In this section I will address the least complex version of the transmission line model. Figure shows the geometry of this antenna type. In this model. At resonance. The popularity of the transmission line model may be gauged by the number of extensions to this model which have been developed.
Chapter 2 Rectangular Microstrip Antennas 2. The driving point impedance Zdrv at any point along the center line of a rectangular microstrip antenna can be computed using the transmission line model.
The transmission line model is most easily represented mathematically using the transmission line equation written in terms of admittances. The impedance measured at the point where the antenna is connected to the transmission line is called the driving point impedance or input impedance..
These edges are called radiating edges. Rectangular Microstrip Antennas 11 Figure Rectangular microstrip patch geometry used to describe the transmission line model. The driving point or feed point of an antenna is the location on an antenna where a transmission line is attached to provide the antenna with a source of microwave power. The driving point admittance Ydrv is then computed at the end of this feed line.
A driving point is chosen along the antenna length L which can be represented as a sum of L1 and L2. The antenna is readily analyzed using a pair of edge admittances Ye separated by two sections of transmission line of characteristic admittance Y0. In this case. The two transmission line sections contribute to the driving point impedance.
Using equation 2. This is shown in Figure a. The two loads are separated by a microstrip transmission line of characteristic admittance Y0: In other words. This feed method is modeled in an identical manner to the coaxial probe feed when using the transmission line model. The coaxial center conductor then passes through the dielectric substrate of the patch antenna and connects to the patch. Feeding the antenna in the center i.. This feed symmetry enforces the purest linear polarization along the length of the patch which can be achieved with a single direct feed.
The second feed method. Metal is removed from the groundplane which is generally the same radius as the inside of the coaxial shield. Figure presents four common methods used to directly feed a microstrip antenna. The third feed method. The outer shield of a coaxial transmission line is connected to the groundplane of the microstrip antenna. The extra electrical length causes a dipole antenna to resonate at a length which is closer to 0.
Rectangular Microstrip Antennas 15 Figure Common methods used to feed a rectangular microstrip antenna. In this special case. A quarter-wave transformer has a larger bandwidth than the antenna element and therefore does not limit it.
In general. Numerical methods for obtaining the roots of an equation such. A study by Basilio et al. A fourth feed method. The patch width is large enough in this case to increase the antenna gain considerably. The inset distance into the patch goes to zero.
Equation 2. Early investigation of the rectangular microstrip antenna. The feed point location is 5. A sinusoidal source at 3. We see two radiating edges at either end of the antenna in the lowest mode.
In The predicted position of a desired driving point impedance to feed the antenna is generally close to measurement as long as the substrate height is not larger than about 0. This model further allows for the inclusion of higher order linear transmission line modes.
After Derneryd . The LCD visualization shows the next higher order mode one would expect from transmission line theory. As before. In reality. The transmission line model also does not take into consideration the possible excitation of modes which are not along the linear transmission line. This distance R is generally accepted for most practical purposes to be 2d 2. The cavity model. The next mode is reported by Derneryd to exist at 9.
The transmission line model is often inaccurate when used to predict the impedance bandwidth of a rectangular microstrip antenna for thin substrates. Rectangular Microstrip Antennas 19 tions from each side of the nonradiating edges cancel.
The cavity model is the dual of a very short piece of rectangular waveguide which is terminated on either end with magnetic walls. The driving point current can be mathematically manipulated to produce the ratio of voltage to current on the left side of equation 2. The electric current on the rectangular patch antenna is further assumed to equal zero normal to each edge.
This creates an. The effect of radiation and other losses is represented by lumping them into an effective dielectric loss tangent [equation 2. Rectangular Microstrip Antennas 21 expression which can be used to compute the driving point impedance [equation 2.
The Q of the surface wave loss Qsw is related to the radiation quality factor Qr: When it is fed along the centerline of dimension a. The self-inductance of a coaxial probe used to feed the rectangular microstrip antenna is not included in this model.
In the case of the TM10 mode.. The TM01 mode is the next highest order mode and has the next lowest resonant frequency Figure Figure shows a narrow patch driven in the TM When it is thicker than this. TM01 becomes the mode with the lowest resonant frequency and TM10 has the next lowest resonant frequency.
The TM01 mode has the next highest resonant frequency. The TM00 mode is the static DC term of the series. Figure a shows the general network model used to represent a rectangular microstrip antenna.
This allows a designer the option of placing a shorting pin in the center of the rectangular patch without affecting the generation of either of the two lowest order modes. When this is the case. In many cases the buildup of static charge on the patch is undesirable from an electrostatic discharge ESD point of view.
This shorting pin or via forces the groundplane and rectangular patch to maintain an equivalent direct current DC electrostatic potential. As the substrate thickness h of a microstrip. The convergent sum of these inductances may be lumped into a single series inductor which represents the contribution of the higher order modes to the driving point impedance.
Table a A 2. The cavity model is accurate enough to use for many engineering designs. Its advantage is that it is expressed with closed form equations. Rectangular Microstrip Antennas 27 Figure Comparison to measurement of predicted negative return loss of a rectangular microstrip patch of parameters in Table by the cavity model and FDTD analysis. The feed point is 7. These two properties impedance bandwidth and match may need to be traded off in a design. The cavity model does not include the small amount of intrinsic self-inductance introduced by a coaxial feed probe.
Its disadvantage is its accuracy when compared with more rigorous methods. The impedance results for the cavity model. The measured maximum return loss of a patch fabricated using these dimensions is These resonance values are presented in Table The cavity model predicts a maximum return loss at 2.
FDTD analysis predicts 2. This is illustrated in Figure a. The FDTD method was also used to analyze this patch antenna. This implies that the radiation pattern would be comparable to a pair of radiating slots centered about each radiating edge of the patch driven in phase.
The groundplane size of the fabricated antenna. Rectangular Microstrip Antennas 29 Figure a Top view of a rectangular microstrip patch with a pair of equivalent slots located at a distance a apart.
When the dielectric substrate is air. The two slots form an array. When a pair of radiation sources. The radiating slots have a length b and are estimated to be of h the substrate thickness across.
Note the virtual short circuit at the center of the patch under the antenna is clearly visible. We can see that the two radiating edges. As the dielectric constant increases. The directivity of a microstrip antenna can be approximated by starting with the directivity of a single slot: The slots no longer optimally add broadside to the rectangular microstrip antenna. It is always best to use a more powerful technique of analysis. The directivity estimates and pattern functions do not take groundplane effects into account and are often lower than measured.
These equations are very useful for estimating the directivity and radiation pattern of a rectangular microstrip antenna. The FDTD method results were obtained using a single-frequency square coaxial source and the patterns calculated using the.
Figure shows measured E. Table Directivity dB of a square linear microstrip antenna vs. It is possible to achieve a directivity of almost 10 dB with an air loaded rectangular microstrip patch antenna. The slot model can be useful for estimating directivity. This spacing produces an array spacing for the slot model which produces maximum directivity.
Table presents a comparison of the directivity predicted by the slot model and FDTD method for a square microstrip antenna. As the substrate dielectric constant of a rectangular microstrip antenna increases. The slot model does not take groundplane affects into account.
Rectangular Microstrip Antennas 33 surface equivalence theorem. As the dielectric constant of the substrate is increased. This rectangular microstrip antenna design is known as a quarter-wave microstrip patch or half-patch antenna. Post and Stephenson Figure A quarter-wave microstrip antenna has a shorting wall which replaces the virtual short found in a half-wave microstrip antenna.
In the case where a microstrip antenna is fed to excite the TM01 mode exclusively. Only a single radiating edge remains with this design. The admittance at the driving point from the section of transmission line that translates the edge admittance Ye along a transmission line of length L2 resonates when its susceptance cancels the susceptance of the shorted stub. This change in mutual coupling also affects the cavity Q. To maintain the central short.
This is because. The two modes are orthogonal and therefore inde-. This causes all four edges to become radiating edges. If the patch is fed along the diagonal.
We can remove one section i. Because they are in phase. We can replace the virtual shorting planes. When a square microstrip antenna is driven along the diagonal. This produces an antenna that has one-fourth the area of a square patch antenna. When a square microstrip patch is operating with identical TM01 and TM10 modes. Replacing the virtual shorting planes with physical shorting planes allows one to remove a quarter section of the original antenna and drive it independently.
In Figure we see four common methods used to create circularly polarized radiation from a rectangular microstrip antenna with a single driving point. III Cutting off corners to create orthogonal modes.
IV Introduction of a diagonal slot. The second method presented in Figure II is essentially the same as I. This slightly nonresonant condition causes the edge impedance of each mode to possess a phase shift. Figure presents the results of a cavity model analysis of a patch radiating left-hand circular polarization LHCP using a rectangular microstrip.
Neither mode is exactly at resonance.
One could use a single tab. The fourth method in Figure IV is to place a slot diagonally across the patch. This impedance relationship clearly reveals itself when the impedance versus frequency of the patch is plotted on a Smith chart.
One only wishes to produce a phase shift between modes. The dimensions of the slot can be adjusted to produce circular polarization. It is important to keep the slot narrow so that radiation from the slot will be minimal.
The frequency of optimum circular polarization is the point on a Smith chart which is the vertex of a V-shaped kink. This patch will excite the TM10 and TM01 modes with identical amplitudes and in phase.
Figure a shows a perfectly square patch antenna probe fed in the lower left along the diagonal. The third method illustrated in Figure III is to remove a pair of corners from the microstrip antenna.
This situation is the most general geometry describing this type of circularly polarized patch. The two radiating edges which correspond to each of the two modes have a phase center that is located at the center of the patch. The TM10 mode shifts down in frequency and the TM01 mode shifts up compared with the original resonant frequency of the slant linear patch.
Therefore the phase center of the radiation from the TM10 and TM01 modes coincide and are located in the center of the patch. The rectangular plot shows the impedance as real and imaginary.
These two modes add together and produce linear polarization along the diagonal of the patch antenna. Rectangular Microstrip Antennas 41 Figure Development of a rectangular patch with circular polarization from a square patch. In both situations. If all the energy is stored in a single TM10 or TM When a patch is square. The antenna operates at 2. One method is to start with the case of the slant linear patch. The center frequency of LHCP operation is 2.
The total Q i. The new patch has a resonance at 2. This average gives us a value of a slant linear patch on which we can apply equation 2. The design values for that example were developed by adjusting the patch aspect ratio by trial and error until a circular polarization kink appeared.
Rectangular Microstrip Antennas Table 43 2. We arrive at a slant linear patch design by taking the average of the values used to create the circularly polarized patch of Table Q0 from the cavity model is computed to be The cavity model can be used to compute the axial ratio of a circularly polarized rectangular patch. This is about half the input resistance value of the slant linear patch.
This calculation provides some insight into the sensitivity of the driving point impedance location of the design to physical parameters of the patch. The input impedance at 2. Table illustrates that often the driving point location which produces optimum axial ratio performance and driving point match is not exactly along the patch diagonal.
The cavity model often does not produce as accurate values for the Q of the slant linear patch as does the FDTD method or direct measurement. When the antenna is matched and driven in a single RLC-type impedance mode. The real and imaginary components of the driving point impedance are plotted with the computed axial ratio in dB.
Table 2. Figure III has a pair of corners cut off to produce circular polarization. Rectangular Microstrip Antennas 47 Equation 2.
This creates a pair of diagonal modes no longer TM10 and TM In Figure we see that if the upper right-hand corner and lower left-hand corner are reduced.
This type of design is undertaken experimentally. The opposite diagonal from lower right to upper left remains unchanged and has a larger capacitance by comparison. A more complex iterative approach that uses the cavity model to compute single-feed circularly polarized rectangular patch designs is presented by Lumini et al. The antenna is fed along the centerline in this case so it will excite each of the diagonal modes with equal amplitude.
This situation creates right-hand circular polarization RHCP. Leaving the feed point position unchanged and removing the opposite pair of corners reverses the phase. The high dielectric constant also decreases the size of the patch.
Figure II uses indentation tabs to produce circular polarization. Experience with genetic algorithms indicates that it produces a design which is no better than the more straightforward method previously described. The total area S of the unperturbed square patch prior to the corner removal to produce circular polarization is. When a high dielectric constant is used as a substrate.
Figure One may cut off a pair of opposing corners of a rectangular microstrip antenna to produce circular polarization. One can view cutting off a corner as reducing the capacitance of that diagonal mode. Reversing the position of the corners reverses the polarization sense. The area to be cut from each corner of the unperturbed patch, as shown in Figure III , is half of the perturbation area S calculated using equation 2. Figure IV uses a diagonal slot to produce circular polarization.
In this case, one begins with a square microstrip antenna. The TM01 and TM10 modes will have the same resonant frequency and are orthogonal.
The branchline hybrid will enforce equal amplitudes and nearly correct phase over a wide bandwidth, but as the patch edge impedance mismatches with frequency, the rejected power will appear at the terminated port, and power is lost to maintain good circular polarization compared with a singlefeed design. The design of a rectangular patch with circular polarization Section 2.
The left-hand illustration of Figure b shows a branchline hybrid as it would appear realized in stripline or microstrip. The shunt branches have a characteristic impedance Zs and the through or series branch has a characteristic impedance of Zt. The illustration on the right of Figure b shows how a commercial hybrid appears with coaxial connectors. Some hybrids have a built-in load on one port, as shown, while others require the user to provide a load. This allows a system to switch between polarization if desired.
Microstrip and Printed Antenna
When port 1 is used as an input port, then port 2 receives half of the input power and is the phase reference for port 3.
The split waves cancel at port 4, which is called the isolated port. A load is generally placed on this port to absorb any imbalance, which stabilizes the phase difference between port 2 and 3.
In practice, there is often a slight imbalance in the power split between ports 2 and 3. We note that equation 2. This allows one to change the characteristic impedance of the shunt branches slightly and obtain a more even power split. One must also take the discontinuities at the transmission line junctions into account to produce a design which operates as desired.
Microstrip and Printed Antenna | Transmission Line | Antenna (Radio)
One can increase the bandwidth of a branchline coupler by adding cascading sections. The impedance bandwidth of a rectangular microstrip antenna can be determined with the total Q used in the cavity model. The perfect match at one frequency is traded for a larger overall 2: The effect substrate thickness and dielectric constant have on impedance bandwidth as computed with the cavity model is illustrated in Figure for a square linearly polarized microstrip antenna.
One must recall that as the substrate thickness is increased, higher order modes provide a larger and larger contribution to an equivalent series inductance, which in turn produces a larger and larger driving point mismatch. A desirable driving point impedance must be traded for impedance bandwidth. This reveals that the impedance bandwidth of a circularly. The two detuned resonances which sum to create circular polarization increase the total impedance bandwidth.
Rectangular Microstrip Antennas 53 Figure Normalized bandwidth of a square microstrip antenna as a function of substrate thickness and relative dielectric constant predicted by the cavity model.
In equation 2. This allows us to write: QT Qr 2. The receive power bandwidth is larger than the axial ratio or impedance bandwidth. Langston and Jackson have written the above expressions in terms of a normalized frequency variable for comparison. The stored energy is identical for all the cavity Qs. We can readily see from equation. The next largest loss is that due to the dielectric.
When these are added together. It is instructive to calculate the losses from each of the mechanisms separately. The surface wave loss increases in proportion to the thickness of the substrate. If a designer wants to maximize the space wave contribution in this case. As the thickness h of the antenna is increased. Rectangular Microstrip Antennas 55 Table Losses in a square linear microstrip antenna versus h 2.
The best compromise to maximize the losses due to the space wave. Computing the losses separately can be very useful to a designer when evaluating the choice of substrate thickness for a given design. The thinnest substrate only radiates As h increases from 0.
These can range from vacuum-molded. A number of approaches have been forwarded to analyze a microstrip antenna with a dielectric cover. Bonding dielectric material directly to the antenna can provide a high degree of hermetic sealing. A quasi-static analysis of a microstrip transmission line with a dielectric cover forms the basis of this analysis. In these cases. Rectangular Microstrip Antennas 57 or injection-molded plastic enclosures which leave an air gap between the radiating patch and the radome.
In some commercial applications. The feed point is represented by the black dot. When a microstrip antenna is covered with a dielectric substrate in practice. The integration of equation 2.
The left-hand term inside of equation 2. This air gap has a strong effect on the effective dielectric. If the design requires a microstrip feed.
A narrower patch has slightly decreased bandwidth compared with a wide patch. A quarterwave transformer feed on a radiating edge produces the least amount of perturbation of the patch radiation.
If the impedance bandwidth requirement is greater than a narrow patch can provide. In either case. This value can then be equated to the width of the antenna.
Rectangular Microstrip Antennas 61 Patch thickness is an important parameter to consider. The lowest order surface wave TM0.
This process is continued until the value. Gopinath has presented an analysis which allows one to choose a substrate thickness that maximizes the Q of a microstrip line at a given frequency. For a given maximum frequency of operation. When the patch is too thick. If the patch thickness is too thin. Directivity increases as the dielectric constant decreases and will decrease.
One can also use the cavity model to predict the location of a desired driving point impedance. Tin immersion is another alternative which is useful in some situations to prevent copper degradation. This problem can sometimes be resolved by using a circular microstrip patch which has resonances with different spacings than those of a rectangular patch. The directivity of a linear rectangular microstrip antenna can be estimated using equation 2. Section B. In some design environments.
Experience indicates the relationships used to compute the wall admittance. In some designs. Under large vibrational shock. If electrostatic discharge ESD is a consideration. As discussed previously.
When a patch is probe fed. In other situations. This is discussed in greater detail in Chapter 3. Often this ring-shaped gap is too small to be seen without a microscope. In the case of a linearly polarized rectangular microstrip antenna. The small amount of extra slack that is left as a small radius at the right-angle bend of the strip before the end of the strip is soldered allows for movement. Each strip is soldered to the feed pin.
This slack allows the feed pin to move up and down without solder failure. Cross-polarization is produced by the existence of higher order modes on the patch. The strips are then soldered to the patch with a small radius of slack. This is illustrated in Figure A square microstrip antenna has the property that both TM01 and TM10 modes have the same resonant frequency and the undesired mode may be readily excited by error in the driving point location.
One solution to this problem is to use a pair of thin metal strips soldered along the feed probe and whose ends are bent at right angles with a small amount of slack and soldered to the patch. The feed pin with soldered strips on either side pass through a hole that is large enough to allow the feed pin to move axially without interference.
This will drive the TM01 mode and theoretically not excite the TM10 mode. When a square patch is used to produce circular polarization with two orthogonal microstrip or probe feeds. The Smith chart of Figure illustrates the impedance trace one needs in order to achieve circular polarization. TM01 or TM The Q of a single mode. When only linear polarization is desired. A square patch designed on a substrate with a 2. These examples demonstrate that when feeding a patch with a probe feed.
By shifting the TM10 resonance to a frequency twice that of the 2: The frequency which exists at the vertex of a kink in the Smith chart impedance. Experimental optimization is generally required to complete the design of a circularly polarized rectangular patch antenna. The polarization sense of the antenna may be determined. The resonant frequency tends to be slightly low when the iterated converged value is used.
This antenna design is electrically small at 1. The groundplane dimensions affect the resonant frequency and radiation patterns adversely and these effects must be included in the design. In the case of a probe fed circularly polarized rectangular microstrip antenna.
When a dielectric superstrate radome covers a microstrip antenna Figure that generates circular polarization. The limitations of electrically small antennas are discussed in Chapter 7. Altering the width of a patch generally allows one to match the antenna to the transmission line. Often the impedance at the kink of the impedance trace is not well matched and frequently has a capacitive component.
An example electromagnetically coupled patch designed to operate at 2. Section 7. The dielectric constant.
Rectangular Microstrip Antennas 65 by consulting Figure I. Rectangular Microstrip Antennas Rectangular microstrip patch with an electromagnetically coupled. The antenna has a width W50 and length L. The patch aperture is larger than a conventional patch and so has enhanced gain when compared with a typical patch antenna design.
The patch is centered on the substrate and the feed line extends under the patch to the patch center. Rectangular microstrip antennas that are very wide compared with their resonant length are referred to as ultrawide rectangular microstrip antennas UWMSAs. The example used requires a microstrip antenna with an edge resistance of The antenna has about 3.
The groundplane width and length are Ultrawide microstrip antennas have useful properties compared with microstrip antennas that possess typical widths. This antenna is obtained by increasing the width of the patch beyond that generally suggested. The substrate thickness is 2.
The operating frequency is 5.
As was discussed previously. Rectangular Microstrip Antennas 69 Figure Predicted radiation pattern of the 2. References  Hildebrand. Peter Peregrinus. August Advances in Microstrip and Printed Antennas. Microstrip Antennas.
Rectangular Microstrip Antennas 71  Derneryd. November July John Wiley and Sons. IEE Conference Publication Boca Raton. CRC Press.. Microstrip Antenna Theory and Design.. McGraw Hill.. Antenna Theory Analysis and Design. San Antonio. Modern Antenna Design Rectangular Microstrip Antennas 73  Lu. Microwave Transmission Line Coupler. June 16—21 May Microstrip Antennas: Rectangular Microstrip Antennas 75  Mishra.
Kluwer Academic Publishers. Artech House The next higher order mode is the TM This mode produces a radiation pattern that is very similar to the lowest order mode of a rectangular microstrip antenna. The circular microstrip antenna offers a number of radiation pattern options not readily implemented using a rectangular patch.
An analysis of the circular microstrip antenna. Chapter 3 Circular Microstrip Antennas 3. As with the rectangular microstrip antenna. The fundamental mode of the circular microstrip patch antenna is the TM This is followed in frequency by the TM02 mode. In the late s. The thickness of the substrate is h.
Bessel functions in this analysis are analogous to sine and cosine functions in rectangular coordinates. Circular Microstrip Antennas 77 Figure Circular microstrip antenna geometry. For each mode of a circular microstrip antenna there is an associated radius which is dependent on the zeros of the derivative of the Bessel function.
The constant c is the speed of light in free space and aeff is the effective radius of the patch. In the case of a rectangular microstrip antenna. The modes for a circular microstrip antenna were introduced as TMnm.
Equation 3. Anm TMnm 1. The reversal of indices can be a source of confusion. In this situation. This mode radiates a monopole-type pattern. The lowest order mode. The next resonant mode is the TM21 mode. Circular Microstrip Antennas 79 The form of equation 3. The third mode is the TM02 unipolar mode.
Following the introduction of the mathematical.
This value is designated a1. This mode is essentially similar in design utility to a rectangular microstrip antenna driven in the TM10 mode. The impedance bandwidth is slightly smaller for a circular patch than its rectangular counterpart. The center of a circular patch driven in the TM11 mode may be shorted if a direct current DC short is required.
One must numerically integrate equation 3. We will use a circular microstrip antenna with a radius of Using equation 3. The TM11 bipolar mode has a virtual short at a plane along its center in the same way a rectangular microstrip patch has one. The directivity of the antenna is computed to be 7.
This allows one to place a shorting plane in the center of the circular patch antenna and create a halfpatch circular antenna. As is the case with the rectangular patch. Figure shows the E-plane and H-plane radiation patterns. The ratio of the semimajor to semiminor axes that will produce circular polarization is given by equation 3.
The value of antenna Q can be computed using the cavity model equation 3. One can also measure the Q of the antenna experimentally, or use results from a full-wave analysis such as FDTD with equation 3.
The antenna must have a single apparent resonance with reasonable symmetry for this equation to apply. Figure Circular microstrip antenna and the antenna perturbed into an ellipse to produce circular polarization heavy dot is RHCP feed. The FDTD analysis of the circular patch example produced a negative return loss plot from which we use equation 3. Figure Rotating linear plots of an elliptical patch antenna which produces circular polarization designed using equation 3.
On the left is a cut through the minor axis of the ellipse x-z and on the right is a cut through the major axis of the ellipse y-z. Figure provides synthesized rotating linear principle plane patterns from an FDTD analysis driven with a sinusoidal source with a square coaxial probe at 2. A branchline hybrid is an alternative method one may use to generate circular polarization from a circular patch. Figure shows a TM11 mode. This antenna produces a monopole pattern with circular polarization.
This is analogous to the use of a branchline hybrid to generate circular polarization with a square patch. In practice, the unused port would be terminated with a load. The TM21 mode has the next highest frequency of operation after TM This particular mode is useful in creating a monopole radiation pattern that has circular polarization, as described by Huang.
This angular spacing produces two modes driven orthogonal to each other, as is their radiation. One may obtain better circular polarization axial ratio by feeding the antenna in four probe locations rather than two. These locations are diametrically across from the two original feed points.
These relationships are related in detail by Huang. The pattern will also move further broadside with increasing relative dielectric constant.
In commercial applications, a complex feed structure with its required feed network may be untenable as a design. It is possible to drive a patch in the TM21 mode with a single feed which will produce circular polarization. We will use a patch of radius The substrate thickness is 1. The feed point radius is FDTD was used to analyze a circular patch antenna with the previous parameters and produce a negative return loss plot.
The Q was computed to be Figure 3. The patterns are synthesized rotating linear plots. The patch is probe fed with a square coaxial transmission line. The maximum directivity computed by FDTD analysis is 5. The computed radiation patterns are presented in Figure This can be very useful for replacing a quarter-wave monopole antenna. The feed point radius is 7. On the right is a cut through the plane of the probe.
The small square is the probe feed. The description of driving point impedance is given in equation 3. It has been. The maximum pattern directivity is 5. The permittivity and thickness of the substrate used to create a microstrip antenna determines its cross-polarization performance. The pattern on the left is a cut in a plane perpendicular to the plane which contains the probe feed.
In the E-plane. The origin of the radiated cross-polarization is associated with the generation of higher order modes on the patch. The probe feed is 5. When a patch is designed to be driven in the TM21 mode. Figure presents sketches of the current of a a TM21 mode circular patch antenna and b a TM11 mode circular patch antenna. The cross-polarization performance of a linearly polarized patch is dependent on substrate thickness.
The cross-polarization pattern is consistent with the pattern shape expected from the TM21 mode. When a low dielectric constant is used to design a microstrip antenna element. The E-plane pattern has a small. It could be from an imperfect generation of the TM21 mode. Garcia-Garcia states that when an antenna is driven in the fundamental mode TM An illustrative example was analyzed with the FDTD method.
When a patch is driven in the fundamental TM11 mode. We note the H-plane pattern has the expected TM21 mode pattern shape. The E-plane crosspolarized pattern has a shape consistent with the TM11 mode. The geometry of a circular patch does not enforce a single direction for the TM11 mode as a square patch does for the TM10 mode.
It is very possible the computed cross-polarization is from the generation of a TM11 mode with very small amplitude. Circular Microstrip Antennas 95 Figure a Sketch of the theoretical current distribution of the TM21 mode of a circular patch antenna. Circular Microstrip Antennas Circular patch co. The outer radius is b. Circular Microstrip Antennas 3. We assume the Figure Annular microstrip antenna geometry. The radial component of the surface current will disappear at an edge:
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