ANTENNA ARRAYS - PowerPoint PPT Presentation
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View by Category Toggle navigation. Products Sold on our sister site CrystalGraphics. Tags: antenna arrays concept matching. Latest Highest Rated. By changing the feeding it is possible to construct a directive beam that can be repositioned electronically.
Amplitude control can be used for pattern shaping The beam can be pointed to new direction, narrowed or widened in microseconds. An array that has a main peak at a certain angle can also have other peak values depending on the spacing between the antenna elements.
Solving the problem using numerical methods is not practical. Therefore other effective methods are needed to account for mutual coupling effects. Finite Array Approach Used for small and medium arrays. Active element pattern is calculated separately for each element in the array. Infinite array assumption For large arrays, the central elements that are far away from edges are affected less infinite array concept can then be used It is assumed that for all elements the currents are similar except for some complex constants.
When this approach is used, it is sufficient to analyze only one element completely 11 Mutual Coupling cont. For medium size arrays, the exact AEP methods are difficult to use and average AEP method yields in errors in calculating the array pattern For these arrays the combination of the two methods are used to obtain more accurate results for the array pattern 12 Array Blindness Direct consequence of mutual coupling Can result in complete cancellation of the radiated beam at some scan angle Occurs when most of the central elements of the array have reflection coefficients close to unity 13 Array Performance Array Lattice Array Bandwidth Differences Between Single Element and Array Performances Amplitude Tapering For Sidelobe Level Control Wide-Angle Impedance Matching WAIM 14 Array PerformanceArray Lattice The position of the array elements describes the array lattice and there are basically three types for planar arrays 15 Array PerformanceArray Bandwidth The bandwidth of the array depends on the radiators, phase shifters, feeding networks etc.
Phase shifters and feeding networks possess error transfer functions which grows with increasing bandwidth. The error analysis of the effect on the pattern will determines the bandwidth. Stronger tapering results in reduced sidelobe at the expense of increased beamwidth and reduced gain. The power of percentage in the main beam varies with the number of elements in the array for a given SL 20 Example of illumination coefficients and array pattern for a 20 dB taper applied to a 16 element array 21 Array PerformanceWide-Angle Impedance Matching WAIM Scan impedance is the impedance of an element as a function of scan angle with all elements excited with proper amplitude and phase.
For wide scan angles another mismatch due to the scan angle occurs. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, PowerShow. And, best of all, most of its cool features are free and easy to use.
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But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides.In antenna theory, a phased array usually means an electronically scanned arraya computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving the antennas.
In a simple array antennathe radio frequency current from the transmitter is fed to the individual antennas with the correct phase relationship so that the radio waves from the separate antennas add together to increase the radiation in a desired direction and cancel to suppress radiation in undesired directions.
In a phased array, the power from the transmitter is fed to the antennas through devices called phase shifterscontrolled by a computer system, which can alter the phase electronically, thus steering the beam of radio waves to a different direction.
Since the array must consist of many small antennas sometimes thousands to achieve high gain, phased arrays are mainly practical at the high frequency end of the radio spectrum, in the UHF and microwave bands, in which the antenna elements are conveniently small. Phased arrays were invented for use in military radar systems, to steer a beam of radio waves quickly across the sky to detect planes and missiles.
These systems are now widely used and have spread to civilian applications. The phased array principle is also used in acousticsand phased arrays of acoustic transducers are used in medical ultrasound imaging scanners phased array ultrasonicsoil and gas prospecting reflection seismologyand military sonar systems.
The term "phased array" is also used to a lesser extent for unsteered array antennas in which the phase of the feed power and thus the radiation pattern of the antenna array is fixed. Phased arrays take multiple forms. PESAs are the most common type of phased array.
Active arrays are a more advanced, second-generation phased-array technology which are used in military applications; unlike PESAs they can radiate several beams of radio waves at multiple frequencies in different directions simultaneously.
However, the number of simultaneous beams is limited by practical reasons of electronic packaging of the beam former s to approximately three simultaneous beams for an AESA. A hybrid beam forming phased array can be thought of as a combination of an AESA and a digital beam forming phased array.
It uses subarrays that are active phased arrays for instance, a subarray may be 64, or elements and the number of elements depends upon system requirements. The subarrays are combined together to form the full array.
This approach allows clusters of simultaneous beams to be created. This means that antenna beams can be formed digitally in a field programmable gate array FPGA or the array computer. This approach allows for multiple simultaneous antenna beams to be formed. One possible physical implementation of a phased array is called a conformal antenna. The phase shifters compensate for the different path lengths of the waves due to the antenna elements' varying position on the surface, allowing the array to radiate a plane wave.
Conformal antennas are used in aircraft and missiles, to integrate the antenna into the curving surface of the aircraft to reduce aerodynamic drag. Phased array transmission was originally shown in by Nobel laureate Karl Ferdinand Braun who demonstrated enhanced transmission of radio waves in one direction.
This design is also used for radarand is generalized in interferometric radio antennas. The relative amplitudes of—and constructive and destructive interference effects among—the signals radiated by the individual antennas determine the effective radiation pattern of the array. A phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation. Simultaneous electrical scanning in both azimuth and elevation was first demonstrated in a phased array antenna at Hughes Aircraft CompanyCalifornia in In broadcast engineeringphased arrays are used by many AM broadcast radio stations to enhance signal strength and therefore coverage in the city of licensewhile minimizing interference to other areas.
Due to the differences between daytime and nighttime ionospheric propagation at mediumwave frequencies, it is common for AM broadcast stations to change between day groundwave and night skywave radiation patterns by switching the phase and power levels supplied to the individual antenna elements mast radiators daily at sunrise and sunset. For shortwave broadcasts many stations use arrays of horizontal dipoles. Usually this is in front of a wire grid reflector.
The phasing is often switchable to allow Beam steering in azimuth and sometimes elevation. More modest phased array longwire antenna systems may be employed by private radio enthusiasts to receive longwave, mediumwave AM and shortwave radio broadcasts from great distances. These greatly increase the antenna gainmagnifying the emitted RF energy toward the horizonwhich in turn greatly increases a station's broadcast range. In these situations, the distance to each element from the transmitter is identical, or is one or other integer wavelength apart.
Phasing the array such that the lower elements are slightly delayed by making the distance to them longer causes a downward beam tiltwhich is very useful if the antenna is quite high on a radio tower.
Other phasing adjustments can increase the downward radiation in the far field without tilting the main lobecreating null fill to compensate for extremely high mountaintop locations, or decrease it in the near fieldto prevent excessive exposure to those workers or even nearby homeowners on the ground.
You can change your ad preferences anytime. The basics of antenna arrays. Upcoming SlideShare. Like this document? Why not share! Embed Size px. Start on. Show related SlideShares at end. WordPress Shortcode. Published in: EngineeringTechnologyBusiness. Full Name Comment goes here. Are you sure you want to Yes No. They can help you with any type of writing - from personal statement to research paper.
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Antennas and Antenna Arrays - PowerPoint PPT Presentation
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Products Sold on our sister site CrystalGraphics. Title: Antennas and Antenna Arrays. Description: The directive gain of an isotropic or omnidirectional antenna an antenna that Tags: antenna antennas arrays isotropic. Latest Highest Rated. Title: Antennas and Antenna Arrays 1 Chapter 10 Antennas and Antenna Arrays 2 Overview Antenna structures designed for radiating and receiving electromagnetic energy effectively in a prescribed manner.
Antenna array a number of antennas arranged together to obtain directivity and other desirable properties. Procedure for determining radiation characteristics of an antenna Determine the magnetic potential A. The phasor retarded vector magnetic potential 3 Overview continued where is the wavenumber. Find the magnetic field intensity H from A. Find the electric field intensity E from H with J0 in space. After knowing E and H, all other radiation characteristics of the antenna can be determined.
From Eq. Far fields of a Hertzian dipole The other field components can be neglected. E-plane pattern the magnitude of the normalized field strength with respect to the peak value versus for a constant H-plane pattern the magnitude of the normalized field strength versus for 10 Example Plot the E-plane and H-plane radiation patterns of a Hertzian dipole.
Since in the far zone are proportional to each other, we need only consider the normalized magnitude of E-plane pattern Fig. H-plane pattern Fig. The total time-average power radiated where is the differential solid angle Directive gain of an antenna pattern the ratio of the radiation intensity in the direction to the average radiation intensity 13 Antenna Patterns and Directivity continued The directive gain of an isotropic or omnidirectional antenna an antenna that radiates uniformly in all directions unity.
Antenna directivity, D the maximum directive gain of an antenna, the ratio of the maximum radiation intensity to the average radiation intensity.Perhaps tweeting, texting or blogging is your way of coping with stress or angry feelings.
Or maybe you have trouble relating to others, or are excessively shy with people in real life and find it easier to communicate with people online. Building skills in these areas will help you weather the stresses and strains of daily life without relying on your smartphone.
Recognize any underlying problems that may support your compulsive behavior. Have you had problems with alcohol or drugs in the past.
Does anything about your smartphone use remind you of how you used to drink or use drugs to numb or distract yourself. Recognize if you need to address treatment in these areas or return to group support meetings. Think of it more like going on a diet. Just as you still need to eat, you probably still need to use your phone for work, school or to stay in touch with friends. Your goal should be to cut back to more healthy levels of use. Therapy can give you a tremendous boost in controlling smartphone and Internet use.
Cognitive-behavioral therapy provides step-by-step ways to stop compulsive behaviors and change your perceptions about your smartphone. Therapy can also help you learn healthier ways of coping with uncomfortable emotions, such as stress, anxiety, or depression. If your smartphone or Internet use is affecting your partner directly, as with excessive use of Internet pornography or online affairs, marriage counseling can help you work through these challenging issues.
Marriage counseling can also help you reconnect with your partner if you have been using virtual worlds for most of your social needs. Of course, online support groups and forums should be used with caution. Sex Addicts Anonymous may be another place to try if you are having trouble with cybersex or compulsive use of sex and dating apps.
For those in need of greater intervention, there are now specialist treatment centers that offer digital detox programs to help you disconnect from digital media. For help finding these, as well as support groups and therapists, see the Resources and References section below.
The American Academy of Pediatrics (AAP) recommends that kids under age 2 have no screen time, while young children older than 2 should spend no more than 1 to 2 hours a day viewing age-appropriate material. Of course, once kids have their own smartphones, limiting their use becomes that much more difficult. Youngsters lack the maturity to curb their smartphone use on their own, but simply confiscating the device can often backfire, creating anxiety and withdrawal symptoms in your child.
Instead, there are plenty of other ways to help your child find a healthier balance: Be a good role model. Try not to let your own smartphone use distract from parent-child interactions. Other apps can eliminate messaging capabilities while in motion, so you can prevent your teen using a smartphone while driving.
Restrict the use of smartphones or tablets to a common area of the house where you can keep an eye on your child's activity and limit time online. Encourage other interests and social activities.