Antenna Basics And Types Cal

ANTENNA TYPES AND ITS BASICS (By Theoretical Point of View with figures)

Data Compiled by: Engr. Sajjad Hussain Kanju

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ANTENNA TYPES AND ITS BASICS

by:

Engr. Sajjad Hussain Kanju

ANTENNA An antenna (or aerial) is a transducer designed to transmit or receive electromagnetic waves. In other words, antennas convert electromagnetic waves into electrical currents and vice versa. Antennas are used in systems such as radio and television broadcasting, point-to-point radio communication, wireless LAN, radar, and space exploration. Antennas are most commonly employed in air or outer space, but can also be operated under water or even through soil and rock at certain frequencies for short distances. Physical Structure: Physically, an antenna is simply an arrangement of one or more conductors, usually called elements in this context. In transmission, an alternating current is created in the elements by applying a voltage at the antenna terminals, causing the elements to radiate an electromagnetic field. In reception, the inverse occurs: an electromagnetic field from another source induces an alternating current in the elements and a corresponding voltage at the antenna's terminals. Some receiving antennas (such as parabolic and horn types) incorporate shaped reflective surfaces to collect EM waves from free space and direct or focus them onto the actual conductive elements. PARAMETERS:: There are several critical parameters affecting an antenna's performance that can be adjusted during the design process. All of these parameters can be measured through various means. Their short details are given here: 1. Resonant frequency The "resonant frequency" and "electrical resonance" is related to the electrical length of an antenna. The electrical length is usually the physical length of the wire divided by its velocity factor (the ratio of the speed of wave propagation in the wire to c0, the speed of light in a vacuum). Typically an antenna is tuned for a specific frequency, and is effective for a range of frequencies that are usually centered on that resonant frequency. However, other properties of an antenna change with frequency, in particular the radiation pattern and impedance, so the antenna's resonant frequency may merely be close to the center. 2. Gain Gain as a parameter measures the efficiency of a given antenna with respect to a given norm, usually achieved by modification of its directionality. An antenna with a low gain emits radiation with about the same power in all directions, whereas a high-gain antenna will preferentially radiate in particular directions. Specifically, the Gain, Directive gain or Power gain of an antenna is defined as the ratio of the intensity (power per unit surface) radiated by the antenna in a given direction at an arbitrary distance divided by the intensity radiated at the same distance by a hypothetical isotropic antenna. High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully in a particular direction. Low-gain antennas have shorter range, but the orientation of the antenna is relatively inconsequential. For example, a dish antenna on a spacecraft is a high-gain device that must be pointed at the planet to be effective, whereas a typical Wi-Fi antenna in a laptop computer is lowgain, and as long as the base station is within range, the antenna can be in any orientation in space.

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ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

3. Radiation pattern The radiation pattern of an antenna is the geometric pattern of the relative field strengths of the field emitted by the antenna. For the ideal isotropic antenna, this would be a sphere. For a typical dipole, this would be a toroid. The radiation pattern of an antenna is typically represented by a three dimensional graph, or polar plots of the horizontal and vertical cross sections. The graph should show sidelobes and backlobes, where the antenna's gain is at a minima or maxima. 4. Impedance Impedance of an antenna is related to the electrical length of the antenna at the wavelength in use. The impedance of an antenna can be matched to the feed line and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, the impedance is adjusted at the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching sections such as the gamma match. Standing Wave Ratio (SWR) : The ratio of maximum power to minimum power in the wave can be measured and is called the standing wave ratio. A SWR of 1:1 is ideal 5. Efficiency Efficiency is the ratio of power actually radiated to the power put into the antenna terminals. A dummy load may have an SWR of 1:1 but an efficiency of 0, as it absorbs all power and radiates heat but not RF energy, showing that SWR alone is not an effective measure of an antenna's efficiency. 6. Bandwidth The bandwidth of an antenna is the range of frequencies over which it is effective, usually centered on the resonant frequency. The bandwidth of an antenna may be increased by several techniques, including using thicker wires, replacing wires with cages to simulate a thicker wire, tapering antenna components (like in a feed horn), and combining multiple antennas into a single assembly and allowing the natural impedance to select the correct antenna. 7. Polarization The polarization of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation. It has nothing in common with antenna directionality terms: "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. Reflections generally affect polarization. For radio waves the most important reflector is the ionosphere signals which reflect from it will have their polarization changed unpredictably. For line-of-sight communications for which polarization can be relied upon, it can make a large difference in signal quality to have the transmitter and receiver using the same polarization; many tens of dB difference are commonly seen and this is more than enough to make the difference between reasonable communication and a broken link. So horizontal should be used with horizontal and vertical with vertical. Transmitters mounted on vehicles with large motional freedom commonly use circularly polarized antennas so that there will never be a complete mismatch with signals from other sources. In the case of radar, this is often reflections from rain drops. 3|Page

ANTENNA TYPES AND ITS BASICS

by:

Engr. Sajjad Hussain Kanju

8. Transmission and reception All of the antenna parameters are expressed in terms of a transmission antenna, but are identically applicable to a receiving antenna, due to reciprocity. For a transmitting antenna, this is the antenna itself. For a receiving antenna, this is at the (radio) receiver rather than at the antenna. Tuning is done by adjusting the length of an electrically long linear antenna to alter the electrical resonance of the antenna. Antenna tuning is done by adjusting an inductance or capacitance combined with the active antenna. Adjustment of the inductance or capacitance changes this resonance. Antennas used for transmission have a maximum power rating. ANTENNA TYPES:

Parabolic antenna A parabolic antenna is a high-gain reflector antenna used for radio, television and data communications, and also for radiolocation (radar), on the UHF and SHF parts of the electromagnetic spectrum. The relatively short wavelength of electromagnetic radiation at these frequencies allows reasonably sized reflectors to exhibit the desired highly directional response for both receiving and transmitting. With the advent of TVRO and DBS satellite television, the parabolic antenna became a ubiquitous feature of urban, suburban, and even rural landscapes. Extensive terrestrial microwave links, such as those between cellphone base stations, and wireless WAN/LAN applications have also proliferated this antenna type. Earlier applications included ground-based and airborne radar and radio astronomy. However a term dish antenna is often used for a parabolic antenna instead, it connote a spheric antenna as well, which has a portion of spherical surface as the reflector shape.

HRS antenna (Horizontal Radiator Slew able) HRS type antennas are more or less the standard antenna used for long distance high power shortwave broadcasting (> 1000 km). What are HRS type antennas? The curtain antenna is a dipole array, consisting of rows and columns of dipoles. •

•

The curtain antenna is a high gain directional antenna, that is designed for medium and long range shortwave communications. The HR(S) notation is as follows o HR Rows/Columns/Wavelength(s) -- Above Ground

Horn Antenna Antenna 4|Page

ANTENNA TYPES AND ITS BASICS

by:

Engr. Sajjad Hussain Kanju

Horn antennas are very popular at UHF (300 MHz-3 GHz) and higher frequencies (I've heard of horns operating as high as 140 GHz). They often have a directional radiation pattern with a high gain , which can range up to 25 dB in some cases, with 10-20 dB being typical. Horns have a wide impedance bandwidth, implying that the input impedance is slowly varying over a wide frequency range (which also implies low values for S11 or VSWR). The bandwidth for practical horn antennas can be on the order of 20:1 (for instance, operating from 1 GHz-20 Types of horn antenna 1. Conical horn antenna Conical horn antenna can be directly excited from a circular waveguides. 2. Ridge horns Central ridge loads a waveguides and increases the bandwidth by lowering cutoff frequency of the dominant mode 3. Septum horns 4. Corrugated horns: Corrugated horns can provide reduced diffraction, improved pattern symmetry and reduced cross polarization 5. Aperture-Matched antenna

Monopole antenna A monopole antenna is a type of radio antenna formed by replacing one half of a dipole antenna with a ground plane at right-angles to the remaining half. If the ground plane is large enough, the monopole behaves exactly like a dipole, as if its reflection in the ground plane formed the missing half of the dipole (see image antenna). However, a monopole will have a directive gain of 5.19dB (gain is twice (3dB over) that for a half-wave dipole antenna), and a lower input resistance, resulting in overall lower efficiency. Normally used in AM broadcasting.

Satellite dish (Redirect from Satellite Master Antenna Television) A dish is a type of parabolic antenna designed to receive microwaves from communications satellites, which transmit data transmissions or broadcasts, such as satellite television. Types of Satellite dish.

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ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

Motor-driven dish A dish that is mounted on a pole and driven by a stepper motor can be controlled and rotated to face any satellite position in the sky. Motor-driven dishes are popular with enthusiasts. There are three competing standards: DiSEqC, USALS, and 36v positioners. Many receivers support all of these standards. Some designs enable simultaneous reception from multiple different satellite positions without re-positioning the dish. The vertical axis operates as an off-axis concave parabolic concave hyperbolic Cassegrain reflector, while the horizontal axis operates as a concave convex Cassegrain. The spot from the main dish wanders across the secondary, which corrects astigmatism by its varying curvature. The elliptic aperture of the primary is designed to fit the deformed illumination by the horns. Due to double spill-over, this makes more sense for a large dish. VSAT A common type of dish is the very small aperture terminal (VSAT). This provides two way satellite internet communications for both consumers and private networks for organisations. Today most VSATs operate in Ku band, C band is restricted to less populated regions of the world. There is a move which started in 2005 towards new Ka band satellites operating at higher frequencies, offering greater performance at lower cost. These antennas vary from 74cm to 120cm in most applications though C-band VSATs may be as large as 4.0m. Ad hoc The dish is a reflector antenna and almost anything that reflects radio frequencies can be used as a reflector antenna. This has led to dustbin lids, woks and other items being used as "dishes". Coupled with low noise LNBs and the higher transmission power of DTH satellites, it is easier to get a usable signal on some of these "dishes".

Microstrip Antenna Antenna In telecommunication, there are several types of microstrip antennas (also known as printed antennas) the most common of which is the microstrip patch antenna or patch antenna. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate with a continuous metal layer bonded to the opposite side of the substrate which forms a groundplane. Common microstrip antenna radiator shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas eschew a dielectric substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the resulting structure is less robust but 6|Page ANTENNA TYPES AND ITS BASICS by: Engr. Sajjad Hussain Kanju

provides better bandwidth. Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices. They are usually employed at UHF and higher frequencies because the size of the antenna is directly tied to the wavelength at the resonance

frequency frequency Crossed Field Antenna Antenna A crossed field antenna, or CFA, was a type of antenna for long and mediumwave broadcasting, patented in 1986, which was claimed to have the same efficiency as a conventional antenna but only one-tenth the overall height. The invention was received with incredulity from experts in electromagnetics and antenna technology owing to the deficient theoretical justifications offered and the lack of viable experimental verification. The physical structure of a crossed-field antenna is: • • •

A horizontal metal disc (or "D-plate") raised above and insulated from the ground plane; A vertical hollow metal cylinder (or "E-plate") of smaller diameter than the disc, which it is mounted concentrically above and insulated from; A metal lattice funnel (or "extended conical section") radiating above and outward from and connected to the top of the cylinder.

Offset Dish Antenna Antenna

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ANTENNA TYPES AND ITS BASICS

by:

Engr. Sajjad Hussain Kanju

An offset dish antenna is a type of satellite dish. It is so called because the antenna feed is offset to the side of the reflector, in contrast to a typical circular parabolic antenna where the feed is in front of the center of the reflector. Offset feed antennas are most commonly found on Ku Band DBS satellite dishes or ‘mini-dishes’. The benefit of the offset configuration is that it positions the feed horn away from the dish itself so that it does not cast a shadow on the dish. Offset dishes are often referred to as ‘asymmetrical’.

Tactical Vest Antenna System System Tactical Vest Antenna System (TVAS) is a type of wearable antenna designed for use by the U.S. military. It is claimed that troops equipped with the TVAS are more effective than traditional whip antenna-equipped troops due to better concealment of the equipment and mobility improvement to the operator. TVAS for was developed by Wearable Antenna Technologies Inc in early 2008.

Technical details The Tactical Vest Antenna System consists of two radiating elements that are connected by a cable. The cable acts as an extension of the radiating elements, and includes a "quick release" mechanism found in MTV and FSBE designs. Each of the radiating elements of the antenna is laminated between two sheets of polycarbonate plastic. Patch Antenna Antenna A patch antenna (also known as a Rectangular Microstrip Antenna) is a popular antenna type. Its name is attributed to the fact that it consists of a single metal patch suspended over a ground plane. The assembly is usually contained inside a plastic radome, which protects the antenna structure from damage (as well as concealing its essential simplicity). Patch antennas are simple to fabricate and easy to modify and customize. They are the original microstrip antenna as described by Howell [1], which are a length of microstrip transmission line of approximately one-half wavelength. The radiation mechanism arises from discontinuities at each truncated edge of the microstrip transmission line.[2] The radiation at the edges causes the antenna to be slightly larger than its physical dimension electrically. In order to obtain a resonant condition at the antenna driving point, a shorter than a one-half wavelength section of microstrip transmission line is used. A patch antenna is generally constructed on a dielectric substrate, usually employing the same sort of lithographic patterning used to fabricate printed circuit boards. 8|Page

ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

Patch

antenan

MIMO (redirect from intelligent antenna) antenna) In radio, multiple-input and multiple-output, or MIMO (commonly pronounced my-moh or me-moh), is the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology. MIMO technology has attracted attention in wireless communications, since it offers significant increases in data throughput and link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability or diversity (reduced fading). Because of these properties, MIMO is a current theme of international wireless research. Applications of MIMO Spatial multiplexing techniques makes the receivers very complex, and therefore it is typically combined with Orthogonal frequency-division multiplexing (OFDM) or with Orthogonal Frequency Division Multiple Access (OFDMA) modulation, where the problems created by multi-path channel are handled efficiently. The IEEE 802.16e standard incorporates MIMO-OFDMA. The IEEE 802.11n standard, scheduled to be finalized in late 2009, recommends MIMO-OFDM. MIMO is also planned to be used in Mobile radio telephone standards such as recent 3GPP and 3GPP2 standards. In 3GPP, High-Speed Packet Access plus (HSPA+) and Long Term Evolution (LTE) standards take MIMO into account. Moreover, to fully support cellular environments MIMO research consortia including IST-MASCOT propose to develop advanced MIMO techniques, i.e., multi-user MIMO (MU-MIMO). MIMO Technology in WiMAX WiMAX implementations that use MIMO technology have become important. The use of MIMO technology improves the reception and allows for a better reach and rate of transmission. The implementation of MIMO also gives WiMAX a significant increase in spectral efficiency. WiMAX WiMAX is the technology brand name for the implementation of the standard IEEE 802.16. 802.16 specifies the air interface at the PHY (Physical layer) and at the MAC (Medium Access Control layer) . Aside from specifying the support of various channel bandwidths and adaptive modulation and coding, it also specifies the support for MIMO antennas to provide good Non-line-of-sight (NLOS) characteristics.

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ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

Radio Telescope Telescope (section Radio telescope types) A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes. In their astronomical role they differ from optical telescopes in that they operate in the radio frequency portion of the electromagnetic spectrum where they can detect and collect data on radio sources. Radio telescopes are typically large parabolic ("dish") antennas used singly or in an array. This is similar to the locating of optical telescopes to avoid light pollution, with the difference being that radio observatories are often placed in valleys to further shield them from EMI as opposed to clear air mountain tops for optical observatories.

Random wire antenna A random-length wire antenna is a type of radio frequency antenna typically chosen more for convenience than any particular design criteria. This antenna sometimes is called the zig-zag antenna, as it may be strung back and forth between trees just to get enough wire into the air. For example, an antenna for 3MHz might be 20 m (66 ft) - 40 m (131 ft) long. Typically this antenna is constructed from a number 12 or 14 AWG (1.6 to 2.0 mm (0 in) diameter) wire of nearly any length. Such an antenna can be used for transmitting on practically any frequency with a properly tuned matching network.[1] Although random wire antennas can be made from nearly any length of wire, one-quarter wavelength works best, and one half wavelength will work poorly with most tuners.

Indoor antenna An Indoor antenna is a type of Radio or TV Antenna placed indoors, as opposed to being mounted on the roof. Indoor antennas are usually a simple and cheap solution that may work well when the receiver is relatively near to the broadcasting transmitter and the building walls do not shield the radio waves too much. Being close to other electric or electronic equipment in the building, an indoor antenna is prone to picking up more electrical noise that may interfere with a clear (analog) reception. Used for digital broadcast, the noise is less of a factor, which recently makes this type of antenna a more popular solution. 10 | P a g e

ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

Ground dipole (redirect from Ground antenna) Ground dipole antennas are usually used for transmitting and receiving on the ELF and VLF bands. The antenna consists of two electrodes, planted in the ground at some distance from each other. Radio signal currents are sent along wires to the electrodes. The current flows in a loop, around the above-ground wires and through the Earth (where conductive), forming a large conducting loop, which radiates electromagnetic waves.

Dipole Dipole antenna (section Dipole types)

A dipole antenna, created by Heinrich Rudolph Hertz around 1886,[citation needed] is an antenna that can be made by a simple wire, with a center-fed driven element for transmitting or receiving radio frequency energy. These antennas are the simplest practical antennas from a theoretical point of view; the current amplitude on such an antenna decreases uniformly from maximum at the center to zero at the ends.

Fractal Antenna Antenna A fractal antenna is an antenna that uses a fractal, self-similar design to maximize the length, or increase the perimeter (on inside sections or the outer structure), of material that can receive or transmit electromagnetic radiation within a given total surface area or volume.

A fractal antenna's response differs markedly from traditional antenna designs, in that it is capable of operating with good-to-excellent performance at many different frequencies simultaneously. Normally standard antennas have to be "cut" for the frequency for which they are to be used—and thus the standard antennas only work well at that frequency. This makes the fractal antenna an excellent design for wideband and multiband applications.

Helical Antenna Antenna A helical antenna is an antenna consisting of a conducting wire wound in the form of a helix. In most cases, helical antennas are mounted over a ground plane. Helical antennas can operate in one 11 | P a g e

ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

of two principal modes: normal (broadside) mode or axial (or end-fire) mode. Indications are given below: B: Central Support C: Coaxial Cable, E: Spacers/Supports for the Helix, R: Reflector/Base, S: Helical Aerial Element

Directional antenna A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. Directional antennas like yagi antennas provide increased performance over dipole antennas when a greater concentration of radiation in a certain direction is desired.All practical antennas are at least somewhat directional, although usually only the direction in the plane parallel to the earth considered, and practical antennas can easily be omnidirectional in plane.

is one

The most common types are the yagi antenna, the log-periodic antenna, and the corner reflector, which are frequently combined and commercially sold as residential TV antennas. Cellular repeaters often make use of external directional antennas to give a far greater signal than can be obtained on a standard cell phone.

a. YAGI-UDA ANTENNA A Yagi-Uda Antenna, commonly known simply as a Yagi antenna or Yagi, is a directional antenna system[1] consisting of an array of a dipole and additional closely coupled parasitic elements (usually a reflector and one or more directors). The dipole in the array is driven, and another element, typically 10% longer, effectively operates as a reflector. Other parasitic elements shorter than the dipole may be added in front of the dipole and are referred to as directors.

This arrangement gives the antenna directionality that a single dipole lacks. Directional antennas, such as the Yagi-Uda, are also commonly referred to as beam antennas[2] or high-gain antennas (particularly for transmitting).

A1. Corner Reflector

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ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju

A corner reflector is a retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects electromagnetic waves back towards the source. The three intersecting surfaces often have square shapes. This is also known as a corner cube. Corner reflectors are placed on the vessel's masts at a height of at least 4.6 meters above sea level. Popular corner reflectors used on ships are (amongst others) the RORC radar reflectors, Firdel Blippers and EchoMax radar reflectors. Such devices are often used as radar targets or markers and are often employed on ships and, especially, lifeboats; Francis Rogallo invented a target kite incorporating corner reflectors. These normally consist of three conducting metallic surfaces or screens perpendicular to one another.

A2. Log-periodic antenna In telecommunication, a log-periodic antenna (LP, also known as a log-periodic array) is a broadband, multielement, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The individual components are often dipoles, as in a log-periodic dipole array (LPDA). Log-periodic antennas are designed to be selfsimilar and are thus also fractal antenna arrays.

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ANTENNA TYPES AND ITS BASICS

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Engr. Sajjad Hussain Kanju