69. VSWR     This antenna radiates maximally in directions perpendicular to the antenna's axis, giving it a small directive gain of 2.15 dBi. It is a mathematical model that is used as the base of comparison to calculate the directionality or gain of real antennas. one with vertical elements) will receive vertically polarised signals best and similarly a horizontal antenna will receive horizontally polarised signals. The great disadvantage of any small antenna, including small loops, is a very small radiation resistance – typically much smaller than the loss resistance, making small loops very inefficient for transmitting. The polarization of a vertical dipole is vertical. 2.4. Collinear arrays of dipoles, these radiate a flat, fan-shaped beam. Low radiation efficiency c. Both a and b d. None of the above A novel polarization-reconfigurable conical helical antenna based on the liquid metal is presented. Definition− “The Effective length is the ratio of the magnitude of voltage at the open terminals of the receiving antenna to the magnitude of the field strength of the incident wave front, in the same direction of antenna polarization.” Meteor scatter     Plane b. Elliptical c. Circular d. All of the above. Aperture antennas can be resonant or not. Low radiation resistance b. A log-periodic antenna is also named as a log periodic array. Dielectric lens antenna used in millimeter wave radio telescope. Mast radiator antenna of medium wave AM radio station, Germany, Folded unipole with skirt wires connected at a midpoint on the tower. cross-polarised) then in theory no signal would be received. 17% B. Three different types of antennas were used in this ex- periment, as shown in Fig. View Answer: Answer ... View Answer: Answer: Option D. Solution: 24. A. ▶︎ Rohde &Schwarz Focus on Test Zone. Segmented helical antennas, such as square cross section helical antennas provide approximately equivalent performance compared to the conventional helical antennas. Endfire arrays are fed out-of-phase, with the phase difference corresponding to the distance between them; they radiate within the antenna plane. In the case of linear polarization, we have the decomposition formed by two circular waves in opposite directions and with equal magnitudes. Wire dipoles suspended between towers. The tapered helical shape also provided wide bandwidth in circularly polarized mode. It is the simplest antenna, which provides circularly polarized waves. Antennas can be classified in various ways. [2][6][7] Parasitic arrays consist of multiple antennas, usually dipoles, with one driven element and the rest parasitic elements, which radiate a beam along the line of the antennas. Polarity is as important as gain, radiation pattern and VSWR, in the selection of an antenna. Helical antennas and crossed-Yagis antennas. For most antennas it is very easy to determine the polarization. There are several categories of polarisation, and within each type there are several sub categories. [2][9][10] There are essentially two broad categories of loop antennas: large loops (or full-wave loops) and small loops.     Return to Antennas & Propagation menu . - Published on 01 Oct 15 a. a. Log-Periodic Antennas. They have linear polarization (except for the helical antenna). Antenna Basic Theory Tutorial Includes: Deployable microwave origami antenna - Published on 01 Oct 15 a. X band marine radar slot antenna on ship, 8 – 12 GHz. Parabolic reflector antenna     According to depth of penetration, what is the percentage proportion of attenuated wave w.r.t its original value? In testing transmitter to prevent interfering with other stations, which type of antenna must be used? The proposed plasma-based HA is suitable for integration with electronic circuit components used in system-on-chip applications. Helical antennas can receive signals with any type of linear polarisation, such as horizontal or vertical polarisation, but when receiving circularly polarized signals the handedness of the receiving antenna must be the same as the transmitting antenna; left-hand polarized antennas suffer a severe loss of gain when receiving right-circularly-polarized signals, and vice versa. However, small loops are very effective receiving antennas, especially at low frequencies, where all feasible antennas are "small" compared to a wavelength. The same situation exists when a circularly polarised antenna receives a linearly polarised signal. In this way the maximum signal is obtained. Ground plane reflector behind helix of shape circular or square is used. Has circular polarization. It is used in extra-terrestrial communications in which satellite relays etc., are involved. The other two are also type III antennas but have 180” helical twists instead of the straight horizontal 2. It may have a wide bandwidth with up to 12 dB of forward gain but with very narrow beamwidth of approximately 60 degrees. the quadrifilar helical antenna provides circular polarization and complete hemispherical reception which is precisely what is needed to receive the polar orbiting weather satellites and as a 2 meter antenna it will receive horizontal vertical and clockwise circular polarization . This means that for some forms of broadcasting, radio communications or for some wireless systems, different forms of polarisation may be used. The helix antenna works as unidirectional antenna. Antennas Applications - Electronic Engineering (MCQ) questions & answers Home >> Category >> Electronic Engineering (MCQ) questions & answers >> Antennas Applications 1) If the tower antenna is not grounded, which method of excitation is/are applicable for it? Only one design, a "halo" antenna, that is usually called a loop does not fit into either the large or small loop categories. In radio systems, many different antenna types are used with specialized properties for particular applications. There will be some degradation because the signal level will be 3 dB less than if a circularly polarised antenna of the same sense was used. As the received signal is the sum of the direct signal plus a number of reflected signals the overall polarisation of the signal can change slightly although it remains broadly the same. This makes them inefficient as transmitting antennas. Traveling wave antennas are nonresonant types, the current and voltage waves travel in one direction along the antenna elements. Small monopoles are used as nondirectional antennas on portable radios in the HF, VHF, and UHF bands. Vertical antennas     1. Along with this the relevant antennas have corresponding polarisations. B. https://en.wikipedia.org/w/index.php?title=Antenna_types&oldid=982874288, Creative Commons Attribution-ShareAlike License, This page was last edited on 10 October 2020, at 22:10. The Helical is the most commonly encountered antenna designed for circular polarization. Figure 1: Types of Polarization Radiated by the Helical Antenna It can be shown that the elliptical polarized wave can be decomposed into two waves of opposite circular directions and different intensities. A planar helical antenna is presented for achieving wideband end-fire radiation of circular polarization while maintaining a very low profile. Ionospheric propagation     For terrestrial radio communications applications it is found that once a signal has been transmitted then its polarisation will remain broadly the same. However, the bulkiness of the helical can provide difficulty during safe transportation of the antenna and installation on the video receiver. Full loops have the highest radiation resistance, and hence the highest efficiency of all antennas: Their radiation resistances are several hundreds of Ohms, whereas dipoles and monopoles are tens of Ohms, and small loops are a few ohms, or even fractions of an Ohm.[10]. Dipole     Which kind of polarization is provided by helical antennas? a. 68) Which kind of polarization is provided by helical antennas? The helical design is a directional circularly polarized antenna. It is a multi … The first is the well known13 Nagoya type III antenna, which has m= + 1 symmetry and plane polarization. One area that takes advantage of this property is satellite communications. Inst of Tech-NU/Ant Theory/ch-6/Shailesh Pandey Principles and benefit • Most popular helical antenna is a traveling wave antenna, produces radiation along the axis of the helix. 70. There are several categories of polarisation, and within each type there are several sub categories. The helical antenna when in axial mode is incredibly wide band which makes it great to receive our wide band analog signals as well as making it great for construction because building tolerances are incredibly loose. Which kind of polarization is provided by helical antennas? A. Loop antennas consist of a loop (or coil) of wire. Uses X band, 8 – 12 GHz. Helical antennas have long been popular in applications from VHF to microwaves requiring circular polarization, since they have the unique property of naturally providing circularly polarized radiation. Log periodic antenna     Horizontal polarisation: This form of antenna polarisation has horizontal elements. Yagi     Feed impedance. Loop antennas interact directly with the magnetic field of the radio wave, rather than its electric field, making them relatively insensitive to electrical noise within about a quarter-wavelength of the antenna. Abstract: A wideband circularly polarized (CP) multi-turns plasma helical antenna (HA) with reconfigurable bandwidth is investigated for wireless communications in the x-band. Aperture antennas are the main type of directional antennas used at microwave frequencies and above. It is important to match the polarization of the RF antenna to that of the incoming signal. A. The frequency of the radiated wave . Array antennas consist of multiple simple antennas working together as a single compound antenna. 33) Which kind of polarization is provided by helical antennas? Polarization and operating frequency can be switched by mechanically folding and unfolding the antenna. If they were at right angles to one another (i.e. Plane B. Elliptical C. Circular D. All of the above. As end-fire helical antennas offer circularly polarized waves over a wider bandwidth. Helical Antenna. Helical antennas easily offer the wanted circular polarization, depending on how they are constructed. Dummy antenna ... D. Helical antenna . The most popular helical antenna (helix) is a travelling wave antenna in the shape of a corkscrew that produces radiation along the axis of the helix antenna. An isotropic antenna (isotropic radiator) is a hypothetical antenna that radiates equal signal power in all directions. Quarter-wave whip antenna on an FM radio for 88-108 MHz. 68. Waveguide     Ans: Circular. However reflections from objects in the path can change the polarisation. Although half-wave dipoles are used alone as omnidirectional antennas, they are also a building block of many other more complicated directional antennas. Helical antennas are the most frequently seen circularly polarized antennas in the pro sound world. Rubber ducky antenna on UHF 446 MHz walkie-talkie with rubber cover removed. Diameter of the wire is about 1/3 of wavelength and spacing between turns is about 1/4 of wavelength. T-antenna of amateur radio station, 80 ft high, used at 1.5 MHz. Microwave horn antenna bandwidth 0.8–18 GHz. Ferrite rod     MIMO     Enter the code shown above: (Note: If you cannot read the numbers in the above image, reload the page to generate a new one.) 4. The ground waves used for broadcasting at low frequencies must be vertically polarized, so large vertical monopole antennas are used for broadcasting in the MF, LF, and VLF bands. In general the advantages and disadvantages of the various forms of polarisation are relatively subtle, but form some forms of broadcasting, wireless links of for radio communications or mobile communications systems these small differences can make a large difference. a. The experimental results show that a good agreement between simulations and measurements is obtained. Antenna grounding     ▶︎ Check our Supplier Directory, Oscilloscope Triggering: how to trigger a scope. B. Different types of electromagnetic wave polarisation propagate in slightly different ways under some circumstances. Void antenna . It is possible for linearly polarised antennas to receive circularly polarised signals and vice versa. Tropospheric propagation     ANSWER: Both a and b. The popular "quad" antenna design is necessarily a full-wave loop, so no other distinction is needed. It picks up and radiates horizontally polarised signals, i.e. Discone     4(b) shows a quasi-taper helical frequency and polarization reconfigurable origami antenna . This is important when looking at antennas because they are sensitive to polarisation, and generally only receive or transmit a signal with a particular polarization. Unlike the above antennas, traveling-wave antennas are not resonant so they have inherently broad bandwidth. This type of antenna is considered to be an ideal antenna and taken as a reference for most of the calculations related to propagation of E.M waves. A monopole antenna consists of a single conductor such as a metal rod, usually mounted over the ground or an artificial conducting surface (a so-called ground plane). Hence is widely used than broadside helical antennas. Sector antennas (white bars) on cell phone tower. For the electromagnetic wave the polarization is effectively the plane in which the electric wave vibrates. Polarisation     The gain of the antenna achieves higher than … The driven element of a Helical antenna is typically constructed from a wire or ribbon wrapped in a helix, positioned above ground plane. 27% C. 37% D. 57%. Coax cable     The radio waves reflected from the ground plane seem to come from an image antenna below the ground, with the monopole and its image forming a dipole, so the monopole antenna has a radiation pattern identical to the top half of the pattern of a similar dipole antenna. US Air Force PAVE PAWS phased array radar antenna for ballistic missile detection, Alaska. A helix becomes a linear antenna when its diameter approaches zero or pitch angle goes to 90º. Taming the Quadrifilar Helical Antenna - The Quadrifilar Helical antenna provides circular polarization and complete hemispherical reception, which is precisely what is needed to receive the polar orbiting weather satellites, and as a 2 meter antenna it will receive horizontal, vertical and clockwise circular polarization. Low radiation resistance b. Fig. Nevertheless, the polarisation of the antenna is still important. In practice it's a large air-coil onto a boom, where ClockWise (CW) winding gives RHCP and Counter ClockWise gives LHCP. No real antenna can have an isotropic radiation pattern, but the isotropic radiation pattern serves as reference for comparing the radiation intensity of other antennas, regardless of type. ... Helical Antenna. Radiates horizontal beam at 5-9 MHz, 100 kW, Array of four axial-mode helical antennas used for satellite tracking, France. A basic dipole antenna consists of two conductors (usually metal rods or wires) arranged symmetrically, with one side of the balanced feedline from the transmitter or receiver attached to each. The antenna is implemented by using truncated structure, variable pitch angle, a matching stub, and a mechanical autorotation device. Curtain array shortwave transmitting antenna, Austria. About 6-8 turns are usually used in this type of antenna. Where ever there is Wireless Communication, there is an Antenna. Depending on the physical dimensions of the Helix, it may be either made to radiate along its axis or orthogonal (broadside) to the axis. "Rabbit ears" dipole variant for VHF television reception. Focus on Test from Rohde & Schwarz offers a huge number of informative PDFs, white-papers, webinars videos and general information on many test topics. [2][12] They consist of a small dipole or loop feed antenna inside a three-dimensional guiding structure large compared to a wavelength, with an aperture to emit the radio waves. What determines antenna polarization? Low radiation efficiency c. Both a and b d. None of the above. Antenna polarisation is an important factor when designing and erecting radio antennas or even incorporating them into small wireless or mobile communications systems. Four-bay batwing television broadcasting antenna, Germany. Axial mode conventional helical antennas are widely used in satellite communications and global positioning systems due to their high gain and circular polarization. Corner reflector UHF TV antenna with "bowtie" dipole driven element at its center. Two-element turnstile antenna for reception of weather satellite data, 137 MHz. As the name suggests helical antenna is made of coil surrounding the insulating support. The dipole, monopole, array and large loop antenna types below typically function as resonant antennas; waves of current and voltage bounce back and forth between the ends, creating standing waves along the elements. Selecting the right form of polarisation can provide some advantages, and therefore can be quite important. 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