PART 4: MCQ from Number 151 - 200 Answer key . Gain is often incorrectly used as a means of performance comparison between antennas, where the model with the highest gain figure represents the highest performance. Has maximum radiation in a vertical direction b. some attempts have been made to improve the directivity of open-slot antennas. RF Cafe Quiz #16 Answers: Antennas - RF Cafe A half-wave antenna has a radiation resistance of: much larger than for a Hertzian dipole antenna! Understanding Antenna Gain, Beamwidth, And Directivity To accomplish this power distribution change, the hypothetical antenna at the sphere's center must be replaced by an antenna with the ability to direct radiated power in a desired direction. Assume free space propagation. Answer: Directivity. Directivity is associated with antenna gain and antenna efficiency. Which Direction Should a TV Antenna Face? - Long Range Signal As antennas tend to have higher gain levels as they become larger, so it can intuitively be seen that the gain and directivity of the horn antenna will increase with frequency. If the beam width of an antenna in two orthogonal planes are 30 0 and 60 0. The dimensions of the flare must be sufficiently large and this sometimes makes the antenna bulky. As its alias suggests, gain represents the directivity of an antenna in the sense that performance is increased in the direction or axis of peak gain by decreasing performance in another direction or axis. It is already shown that an antenna with larger dimensions has a lower Q and better radiation efficiency. It is often easier to visualise the radio antenna is terms of its radiated power, however the antenna performs in an exactly equivalent manner for reception, having identical figures and specifications. When the directivity is converted to decibels we call it the antenna gain relative to an isotropic source (dBi). Since all antennas will radiate more in some direction that in others, therefore the gain is the amount of power that can be achieved in one direction at the expense of the power lost in the others. C16 In general, for high frequency design, which of the following transmission lines has the largest bandwidth: (a) Microstrip line (b) Coaxial cable (c) Waveguide (d) Twin line. Antenna Gain View Answer: Answer: Option A. B. So, you might wonder why some antennas on the market, such as sector a. While for the receiving antenna, directivity represents the ability of the antenna to gather most of the radiated energy from a specific direction.. Introduction. What is its gain in dB? 19. The directivity of the antenna is dependent on the flare angle. Directivity can be as low as 1.76 dB for a real antenna (example: short dipole antenna), but can never theoretically be less than 0 dB.However, the peak gain of an antenna can be arbitrarily low because of losses or low efficiency. Further, this antenna must be tunable over at least an octave of frequency to track the local Critical Frequency (CF). Has maximum radiation in a vertical direction b. b) Folded dipole. For every 6 dBi in gain, you double the range of the antenna. So far, the directivity has been defined with respect to an isotropic source and hence has the unit dB i. a) An antenna that radiates equally in all directions. The phased array antenna has a directivity of 11.92 dBi and the main beam direction can be switched between the angles of ±25 degrees with a 3dB beam-width of 23 degrees. Hence, if the antenna is 100% efficient, then the directivity would be equal to the antenna gain and the antenna would be an isotropic radiator. 9. An antenna that radiates equally in all directions would have effectively zero directionality, and the directivity of this type of antenna would be 1 (or 0 dB). Then, Directivity D = maximum radiation intensity of a test antenna/radiation intensity of an isotropic antenna. Typically, antennas with gain will lose the vertical propagation or "roundness" of the pattern and become flattened and elongated with the higher gain antenna you choose. A logical assumption is that a larger antenna can also concentrate the radiation better in one direction and, thus, has higher directivity and gain. Third, the pattern has only small sidelobes, nearly 7.5 dB below the main lobe. Questions and Answers in Antennas Series. Antenna gain also has a direct correlation to both antenna directivity and beamwidth. Impedance for 2-fold dipole antenna is =22 =4 2-fold dipole antennas are used in Yagi-Uda Antennas for TV reception using balanced line of Z 0 = 300 Ω In scientific lingo, this is said to be an "isotropic radiator", because it has no preference for radiation in any direction … in other words it has no "directivity". An isotropic antenna is a theoretical antenna that radiates equally in all directions. b. The uniformly illuminated aperture type of antenna has been found to give a higher gain in practice than other antennas, at least for large apertures. Design of patch antennas based on the Sierpinski fractal method has kept the size of the antennas small with a patch size of 40mm£40mm to achieve a directivity of 10.9dBi at 3.866GHz [2]. Which type of antenna would typically have the highest directivity? If an antenna has a directivity of 16 and radiation efficiency of 0.9, then the gain of the antenna is: A. If this antenna were encapsulated in the center of a sphere, it would illuminate all parts of the sphere equally and uniformly. Directivity (D) - the ratio of the radiation intensity in a given direction from the antenna to the radiation intensity averaged over all directions. Must have a horizontal receiving antenna for the best reception c. Must use a receiving antenna which has an electric field in a horizontal direction d. Must have a vertical receiving antenna for the best reception d) Parabolic. Making it longer will degrade its performance. Then the directivity is: This question was previously asked in. b. bandwidth ratio . If the higher directivity is not necessary, the physical area of the antenna can be properly reduced to increase the aperture efficiency. The proposed antenna structure consists of a single-stage director, two arms of driven elements and a concave parabolic reflector. Clarification: Beamwidth and directivity are both measures of the focusing ability of an antenna. Horn antenna theory: flare vs gain. d. 28 degrees . 1. a) 1/4-wave whip. Here, the isotropic antenna is an ideal . Solution: D 7 0 dB corresponds to D 5 0. 20. Saying any 2.2 dBi antenna will yield the same distance ignores the antenna's directivity. So, the gain of the antenna in a given direction is the amount of energy radiated in this direction as compared to an isotropic antenna, given that both antennas have the same signal source. An Antenna is in below figure in which dipoles are arranged in vertical polarization. Depending on the size, degree of curvature, and the edge properties of the parabolic dish, gain (directivity, which is generally interchangeable with gain for high efficiencies) can be very high. antenna. Antenna gain is closely related to the directivity, but it is also a measure that takes into account the efficiency of the antenna. Students in RF usually start with the dipole antenna, which is half a wavelength in size. 3. However, the size of the antenna will be increased because that the distance between So the higher the dBi rating, the more powerful the antenna is and whether it will cover the area you need. An Antenna radiates power, but the direction in which it radiates matters much. Log periodic antenna is basically a: (A) Directional antenna (B) Frequency independent antenna (C) Frequency dependent antenna (D) None of the above. While the feed point impedance has definitely dropped below the several thousand ohms present at the end of a half-wavelength antenna, it is still quite a bit higher than that of 50-ohm coaxial cable. An antenna with higher directivity will achieve the 100 m with less power than a less directive . Which type of antenna would typically have the highest directivity? The directivity of small current element of length l/20 s : kW of power to produce a given signal strength to a particular distant point. An antenna is basically synonymous to a: (A) Regulator (B) Reflector (C) Transformer (D) Generator. An antenna that has more gain means that the beam is stronger and more directed.

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