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EM behavior when the wavelength is about the same size as the object
Published in James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney, Basic Introduction to Bioelectromagnetics, 2018
James R. Nagel, Cynthia M. Furse, Douglas A. Christensen, Carl H. Durney
Dipole antennas are seen only rarely in medical applications, because they require two arms of equal length. More commonly, one arm of a linear antenna (a wire) will be placed above a conducting ground plane, creating a monopole antenna. The ground plane creates a virtual reflection below the plane, making the monopole appear electrically like a dipole antenna, as shown in Figure 3.53. The shape of the top half of the radiation pattern for a monopole is identical to a dipole, but since a dipole sends the power into both the top and bottom halfspaces, while the monopole sends it only into the top halfspace, if both antennas were fed with equal power, the dipole antenna would radiate half as much in any given direction. Also, the feedpoint electrical impedance is half as much for a monopole as a dipole antenna. Monopole antennas are used to deliver localized power and therefore to heat very focused regions of the body for applications such as cardiac ablation and hyperthermia for cancer therapy. They are also used for measuring the electrical properties of materials. As shown in the patterns of Figures 3.51 and 3.52, dipole and monopole antennas are considered to be between directional and isotropic.
Basic Antenna Parameters and Definitions
Published in Victor Rabinovich, Nikolai Alexandrov, Basim Alkhateeb, Automotive Antenna Design and Applications, 2010
Victor Rabinovich, Nikolai Alexandrov, Basim Alkhateeb
A simple monopole antenna mounted on an infinite metal screen has only an omnidirectional radiation pattern Fθ (θ, φ) that does not depend on the φ angle value (Fφ (θ, φ) = 0). A whip antenna mounted on a fender has components Fθ (θ, φ) and Fφ (θ, φ) in horizontal and vertical planes due to the effects of car body shadow. Both components in horizontal plane (θ = 90 degrees) are not omnidirectional. The important parameter γ that equals the maximum-to-minimum ratio of the radiation pattern value in horizontal plane when measuring 360 degrees around a car determines the quality of the whip antenna design. Whip antennas usually meet the requirement when γ is less than 12 to 15 dB for the Fθ (θ = 90°, φ) component. Antennas printed on window glass suffer from more dip variations of directionality over a 360 degree span (sometimes more than 25 dB). However, these dips are generally very narrow and do not exceed a few degrees. As a rule, radiation pattern levels are relative values with respect to certain reference values and expressed in decibels.
M
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
monopole antenna an antenna consisting of a straight conducting rod, wire, or other structure oriented perpendicularly to a ground plane and fed at the junction of the structure and the ground plane. monostatic scattering the reflection of a portion of an electromagnetic wave back in the direction of the wave source. Monostatic scattering is measured by having the transmitter and receiver collocated. Monte Carlo method a numerical technique that replaces a deterministic description of a problem with a set of random descriptions that have been chosen based on distributions that match the underlying physical description of the problem. This technique is widely used to investigate transport and terminal characteristics in small semiconductor structures.
Metamaterial Loaded Antenna with Improved Efficiency and Gain for Wideband Application
Published in IETE Journal of Research, 2023
KM Neeshu, Anjini Kumar Tiwary
Radiation pattern of the proposed antenna is analyzed at the frequencies 4, 8, and 12 GHz. It is observed in Figure 7(a) that the radiation pattern is omnidirectional similar to that of monopole antenna, at 4 GHz. The radiation pattern at 8 GHz and 12 GHz are presented in Figure 7(b,c), respectively. It is observed that the maximum radiation is in the opposite direction of antenna ground plane. The radiation pattern changes from omnidirectional to directional due to the ground plane [15] which acts as a reflector for higher frequencies. At 3 GHz, the ground plane size of around 8 mm (λ/10) is too small to serve as a reflector, whereas for higher frequencies 8 GHz (λ/5) and 12 GHz (λ/3), the ground plane gives significant impact to act as a reflector. Figure 8 illustrates the simulated and measured radiation pattern of the antenna, including the co-polarization and cross-polarization in the xz and yz planes. It shows nearly omnidirectional pattern in the xz plane, whereas directional pattern in the yz plane. The antenna has large cross-polarized power level in the plane due to the asymmetrical feed line. There is some discrepancy between the measured and simulation results due to testing environment and manufacturing constraints.
A circularly polarised monopole antenna with switchable frequency, pattern and polarisation
Published in International Journal of Electronics, 2022
Ankit Bhattacharjee, Santanu Dwari
On the other hand, from the application point of view, monopole antenna has been a good choice because of its various advantages like simplicity in design, easy understandable mechanism, straightforward way of achieving narrow band, multiband and also wide band performances, easy implementation on planar form, compact in size etc. So, reconfigurable techniques have also been applied to different monopole configurations to modify various antenna parameters electronically in (Bhattacharjee et al., 2019; Boudaghi et al., 2012; Cao et al., 2015; Juan et al., 2017; Liang et al., 2015; Raman et al., 2013; Shi et al., 2012; A. Singh et al., 2019). Frequency reconfiguration is achieved with the help of a circular monopole antenna with PIN diode based switchable slotted ground plane in Boudaghi et al. (2012) and a monopole with water filled substrate milled channels in A. Singh et al. (2019). Switchable parasitic elements based designs are introduced in Juan et al. 2017) and Shi et al. (2012) for controlling the radiation beam from a driven monopole. Reconfigurable operation for circular polarisations are done in Bhattacharjee et al. (2019) and Cao et al. (2015) with the simple ring monopole and meandered monopole respectively. However, all the reported works in Bhattacharjee et al. (2019); Boudaghi et al. (2012); Cao et al. (2015); Juan et al. (2017); Shi et al. (2012); A. Singh et al. (2019) are based on single parameter reconfiguration, reconfigurable mechanism is complex in A. Singh et al. (2019) and Cao et al. (2015), and configurations are not planar in Juan et al. (2017) and Shi et al. (2012).
Scanning the Issue
Published in IETE Journal of Research, 2020
The next paper on “Normal Mode Helical Antenna on Small Circular Ground Plane,” presents a method for input impedance matching for a Normal Mode Helical Antenna with a circular ground plane without requiring any external impedance matching network. It has advantages of small size and ease of installation compared to conventional monopole antenna. The effects of varying the geometry of ground place, radius of wire on the input impedance and other parameters of the antenna are discussed. The paper also presents the effect of varying the ground plane shapes on the input impedance matching. The simulation study is augmented with measurements done on a fabricated antenna and comparisons between the two sets of performance parameters is presented and discussed.