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Antennas for Wearable 5G Communication and Medical Systems
Published in Albert Sabban, Wearable Systems and Antennas Technologies for 5G, IOT and Medical Systems, 2020
The variation of the radiation pattern with direction is sin θ, the same as dipole antennas. The fields of a small loop have the E and H fields switched relative to that of a short dipole. The E field is horizontally polarized in the x-y plane.
Pattern and Polarization Diversity in Antennas
Published in Binod Kumar Kanaujia, Surendra Kumar Gupta, Jugul Kishor, Deepak Gangwar, Printed Antennas, 2020
Ashwani Kumar, Prashant Chaudhary
Next, we shall see the effect of an electromagnetic band gap (EBG) surface between the two dipoles. These dipole antennas are linearly polarized. Figure 5.9 presents a two dipole antenna with an EBG, and the EBG surface is placed between the two diagonally orthogonal dipole antennas. The EBG acts as a reflector having a reflection coefficient of Γ = +1, and it behaves as a perfect magnetic conductor (PMC) [15]. The EBG surface reflects the radiation pattern normal to the surface; the omnidirectional radiation pattern becomes directional. The dipole antennas with the EBG shows the pattern diversity phenomena. Here, both the dipoles are placed obliquely (at ±45°) parallel to the EBG surface and it also gives circular polarization [15], which we shall discuss in detail in Section 5.2 in the name of polarization diversity. The perfect magnetic conductor changes the linearly polarized antenna to a circularly polarized one. The ECC and DG are given in Figure 5.9f and g. The EBG surface not only provides isolation, but also changes the polarization of the antennas. By using the EBG surface, a compact antenna with a high isolation and pattern diversity can be designed, and it is useful for the modern communication systems. These simple examples are presented here to become familiar with the term of pattern diversity and in what sense we can achieve it.
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
Antennas are classified into several groups: wire antennas, aperture antennas, array antennas, reflector antennas, and lens antennas. Wire antennas are various combinations of wires or rods. Some commonly used ones are shown in the upper part of Figure 3.50. A dipole antenna consists of two segments of rod or wire, with a transmission line connected between them. The length of a dipole antenna is typically one-half of a wavelength. A folded dipole, as the name indicates, is a dipole with an additional connection between the ends. Loop antennas may be circular, square, or other shapes.
Ground penetrating radar (GPR) applications in concrete pavements
Published in International Journal of Pavement Engineering, 2022
Alireza Joshaghani, Mehran Shokrabadi
Since the polarisation sensitivity of the antenna arrangements is different depending on the type of target and subsurface conditions, it is important which antenna to choose for a GPR field survey. Dipole antennas discharge linearly polarised energy with the majority of the emitted electric field oriented along the long dipole axis. Co-pole antennas receive reflected energy that has the same polarisation as the incident energy (Guy, Daniels et al. 1999). The cross-pole arrangement is more sensitive to targets that yield more depolarised energy rather than smooth planer targets (Roberts, Daniels et al. 1992). Optimised amplitudes are found over rebars when crossed-dipoles are placed at an angle of 45◦ to the rebars (He, Zhu et al. 2009). To improve imaging quality and interpretation of rebars, polarisation can be combined with other methods. Polarisation can also be used to discriminate rebar from other linear targets and detect dual-layer rebar mesh (Zhang, Wei et al. 2008).
An infrared energy harvesting device using planar cross bowtie nanoantenna arrays and diode-less rectification based on electron field emission
Published in Journal of Modern Optics, 2020
A. Chekini, S. Sheikhaei, M. Neshat
Dipole is inherently a narrow bandwidth antenna, in which, each of its two wire sections has a length equal to a quarter of a wavelength. To increase the bandwidth, the wire width should be increased. Bowtie is in fact a relatively wide bandwidth dipole antenna. Cross bowtie is wideband as well. With increasing the flare angle (angle of the bowtie antenna tip), the field amplification is decreased, whereas the bandwidth is increased. The other antennas including sinuses, spiral and square spiral are wideband, as well. However, they do not perform so well as bowtie in field enhancement. In those three antennas, to decrease the minimum frequency, the outer length or diameter should be increased, and also, to increase the maximum frequency, the inner length or diameter should be decreased [22, 44].
Optimal Design of Linear Antenna Arrays of Dipole Elements Using Flower Pollination Algorithm
Published in IETE Journal of Research, 2019
Gopi Ram, Rajib Kar, Durbadal Mandal, Sakti Prasad Ghoshal
The dipole antenna is one of the utmost influential and generally used radio frequency (RF) antennas. Dipole antenna is generally used independently and also can be incorporated in many other RF antenna designs where it forms the driven element for the antenna. Dipole antenna is constructed with two thin dipole elements that are symmetrically fed at the centre by a balanced two-wire transmission line [1]. Dipole antennas are of various types like Hartzian dipole, half-wave dipole, small dipole [2] etc. To match with the line impedance, the radiation resistance of the dipole antenna should be of 73 ohms. In this paper, linear array of dipole element is considered. The radiation properties of the antenna arrays can be modified by their geometrical configurations or by the variable parameters of the array factors [1–9].