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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
heirarchical coding coding where image data are encoded to take care of different resolutions and scales of the image. Additional data is transmitted from the coder to refine the image search. See also progressive transmission. heirarchical interpolation a technique of forming image pyramids. In this method, pixels are interpolated to higher levels in the hierarchy. Thus, only the interpolated pixels need a residual in order to be reconstructed exactly, since the subsampled pixels are already correct. helical antenna a wire antenna that is helical in shape. Typically, the helical antenna is fed by a coaxial cable, the outer conductor of which is connected to a ground plane and the inner conductor of which protrudes through the ground plane and
Communications
Published in Diego Galar, Uday Kumar, Dammika Seneviratne, Robots, Drones, UAVs and UGVs for Operation and Maintenance, 2020
Diego Galar, Uday Kumar, Dammika Seneviratne
Helical antennas comprise a single wire or limited tape wound like a right- or left-hand screw, self-supporting, or turned on a dielectric cylinder (Kraus, 1947). Because they are practical and easy to use, helical antennas are extensively used in practice. They are widely used to get microwaves from VHF. They are also used in satellite communication where high gain is required. In a parabolic dish, higher gain is needed, so helical antennas are installed for this application as well.
Foundations of electromagnetism
Published in Riadh Habash, BioElectroMagnetics, 2020
Helical antenna: This is a wire wound in the form of a helix. Helical antennas can easily generate circular-polarized waves. They operate in a wide frequency bandwidth. When the helix circumference is one wavelength, maximum radiation is generated along the helix axis.
A broadband helical saline water liquid antenna for wearable systems
Published in International Journal of Electronics, 2018
Gaosheng Li, Yi Huang, Gui Gao, Cheng Yang, Zhonghao Lu, Wei Liu
For a metal helical antenna, it has been proved that the antenna with a certain ratio of the diameter to the operating wavelength will present three statements of radiation patterns, as shown in Figure 3 (Nie, 2014).