first Fresnel zone

first Fresnel zone

[¦fərst frə′nel ‚zōn]
(electromagnetism)
Circular portion of a wavefront transverse to the line between an emitter and a more distant point, where the resultant disturbance is being observed, whose center is the intersection of the front with the direct ray, and whose radius is such that the shortest path from the emitter through the periphery to the receiving point is one-half wavelength longer than the direct ray.
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References in periodicals archive ?
There are path profiles that have clear LOS but with inadequate 60% clearance of the first Fresnel zone. The ground reflection in our proposed work is ignored in the Terrain Peak Calculation.
Only the waves that propagate in the first Fresnel zone (e.g., direct and multipath waves) are generally strong enough and detectable in the EMRE system.
The volume of the first Fresnel zone (prolate spheroid) is an important factor when considering the rays that have the largest significance in the detection.
In addition, the smallest structure that can be resolved is estimated by the width of the first Fresnel zone, or objects with dimensions smaller than the width can be distinguished from the background.
When several sections are included in the measurement plan, it is possible to also delineate the targets that may not be situated directly in the cross section but somewhere in the first Fresnel zone.
* The essence of the near shadowing phenomenon [13] is that the line of sight (LOS) or the first Fresnel zone between transmitter (Tx) and receiver (Rx) is (partially) blocked by the user itself.
In the adjacent region of Tx, the first Fresnel zone is not large enough to touch any wall of the tunnel.
The essence of the near shadowing phenomenon is that the first Fresnel zone, especially the 60% of the first Fresnel zone is blocked by the vehicle itself.
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] denotes the location of the Dividing Point 1 when only the wall [f.sub.i](x, y, z) could be touched by the Maximum first Fresnel zone. Details and simplified formulas of the Dividing Point 1 in arbitrary cross-sectional tunnels are given by [19].
When the large-size vehicle is in front of the transmitter (Tx), the signal power of receiver (Rx) suffers strong attenuation because the first Fresnel zone is blocked by the vehicle itself to some extent [13].
Such effect occurs when the first Fresnel zone, especially the 60% of the first Fresnel zone is blocked by the vehicle.
If this distance is larger than the radius of the Maximum first Fresnel zone plate, the first Fresnel zone can be treated as almost clear.