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Fresnel zone

A Fresnel zone is a theoretical ellipsoidal region surrounding the direct line-of-sight path between a wave source and receiver, where the path length from source to a point on the zone boundary to receiver exceeds the direct path by an integer multiple of half the wavelength (λ/2), enabling analysis of constructive and destructive interference in diffraction.^[1] These zones, first conceptualized by French physicist Augustin-Jean Fresnel in his 1818 prize-winning work on diffraction, divide the wavefront into alternating annular areas of positive and negative phase contributions relative to the observation point.^[2] In optics, Fresnel zones underpin the understanding of near-field diffraction patterns, such as those observed in circular apertures, where the first zone contributes maximally to on-axis intensity, while successive zones alternate in sign, leading to oscillatory irradiance that approximates four times the unobstructed value when fully exposed.^[2] The radius of the nth zone in the aperture plane is given by r_n = \sqrt{n \lambda b}, where b is the reduced distance (harmonic mean of source and observation distances), assuming paraxial approximation.^[2] This framework extends to Fresnel zone plates, diffractive optics consisting of alternating transparent and opaque rings that focus light by blocking every other zone, achieving focal lengths determined by the zone radii and mimicking convex lenses for applications in microscopy and X-ray imaging.^[3] In radio wave propagation, particularly for microwave and VHF links, Fresnel zones are essential for line-of-sight (LOS) path planning, with the first zone's clearance ensuring minimal diffraction loss (<1 dB) and approximating free-space conditions.^[1] The radius of the Nth Fresnel zone at a point d along the path of total length D is r_N(d) = \sqrt{N \lambda d (D - d)/D}, highlighting the need for terrain and obstacle avoidance to prevent signal attenuation from multipath interference or knife-edge diffraction.^[1] Violations in the first zone can degrade link reliability, influencing antenna tower heights and site selection in telecommunications infrastructure.^[4]

Introduction and History

Definition and Basic Concept

Fresnel zones represent concentric ellipsoidal regions of space surrounding the direct line-of-sight path between a wave source, such as a transmitter, and an observation point, such as a receiver, in the propagation of waves like electromagnetic or acoustic signals. These zones arise because waves from secondary sources along a wavefront, as described by Huygens' principle, reach the observation point with varying path lengths, creating areas where the excess path length relative to the direct path falls within successive increments of half a wavelength (λ/2). In essence, wavefronts—surfaces of constant phase in wave propagation—emit secondary spherical wavelets from every point, and the differences in travel distance for these wavelets to the receiver define the boundaries of the zones.^[2]^[5] The zones are numbered sequentially starting from the innermost one adjacent to the direct path. Odd-numbered zones, particularly the first, contribute to constructive interference at the receiver because the path length differences result in phase shifts less than π radians, aligning wave crests to amplify the signal. In contrast, even-numbered zones lead to destructive interference, as their path differences introduce phase shifts around π radians, causing wave crests from one part to cancel with troughs from adjacent areas. This alternating pattern helps explain how obstructions in specific zones can either enhance or degrade the received signal strength through diffraction effects.^[2] Conceptually, in a simplified two-dimensional view assuming free space and symmetric source-receiver distances, the zones appear as alternating circular bands centered on the direct path, with each band's edge marking an additional λ/2 path difference. These regions illustrate the volume through which waves propagate and interfere, emphasizing that unobstructed zones preserve the intended signal integrity. While primarily conceptual here, such zones play a key role in understanding diffraction patterns in near-field propagation.^[2]

Historical Development

The concept of Fresnel zones originated with French physicist Augustin-Jean Fresnel in 1818, as he developed his theory of diffraction to support the wave nature of light. In his seminal memoir submitted to the French Academy of Sciences, Fresnel introduced half-period zones—later termed Fresnel zones—as ellipsoidal regions where secondary wavelets from a wavefront interfere constructively or destructively, providing a mathematical framework to predict diffraction patterns around obstacles.^[6] This innovation resolved longstanding puzzles in optics, such as the appearance of bright spots in shadowed regions, and marked a pivotal shift from Newton's corpuscular theory toward wave optics.^[7] Fresnel's formulation drew directly from Christiaan Huygens' 17th-century principle of secondary wavelets, which posited that every point on a wavefront acts as a source of new spherical waves. Fresnel refined this by incorporating interference effects and phase differences, enabling precise calculations of light propagation beyond simple geometric optics. His 1818 work, awarded a prize by the Academy in 1819, laid the groundwork for understanding how zones of equal path length difference contribute to the overall wave amplitude at an observation point.^[8] By the 1930s, engineers began adapting Fresnel zone theory to radio wave propagation, with practical applications in microwave links emerging in the 1940s at Bell Laboratories. Researchers there applied the principles to designs such as the New York-Boston microwave repeater circuit, ensuring adequate clearance around transmission paths to minimize diffraction losses.^[9] This marked the transition from optical to electromagnetic applications, with key advancements in the 1930s including analyses of zone effects in shortwave and VHF systems for improved reliability in terrestrial communications. In the 2000s, Fresnel zone theory advanced through computational models that incorporated numerical simulations for complex environments, such as urban or terrain-obstructed propagation scenarios. These methods, often using finite-difference time-domain or ray-tracing techniques, allowed for accurate modeling of multipath interference and zone interactions in modern wireless systems, extending Fresnel's original insights to high-frequency bands like millimeter waves.^[10]

Mathematical Foundations

Wave Propagation Principles

Wave propagation in free space occurs through the linear superposition of waves, where electromagnetic or acoustic disturbances travel as plane or spherical wavefronts without alteration, governed by the wave equation derived from Maxwell's equations for electromagnetics or the scalar Helmholtz equation for acoustics.^[11] In the absence of obstacles, waves maintain their phase coherence over large distances, but the introduction of barriers or apertures induces diffraction, allowing waves to bend around edges and spread into shadowed regions. This phenomenon arises because partial obstruction disrupts the wavefront, leading to interference patterns that deviate from geometric optics predictions.^[12] The foundational explanation for diffraction stems from Huygens' principle, which posits that every point on a wavefront serves as a source of secondary spherical wavelets that propagate forward and interfere to form the subsequent wavefront.^[11] Path length differences between these wavelets determine the interference outcome: a difference of \lambda/2 (half the wavelength) introduces a \pi radian phase shift, resulting in destructive interference, while integer multiples of \lambda yield constructive interference.^[11] This phase-dependent superposition explains how waves reconstruct beyond obstacles, with the amplitude at an observation point being the vector sum of contributions weighted by their relative phases and distances. Kirchhoff's diffraction formula provides the rigorous theoretical basis for these effects, derived from Green's theorem applied to the scalar wave equation, expressing the field at a point as a surface integral over the wavefront or aperture of secondary contributions modulated by an obliquity factor.^[13] For near-field (Fresnel) diffraction—relevant when observation distances are finite but much larger than the wavelength—the formula employs the Fresnel approximation, which simplifies the phase term by expanding the path length in a binomial series, assuming small angles and distances where higher-order terms are negligible.^[12] This approximation holds under the condition that the propagation distance significantly exceeds the wavelength, enabling efficient computation of interference without full spherical wave integration.^[12] Fresnel zone concepts, rooted in these principles, apply broadly to both scalar waves (as in acoustics) and vector waves (as in electromagnetics), though introductory analyses often simplify to the scalar case for clarity in understanding phase and path effects.^[11]

Zone Boundary Formulation

The boundaries of Fresnel zones are defined as the loci of points in space where the path length from a transmitter to a receiver via that point exceeds the direct line-of-sight path length by an integer multiple of half the wavelength, specifically n \lambda / 2 for the nth zone, with n = 1, 2, 3, \dots and \lambda the wavelength.^[2] This condition arises from the Huygens-Fresnel principle applied to wave propagation, where constructive and destructive interference depends on phase differences corresponding to these path increments. To derive the zone boundary equation, consider two points: a transmitter at position 0 and a receiver at distance D along the line of sight. At an arbitrary point along the path located a distance d_1 from the transmitter (so d_2 = D - d_1), the boundary of the nth zone lies on a surface where a ray passing through a point at radial distance r_n from the line of sight satisfies \sqrt{d_1^2 + r_n^2} + \sqrt{d_2^2 + r_n^2} = D + n \lambda / 2. This surface forms a prolate ellipsoid with foci at the transmitter and receiver.^[2] Under the paraxial approximation, where r_n \ll d_1, d_2 (valid for far-field conditions), the binomial expansion simplifies the path lengths: \sqrt{d_i^2 + r_n^2} \approx d_i + r_n^2 / (2 d_i) for i = 1, 2. Substituting yields r_n^2 / (2 d_1) + r_n^2 / (2 d_2) \approx n \lambda / 2, or r_n^2 (d_1 + d_2) / (2 d_1 d_2) \approx n \lambda / 2. Solving for r_n gives the standard formula for the nth Fresnel zone radius:

r_n = \sqrt{ \frac{n \lambda d_1 d_2}{d_1 + d_2} }.

^[2] This equation assumes free-space propagation without atmospheric effects or obstacles, and the paraxial approximation holds, ensuring higher-order terms like r_n^4 / (8 d_i^3) are negligible. At the midpoint (d_1 = d_2 = D/2), it simplifies to r_n = \sqrt{n \lambda D / 4}. For example, with \lambda = 0.3 m (corresponding to 1 GHz) and D = 1 km, the first-zone radius is approximately 8.7 m, illustrating the scale relevant to microwave link design. The formula generalizes to any location along the path by varying d_1 and d_2 accordingly, yielding r_n(x) = \sqrt{ n \lambda x (D - x) / D } where x is the distance from the transmitter; the maximum radius occurs at the midpoint (x = D/2). This variation reflects the ellipsoidal geometry, with radii decreasing toward the endpoints. In practical units for radio engineering, the first-zone radius (n=1) is often expressed as r_1 \approx 17.3 \sqrt{ d_1 d_2 / [f (d_1 + d_2)] } meters, with frequency f in GHz and distances in km.

Physical Structure and Interpretation

Geometry of Fresnel Zones

Fresnel zones are conceptualized as a series of confocal prolate ellipsoids of revolution in three-dimensional space, with the transmitter and receiver positioned at the two foci of each ellipsoid. The surface of the nth Fresnel zone consists of all points where the path length from the transmitter to the point and then to the receiver exceeds the direct line-of-sight distance by exactly n \lambda / 2, where n is a positive integer and \lambda is the wavelength of the propagating wave.^[14]^[15] This geometric configuration arises from the principles of wave diffraction, defining concentric volumes that envelop the line-of-sight path. In cross-sectional views, the geometry reveals distinct shapes depending on the plane of observation. A plane perpendicular to the line-of-sight axis intersects each Fresnel zone in a circle, with the radius increasing as the square root of n at the point of maximum extent midway between the foci. Conversely, in the sagittal plane containing the line-of-sight axis, the cross-section forms an ellipse, elongated along the propagation direction to reflect the prolate nature of the ellipsoid. The volume enclosed by the nth zone progressively increases with n, owing to the larger radial dimensions of outer zones compared to inner ones.^[16]^[14] For visualization in propagation analysis, the first Fresnel zone is particularly significant, as it encompasses approximately 50% of the total signal power along an unobstructed path, while successive zones contribute portions that alternate in their effect on the overall field. This layered structure aids in understanding diffraction phenomena, where partial obstructions within these volumes can alter signal strength. In two-dimensional approximations commonly used for simplified modeling, such as assessing clearance over flat terrain in radio links, the zones are depicted as semi-circles symmetric about the path; however, full three-dimensional ellipsoidal representations are essential for precise analysis of complex environments.^[17]^[18]

Phase and Interference Effects

In Fresnel zone theory, the phase of wave contributions varies continuously within each zone due to differences in path length from points along the ellipsoidal surface to the receiver. For the first zone, this path difference ranges from 0 to λ/2, corresponding to a phase shift from 0 to π radians, while subsequent zones extend this range by additional multiples of π. This gradual phase progression within a zone results in partial self-cancellation of the contributions, which are modeled as a vector sum in the phasor diagram, with the net effect approximating an average phase of π/2 for the first zone and alternating thereafter. The interference between zones arises from the π phase difference at their boundaries, leading to constructive contributions from odd-numbered zones (1, 3, 5, ...) that align with the direct path phase, and destructive contributions from even-numbered zones (2, 4, 6, ...) that oppose it. Each successive zone has approximately equal area and thus similar amplitude magnitude, assuming paraxial approximation and negligible obliquity factor variation. Consequently, the total electric field at the receiver under unobstructed conditions is roughly half the field contributed by the first zone alone, as the alternating additions and subtractions cause pairwise cancellations that diminish the net sum beyond the initial zone.^[19]^[20] When an obstacle partially blocks a Fresnel zone, particularly the first, the resulting diffraction alters the interference pattern, with the field strength computed via Fresnel integrals that integrate the phase-shifted contributions over the unobstructed aperture. For edge diffraction, such as a knife-edge obstacle, these integrals yield oscillatory behavior near the shadow boundary, where the parameter v = h \sqrt{\frac{2(d_1 + d_2)}{\lambda d_1 d_2}} (with h as obstacle height and d_1, d_2 as distances to transmitter and receiver) determines the diffraction gain relative to free space. The first zone alone, if fully clear, delivers approximately twice the unobstructed field strength, underscoring its dominance in signal propagation.^[21] This phase-based interference model underpins the design of zone plates, diffractive optics that block even zones to eliminate destructive contributions, thereby concentrating the field from odd zones at a focal point with enhanced intensity, mimicking a convex lens but via interference rather than refraction.

Applications Across Fields

In Radio Frequency Propagation

In radio frequency (RF) propagation, Fresnel zones play a critical role in ensuring reliable line-of-sight (LOS) communication for microwave and satellite links, where maintaining clear propagation paths is essential to minimize signal attenuation from diffraction and interference. For terrestrial microwave links operating in the 1-40 GHz range, engineers typically require at least 60% clearance of the first Fresnel zone (0.6 F1, where F1 is the radius of the first zone) along the entire path to approximate free-space propagation conditions and avoid excessive diffraction loss. This clearance criterion stems from diffraction theory, which indicates that obstructions encroaching more than 40% into the first zone can introduce losses of about 6 dB or more, potentially degrading link performance and increasing outage risk.^[22] Similarly, in satellite-to-ground links, the same 60% clearance guideline applies to the earth-space path to mitigate atmospheric and terrain-induced diffraction effects. Multipath fading in RF propagation arises from terrain reflections that create secondary signal paths, which interfere with the direct LOS wave; Fresnel zones provide a framework for analyzing these interactions by quantifying the phase contributions of reflected or diffracted components. When terrain features like hills or ridges partially obstruct the path, knife-edge diffraction models are employed to predict the resulting signal attenuation, using the Fresnel diffraction parameter v = h \sqrt{\frac{2 (d_1 + d_2)}{\lambda d_1 d_2}}, where h is the obstacle height relative to the LOS, d_1 and d_2 are the distances from the transmitter and receiver to the obstacle, and \lambda is the wavelength. These models, based on the Huygens-Fresnel principle, show that obstructions penetrating deeply into the first zone amplify fading depth, with losses calculated from standard tables or approximations like A_d \approx 6.9 + 20 \log_{10} \left( \sqrt{1 + (1 + 0.1 v)^2} - 0.1 v - 1 \right) dB for v > -0.7. By designing paths with adequate Fresnel zone clearance, multipath fading can be mitigated, as reduced obstruction minimizes the amplitude and phase variability of reflected signals, stabilizing the overall link reliability. In modern applications such as 5G millimeter-wave (mmWave) planning, Fresnel zones are particularly sensitive due to the short wavelengths, resulting in zone radii on the centimeter scale that demand precise antenna alignment to avoid blockage. For instance, at 28 GHz with a wavelength of approximately 10.7 mm, the first Fresnel zone radius for a 50 m LOS link is approximately 37 cm, making even minor misalignments or obstacles like foliage capable of causing near-total signal blockage and forcing reliance on diffraction or non-LOS paths. This necessitates advanced beamforming and site surveys in urban deployments to maintain zone clearance, enhancing coverage and reducing outage probabilities in high-frequency bands. The Federal Communications Commission (FCC) and International Telecommunication Union (ITU) standards emphasize 0.6 F1 clearance as a benchmark for achieving 99% link availability in microwave systems, accounting for refractive fading under sub-refractive conditions while balancing diffraction risks.^[23]

In Optics and Diffraction

In optics, Fresnel zones provide a foundational framework for analyzing diffraction in the near-field regime, where the observer is at a finite distance from the diffracting aperture or obstacle. This approach divides the wavefront into concentric zones of equal area, each contributing path length differences of λ/2, leading to alternating constructive and destructive interference that manifests as bright and dark fringes along shadow edges. A classic demonstration is the Arago spot, or Poisson's spot, predicted by Augustin Fresnel's 1818 diffraction theory and experimentally verified that same year. In this setup, light diffracting around a circular opaque disk produces a bright spot at the shadow's center because contributions from all Fresnel zones arrive with equal phase at that point, counterintuitively illuminating the geometric shadow due to the wave nature of light.^[24] Fresnel zone plates exploit this zonal interference to create focusing elements, functioning as diffractive lenses without relying on refraction. These devices consist of alternating transparent and opaque rings corresponding to the Fresnel zones, typically blocking even-numbered zones to ensure that light from the remaining odd zones interferes constructively at a designated focal point. The resulting focal length f is determined by the radius r_1 of the innermost zone and the wavelength \lambda, given by the relation

f = \frac{r_1^2}{\lambda},

which arises from the condition that path differences from the zone boundaries align for in-phase summation at distance f. This design allows multiple focal orders, with the primary focus at f, though higher orders reduce efficiency.^[2] Fresnel zone principles underpin advanced applications in holography and microscopy, particularly for modeling near-field imaging where precise control of interference is essential. In holography, zone-based constructions like Fresnel holograms serve as both focusing and dispersive elements, enabling the recording and reconstruction of three-dimensional images by capturing quadratic phase variations in the interference pattern. For microscopy, zone plates are integral to high-resolution setups, especially in X-ray optics, where their diffractive focusing overcomes limitations of refractive lenses at short wavelengths. Notable examples include multilayer zone plates achieving sub-40 nm resolution in soft X-ray spectromicroscopy for biomedical imaging, such as visualizing cellular nanostructures, and compound designs reaching below 25 nm in laboratory hard X-ray microscopes to probe materials at the nanoscale.^[25]^[26]^[27] A distinguishing feature of Fresnel zones in optics is their dominance in near-field diffraction, contrasting with Fraunhofer diffraction's far-field linear phase approximations. Fresnel propagation incorporates quadratic phase factors, such as \exp\left(i \pi (x^2 + y^2)/(\lambda z)\right), which model the spherical wavefront curvature and enable accurate prediction of interference patterns close to the source.^[28]

Engineering and Practical Considerations

Line-of-Sight Clearance Analysis

In line-of-sight (LOS) clearance analysis for radio links, the primary goal is to ensure that the propagation path maintains an unobstructed volume sufficient to prevent excessive diffraction losses from terrain, structures, or vegetation. The standard clearance criterion requires that the LOS path clears obstacles by at least 60% of the first Fresnel zone radius (0.6 r_1) both vertically and horizontally, which typically limits additional path loss to less than 1 dB. This threshold is derived from diffraction theory, where partial obstruction encroaching beyond 40% of r_1 begins to introduce noticeable signal attenuation due to phase interference at the zone boundary. To apply this criterion, the Fresnel zone radius formulation is integrated into the path profile analysis. The path profile is constructed using digital terrain elevation data, adjusted for atmospheric refraction via the effective earth radius factor K (commonly 4/3 under standard conditions, accounting for ray bending). Earth bulge height at a point along the path, given by h_b = \frac{d_1 d_2}{2 K a} where d_1 and d_2 are distances (in km) from the endpoints and a \approx 6371 km is Earth's radius, must be cleared by the required zone volume; for a 10 km path at midpoint, h_b \approx 1.5 m under K = 4/3.^[29] Vegetation intrusion is assessed by modeling foliage heights and densities, ensuring they do not penetrate the 0.6 r_1 boundary, as even sparse trees can cause 0.1–0.5 dB/km attenuation if within the zone. A systematic step-by-step analysis employs path loss prediction models like the Longley-Rice irregular terrain model (ITM), which simulates propagation over varied topography by combining free-space loss, diffraction, and absorption effects. The model uses a Fresnel clearance parameter K = \frac{\text{clearance distance}}{r_n}, where clearance distance is the perpendicular separation from the LOS to the obstacle crest and r_n is the local nth zone radius; for the first zone, K \geq 0.6 ensures losses remain under 1 dB for LOS paths. The process involves: (1) generating the refracted ray path with K-factor adjustment; (2) computing r_1 at discrete profile points using the zone boundary equation; (3) plotting the clearance envelope at 0.6 r_1 below the ray; (4) identifying intrusion depths and local K values; and (5) running the ITM simulation to quantify total median path loss, iterating antenna heights if exceedances occur. This method prioritizes the worst-case sub-paths, such as mid-link bulges or ridge crossings, for reliability exceeding 99.99%. For a practical numerical example, consider a 10 km LOS microwave link at 6 GHz (\lambda = c/f = 3 \times 10^8 / 6 \times 10^9 = 0.05 m). The first Fresnel zone radius at the midpoint (d_1 = d_2 = 5 km) is calculated as r_1 = \sqrt{\frac{\lambda d_1 d_2}{d_1 + d_2}} = \sqrt{\frac{0.05 \times 5000 \times 5000}{10000}} = \sqrt{125} \approx 11.2 m (approximated as 15 m in some engineering contexts accounting for slight off-midpoint maxima or conservative estimates). The required clearance is thus 0.6 r_1 \approx 6.7–9 m. With an earth bulge of h_b = \frac{5 \times 5}{2 \times (4/3) \times 6371} \approx 1.5 m at midpoint, if terrain profiling reveals a 5 m obstruction relative to flat-earth LOS, one tower height must be increased by approximately 3.5–5.5 m to restore K \geq 0.6, ensuring the zone volume clears vegetation and bulge without exceeding 1 dB loss per ITM prediction.

Obstruction Impact and Mitigation

Obstructions within the Fresnel zones, particularly partial blockages of the first zone, induce diffraction losses that degrade signal strength through destructive interference and scattering. When an obstacle tangents the line-of-sight path at the edge of the first Fresnel zone (corresponding to a Fresnel parameter v = 0), the diffraction loss is approximately 6 dB, increasing to 10-20 dB for deeper intrusions (e.g., v = 2 to v = 4) as determined by Fresnel diffraction gain curves. Conversely, full obstruction of even-numbered zones, which contribute to phase cancellation, can enhance the received signal by up to 6 dB by eliminating destructive contributions, thereby improving overall propagation efficiency.^[30] To quantify and model these effects, engineers employ the knife-edge diffraction model for sharp obstacles and extensions for rounded obstacles, both relying on the Fresnel-Kirchhoff parameter v, defined as

v = h \sqrt{\frac{2(d_1 + d_2)}{\lambda d_1 d_2}}

where h is the obstacle height above the line-of-sight, d_1 and d_2 are the distances from the transmitter and receiver to the obstacle, and \lambda is the wavelength. This parameter determines the diffraction gain J(v) in dB, approximated for v > -0.78 as J(v) = 6.9 + 20 \log_{10} \left( \sqrt{(v - 0.1)^2 + 1} + (v - 0.1) \right) dB, with curves showing losses escalating nonlinearly for positive v values indicative of first-zone blockage. These models, standardized in ITU recommendations, enable prediction of signal attenuation without full wave simulation.^[17] Mitigation strategies focus on minimizing zone intrusions post-design. Path rerouting adjusts the propagation trajectory to avoid obstacles, while antenna tilting elevates the effective line-of-sight to restore clearance. Diversity techniques, such as spatial (multiple antennas) or frequency (multi-carrier) diversity, provide redundant paths to bypass blocked zones and average out fading. Modern ray-tracing software simulates complex environments to identify and resolve blockage hotspots proactively.^[31]^[32] In urban 5G deployments using mmWave bands, building obstructions within Fresnel zones contribute to significant coverage gaps, with simulations indicating up to 35% uncovered areas in dense scenarios like San Francisco due to blockage-induced outages. Beamforming mitigates this by directing narrow, high-gain beams around obstacles, enhancing non-line-of-sight reliability and extending effective coverage.^[33]

References

[1]
[PDF] Chapter 2: Radio Wave Propagation Fundamentals - KIT - IHE
Nov 12, 2018 · Fresnel Reflection & Transmission Coefficients. Chapter 2: Radio Wave Propagation ... Nth Fresnel zone is bounded by an ellipsoid, where the Tx-Rx ...
[2]
[PDF] Fresnel Diffraction.nb
In the study of Fresnel diffraction it is convenient to divide the aperture into regions called Fresnel zones. Figure. 1 shows a point source, S, ...
[3]
Section 4.4 ZONE PLATES - X-Ray Data Booklet
A zone plate is a circular diffraction grating. In its simplest form, a transmission Fresnel zone plate lens consists of alternate transparent and opaque rings.
[4]
[PDF] Planning a Microwave Radio Link
The area that the signal spreads out into is called the Fresnel zone (pronounced fra-nell). If there is an obstacle in the Fresnel zone, part of the radio ...
[5]
[PDF] PROPAGATION NEAR THE EARTH'S SURFACE - Faculty
is called the nth Fresnel zone. In three dimensions the surfaces are ellipsoids centered on the direct path between the transmitter and receiver. t h.
[6]
The Fresnel Approximation and Diffraction of Focused Waves - MDPI
Fresnel proposed the principle of half-period zones (∼1818) as a mathematical model for Huygens' principle of secondary waves (∼1678).
[7]
July 1816: Fresnel's Evidence for the Wave Theory of Light
That became the basis for his 1818 treatise, Memoir on the Diffraction of Light. But Fresnel had published his preliminary results in July 1816, with the goal ...
[8]
Augustin Fresnel and the wave theory of light - Photoniques
Fresnel initially studied diffraction, using improvised equipment to explore the shadow of a narrow wire lit by a ray of sunshine. He noticed that with a ...
[9]
History and evolution of Fresnel zone plate antennas for microwaves ...
This paper summarizes some of the growth in technology for Fresnel zone plate antennas in the microwave and millimeter-wave regions.Missing: engineering | Show results with:engineering
[10]
Full waveform numerical simulations of seismoelectromagnetic ...
Jul 26, 2002 · We present a full-waveform modeling technique of the coupled seismoelectromagnetic wave propagation in fluid-saturated stratified porous ...
[11]
https://phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Essential_Graduate_Physics_-_Classical_Electrodynamics_(Likharev)/08%3A_Radiation_Scattering_Interference_and_Diffraction/8.05%3A_The_Huygens_Principle
[12]
[PDF] Chapter 15S Fresnel-Kirchhoff diffraction - bingweb
Jan 22, 2011 · He is perhaps best known as the inventor of the. Fresnel lens, first adopted in lighthouses while he was a French commissioner of lighthouses,.Missing: history | Show results with:history
[13]
None
Summary of each segment:
[14]
https://faculty.nps.edu/jenn/EC3630/NearSurface(v1.8.4).pdf
[15]
[PDF] 19650013729.pdf
For any given observation and source points there is an ellipsoidal shaped first Fresnel zone surrounding the stationary phase point on each wall. Suppose the ...
[16]
[PDF] Last revised April 11, 2011
Mar 2, 2019 · Therefore, the first Fresnel zone bounds the volume contributing significantly to wave propagation and if the first Fresnel zone is clear of any.
[17]
P.526 : Propagation by diffraction
### Summary on Fresnel Zones and Signal Power (ITU-R P.526)
[18]
[PDF] The Practical Behavior of Various Edge-Diffraction Formulas
The Fresnel zones are labeled moving from the first ellipsoid outward. The practical significance of the Fresnel zones can be shown by magnifying the KED ...
[19]
Fresnel Zone - an overview | ScienceDirect Topics
Subsequent Fresnel zones are defined as larger imaginary rings, where the difference in path lengths is nλ/2, where n is an integer larger than 1 and λ is the ...
[20]
18-452/18-750 Wireless Networks and Applications Outline The ...
• Odd zones create constructive interference, even zones destructive. • Also want clear path in most of the first Fresnel zone, e.g. 60%. • The radius Fn of ...
[21]
https://www.sciencedirect.com/science/article/pii/B9780750672917500352
[22]
First- and second-order Poisson spots | American Journal of Physics
Aug 1, 2009 · In 1818 Fresnel submitted a treatise, Memoir on the Diffraction of Light,1 to the French Academy claiming that first-order diffraction effects ...
[23]
Experimental realization of a Fresnel hologram as a super spectral ...
Oct 21, 2021 · In this study, our Fresnel hologram is designed to function not only as a focusing but also a dispersive element along an optical axis.
[24]
Hard-X-ray Zone Plates: Recent Progress - PMC - NIH
Hard-X-ray microscopy with Fresnel zone plates reaches 40 nm Rayleigh resolution. ... Multilayer Fresnel zone plate for soft X-ray microscopy resolves sub-39 nm ...
[25]
Sub-25-nm laboratory x-ray microscopy using a compound Fresnel ...
We present a laboratory x-ray microscope based on a compound zone plate. The compound zone plate utilizes multiple diffraction orders to achieve high resolution ...Missing: micron | Show results with:micron
[26]
Fresnel diffraction and the fractional-order Fourier transform
This factor can also be written as exp(−iπs2 sin2 α/λD). It is a quadratic phase factor representing a quadratic approximation to a spherical wave ...Missing: source | Show results with:source
[27]
[PDF] Techniques for computing refraction of radio waves in the troposphere
effective earth's radius factor of ll/4, and the effective earth's radius ... r. = a + h, , and a is the radius of the earth, k k a = 6370 km. It should be ...Missing: bulge | Show results with:bulge
[28]
Fresnel Zone - Planning - CableFree
The concept of Fresnel zone clearance may be used to analyse interference by obstacles near the path of a radio beam. The first zone must be kept largely free ...Missing: engineering | Show results with:engineering
[29]
[PDF] Report ITU-R M.2541-0 (05/2024) - Technical feasibility of IMT in ...
6.4.3 Beam-tracking. The use of directional antennas can potentially help mitigate high path loss and blockage challenges in frequencies above 92 GHz, the ...<|separator|>
[30]
Multipath Mitigation - Inside GNSS - Global Navigation Satellite ...
Mar 23, 2023 · The Fresnel zone concept is illustrated in this work, and can be used to evaluate assumptions made in ray tracing, e.g., building model, ...
[31]
[PDF] Understanding mmWave for 5G Networks 1 - 5G Americas
Dec 1, 2020 · Inversely, if the first Fresnel zone is blocked, then propagation of the signal will be heavily impacted and will have to rely upon diffraction.