• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
LENS ANTENNAS
Loaded Microwave Lens

Neets Module 11-Microwave Principles
Page Navigation
  140    141    142    143    144  145  146    147    148    149    150  
3-11 Figure 3-10B.—Waveguide lens. The radiated energy consists of an infinite number of RADIAL SECTIONS (RAYS). Each of the radial sections contains mutually perpendicular E and H lines and both are perpendicular to the direction of travel. Because each of the radial sections travels in a different direction, the point source, in itself, has poor directivity. The purpose of the lens is to convert the input spherical microwave segment (which consists of all of the radial sections) into parallel (collimated) lines in a given direction at the exit side of the lens. The focusing action of the lens is accomplished by the refracting qualities of the metallic strips. The collimating effect of the lens is possible because the velocity of electromagnetic energy propagation through metals is greater than its velocity through air. Because of the concave construction of the lens, wavefronts arriving near the ends of the lens travel farther in the same amount of time than do those at the center. Thus, the wavefront emerging from the exit side of the lens appears as a plane wave. It consists of an infinite number of parallel sections (with both the E field and H field components) mutually perpendicular to the direction of travel. Delay lens Another type of lens that you may see is the DIELECTRIC or METALLIC DELAY LENS shown in figure 3-11. The delay lens, as its name implies, slows down the phase propagation (velocity) as the wave passes through the lens. The delay lens is convex and is constructed of dielectric material. The delay in the phase of the wave passing through the lens is determined by the DIELECTRIC CONSTANT (REFRACTIVE INDEX) of the material. In most cases, artificial dielectrics, consisting of conducting rods or spheres that are small compared to the wavelength, are used. (Artificial dielectrics are of three-dimensional construction and act as a dielectric to electromagnetic waves.) In this case the inner portion of the transmitted wave is decelerated for a longer interval of time than the outer portions. The delay causes the radiated wave to be collimated.






Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.