Characterization of the Far-Field Environment of Antennas Located Over a Ground Plane and Implications for Cellular Communication Systems Articles uri icon

publication date

  • December 2010

start page

  • 19

end page

  • 40

issue

  • 6

volume

  • 52

International Standard Serial Number (ISSN)

  • 1045-9243

Electronic International Standard Serial Number (EISSN)

  • 1558-4143

abstract

  • In this paper, we look at the characterization of the far-field regions of antennas located over a ground plane. For antennas radiating in free space, the far field starts at a distance 2L2/lambda, where L is'
    the effective size of the antenna, and lambda is the wavelength. The question
    now is if this same radiating antenna is placed at a height H over a
    ground plane, then where does the far field of that antenna start? The
    goal of this paper is to demonstrate that for antennas radiating with
    either polarizations located over a ground plane, the far field starts
    at a distance 2H2/lambda (here, H ≫ L). We illustrate the validity
    of some rules of thumb through numerical simulations, and by using the
    definition of the far field as the region where the radial component of
    the field is negligible compared to the other components, and for
    regions where the ratio of the electric field to the magnetic field is
    characterized by eta, the characteristic impedance of free space. We also
    look at the validity of this rule of thumb when antennas are located
    over an imperfect ground plane. Finally, we examine the phenomenon of
    height-gain in wireless cellular communications. We illustrate that
    under the current operating scenarios, where the base-station antennas
    are deployed over a tall tower, the field strength actually decreases
    with the height of the antenna over a realistic ground, and there is no
    height gain. Therefore, to obtain a scientifically meaningful
    operational environment, the vertically polarized base-station antennas
    should be deployed closer to the ground. When deploying antennas over
    tall towers, it may be more advantageous to use horizontally polarized
    antennas than vertically polarized antennas for communication in
    cellular environments. Numerical examples are presented to illustrate
    these cases.