Wiedza Antenna Tilt : Mechanical vs Electrical

Discussion in 'Research Tuts/Notes' started by Silas Mariusz, Feb 19, 2019.

Loading...
  1. Silas Mariusz
    Offline

    Silas Mariusz SysOp Administrator

    Joined:
    Apr 5, 2008
    Messages:
    8,748
    Local Time:
    5:13 AM
    Ratings:
    +1,826 / 39 / -9
    Followers:
    37
    QNAP:
    TS-x77
    Ethernet:
    1 GbE
    TS-x77 1 GbE
    For RF optimization and Design purposes, engineers/SON algorithms generally recommend tilt changes (not getting into optimization details in this blog), antenna tilt can be changed by two types of mechanisms:

    • Mechanical Down-Tilt: where the antenna is tilted as a whole, including all its segments.
    • Electrical Down-Tilt: where there is adjustment of phase of the control signals given to individual segments of the antenna. As a result the virtual distance between the antenna back-plate and each single segment varies so that an apparently tilted surface of the antenna front plate is resulting.
    The below figures give a bird’s eye view of the two mechanisms:

    There is no specific comparison between both these tilts as differences depend on case-to-case scenarios. However, a broad comparison is shown below for the two mechanisms:

    Mechanical Tilt

    Electrical Tilt
    Mechanical tilt will decrease coverage lengthwise from the sector, but in width, the coverage will stay the same, more like an ellipse shape type coverage on the ground

    Electrical tilt decreases both length and width, like a circle on the ground which is getting smaller and smaller, but stays a circle

    Mechanical tilt is used on tall sites, typically on top of hills, because electrical tilt is not enough. Recommended for sites which are not tall and inside city limits.
    Decrease coverage and Does not add Interference as in case of Electrical tilts Decrease coverage and does not increase overlap in sectors
    Sector overlaps are increased Increases interference, as portion of energy based on electrical tilts is transmitted in the upper side lobe reducing the energy in lobe facing towards ground hence reducing coverage.
    Mechanical tilt will lift up the back lobe of the antenna, so go easy with mechanical tilt.
    Electrical tilt does not induce increase of back lobe

    To have an idea about how the cell radius will be based on the tilt angle, we can approx use the following model to calculate it:

    t1.

    Depending on the chosen down-tilt, a geometric cell radius is given as:

    t2.

    Generally, from an industrial view-point, electrical tilt is preferred compared to mechanical tilt. An adaptation of the antenna settings to the expected traffic distribution and cell-size is recommended anyway. Basically, a rule of thumb applies that the smaller the cell-size, the larger is the antenna down-tilt, and the higher the traffic load per cell, the smaller the antenna down-tilt should be.