Antenna information by Mark van der Hoek
Mark notes, "The antennas were mounted this way to meet zoning requirements for setbacks from the edge of the roof. The two brown boxes in the 'southeast' picture are the Ericsson remote base stations, painted to match the brick. The antennas are EMS (external link) dual polarized antennas, with a 65 degree vertical beamwidth and no downtilt." This remote base station is used in IS-95 or CDMA networks.
"Most manufacturers put the entire Base Station in one package, which is connected to the antennas by coax. Ericsson put most of the brains in a main unit (same size as the remotes) and the amplifiers and some brains in the remotes. That allows you to hang remotes in places the competition can't, like up on power poles, stadium lights, etc. It also shortens your coax run, which is A Very Good Thing. One remote for each sector, one main for 3 remotes."
[Editor's note. This base station, the Ericsson CDMA RBS, is the same kind Britney Spears installed last year.]
Typical 1850 to 1900 MHz cellular radio antenna. 72" high, 8" wide, 2.75 inches deep. Dual polarized. "The polarization is 45 degrees. Looking at the antenna from the front, with radome removed, you see some radiating elements that look like Xs. Therein lies the polarization." Remember, a microwave frequency is very short in length. Hence an antenna in that frequency band is short in length.
"As to terms, dual polarized means two antennas in one radome or housing. Each antenna within that radome has a different polarization or orientation. The horizontal beamwidth is 65 degrees. Beamwidth is defined as the width of the beam (in degrees) from the 3 dB point to the 3 dB point. (The half power point to a Brit.) That is, as you go left or right from the center of the main lobe, you reach a point where the field strength is 3 dB down from the highest point, which is at the center." More on the decibel is here.
An elevation radiation pattern of the above antenna. Without explaining any technical details, the pattern shows in concept what the radio wave looks like when projected from the antenna.
"An antenna plot is like a road map. It tells you where the radiation is concentrated. Patterns are usually referenced to the outer edge of the plot which is the maximum gain of the antenna. This makes it easy to determine other important antenna characteristics directly from the plot.
"Most antenna users are interested in the directivity or beamwidth of the antenna. As mentioned earlier, this is usually referred to as the "half-power" or 3 dB beamwidth, the points between which half the power is radiated or concentrated, and specified in degrees. As an example, the typical half-power beamwidths of a 3, 6 and 10 element Yagi are 60, 40 and 30 degrees respectively. . ."
The graphic above was from a most excellent web page entitled, Understanding and Using Antenna Radiation Patterns by Joseph H. Reisert, Technical Consultant. The link below now seems dead: http://www.astronantennas.com/radiation_patterns.html (external link)
A Different Look at a Directional Antenna
Mark describes these images, possibly from EMS Wireless, in the following way,
"These images represents a 3D view of an antenna pattern, one viewed pretty much head on and one from the side. The 'surface' of the object represents the points in space where the energy from the antenna is 3dB below the maximum radiated energy. As you can see, there are deep nulls spaced above and below the antenna. In the real world, these nulls get filled in with reflections.
"This is the best visualization of an antenna pattern that I've seen - really helps you get ahold of what is going on with a directional antenna."
"A similar drawing for an omni would look like a donut with a closed center - the hole shrunk down until it meets in the middle. The lowest radiation from an omni is straight up and straight down."
Misc. Cellular Photos from Mark: A Portable Cell Tower
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