Page 23 - Antennas for Base Stations in Wireless Communications

xxii Introduction

Chapter 2
Chapter 2 begins with a description of the operational requirements
for base station antennas and relates those requirements to antenna
specification parameters and the means by which each of these param-
eters are controlled. The use of space- and polarization-diversity sys-
tems is described, and the required antenna parameters related to
dual-polarized antennas are reviewed. As a major design consideration,
the description of a variety of construction methods emphasizes both
antenna performance and cost. The role of modern electromagnetic sim-
ulation tools is discussed in the context of base station antenna design.
A variety of practical radiating elements are described to provide the
designer with potential starting points for new designs. Array designs
are also examined. The general practice of multiplexing a number of
transmitters and receivers into a common antenna system creates
severe requirements for avoiding passive intermodulation products
(PIMs). Methods for minimizing PIMs are thus examined. This chapter
includes descriptions of a variety of mechanical design approaches and
provides a guide to good design practice.
It has become general practice to control the elevation beam direction
(beamtilt) of base station antennas, either locally or remotely, with the
expectation being that this control will be integrated with the manage-
ment of traffic loading and the optimization of system capacity. Remote
control is also being applied to the azimuth radiation pattern for chang-
ing the beamwidth and pointing the beams to desired directions. These
developments are described, together with some of the design consid-
erations involved in their realization. The measurement of base station
antenna arrays is also discussed, along with techniques for optimiz-
ing and diagnosing common problems encountered during design. The
installation of base stations is often the occasion for objections related
to potential visual and electromagnetic impact on the local environ-
ment. These topics and alternative methods for reducing their impact
are discussed and examples are provided. In the last part of the chapter,
some suggestions are made about possible future developments of base
station antennas.

Chapter 3
Chapter 3 describes the commercial requirements for the performance of
both indoor and outdoor base station antennas for various mobile phone
systems. Conventional techniques for developing base station antennas
are also reviewed, including directed dipoles and aperture-coupled patch
antennas. The L-probe fed patch antenna is a wideband design that
has attracted much interest in the antenna community in recent years
due to its simple structure and low cost. By examining five different