Page 232 - Antennas for Base Stations in Wireless Communications

6
Chapter

New Unidirectional Antennas for

Various Wireless Base Stations

Hang Wong and Kwai-Man Luk
City University of Hong Kong

6.1 Introduction
The greatest triumph in mobile communication service boosts the devel-
opment of the third-generation (3G), WiFi, WiMax, UWB, and forthcom-
ing 4G systems, and creates high demand for wideband unidirectional
antennas to accommodate several wireless communication systems with
excellent electrical characteristics such as wide impedance bandwidth,
low cross-polarization, low back radiation, a symmetric radiation pat-
tern, and stable gain over the operating band for cost-effectiveness,
space utilization, and environmental friendliness. Among many types
of antenna elements, there are at least three conventional means for
implementing wideband low-profile antennas with a directional pattern.
These approaches are (1) directed dipoles, (2) wideband patch antennas,
and (3) complementary antennas. Dipole antennas are popularly used
in wireless communication systems because of their several advantages:
reasonable bandwidth, good radiation characteristics, ease of construc-
tion, and the possibility of obtaining directional or bidirectional radia-
tion patterns. 1–3 Many researchers have focused on developing wideband
dipole antennas for present and future communication systems because
of the continuously expanding range of wireless telecommunication
services for voice and data transmission. Some methods have been
suggested to achieve wide impedance bandwidth for dipole antennas
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7
such as flared dipole arms, bowtie-shaped dipoles, 5–6 flat dipoles, and
8
the use of parasitic elements. These designs can obtain a bandwidth
of more than 30% to 100%, but a wideband balun must be included.
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