Page 274 - Antennas for Base Stations in Wireless Communications

Antennas for WLAN (WiFi) Applications 247

E. Cables and Connectors Low-cost coaxial cables such as the RG-58/U
(50 Ω), RG-178/U (50 Ω), and RG-59/U (75 Ω) are commonly used to con-
nect the antenna and the radio. The cable length is often kept as short
as possible in order to minimize the loss and phase shifting of signals,
so that the integrity of the received signal can be preserved. Connectors
include the SMA, N-type, U.FL/IPEX, and MMCX. They provide both
RF shielding and mechanical transition between the cable and the feed
of the antenna.

7.2.1.2 Fabrication Process Fabrication processes usually include
machine tooling, injection molding, assembling, soldering, quality con-
trol, and testing. The Six Sigma (6s) strategy is used by companies to
reduce defects and errors in the manufacturing process. Each process
has various degrees of manufacturing tolerances. For example, a co-
planar waveguide feeding structure with a ground plane (CPWG) having
an eight mil gap between the strip and ground plane is easily fabricated
on a PCB. However, it is difficult to fabricate suspended metallic struc-
tures with high precision using low-cost turret punching and millings.
Therefore, costly laser cutting and wire electrical discharge machining
(EDM) are needed for such high-precision metal cutting.

7.2.1.3 Time to Market Time to market (TTM) is also a critical factor
for new products and solutions. The appropriate design tools, prag-
matic estimations, and swift prototyping will shorten the overall time
required. For example, a common RF board that supports multiple mini-
PCI express radio cards, as well as several different versions of broad-
band antenna designs, will be more cost effective.

7.2.1.4 Deployment and Installation Figure 7.1 depicts the various radio
deployment scenarios for (a) base station (BS), (b) subscriber station (SS),
and (c) access point (AP) antennas. Despite the differences in radiated
power, they have many similarities in their antenna design consider-
ations in terms of impedance, polarization, gain, and radiation pattern.
These antennas can be linearly (vertically or horizontally) polarized
(LP). Circularly polarized (CP) antennas are also used for P2P
communication links, so as to reduce the effects of multipath and
depolarization of the radiated fields. Dual-polarized (DP) antennas
are also often employed, which make use of the orthogonal property of
electromagnetic waves to provide channel isolation by transmitting both
the horizontally and vertically polarized waves simultaneously.
BS P2P antennas typically have high gain (> 12 dBi) and narrow
beamwidth (< 40°) in both the E- and H-planes. Low-gain antennas such
as half-wavelength dipole and single microstrip patch antennas are not