Page 221 - Antennas for Base Stations in Wireless Communications

194 Chapter Five

Without conductors
With conductors
90
0
120 60
−10 150 30

−20
Normalized directivity [db] −30 180 φ = 0 [degree]

−40

−30
−20

−10 210 330
0 240 300
270
Figure 5.19 Radiation patterns of dual-beam antenna

5.3.3 SpotCell (Micro-Cell) Antenna
In addition to sectors, base stations are often installed in hotspot areas.
The purpose is to plug small black-hole areas that are caused mainly
by surrounding environments. Usually, omnidirectional antennas are
used in micro-cells or spot cells.
z
y Figure 5.20 shows an omnidirec-
tional antenna with a parasitic
x conducting cylinder operating
Ground plane in the 900-MHz band. 19–21 The
Dielectric substrate
antenna has been etched onto
a 30-mm wide slab of dielec-
tric substrate with a dielectric
constant of 3.6. A rectangular
Slot
slot with a width of 15 mm has
Parasitic aluminum been cut onto the ground plane
cylinder and fed at its bottom side by a
microstrip feed line that has
been etched onto the dielectric
substrate. Such a design is good
Feed line for mass production with low
material and manufacturing
loss. The slot is asymmetrically
Figure 5.20 Omnidirectional antenna cut by the edge of the dielectric