Page 45 - Antennas for Base Stations in Wireless Communications

18 Chapter One

W Side view
Patch
L
Patch

Ground plane h
Feeding
probe Ground plane
Figure 1.8 Suspended plate antenna patch fed by an L-shaped
probe

Disadvantages:
■ High cross polarization
■ Thick Antenna compared to conventional microstrip antenna

Feeding Methods:
■ Coaxial probe (poor matching BW is only 8%)
Bandwidth can be improved using these techniques: 17

■ A dual probe-feeding arrangement consisting of a feed probe and a
capacitive load 18
■ Long U-shaped slot, cut symmetrically from the plate (BW is
10%–40%)
■ L-shaped probe (BW reaches 36%) 19
■ T-shaped probe (BW reaches 36%)
■ A half-wavelength feeding strip
■ A center-fed SPA with a symmetrical shorting pin
■ Stacked suspended plate antenna 20

1.2.3 Planer Inverted-L/F Antennas
A planar inverted-L/F antenna is an improved version of the monopole
antenna. The straight wire monopole is the antenna with the most basic
form. Its dominant resonance appears at around one-quarter of the oper-
ating wavelength. The height of quarter-wavelength has restricted their
application to instances where a low-profile design is necessary. 17