Page 248 - Antennas for Base Stations in Wireless Communications

New Unidirectional Antennas for Various Wireless Base Stations 221

complementary sources—(1) equal E- and H-plane patterns, (2) low back
radiation, (3) low cross-polarization radiation, and (4) stable gain across
the operating bandwidth obtained—are accomplished.

6.3.2 Complementary Antennas Composed
of Slot Antenna and Parasitic Wires
35
Apart from Clavin’s method, some studies 36–40 were conducted for dem-
37
onstrating the complementary antenna approach. King deliberated
modifying a slot antenna by placing a passive dipole in front of the slot.
39
40
Then Gabriel and Wilkinson subsequently used a slot-dipole antenna
to implement the complementary antenna. These antennas 36–40 are all
based on combining a slot antenna and a dipole to achieve the goal.
Figure 6.14 shows one of the antennas presented by Clavin again in
36
1974. Two parasitic inverted-L wires are placed beside a rectangular
slot antenna. This arrangement is equivalent to providing a magnetic
dipole from the slot and an electric dipole from the inverted-L wires. The
configuration of this structure is very simple. The achievable bandwidth
is about 10–20%.

6.3.3 Complementary Antennas with
a Slot Antenna and a Conical Monopole
In addition to the slot-dipole antenna, some have proposed slot-monopole
52
antennas 52–53 for realizing similar E- and H-plane patterns. Itoh utilized a
crossed slot and a monopole element to obtain steerable cardioid patterns.
53
Mayes employed a conical monopole with a slot for studying a broadband
unidirectional antenna. Figure 6.15 depicts the antenna presented by
53
Mayes. The conical monopole is placed with an offset distance from the
center of the slot, such that the proper amplitude and phase of these two
radiating elements can be adjusted to provide a desirable directional
pattern. This antenna has a very wide impedance bandwidth that is
about 60%.

L-wire

z
Slot

Ground plane
x y
Figure 6.14 Configuration of a complementary antenna
with a slot and inverted-L wires 36