II. ANTENNA DESIGN
Fig.1 shows the basic structure of the proposed element.
The driving square patch is printed on layer 3, which is driven
directly by a microstrip line at H-port and is aperture-coupled
at V-port with orthogonal polarization. The parasitic patch is
printed on Layer 1 and is separated from the driven patch by
Layer 2, a foam layer. The H-shaped coupling aperture and
microstrip feed line are etched on the both side of the feed
substrate, Layer 4. The slot is electromagnetically excited by
microstrip line. A ground reflector plane is located at the back
of the feed line to reduce the back radiation and improve the
radiation efficiency. To decreased coupling behavior between
orthogonal ports, a slot is etched on the driven patch to cut off
some current components (contributing to S12). The length and
width of the slot are optimized for better isolation. In the
wireless communication systems, the antenna needs to have a
high gain and a narrow beamwidth, for which the array antenna
is required. A broadband dual-band array antenna of 256
antenna units is designed. The feed networks of both bands are
consisted of 255 elementary two-way splitters. The two-way
splitter is constructed based on the quarter-wave matched Tjunction
with the 100Ωtransmission line and a 70.7Ωquarterwave
impedance-transforming section.
1 Port1(V-port) feed line 2 Port2(H-port) feed line 3/5/6
substrate (Taconic TLY-5) 4/7 Foam 8 Backed ground