Page 334 - System on Package_ Miniaturization of the Entire System

308 Cha pte r F i v e

legs are connected to ground to achieve signal-ground excitation. The input impedance
of this dual antenna is 20 + j112.5 Ω to match to an IC input impedance of 20 – j113 Ω.
The radiation efficiency is 98 percent since the current flow as shown in the figure adds
up constructively for the far-field electromagnetic radiation, something that results in
an optimized performance in terms of the read rage and environment versatility. The
radiation pattern of the dual polarized antenna is omnidirectional in the yz plane with
a maximum directivity of 2.25 dBi.
Dual-Body Configuration
The design of a high-directivity RFID antenna is an effective method to increase the
read range of a tag. However, the performance of most RFID antennas is constrained by
their intrinsic dipole nature, and a high directivity, especially for narrow-beamwidth
conveyor belt applications, is very difficult to achieve. Adding another radiating body
is a solution to this. A new topology, named dual-body configuration, is presented in
Figure 5.43. Two meander line arms are placed in the same side of the feeding loop as
shown, and a directivity of 2.69 dBi is achieved. In Figure 5.39b, two meander line arms
are placed in each side of the feeding loop. In this case, the current directions are
opposite along the arms and the radiation patterns cancel out each other in most of the
directions. Thus, in this inductively coupled RFID antenna, the radiating energy is
focused directionally in a dumbbell shape, and a high directivity of 5.62 dBi is observed
with 79.9 percent radiation efficiency. In general, a highly increased effective range is
expected to be achieved with RFID antennas in such a configuration. In addition, a
dual-body configuration can also be used to enhance the antenna bandwidth performance.
Radiating bodies can resonate in adjacent frequencies by adjusting the length of each
arm. In this way, an antenna can resonate at multifrequencies to enlarge the bandwidth
and make possible multiband and multistandard RFID tags.

5.5 Integrated RF Modules

5.5.1 WLAN
Wireless LANs are becoming extremely popular since they provide seamless
connectivity without the need for wires. With the trend toward including mobility in
laptop computers using PCI and mini-PCI express cards, the need for miniaturization
of radios becomes very important. With the progress being made in multiple-input
and multiple-output (MIMO) architectures, there is a compelling need for including
multiple radios in laptop computers without increasing the space available on the
cards. SOP technology can be used to miniaturize such systems at low cost, especially
for systems operating at 5.8 GHz (IEEE 802.11a) or 2.4 GHz (IEEE 802.11b) without
compromising RF performance.
An example of an SOP-based 3D antenna-integrated transceiver module is shown
in Figure 5.44. Three different subsystems, that is, the transceiver, filter, and antenna,
are vertically stacked and connected through vias (Figure 5.44a). The presented module
utilizes 20 LTCC layers. The antenna, filter, and transceiver utilize 8, 10, and 2 layers,
respectively. The total size of the module is 14 mm × 19 mm × 2 mm, including all the
RF functional blocks [29–30]. The grounds are connected through vias to suppress the
unwanted parasitic modes.