Page 301 - System on Package_ Miniaturization of the Entire System

Radio Fr equency System-on-Package (RF SOP) 275

(a) (b)
FIGURE 5.13 Photograph of the (a) fabricated antenna arrays and (b) demonstration of
mechanical fl exibility.

Conformal antennas can also be used for higher-frequency applications such as the
dual-frequency (14 and 35 GHz), dual-polarization microstrip conformal antenna
utilizing LCP technology, as shown in Figure 5.13 [31]. This particular antenna array
has been developed for space radar applications and is the first demonstration of a
multilayer antenna array on an organic technology. The bonding of LCP layers is the
most critical step in the fabrication process and has to be understood thoroughly to
create multilayer LCP structures reliably. Several experiments were carried out to
optimize the temperature, the tool pressure, and the process times to achieve good
bonding while preventing shrinkage, formation of bubbles, and melting of core layers.
The bubbles can result in air gaps that can affect the array performance at millimeter-wave
frequencies. The top layer, visible in the picture, shows the 35-GHz antennas. The 14-
GHz ones are similar and embedded in the bottom layer.
The simulated and measured return loss plots for the 14- and 35-GHz arrays are
shown in Figure 5.14a and b, respectively. The simulated and measured 2D radiation
patterns for the 14-GHz array and the 35-GHz array are shown in Figure 5.15a and b.
These results show the excellent radiating characteristics of antennas developed on
LCP technology.
Antennas on Magneto-Dielectric Substrates
As mentioned earlier, when only the dielectric constant of the material is increased to
reduce the antenna size, the electromagnetic fields get trapped in the substrate. Hence,
the antenna behaves more like a capacitor than a radiator of energy. A similar
phenomenon can be seen if only the permeability of the substrate material is increased.
However, if both the permittivity and permeability of the substrate material is increased
simultaneously and matched to each other, then the radiation characteristics of the
antenna can be maintained while decreasing size. This material, called the magneto-
dielectric material, has large benefits for reducing the size of antennas for consumer