Published in IET Microwaves, Antennas & Propagation
Received on 19th November 2012
Revised on 21st December 2012
Accepted on 17th March 2013
doi: 10.1049/iet-map.2012.0672
ISSN 1751-8725
Investigation of the electric field inside differential
antenna-in-package
Guorui Han, Liyun Yan, Liping Han, Wangbao Yin, Wenmei Zhang
College of Physics and Electronics Engineering, Shanxi University, Taiyuan 030006, People’s Republic of China
E-mail: zhangwm@sxu.edu.cn
Abstract: For antenna-in-package (AiP), ther e will be an interact ion between the antenna and packaged components and this
interac tion always takes place in the zone of the near field. So, it is necessary to study an electric field inside the package cavity
and how to reduce it. In this study, the finite difference time domain model for the differe ntial AiP is presented. Based on it, the
distributions of the electric field inside the package cavity with the whole ground and gridded ground are analysed separ ate ly . The
near fields E
X
and E
Y
are far less than E
Z
and approa ch to zero. Also, the maximum E
Z
appears at the edge of cavity and it is 57
dB V/m. According to this featur e, a new pack age configuration re ducing near field is presented. The measured and simulat ed
results show that the new packaging structure can decrease the electric field inside the package cavity to about 20 dB V/m.
1 Introduction
In recent years, because of the pervasive use of wireless
applications such as Bluetooth, wireless local area networks
and cellular phones, there is a demand for small size and
high-performance integrated radio-frequency (RF) devices.
One effective method of reducing the size and improving
the integration is to integrate the antenna and circuits into a
package. Lots of different designs of integrating antenna
and circuits of an RF transceiver for wireless applications
are proposed [1–4]. The circuit in package will be impacted
by the electromagnetic field of an antenna. Electromagnetic
compatibility has become increasingly important. Weiping
Dou and Chia exploited wire bonding technique to design a
novel miniature packaged antenna [5]. Zhang and Wang
presented a circuit model of a microstrip patch antenna on a
package for the antenna-chip co-design of a highly
integrated RF transceiver [6]. In practice, there is the
interaction effect between the antenna and packaged
components and this interaction effect always take place in
the near field [7, 8]. Some effective methods of reducing
the internal electric field are commonly proposed, for
example, reducing the antenna backward radiation and
creating metal via fences. Guang-Tsai Lei et al. described a
strategy to characterise power and ground-plane structures
using a full cavity-mode frequency-domain resonator model
[9]. Suzanne Huh et al. investigated the method to reduce
the interference by creating metallic surrounding structures
around the chip ‘cavity’ [10]. Antonio Orlandi et al.
investigated the power integrity behaviour of the embedded
EBG by placing vias shorting the solid planes [11]. José
E. Rayas-Sánchez and Vargas-Chávez designed an
optimisation method to achieve reduction of crosstalk and
transmission losses by the use of via fences without a
significant deterioration of impedance matching [12].
In this paper, the finite difference time domain (FDTD)
model for the differential antenna-in-package (AiP) is
presented firstly. Then, the near field of the differential AiP
with grid ground is analysed. The distribution of the electric
field inside the package cavity is simulated and measured.
Third, a package structure that can reduce the near field
inside the package cavity is proposed. Using via fences, the
electric field inside the package cavity is decreased to about
20 dB V/m.
2 Configuration of AiP
The con figuration of the differential AiPis shown in Fig. 1.
It consists of four metallisation layers and three
low-temperature co-fired ceramic (LTCC) laminated layers.
The relative dielectric constant of LTCC laminated layers is
ɛ
r
= 5.9 and loss tangent is 0.002 at 6 GHz. The thickness
of the three LTCC layers is h
1
= 0.8 mm and h
2
= h
3
= 0.5
mm. There are cavities in the middle of the second and
third layers. The electronic components can be placed in the
cavity and connected to signal traces through bond wires.
The details of the differential AiP are shown in Fig. 2.
Fig. 2a shows the patch of the differential antenna. The
optimised parameters of the antenna are, a = 11.6 mm, b =
11.6 mm, c = 2.5 mm, d = 6.3 mm, e = 1.6 mm, w = 1.4 mm
and g = 0.6 mm. The antenna is fed by two vertical probes
marked as S. Fig. 2b shows the ground plane of the
antenna. The centre of the antenna ground plane is chosen
as the origin of coordinates, and the driving points are at ±
8.2 and 0.5 mm. Two small cuts marked as K on the
antenna ground are etched to avoid that the feeding probes
contact with antenna ground. Fig. 2c shows the package
ground and signal traces. As shown, there are 12 signal
traces on each side and 48 signal traces in all. The
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The Institution of Engineering and Technology 2013 doi: 10.1049/iet-map.2012.0672