Floating-patch MEMS antennas on an HRS substrate for millimeter-wave applications

Floating-patch MEMS antennas on an HRS
substrate for millimeter-wave applications
Yong H. Cho, Man-Lyun Ha*, Wonkyu Choi**, Cheolsig Pyo**,
and Young-Se Kwon*
School of Information and Communication Engineering
Mokwon University, 800 Doan-dong, Seo-gu, Daejeon, 302-729,
Republic of Korea
Tel: +82-42-829-7675, Fax: +82-42-825-5449
E-mail: yhcho@mokwon.ac.kr
*Department of Electrical Engineering and Computer Science
Korea Advanced Institute of Science and Technology (KAIST)
373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, Republic of Korea
**RFID Technology Research Team
Electronics and Telecommunications Research Institute (ETRI)
161 Gajeong-dong, Yuseong-gu, Daejeon, 305-350, Republic of Korea

Floating-patch MEMS antennas on an HRS
substrate for millimeter-wave applications
Yong H. Cho, Man-Lyun Ha, Wonkyu Choi, Cheolsig Pyo,
and Young-Se Kwon
Novel floating-patch MEMS (Micro-Electro-Mechanical System) antennas are
proposed for millimeter-wave applications. The floating-patch MEMS
antennas are fabricated on a high resistivity silicon (HRS) substrate using the
surface micromachining technology. Simulation and experimental results for
reflection coefficients and radiation patterns are presented.
I. Introduction: An integrated antenna [1-3] has been extensively studied to
obtain the compact integration of active devices and antennas. In [1],
integrated horn antennas are developed with a dielectric membrane and
stacked silicon wafers. The selective lateral etching method based on the bulk
micromachining has been used to improve radiation characteristics of
microstrip antennas on a high-index material [3]. In this letter, we propose the
novel floating-patch MEMS antennas on an HRS substrate using the surface
micromachining technology [4]. The floating patch on an HRS substrate
allows us to obtain wideband and high-efficiency characteristics for antennas.
Note that the MEMS antennas were designed for the BWA (Broadband
Wireless Access) of IEEE 802.16 using the 42 GHz RF band [5].
II. Configuration of MEMS Antennas: The MEMS antennas in Fig. 1 consist
of an HRS substrate, microstrip lines, matching stubs, square rectangular
patches, and metallic posts. The geometry of type I is shown in Fig. 1(a) and

1(b). The Z0 of a microstrip line is set to 50 Ω. The length of a square patch, T
is determined as βπ /=T in terms of the TM0 surface wave on an HRS (εr)
substrate. The dispersion relation of the TM surface wave is obtain as
)tan()tan( 1
22
0
22
02
2222
0 gkkgkk ββεββε −−=−− (1)
where rεεε 0= , εµω 0=k , and 000 εµω=k . Next, the parameters, d, h1,
and h2 are designed for the mechanical support of a square patch. The
dimensions of a matching stub, a and b are optimized to obtain the antenna
resonance. The geometries of types II and III are illustrated in Fig. 1(C). A
metallic post is moved to a radiation edge to control the reflection coefficients.
III. Simulation and Experimental Results: An HRS wafer with εr = 11.2 and
g2 = 300 um is used to build up the MEMS antennas. The parameters, g1, t,
and l are set to 300 um, 10 um, and 0.29 mm, respectively. Simulations are
performed with the Ansoft DesignerTM
1.0 based on the MoM (Method of
Moments). Other parameters are shown as follows: 1) Type I: a = 0.54 mm, b
= 0.89 mm, T = 2.12 mm, d = 0.2 mm, h1 = 0.5 mm, h2 = 0.25 mm, 2) Type II:
a = 0.69 mm, b = 0.75 mm, T = 1.78 mm, d = h1 = 0.15 mm, h2 = 0.1 mm, 3)
Type III: a = 0.62 mm, b = 0.6 mm, T = 1.41 mm, d = 0.15 mm, h1 = 0.4 mm,
h2 = 0.1 mm. To verify our designs, the floating-patch MEMS antennas are
fabricated with the help of the Opto-Electronics Laboratory, the Korea
Advanced Institute of Science and Technology (KAIST) using the surface
micromachining technology including the thick photoresist (THB-151NTM
)

lithography process. Fig. 2 shows reflection coefficients versus frequency for
types I, II, and III. For type I, the bandwidth is almost 6 GHz (40 to 46 GHz).
Fig. 3 shows radiation patterns for type I. To measure radiation patterns, the 2
X 2 array of type I is formed. The measured antenna gain and the 3dB
beamwidth are 12 dBi and 30○
at 42 GHz, respectively. Note that the
simulated antenna gain is 13.2 dBi. Fig. 4 shows resonant frequency shifting
characteristics versus h2 for type III in terms of the simulation. The increase in
a strip length, h2 results in the decrease in a resonant frequency. This is due
to the increase in the capacitive loading at a radiation edge. The frequency
shifting characteristics can be used to implement a reconfigurable antenna
using the MEMS RF switch or the NafionTM
actuator.
References
[1] G. M. Rebeiz, L. P. B. Katehi, W. Y. Ali-Ahmad, G. V. Eleftheriades, and C.
C. Ling, “Integrated horn antennas for millimeter-wave applications”, IEEE
Antennas Propagat. Magazine, vol. 34, no. 1, pp. 7 ~ 16, Feb. 1992.
[2] K. Chang, R. A. York, P. S. Hall, and T. Itoh, “Active integrated antenna,”
IEEE Trans. Microwave Theory Tech., vol. 50, no. 3, pp. 937-944, March
2002.
[3] I. Papapolymerou, R. F. Drayton, and L. P. B. Katehi, "Micromachined
patch antennas," IEEE Trans. Antennas Propagat., vol. 46, no. 2, pp. 275-283,
Feb. 1998.
[4] M.-L. Ha, Y. H. Cho, C.-S. Pyo, and Y.-S. Kwon, “Q-band micro-patch
antennas implemented on a high resistivity silicon substrate using the surface
micromachining technology,” 2004 IEEE Microwave Theory Tech. Society
Digest, pp. 1189-1192, June 2004.
[5] J.-M. Lee, Y. H. Cho, C.-S. Pyo, and I.-G. Choi, “A 42-GHz wideband
cavity-backed slot antenna with thick ground plane,” ETRI Journal, vol. 26, no.
3, pp. 262-264, June 2004.

Figure captions:
Fig. 1 Geometry of floating-patch MEMS antennas
(a) Top view of type I (b) Side view of Type I (c) Top view of types II (d = h1)
and III (d ≠ h1)
Fig. 2 Behaviors of reflection coefficients versus frequency for types I, II, and
III
—–—— type I (simulation)
O type I (measurement)
– . – . – type II (simulation)
X type II (measurement)
……… type III (simulation)
+ type III (measurement)
Fig. 3 Behaviors of normalized radiation patterns versus observation angle for
the 2 X 2 array of types I
—–—— E-co (simulation)
O E-co (measurement)
– – – – H-co (simulation)
X H-co (measurement)
– . – . – E-cross (simulation)
+ E-cross (measurement)
……… H-cross (simulation)
□ H-cross (measurement)
Fig. 4 Resonant frequency shifting characteristics versus h2 for type III
—–—— h2 = 0.53 mm
– – – – h2 = 0.40 mm
– . – . – h2 = 0.28 mm
……… h2 = 0.15 mm

Figure 1(a) and 1(b)
T
a
b
d
l
h2 h1
Port
Post
Patch
T
d
g 1
Patch
Ground HRS
Post
g 2
t
t
t

Figure 1(c)
h 2
Port
Patch
Post
h2
h1

Figure 2
38 40 42 44 46
-25
-20
-15
-10
-5
0
Frequency [GHz]
Reflectioncoefficients[dB]

Figure 3
-90 -60 -30 0 30 60 90
-60
-50
-40
-30
-20
-10
0
Angle [Degree]
Normalizedradiationpower[dB]

Figure 4
38 40 42 44 46 48 50
-25
-20
-15
-10
-5
Frequency [GHz]
Reflectioncoefficients[dB]

Floating-patch MEMS antennas on an HRS substrate for millimeter-wave applications

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