miércoles, 10 de febrero de 2010
Abstract.-This paper presents the overview of RF MEMS
(Radio Frequency-MicroElectroMechanical Systems)
components and reconfigurable antennas designed and
produced in Middle East Technical University (METU)
using the in-house fabrication process. The design and
measurement results of various components such as
switches, impedance tuners, phase shifters, frequency
tunable antennas, a phased array antenna with RF MEMS
phase shifters, and a reflectarray design are summarized.
It is shown that the fabricated RF MEMS components
satisfy the design specifications and have better performance
and reconfigurability capabilities compared to their
MEMS technology is a powerful way of merging the
functions of sensing and actuation with computation
and communication to control physical parameters
at the microscale. Present markets of MEMS technology
are mainly in pressure and inertial sensors, inkjet print
heads, and high-resolution digital displays. Future and
emerging applications include tire pressure sensing,
fiber optical components, fluid management and
processing devices for chemical microanalysis,
medical diagnostics, and drug delivery, and RF
and wireless electronics, namely RF MEMS. The
application of MEMS technology to RF systems
enables production of components with low power
consumption, high linearity, low insertion loss, and
high isolation. RF MEMS components are particularly
attractive for researchers due to their tunable properties.
This technology is used to implement many tunable
circuits and systems in a miniaturized way that has
never been implemented before using any other
This paper presents some of the RF MEMS
components and reconfigurable antennas designed
and produced in METU using the in-house fabrication
process developed at the Microelectronics Facilities
(METU MET). Section II gives the RF MEMS switch
structures, which are the key element of technology.
Section III and Section IV present the impedance tuner
and reconfigurable antennas, respectively. Section V
gives the monolithic phased array structure implemented
with MEMS technology and the proposed reflectarray
RF MEMS Switches
Metal-to-Metal Contact RF MEMS
Shunt Switch RF MEMS
Switches are the key elements in the design of the
complete systems hence the improvement in one
switch can affect the whole system performance.
We have designed a metal-to-metal contact switch
operating at 1-6 GHz band to obtain a better performance
than the existing ones. The switch, shown in Figure 1,
consists of two cantilevers located on ground planes
of a coplanar waveguide (CPW) transmission l
ine. With the help of actuation electrodes beneath
the cantilevers, the switching of the RF signal is maintained.
According to the measurement results,
the switch has isolation better than 20 dB in the 1-6 GHz
band and better than 10 dB in the 1-20 GHz band.
Insertion loss of the structure is better than the 0.3 dB
in the 1-20 GHz band. The switch has a measured actuation
voltage of 7 V.
Capacitive ContactRF MEMS
A capacitive contact RF MEMS shunt switch is designed
as shown in Figure 3 (a). The switch has recessed sections
on the ground plane of coplanar waveguide and the
meanders supporting the bridge increase the series
inductance of the bridge, which is used to tune the
switch to operate at Ku-band . The switch has a measured
down-state capacitance of 2.08 pF which results in better
than 20 dB measured isolation and better than 0.2 dB insertion
loss for the 11-17 GHz band as shown in Figure 3 (b).
The measured actuation voltage of the switch is 13 V.
Reconfigurable double-stub and triple stub impedance
tuners are designed and produced for X and Ku-band
applications. These can be used for LNA matching, antenna
matching, noise parameter, and load-pull measurements.
One of the designs has a double-stub structure which has
10 CPW based MEMS switches distributed evenly on the
two stubs forming a distributed structure . Figure 4 (a)
shows the schematic view of this design. The capacitive
MEMS switch used has a specific design which uses two
variable capacitors between the signal and the ground of
the CPW for discrete biasing requirements for each MEMS
switch of the matcher.
The design is capable of matching 25 different points on the
Smith Chart with a maximum measured VSWR of 5.27 at
18 GHz when a single MEMS switch is actuated from each
stub. The design can also be operated by actuating more
than one MEMS switch resulting with 1024 (210) combinations
which has a maximum VSWR of 50.8 at 18 GHz. Smith
Chart shows distribution of all possible states. It should
be noted here that external SMT resistors were used for
the DC biasing of the MEMS switches.
RF MEMS components have tunable characteristics;
thus the integration of these components with radiators
may yield several advantages such as reconfigurability
in polarization, frequency, and radiation pattern. One
of the reconfigurable antenna structure designed and
fabricated is a tunable frequency CPW fed rectangular
slot antenna . In order to achieve a shift in the
resonant frequency, a short circuited stub with
RF-MEMS capacitors is inserted opposite to the
feeding transmission line as shown in Figure 6 (a).
Measured reflection coefficient characteristics for
different actuation voltages are shown in Figure 6 (b).
It is observed that the resonant frequencies can be
shifted from 8.7 GHz to 7.7 GHz, and from 10.57 GHz to
10.22 GHz by changing the actuation voltage, -hence
the height of the MEMS capacitors-, from 0 to 16 volts.
The measurement results are in a good agreement with
the simulations. The antenna radiates broadside for all
of the four resonances and increasing the capacitance
by lowering down the bridges does not cause any
adverse effect on the radiation patterns. The other
reconfigurable antenna structure employs the idea
of loading a microstrip patch antenna with a stub
on which MEMS capacitors are placed periodically
as shown in Figure 7 (a) . MEMS capacitors are
electrostatically actuated with a low tuning voltage
in the range of 0-11.9 V. The antenna resonant
frequency can continuously be shifted from
16.05 GHz down to 15.75 GHz as the actuation
voltage is increased from 0 to 11.9 V.
This section presents the phased array system
designed at 15 GHz employing 3-bit DMTL type
phase shifters which are monolithically integrated
with the feed network of the system and the
radiating elements on the same substrate . The
phase shifter can give 0°-360° phase shift with 45°
steps at 15 GHz which is used to obtain various
combinations of progressive phase shift in the
excitation of radiating elements. The phased array
is composed of four linearly placed microstrip
patch antennas. Figure 8 (a) shows the
photograph of the phased array fabricated on
a glass substrate. The digital phase shifter
used in the system is composed of a periodically
loaded high-impedance transmission line (> 50 _)
with MEMS bridges in series with lumped
capacitors, forming a DMTL. Figure 9 (a) and
(b) shows the unit cell of the fabricated DMTL
phase shifter and its circuit model [ ]. Measured
inserted phase shifts for different states are shown
in Figure 9 (c). Figure 8 (b) shows the measured
radiation pattern results for different progressive
phase shift. The main beam can be steered by
4°, 14° as the phase shifter states are adjusted
Another application of the MEMS technology
is to use MEMS components in reflectarrays to
scan the beam. In this work, in order to control
the phase of the wave reflected from each element
of reflectarray, the lengths of the microstrip lines
are changed using RF MEMS series switches .
Thus, progressive phase shift between the elements
are changed and reflectarray with reconfigurable main
beam is obtained by the help of MEMS technology.
In the proposed design, the patch antenna at
26.5GHz is printed on a glass substrate bonded to
another glass substrate which contains the
transmission lines with MEMS switches.
Transmission line with series RF-MEMS switch
is shown in Figure 10 (a). Transmission lines are
coupled to the patch antenna by means of a slot
in the ground layer between the two glass
substrates as shown in Figure 10 (a) and (b).
Control of the reflection phase from each unit element
is achieved by the help of phase design curve
obtained from infinite array simulations in HFSS.
The phase design curve shown in Figure 10 (c) indicates
the dependence of the reflection phase on the
transmission line length. Required transmission line
lengths are chosen from this phase design curve.
To switch the beam from broadside to 40°, two sets
of lengths have been chosen by the ON-OFF states
of RF MEMS switch. HFSS simulations have also
been performed for transmission line with RF MEMS
switch for further tuning of the phase.
This paper reviews some examples of RF MEMS
components and antennas designed and fabricated
in the facilities of METU. It is shown by the
measurement results that the fabricated components
satisfy the design specifications. More components,
as well as production, modeling and packaging studies
will be presented and discussed during the presentation
in the conference.
Página: www. radantmems.com
Realizado: Franco A Rivera C.
Publicado por Tecnología en Telecomunicaciones - conocimientos.com.ve en 13:21
Etiquetas: Franco A Rivera C.