Rainee N. Simons

Glenn Research Center, Cleveland, Ohio

Novel On-Wafer Radiation Pattern

Measurement Technique for MEMS

Actuator Based Reconfigurable

Patch Antennas

NASA/TM—2002-211816

October 2002
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Rainee N. Simons

Glenn Research Center, Cleveland, Ohio

Novel On-Wafer Radiation Pattern

Measurement Technique for MEMS

Actuator Based Reconfigurable

Patch Antennas

NASA/TM—2002-211816

October 2002

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

24th Annual Antenna Measurement Techniques Association Meeting and Symposium

cosponsored by the Aeroflex Lintek Corporation and Mission Research Corporation

Cleveland, Ohio, November 3–8, 2002
Acknowledgments

This work was funded under the NASA CICT TASK entitled “MEMS Actuator-Based Antenna Technology”

under Code R.

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NASA/TM—2002-211816 1

NOVEL ON-WAFER RADIATION PATTERN MEASUREMENT TECHNIQUE

FOR MEMS ACTUATOR BASED RECONFIGURABLE PATCH ANTENNAS

Rainee N. Simons

National Aeronautics and Space Administration

Glenn Research Center

21000 Brookpark Road

Cleveland, Ohio 44135

Phone: 216–433–3462, Fax: 216–433–8705

E-mail: Rainee.N.Simons@grc.nasa.gov

ABSTRACT

The p ap er present s a n ov el on -w a fer, a nt en n a fa r f ield 

p at tern meas u rement tech n iq ue f o r micro elect ro -

mecha nical s y st ems ( MEMS ) b as ed reco n figu ra b le p a tch

a nt en na s . Th e mea su remen t t echn iqu e s ig nifican tly 

red uces th e t ime an d t he co st a s so cia ted wit h th e

cha ra ct eriza t io n of prin t ed a nt enn as , f ab ricat ed on a 

s emicon d ucto r w af er or d ielectric su b st ra te. To mea su re

t he rad iat io n p at terns , t he R F p ro b e st at ion is mod if ied t o 

a ccommo d at e a n op en - en ded recta n gu la r w av eg u id e a s

t he rot a ting linearly po larized sa mp lin g an t en na . The

o pen- en d ed w a vegu id e is a tt ached t hro ug h a coa xia l

rot ary j oint to a Plex ig las TM arm a nd is d riv en a lon g an 

a rc b y a s tep per mo t or. Thu s, t h e sp inn in g o pen- end ed 

w av eg uid e ca n s ample t he rela tiv e field int ens it y o f th e

p at ch a s a f u nction of t h e an gle f ro m b ore s ig ht . The

exp eriment al resu lt s includ e th e mea s ured linearly

p olarized an d circu larly po la rized ra diat io n p at t erns f o r

M EM S- ba s ed f req uency reco nf ig ura ble recta ng u la r a nd 

p olariza tion reco nf igu ra b le n ea rly s q ua re p a tch

a nt en na s , res pect iv ely .

1. Introduction

Microelectromechanical systems (MEMS) based actuators

have emerged as a viable alternative to solid state control

devices in microwave circuits. The MEMS actuators offer

several advantages [1]. First, significant reduction in

insertion loss, which results in higher figure-of-merit.

Second, they consume insignificant amount of power

during operation, which results in higher efficiency. Third,

they exhibit higher linearity and as a result lower signal

distortion when compared to semiconductor devices. Last,

MEMS actuators have the potential to dynamically

reconfigure the frequency, polarization, and radiation

pattern of antennas thus providing total reconfigurability.

These advantages have been the motivation to integrate

MEMS switches/actuators with planar antennas for beam

steering and frequency/polarization reconfiguration.

Typical examples of MEMS based antennas are reported in

references [1–9]. In these examples, the antennas and arrays

are fabricated on a semiconductor wafer, such as high

resistivity silicon, semi-insulating GaAs or a dielectric

substrate, such as alumina or fused quartz, using

conventional photolithography techniques. One of the

challenges faced with the characterization of MEMS based

antennas on semiconductor wafers is the need for a fast and

inexpensive technique to measure the radiation patterns

without having to saw the wafer. Measurement techniques

reported in the literature [10–12] are more suited for

conventional printed antennas.

I n th is paper , we d emo ns trate a no vel o n- waf er , anten na far

f ield p atter n m easu r em en t techn iqu e f or MEMS -b as ed

r econ fig ur ab le patch antenn as f abr icated on a hig h resis tivity

s ilicon wafer . Th is tech n iq ue r equ ir es a co p lanar w av eg u id e

( CP W) g r ou nd - sign al- gr ou n d (G -S - G) m icr ow av e p ro b e

( Pico pr o be Mo del 40 A, p itch 25 0 μ m) , a RF w af er pr ob e

s tation (Cas cad e Mo d el 4 2 ), and an au to matic n etw or k

analy zer /m icr ow av e r eceiv er . Th e adv antag es of th is 

techn iq u e ar e ( 1) it elim in ates th e n eed to saw the w af er in to

s maller in div id ual p atch an tenn a f or ch ar acter ization ,

m in im izing lo ss d ue br eak ag e an d enh ancin g y ield , and ( 2 ) it

eliminates th e need fo r cus to m- b uilt test f ixtur es with sp ecial

lau ncher s/tr ans itio n s, r edu cing th e com plex ity , d ev elop m en t

tim e, an d co s t. I n a p ro d uction en vir on ment, this techn iqu e is

extremely fas t an d inexp ens iv e w hen autom ated fo r r ep eated 

m easu rem en ts .

2. Patch Antennas with Integrated

MEMS Actuators

Figures 1(a) and (b) are wafer maps illustrating patch

antennas on a 3-in. diameter high resistivity silicon wafer

(εr = 11.7) with integrated MEMS actuator for frequency

and polarization reconfiguration, respectively. In these
NASA/TM—2002-211816 2

circuits a microstrip line of characteristic impedance equal

to 50 Ω excites the patch antennas. The length of this line is

kept small to minimize feed losses. The microstrip feed is

terminated at the opposite end in a microstrip-to-CPW

Figure 1(b).—Patch Antennas With Integrated MEMS Actuator for

 Polarization Reconfiguation On a 3 Inch Diameter High Resist-

 ivity Silicon Wafer.

Figure 1(a).—Patch Antennas With Integrated MEMS Actuator for 

 Frequency Reconfiguation On a 3 Inch Diameter High Resist-

 ivity Silicon Wafer.

transition for on-wafer characterization using CPW RF

probes, as illustrated in figure 2. The transition makes use

of a radial stub to provide a virtual RF short circuit between

the ground contacts of the CPW RF wafer probe and the

substrate ground plane [13]. A typical frequency

reconfigurable and polarization reconfigurable patch

antennas with integrated MEMS actuator are illustrated in

figures 3 (a) and (b), respectively. The design and

fabrication of these antennas are described in references [3]

and [4], respectively. Briefly, the frequency reconfigurable

patch antenna operates at its normal frequency as

determined by the dimension b when the actuator is in the

OFF-state. In the ON-state, the excess capacitance provided

by the actuator tunes the patch to a lower operating

frequency thus providing frequency reconfiguration.

Figure 2.—Schematic Illustrating the Experimental Setup for

 Measuring the Return Loss of a Patch Antenna.

Probe tip

Patch antenna

Ground plane

G

G S

Coaxial connector

Ground-Signal-Ground 

wafer probe

Detail of 

probe tip (G)

Microwave 

absorber

(S)

(G)

Wafer (0r

)
NASA/TM—2002-211816 3

MEMS 

actuator 

 #1

MEMS 

actuator

#2

Microstrip

feed

DC bias

pad G-S-G

RF probe

pads

b

W

L a

Figure 3(a).—Frequency Reconfigurable Patch Antenna Element 

 With Two Independent MEMS Actuators, L = 580 μm, 

 W = 50 μm, a = 2600 μm, b = 1500 μm.

Patch 

Dielectric antenna

film

Via 

hole

DC 

bias 

pad

Metal strip

and stub Moveable

overpass

Figure 3(b).—Polarization Reconfigurable Patch Antenna Element

 With Integrated MEMS Actuator, c = 1500 μm and d = 1492 μm.

MEMS

actuator

Impedance

matching

transformer

Nearly square

patch antenna

Vertical pol

Horizontal pol

Microstrip

feed

GSG

RF probe

pads

DC bias

pads

c

d

In the case of polarization reconfigurable patch antenna, the

nearly square patch with notches is designed to support two

degenerate orthogonal modes when excited at a corner.

When the MEMS actuator is in the OFF-state, the

perturbation of the modes is negligible and hence the patch

radiates a circularly polarized (CP) wave. In the ON-state,

the excess capacitance perturbs the phase relation between

the modes causing the patch to radiate dual linearly

polarized (LP) waves.

3. Measurement Methodology

3.1 Return Loss

The CPW G-S-G RF probes are calibrated to the tips using

an automatic network analyzer (ANA) (HP 8510C) and a

short circuit, open circuit, and a matched load as standards.

The probe manufacturer provides, on an impedance

standard substrate (ISS) and on a disc, the calibration

standards and the software necessary to carry out the

calibration. The calibration corrects for the errors, the losses

as well as the parasitics associated with the experimental

set-up, which includes the CPW RF probes. The calibrated

Figure 4.—Computer Controlled On-Wafer CP Radiation Pattern 

 Measurement Set-Up Using a Rotating Linearly Polarized Pick-

 Up Antenna for MEMS Actuator Based Patch Antennas. (Sur-

 rounding Microwave Absorber Panels Have Been Removed).

Swivelable

microscope

Microwave

absorber

RF G-S-G

probe

Silicon wafer with

patch antennas

RF 

probe

station

Rotating linearly

polarized pick 

up antenna

Coaxial rotary

joint Coaxial

detector

Motor

Stepper motor

Swinging PlexiglasTM

arm

probe is then made to contact the circuit under test as

shown in figure 2. Thus, the intrinsic return loss of the

antenna is displayed on the ANA and can be recorded. In

addition, the feed losses as well as the input impedance of

the antenna can be de-embedded as demonstrated in

references [14,15].

3.2 Radiation Pattern

To measure the radiation patterns, the RF probe station is

modified to accommodate an open-ended rectangular

waveguide (e.g., WR–42) as the rotating linearly polarized

sampling antenna. The open-ended waveguide is attached to

a custom-built PlexiglasTM fixture. The fixture arm is

positioned along a virtual arc, extending from –90° to +90°

in increments of few degrees, by a stepper motor.

Simultaneously, a miniature DC motor attached to the

PlexiglasTM arm spins the open-ended waveguide. The

spinning open-ended waveguide samples the relative field

intensity of the circularly polarized radiation from the patch

as a function of the angle from bore sight. The signals

picked up by the waveguide are coupled to a detector

through a coaxial rotary joint. The experimental setup is

illustrated in figure 4. Figure 5 presents a close-up of the

experimental set-up showing the CPW RF and the DC

probes for exciting the patch and biasing the MEMS

actuator.
NASA/TM—2002-211816 4

Figure 5.—Close-up of the Measurement Set-Up.

RF Probe

DC Probe

Wafer

4. Measured Return Loss Characteristics

4.1 Frequency Reconfigurable Patch

The measured return loss for the two states of the actuators

are shown in figures 6(a)–(c). When both the actuators are

in the OFF-state, the patch resonates at its nominal

operating frequency of about 25.0 GHz as shown in

figure 6(a). The –10.0 dB return loss bandwidth of the patch

is about 3.3 percent. When actuator #1 is in ON-state and

actuator #2 is in the OFF-state, the resonant frequency (fr)

shifts to about 24.8 GHz as shown in figure 6(b). Similarly,

when actuator #1 is in the OFF-state and actuator #2 is in

the ON-state, the fr shifts to 24.8 GHz. This result is

expected since the two actuators are identical in

construction. The step change of 200 MHz in the fr for both

cases is about 0.8 percent of the patch nominal operating

frequency. Finally, when both actuators are in the ON-state,

the fr is 24.6 GHz as shown in figure 6(a). The shift is twice

as much as the case when a single actuator is turned ON.

Furthermore, at resonance the magnitudes of the return loss

are almost equal for the two states, implying minimum loss

of sensitivity. Thus for this configuration, the patch antenna

can be dynamically reconfigured to operate at different

bands, separated by a few hundred MHz, by digitally

addressing either or both actuators. This is a desirable

feature in mobile wireless systems to enhance capacity as

well as combat multipath fading.

4.2 Polarization Reconfigurable Patch

The measured return loss for the OFF-state of the actuator

is shown in figure 7. The patch is well matched to the 50Ω

feed line and resonates at a frequency of 26.7 GHz. In the

OFF-state the patch radiates a circularly polarized wave.

The measured return loss for the ON-state of the actuator is

also shown in figure 7. In the ON-state also the patch is also

well matched to the 50Ω feed line and resonates at a

Figure 6.—Measured Return Loss Demonstrating Frequency 

 Reconfigurability. (a) Both Actuators Are Either in the OFF 

 State or ON State. (b) Actuator #1 is ON and Actuator #2 

 is OFF. (c) Actuator #1 is OFF and Actuator #2 is ON. 

23.50 23.96 24.42 24.88 25.80

–18

–6

–12

0

Frequency, GHz

Return los, S11, dB

25.34

Both actuators OFF

Both actuators ON

(a)

23.50 23.96 24.42 24.88 25.80

–18

–6

–12

0

Frequency, GHz

Return los, S11, dB

25.34

(b)

23.50 23.96 24.42 24.88 25.80

–18

–6

–12

0

Frequency, GHz

Return los, S11, dB

25.34

(c)

Figure 7.—Measured Return Loss of Nearly Square

 Patch Antenna.

26.625

GHz

25 30 26 27 28 29

0

–15

–6

Return loss, S11, dB

Frequency, GHz

–3

–9

–12 26.7 GHz

OFF-state

ON-state

frequency of 26.625 GHz. The change in the resonance

frequency for the two states is considered to be small. In the

ON-state, the patch radiates dual linearly polarized waves.
NASA/TM—2002-211816 5

5. Measured Radiation Patterns

5.1 Frequency Reconfigurable Patch

The measured E- and H-plane radiation patterns are shown

in figure 8.

5.2 Polarization Reconfigurable Patch

In the OFF-state, the patch radiates a circularly polarized

wave. The measured radiation patterns along the two

orthogonal planes are shown in figure 9. The measured

axial ratio at boresight is about 2.0 dB. In the ON-state,

the patch radiates dual linearly polarized waves. The

measured E- and H-plane radiation patterns for the vertical

polarization are shown in figure 10. Similar radiation

patterns are observed for the horizontal polarization.

Figure 8.—Measured E and H-plane Radiation Patterns of The 

 Frequency Reconfigurable Patch Antenna.

–90 –60 0 60 90

–20

–30

–10

0

Angle, deg

Relative amplitude, dB

–30 30

H-plane

E-plane

–90 –60 90 –30 0 30 60

0

–40

–30

–20

–10

Relative magnitude, dB

Angle, deg



x

y

z

Figure 9.—Measured Circularly Polarized Radiation

 Patterns of Nearly Square Patch Antenna.

= 0° plane

= 90° plane

–90 –60 90 –30 0 30 60

0

–40

–30

–20

–10

Relative magnitude, dB

Angle, deg

Figure 10.—Measured Linearly Polarized Radiation

 Patterns for Vertical Polarization of Nearly Square

 Patch Antenna.

E–plane

H–plane

6. Sources of Measurement Errors

One of the major sources of error is the reflection of the

signal radiated from the patch antenna by the probe station

positioners and fixtures. This causes distortion in the

measured radiation patterns. This problem can be reduced

with the use of high quality microwave absorbing material

covering the probe station metal surfaces. A second source

of error is due to misalignment of the patch antenna and the

sampling antenna. The wafer with the patch antennas can be

horizontally aligned and the open-ended waveguide

sampling antenna can be vertically aligned using a precision

level and a plumb bob, respectively. In addition, the angular

alignment of the wafer can be done optically with the help

of a microscope. Last, the errors associated with the CPW

G-S-G RF probes can be calibrated out as discussed in

section 3.1.

7. Conclusions and Future Directions

A novel fast and inexpensive on-wafer far field radiation

pattern measurement technique for characterizing patch

antennas with integrated MEMS actuators is demonstrated.

This technique eliminates the need to saw the wafer into

smaller individual patch antennas, thus minimizing loss due

breakage and enhancing yield. In addition, eliminates the

need for custom-built test fixtures with special

launcher/transition, thus reducing the complexity,

development time, and cost.

We plan to extend this effort to the measurement of gain

and cross-polarization. The gain can be determined by the

reflection method [16]. The cross-polarization can be

measured using a circularly polarized sampling antenna

whose sense of polarization is known.
NASA/TM—2002-211816 6

 8. REFERENCES

[1] J.K. Smith, “Reconfigurable Aperture Program

(RECAP) –MEMS Revolutionary Impact on RF Systems,”

Notes of the Workshop “RF MEMS for Antenna

Applications,” 2000 IEEE Ant. and Prop. Inter. Symp.,

Salt Lake City, UT, July 16, 2000.

[2] R.N. Simons, D. Chun, and L.P.B. Katehi,

“Microelectromechanical Systems (MEMS) Actuators for

Antenna Reconfigurability,” 2001 IEEE MTT-S Inter.

Microwave Symp. Dig., Vol. 1, pp. 215–218, Phoenix, AZ,

May 20–25, 2001.

[3] R.N. Simons, D. Chun, and L.P.B. Katehi,

“Reconfigurable Array Antenna Using Microelectromechanical Systems (MEMS) Actuators,” 2001 IEEE Ant.

and Prop. Inter. Symp. Dig., Vol. 3, pp. 674–677, Boston,

MA, July 8–13, 2001.

[4] R.N. Simons, D. Chun, and L.P.B. Katehi,

“Polarization Reconfigurable Patch Antenna Using

Microelectromechanical Systems (MEMS) Actuators,”

2002 IEEE Ant. and Prop. Inter. Symp. Dig., Vol. 2,

pp. 6–9, San Antonio, TX, June 16–21, 2002.

[5] J.H. Schaffner, D.F. Sievenpiper, R.Y. Loo, J.J. Lee,

and S.W. Livingston, “A Wideband Beam Switching

Antenna Using RF MEMS Switches,” 2001 IEEE Ant. and

Prop. Inter. Symp. Dig., Vol. 3, pp. 658–661, Boston, MA,

July 8–13, 2001.

[6] C.-W. Baek, S. Song, C. Cheon, Y.-K. Kim, and

Y. Kwon, “2-D Mechanical Beam Steering Antenna

Fabricated Using MEMS Technology,” 2001 IEEE MTT-S

Inter. Microwave Symp. Dig., Vol. 1, pp. 211–214,

Phoenix, AZ, May 20–25, 2001.

[7] C. Bozler, et al., “MEMS Microswitch Arrays for

Reconfigurable Distributed Microwave Components,” 2000

IEEE Ant. and Prop. Inter. Symp., Dig., Vol. 2,

pp. 587–591, Salt Lake City, UT, July 16–21, 2000.

[8] J.-C. Chiao, Y. Fu, I.M. Chio, M. DeLisio, and

L.-Y. Lin, “MEMS Reconfigurable Vee Antenna,” 1999

IEEE MTT-S Inter. Microwave Symp. Dig., Vol. 4,

pp. 1515–1518, Anaheim, CA, June 13–19, 1999.

[9] D. Chauvel, N. Haese, P.-A. Rolland, D. Collard, and

H. Fujita, “A Micro-Machined Microwave Antenna

Integrated with its Electrostatic Spatial Scanning,” Proc.

IEEE Tenth Annual Inter. Workshop on Micro Electro

Mechanical Systems (MEMS 97), pp. 84–89, Nagoya,

Japan, Jan. 26–30, 1997.

[10] J.S. Hollis, T.J. Lyon, and L. Clayton, Jr., (Editors),

Microwave Antenna Measurements, Scientific-Atlanta,

Inc., Second Edition, Atlanta, GA, Chap. 10, 1970.

[11] Y.T. Lo and S.W. Lee, (Editors), Antenna Handbook,

Theory, Applications, and Design, Van Nostrand Reinhold

Company, Inc., New York, NY, Chap. 32, pp. 49–64, 1988.

[12] R.C. Johnson, (Editor), Antenna Engineering

Handbook, Third Edition, McGraw-Hill, Inc., New York,

NY, Chap. 23, pp. 1–33, 1993.

[13] D.F. Williams and T.H. Miers, “A Coplanar Probe to

Microstrip Transition,” IEEE Trans. Microwave Theory

Tech., Vol. 36, No. 7, pp. 1219–1223, July 1988.

[14] R.N. Simons and R.Q. Lee, “On-Wafer

Characterization of Millimeter-Wave Antennas for Wireless

Applications,” IEEE Trans. Microwave Theory Tech.,

Vol. 47, No. 1, pp. 92–96, Jan. 1999.

[15] A.J. Zaman, R.Q. Lee, and R.N. Simons, “A New

Design Approach for a Patch Antenna with a Notch Feed,”

Microwave and Optical Technology Lett., Vol. 23, No. 4,

pp. 236–238, Nov. 1999.

[16 ] S. S ilver, (Editor), Microwave Antenna Theory and

Des ign, P eter P eregrinus Ltd., Lo ndon, UK, Sec. 15·20, 19 84.

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E–13508

WU–755–08–0B–00

12

Novel On-Wafer Radiation Pattern Measurement Technique for MEMS

Actuator Based Reconfigurable Patch Antennas

Rainee N. Simons

Antenna measurements; Microelectromechanical systems; MEMS; Automated on-wafer

measurements; Instrumentation; Coplanar waveguide; Microstrip; Radiation pattern;

Circular polarization; Dual linear polarization; Patch antenna; Semiconductor antenna

Unclassified -Unlimited

Subject Category: 33 Distribution: Nonstandard

Prepared for the 24th Annual Antenna Measurement Techniques Association Meeting and Symposium cosponsored by the

Aeroflex Lintek Corporation and Mission Research Corporation, Cleveland, Ohio, November 3–8, 2002. Responsible

person, Rainee N. Simons, organization code 5620, 216–433–3462.

The paper presents a novel on-wafer, antenna far field pattern measurement technique for microelectromechanical systems

(MEMS) based reconfigurable patch antennas. The measurement technique significantly reduces the time and the cost

associated with the characterization of printed antennas, fabricated on a semiconductor wafer or dielectric substrate. To

measure the radiation patterns, the RF probe station is modified to accommodate an open-ended rectangular waveguide as

the rotating linearly polarized sampling antenna. The open-ended waveguide is attached through a coaxial rotary joint to a

PlexiglasTM arm and is driven along an arc by a stepper motor. Thus, the spinning open-ended waveguide can sample the

relative field intensity of the patch as a function of the angle from bore sight. The experimental results include the measured linearly polarized and circularly polarized radiation patterns for MEMS-based frequency reconfigurable rectangular

and polarization reconfigurable nearly square patch antennas, respectively.