which lead to higher selectivity for the passband. They are �35and �37 dB at the frequencies of 4.7 and 6.2 GHz, respectively.In addition, two extra transmission zeros are observed obvi-ously and located at about 7.0 and 9.0 GHz, respectively. Thus,a much sharper filter skirt can be achieved. The external qualityfactor of this filter equals to 25.86 and the coupling coefficientbetween the two resonators is 0.03495. The photograph of thefabricated filter is given in Figure 3. The filter has a compactsize of 10 � 6 mm2.

3. CONCLUSIONS

In this letter, a highly selective microstrip bandpass filter usingimproved cross-coupled triangular open-loop resonators is de-signed, fabricated, and measured. The new cross coupling structureis implemented by inserting these two L-shaped stubs into thetriangular open-loop resonators. Results show that the proposedfilter has a low insertion loss and flat characteristics in the pass-band and two additional transmission zeros for high out-of-bandrejection. The filter has a compact size of 10 � 6 mm2 whichamounts to about 0.3 �g � 0.2 �g. Simulations agree well withmeasurement to prove that the proposed filter is compact andexhibits excellent filtering performances.

REFERENCES

1. J.-S. Hong and M. J. Lancaster, Couplings of microstrip square open-loop resonators for cross-coupled planar microwave filters, IEEETrans Microwave Theory Tech 44 (1996), 2099–2109.

2. C.-C. Yu and K. Chang, Novel compact elliptic-function narrow-bandbandpass filters using microstrip open-loop resonators with coupledand crossing lines, IEEE Trans. Microwave Theory Tech 46 (1998),952–958.

3. S.-Y. Lee and C.-M. Tsai, New cross-coupled filter design usingimproved hairpin resonators, IEEE Trans Microwave Theory Tech 48(2000), 2482–2490.

4. J.-S. Hong and M.J. Lancaster, Cross-coupled microstrip hairpin-resonator filters, IEEE Trans Microwave Theory Tech 46 (1998),118–122.

5. B. Wu, C.-H. Liang, Q. Li, and P.-Y. Qin, Novel dual-band filterincorporating defected SIR and microstrip SIR, IEEE MicrowaveWireless Components Lett 18 (2008), 392–394.

6. M.-L. Hsieh, T.-H. Huang, L.-S. Chen, C. H. Sun, S. Wang, M. P.Houng, and S. L. Fu, Multilayer cross-coupled resonator bandpassfilters fabricated on low temperature cofired ceramic substrates, Mi-crowave Opt Technol Lett 49 (2007), 1977–1979.

7. S. Li, J. Huang, Q. Meng, L. Sun, Q. Zhang, F. Li, A. He, X. Zhang,C. Li, H. Li, and Y. He, A 12-pole narrowband highly selective hightemperature superconducting filter for the application in the thirdgeneration wireless communications, IEEE Trans Microwave TheoryTech 55 (2007), 754–759.

8. J.-S. Hong, E.P. McErlean, and B. Karyamapudi, Eighteen-pole su-perconducting CQ filter for future wireless applications, IEE ProcMicrowave Antennas Propag 153 (2006), 205–211.

9. S. Liao, X. Zhang, X. Guo, B. Wei, and B. Lao, A method of doublecross coupling lines for HTS filter design, Microwave Opt TechnolLett 50 (2008), 1874–1876.

10. R. Wu, S. Amari, and U. Rosenberg, Cross-coupled microstrip bandreject filters with non-resonating nodes, IEEE Microwave WirelessCompon Lett 15 (2005), 3585–3587.

© 2009 Wiley Periodicals, Inc.

EXTRACTION MECHANISM STUDY OFTHE MICROWAVE CARDIO-GRAPH(MCG)

Jun Zheng,1 Yong Huang,1 and Jian Qian2

1 College of Information Science and Technology, East China NormalUniversity, Shanghai 200062, China; Corresponding author:jzheng@cc.ecnu.edu.cn2 Department of Electronic Science and Engineering, NanjingUniversity, Nanjing 210093, China

Received 3 January 2009

ABSTRACT: We developed a sensitive microwave cardio-graph (MCG)meter that can extract time-domain heart moving signals. In this article,we first describe the structure of the system, and then analyze the ex-tracting principle focusing on the key step: the carrier-wave cancella-tion and its effect, and finally present the graphs captured by this appa-ratus under various conditions. From the experiment results, we can seethat (1) the MCG signals captured in this way are characteristic, steady,and repeatable; (2) there is no obvious correspondence in position be-tween the peak and valley points of MCG and the P, Q, and R points ofECG; (3) if the distance between the two antennas changes, the MCGwaveform tends to repeat periodically. © 2009 Wiley Periodicals, Inc.Microwave Opt Technol Lett 51: 2348–2354, 2009; Published online inWiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24598

Key words: electric cardio graph (ECG); microwave cardio graph(MCG); penetrating and scattering waves; auto carrier-wave cancella-tion

1. INTRODUCTION

There are a lot of successful examples by using microwave appa-ratus to sense life or heart moving information remotely. Forexample, microwave apexcadiography [1] uses microwave tech-nique to record apexcardiograms (ACG). The system emits a beamof continuous wave CW (2.1–2.5 GHz,) to a human body, and thenreceives the reflected microwave signal from the moving chestwall of the body. This apexcardiographic signal represents theleft-ventricular movement caused by low-frequency displacementsof the precordium overlying the apex of the heart. The nextexample is the noncontact vital signs monitor [2], which measuresphysiological parameters such as the heartbeat rate and respirationwithout physically connecting electrodes. The system directs abeam of frequency-modulated CW radio wave toward the body ofa subject. The reflected signal contains phase information repre-senting the movement of the surface of the body, from whichrespiration and heartbeat information can be obtained. Anotherexample is the microwave life-detection system [3–5], which canremotely detect the breathing and heartbeat signals of humansubjects lying on the ground or located behind barriers, or buriedunder earthquake rubbles. The distance between the eradiatingantenna and the human subject can reach as far as 10 feet or moreunder the lab environment constructed. The system illuminates alow-intensity microwave beam (450 or 1150 MHz) to a humansubject, so that the small amplitude body vibration due to thebreathing and heartbeat of the human subject will modulate thebackscattered microwave signal. The breathing and heartbeat sig-nals can then be extracted from the backscattered signal by phasedetection in the microwave receiving system.

In recent years, some of these kinds of microwave devices areintegrated into single chips, which are compact, lightweight, andcould be inexpensively mass produced. For example, the Single-chip direct-conversion microwave Doppler-radar transceivers [6],

2348 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop

operating at 1.6 and 2.4 GHz, is fully integrated in 0.25-�m siliconCMOS techniques. This chip can potentially be used to detectheartbeat and respiration 50 cm away from the subject, particularlyin the area for sleep apnea monitoring in both infants and adults.

From 2000, we began to start a new research project, named thedesign and development of microwave cardio-graph (MCG) meter.The purpose of this research is to develop a new type of micro-wave apparatus to extract MCG signals. It is different from theaforementioned studies. Previous studies concentrated on remotelyextracting heartbeat and respiration signals and then analyzed themin the frequency domain, mainly for obtaining heartbeat rhythmand breathing frequency. In our research, we focus on extractingECG-like waveform signals the MCG, and then analyze them inboth frequency domain and time domain to get valuable heartmotion features. A preliminary version of this work has beenreported in 2004 [7, 8]. Since then further efforts have been madeto investigate the extraction mechanism and to analyze the MCGgraphs we captured.

2. SYSTEM STRUCTURE

When a beam of microwave ray illuminates and then partly goesinto a human body, the penetrated and reflected waves are modu-lated by the motion of the heart, the lung, and other organs in thechest. Figure 1 is the photo of the MCG application system, whichconsists of four parts: (1) two antennas; (2) an MCG system unit;(3) an electric cardio-graph (ECG) meter; and (4) a PC computer.Of the two horn antennas, one is for emitting microwaves and theother for receiving. The emitting antenna is placed under the body,and the receiving antenna is placed above the body. Experimentresults show that in this way the signals extracted are stronger andthe interferences caused by environment are smaller.

Figure 2 is the schematic diagram of the MCG system unit,which consists of three parts: (1) The microwave circuit part; (2)The microprocessor-based control and PC interface part; and (3)an ECG interface part. The microwave circuit part is used togenerate, amplify, detect, and distribute microwave signals tovarious components. The microprocessor-based circuit completesA/D converts, digital phase shifters and attenuators managements,auto carrier-wave cancellation, and communications with the PCcomputer. The ECG interface part is used to extract ECG signalssimultaneously for comparison with MCG signals.

The working principle of MCG meter is as follows:The microwave source is a CW of 1.15 GHz [9], coming from

a phase-locked oscillator. This power consecutively goes throughtwo-directional couplers and a circulator. In the first coupler, asmall part of power is fed into a balanced mixer for signal extrac-

tion. In the second coupler, a small portion of power is fed into adigital attenuator and a digital phase shifter for auto carrier-wavecancellation. About 70% of the wave power is finally fed into theemitting antenna. A little portion of the emitted power will bereflected due to unmatch. This amount of power will be eventuallyabsorbed by a match load linked to the circulator to avoid inter-ference.

The received wave from the receiving antenna can be dividedinto two categories: (1) useful signals which compose of the carrierwaves modulated by heart and (2) useless signals which composeof unmodulated carrier waves. Because the useless signals areunmodulated, their frequencies are the same as the source fre-quency. The useless signals are expected to be canceled.

The carrier-wave cancellation process is as follows: (1) take asmall part of power directly from the source power as a cancelingwave; (2) use a digital attenuator and a digital phase shiftercontrolled by microprocessor to adjust the amplitude and phase ofcanceling wave; (3) add the canceling wave to the received wavein an adder; and (4) use a detector to check the sum of the adder.If the sum shown on the cancellation indicator is zero whenadjusting, it means that the system is zero balanced. This processmay need to be executed several times.

3. EXTRACTING PRINCIPLE

In our system, we use two horn antennas: one for emitting micro-waves and the other for receiving, as shown in Figure 1, where Ei

is the emitting wave, Es is the penetrating wave and scatteringwaves, and Ei � Es is the receiving wave. We simplify theproblem by assuming: (1) the heart motion (including pulse, bloodflow, and other factors) is periodical with basic frequency �; (2)

(b)

(a)

(c)

(d)

Figure 1 MCG application system: (a) receiving and emitting antennas,(b) MCG system unit, (c) ECG meter, and (d) PC computer

Ei

7 cos( φ(t)+ φ7)

Ei + EsEs

Phase-Locked Oscilator

1.15GHz,100mW

Digital Attenuator

0-30dB

Digital Phase shifter 0-360 .

RF Amplifier 30dB

Balanced Mixer

LF Amplifier & Filter

Detector

A1cos( t+φ1)

Directional Coupler ,6dB

Adder

4 cos( t+ φ(t)+ φ4)

6 cos( t+φ6)

5 cos( t+ φ(t)+ φ5)

A2 cos(ωt+φ2) +

A3 cos(ωt+∆φ(t)+φ3)

Directional Coupler,10dB

2 cos(ωt+φ2)

A/D Converter & Controller & Interface

Directional Coupler,10dB

Circulator

Match load

Receiving Antenna

CancellationIndicator

Emitting Antenna

Microwave Circuits

Microprocessor &PC Interface

ECG Interface

ECGInterface

Figure 2 Schematic diagram of the MCG system unit. [Color figure canbe viewed in the online issue, which is available at www.interscience.wiley.com]

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 2349

the illuminating wave is a plane EM wave with frequency �; and(3) the far-field condition is basically satisfied.

In this case, the amplitude of the emitting wave Ei can beexpressed by the following:

Ei � �Ei0�cos��t� (1)

where Ei0 is the initial amplitude of Ei and � is the carrier-wavefrequency.

Because the heartbeat is periodical, no matter how complex theheart motion is, we can finally expand the Es to Fourier seriesaccording to the base band frequency �. Thus, the scattering waveEs could be reasonably expressed as follows:

Es � �Es0�1

r� �n�0

�

Ansin�n�t � �n�� � cos��t �2�

�r

� �m�0

�

Pmsin�m�t � �m��� (2)

where Es0 is the initial amplitude of Es; � is the carrier-wavefrequency; � is the carrier-wave wave length; � is the basicfrequency of heart motion; r is the distance between the assumedscattering center and the receiving antenna; n and m are indices;An, Pm, �n, and m are the parameters of the component waves,and t is the time variable.

From Eq. (2), we can see that the amplitude of Es is attenuatedin 1/r, and the phase of Es is delayed in 2�r/�. It’s obvious that thehigh-order components will decay quickly. For simplicity, we takethe base band components as the main part and take the high-bandcomponents as the minor disturbance (for example, we take n � 0and 1, and m � 0 and 1), the Eq. (2) becomes as follows:

�Es� ��Es0�

rA0sin�0 � A1sin��t � �1�

� cos��t �2�

�r � P0sin0 � P1sin��t � 1�� (3)

3.1. Phase Part ContributionExpending Eq. (3), we can write the phase part as follows:

cos��t �2�

�r � P0sin0�cosP1sin��t � 1� � sin��t �

2�

�r

� P0sin0�sinP1sin��t � 1� (4)

Considering the following basic math equations

cosP1sin��t � 1� � J0�P1� � 2 �m�1

�

J2m�P1�cos2m��t � 1�

(5)

sinP1sin��t � 1� � 2 �m�1

�

J2m�1�P1�sin�2m � 1���t � 1� (6)

where J(P) is the Bessel function, and substituting Eqs. (5) and (6)into (4), we can get the items for carrier wave and sidebandexpressions as following:

Carrier-wave:

J0�P1�cos��t �2�

�r � P0sin0�

Upper-sideband:

J1�P1�sin��� � ��t �2�

�r � 1 � P0sin0�

Lower-sideband:

J1�P1�sin��� � ��t �2�

�r � 1 � P0sin0�

2nd upper-sideband:

J2�P1�cos��� � 2��t �2�

�r � 21 � P0sin0�

2nd lower-sideband:

J2�P1�cos��� � 2��t �2�

�r � 21 � P0sin0�

· · ·· · ·

� (7)

From Eq. (7), we can see that the phase part contribution is theupper and lower sideband signals with frequency � � �, � �2�. . . . The amplitude of these signals decreases sharply fromlower order to higher order.

3.2. Amplitude Part ContributionNormalizing according to A0sin�0 , the amplitude part becomes asfollows:

1 �A1

A0sin�0sin��t � �1� � 1 � fasin��t � �1� (8)

where fa is the amplitude modulation degree. The product of thispart and phase modulation part generates upper and lower side-band. Because fa is very small, we can only consider the followingpart after neglecting the high order small terms,

fasin��t � �1� � J0�P1�cos��t �2�

�r � �P0sin0�� �

fa

2J0�P1�

�sin��� � ��t �2�

�r � �1 � P0sin0�

� sin��� � ��t �2�

�r � �1 � P0sin0� (9)

From Eq. (9), we can see that the amplitude part contribution is theupper and lower sideband signals with frequency � � �. Com-pared with the phase part contribution, the amplitude part contri-bution is much smaller.

The theoretical analysis above is only suitable for the ideal casewith far-field condition satisfied. In real world situations, theanalysis becomes very complex. Nonetheless, from these analyses,we can see that when a beam of microwave illuminates a humanbody, both the phase and amplitude of the scattered electric fieldare closely related to the heart motion. If we neglect the amplitudepart contribution, the scattering field can be expressed as follows:

Es � Acos�t � ��t� � (10)

where A is the amplitude, �(t) is the phase verification caused bymodulation, and is the phase angle. This is the theoretic basis

2350 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop

that microwave can be used to sense the motion of heart, althoughthis relationship is very intricate, and the higher order componentsof heart motion were not taken into account.

The carrier-wave cancellation is the key step for extractingprocess. Auto cancellation has two functions: (1) Increase thephase modulation degree, which in turn to enhance the intensity ofthe sideband component and (2) Prevent the RF amplifier fromsaturation.

The heart motion modulation mainly results in the phase ver-ification �(t), which can be discomposed into many upper andlower sidebands with frequency � � n� (n � 1, 2, . . . ). Figure3 is a diagram illustrating the composing process of Es and Ec.Here, Es denotes the electric field of one of the sidebands and Ec

denotes the electric field of carrier wave. In our system, the carrierwave frequency is 1.15 GHz, and the heartbeat moving frequencyis only 0.2 to 1.3 Hz, besides, the amplitude of heart moving signalis much smaller than that of carrier-wave signal, so the degree ofphase modulation is very weak.

The sideband signal Es is rotating with the angular velocity �� n�� and the carrier-wave Ec is rotating with the angular velocity�, as shown in Figure 3(a). The dotted line in the figure is thepossible track of Es when vibrating. From this figure, we can seethat the largest phase variation angle � equals to the following:

� � arctan��Es�/�Ec�� (11)

Because Ec comes from Ei, environment reflection, and the Es, sothe amplitude of Ec is much bigger than that of Es. Therefore,normally, the phase verification angle is definitely very small.

If we can minimize the amplitude of Ec (i.e., cancel the carrierwave as much as possible), the phase variation angle � can beincreased greatly, as shown in Figure 3(b). In this case, theintensity of the sideband component will be increased signifi-cantly.

3.3. Prevent the RF Amplifier From SaturationThe amplitude of Ei is very big, so when amplifying Ei � Es, theRF amplifier can be easily saturated. In our method, we onlycancel the carrier-wave component of frequency � without affect-

ing the sideband component of frequency � � n� (n � 1, 2, . . .).Therefore, the sensitivity of the system has increased greatly.

4. EXPERIMENT RESULTS AND DISCUSSION

On each of the following MCG graphs, an ECG signal capturedsimultaneously is superimposed over the corresponding MCG sig-nal for reference. The sampling frequency is 500 Hz, and the totalsampling points is 5000. The x-label is the sampling time rangingfrom 0 to 10 s; the y-label is the normalized amplitude rangingfrom �1 to �1. For simplicity, we omit the y-label and part of thex-label on all MCG graphs shown below.

4.1. MCGs Selected From 24 Different PeopleThe MCGs shown in Figure 4 are selected from hundreds ofdifferent people. The 24 testing human subject is lying betweentwo antennas which are 35 cm apart. From these graphs we can seethe following:

● There is no obvious correspondence in position between thepeak and valley points of MCG and the P, Q, and R points ofECG. The period of MCG is the same with that of ECG.

● MCG graphs are different for different people. The wave-form can roughly be divided into one peak, two peaks,multipeaks, and flat peak.

4.2. MCGs From Four Different People on Different Days Withthe Same Body GesturesThe MCGs shown in Figure 5 are from four different people ondifferent days with the same gestures. On each graph, there arefour lines corresponding to four tests within the duration of 1month. The testing condition is the same as the condition forMCGs in the 24 people cases.

From these graphs we can see the following:

● The MCG graphs are basically the same if the person undertesting keeps the same body gesture.

● The MCG graphs are repeatable, even the testing is carriedon after 1 month.

4.3. MCGs for One Person on the Same Day With the SameGesture on Different Antenna DistancesThe MCGs shown in Figure 6 are collected from one person on thesame day with the same gesture, but the different distance betweentwo antennas. The distance is changed in steps of one eighth wavelength each time.

For these tests, the body gesture were kept unchanged, but thedistance between emitting antenna and receiving antenna changedin the interval of 1/8�. The wavelength of the carrier wave in oursystem is about 26 cm in free space, so the 1/8� distance equals toabout 3.25 cm. The initial distance between two antennas is 35 cm(0�), the next distance is 38.25 cm (1/8�), followed by 41.50 cm(2/8�), and so on until 61.00 cm (9/8�).

From these figures we can see the following:

● The MCG graph varies when the distance between the twoantennas changes.

● The MCG waveform repeats if the distance between twoantennas changes for one wavelength (�).

● The MCG waveform reverses if the distance between twoantennas changes for one half of the wavelength (1/2�).

● When the distance between two antennas increases, the noiseincreases, so the waveform becomes worse.

One of the Sidebands Es

Carrier-wave Ec(before cancellation)

One of the Sidebands Es

2 α

Carrier-wave E2 α c (after cancellation)

(a) (b)

Figure 3 The composition process of carrier-wave Ec and the sidebandof scattering wave Es. (a) Before cancellation, the phase variation angle ofthe composite vector � is small; (b) after cancellation, the new phasevariation angle �� becomes much bigger when carrier wave is cancelledperfectly

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 2351

4.4. MCGs for One Person on the Same Day With the SameGesture on Different Phase VariationThe MCGs shown in Figure 7 are collected from one person on thesame day with the same gesture. A digital phase shifter is inserted

between the receiving antenna and input port of the MCG meter.The phase shifter generates a phase variation in steps of onethirty-second wave length. For these tests, the distance betweentwo antennas is fixed (35 cm), the environments including the body

(b) Waveform: two peaks

(a) Waveform: one peak

(c) Waveform: three peaks

(d) Waveform: flat peak

Figure 4 MCGs selected from 24 different people. Waveforms: (a) one peak, (b) two peaks, (c) three peaks, and (4) flat peak

(a) MCGs for person A tested on four different days.

(b) MCGs for person B tested on four different days

(c) MCGs for person C tested on four different days

(d) MCGs for person D tested on four different days

Figure 5 MCGs from Four different people on different days with the same body gestures

2352 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop

gesture are kept unchanged, but the phase between input port ofMCG meter and receiving antenna changes in the interval of1/32�. Sixteen MCG graphs are collected in one figure. The initialphase is 0, the next phase is 1/32�, followed by 2/32�, and so onuntil 15/32�.

From this figure we can see that:

● The MCG graph varies when the phase between input port ofMCG meter and receiving antenna changes.

● The MCG waveform reverses if the phase change reachesone half of the wavelength (1/2�).

● The interference noise is much smaller.

4.5. MCGs Experiment SummaryThe factors affecting the MCGs are as follows: (1) individual; (2)environment; (3) distance between two antennas; and (4) phasebetween the input port of MCG meter and the receiving antenna.The experiment summary is shown in Table 1.

5. CONCLUSIONS

The structure and working principle of the MCG meter we devel-oped which can be used to extract ECG-like signal was describedand analyzed in this article. The carrier-wave cancellation is thekey step for extracting process. This method increases the phasemodulation degree, which in turn to enhance the intensity of the

0

1/8 λ

1/4 λ

3/8 λ

1/2 λ

5/8 λ

3/4 λ

7/8 λ

1 λ

9/8 λ

Time (seconds)

Figure 6 MCGs for one person on the same day with the same gestureon different antenna distances. The initial distance between two antennas is35 cm (0�), the next distance is 38.25 cm (1/8�), followed by 41.50 cm(2/8�), and so on until 61.00 cm (9/8�), as shown in parts (1)–(10) in thefigure

0

1/32 λ

1/16 λ

3/32 λ

1/8 λ

5/32 λ

3/16 λ

7/32 λ

1/4 λ

9/32 λ

5/16 λ

11/32 λ

3/8 λ

13/32 λ

7/16 λ

15/32 λ

Time (seconds)

Figure 7 MCGs for one person on the same day with the same gestureon different phase variation. The phase shifter generates a phase variationin steps of one thirty-second wave length. The initial phase is 0, the nextphase is 1/32�, followed by 2/32�, and so on until 15/32�, as shown inparts (1)–(16) in the figure

TABLE 1 MCGs Experiment Summary

Factors MCGs Waveform

Individuals Same person Different. (Under some special condition will be the same)Different person Different, the waveform can be roughly divided into four

one peak, two peak, multi peak and flat peak.Environment Surroundings Different. (Under some special condition will be the same)

Body gesture Different.Distance between two antennas Different, the waveform will repeat periodically, the

waveform can be roughly divided into one peak, twopeak, multi peak and flat peak.

Phase inserted between theinput port of MCG meterand the receiving antenna

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 2353

sideband component. Experiment results show that MCG signalcaptured in this way is characteristic, steady, and repeatable. Onething out of our expectations is that there is no obvious correspon-dence in position between the peak and valley points of MCG andthe P, Q, and R points of ECG. The MCG signals are closelyrelated to the environment, including the body gesture of thetesting subject. If the capturing environment changes, the MCGsignal will alter, so the signal lacks of comparability with eachother. If the distance between two antennas is changed, or if thephase inserted between the input port of MCG meter and thereceiving antenna is changed, the MCG waveform tends to repeatperiodically.

ACKNOWLEDGMENTS

This work was supported by the National Science Foundation ofChina (NFSC) under Grant No. 39970210. The authors like tothank Dr. K.M. Chen of the Department of Electrical Engineeringand System Science, Michigan State University for his support andencouragement during the course of this research.

REFERENCES

1. J.C. Lin, J. Kiernicki, M. Kierniki, and P.B. Wollschlaeger, Microwaveapexcardiography, IEEE Trans Microwave Theory Tech 27 (1979),618–620.

2. F.M. Sharpe and M. Steven, Non-contact vital signs monitor, U.S.Patent 4,958,638, Georgia Tech Research Corporation, Atlanta, GA,1990.

3. K.M. Chen, D. Misra, H. Wang, H.R. Chuang, and E. Postow, AnX-band microwave life-detection systems, IEEE Trans Biomed Eng 33(1986), 697–701.

4. H.R. Chuang, Y.F. Chen, and K.M. Chen, Automatic clutter-cancellerfor microwave life-detection systems, IEEE Trans Instrum Meas 40(1991), 747–750.

5. K.M. Chen, Y. Huang, J.P. Zhang, and A. Norman, Microwave life-detection systems for searching human subjects under earthquake rubbleor behind barrier, IEEE Trans Biomed Eng 27 (2000), 105–114.

6. A.D. Droitcour, O. Boric-Lubecke, V.M. Lubecke, J. Lin, and G.T.Kovacs, Range correlation and I/Q performance benefits in single-chipsilicon Doppler radars for noncontact cardiopulmonary monitoring,IEEE Trans Microwave Theory Tech 52 (2004), 838–848.

7. Y.B. Tian, J. Qian, and Y. Huang, Operation mechanism of microwavecardio-graph detector, J Electromagn Waves Appl 18 (2004), 1073–1083.

8. Y. Huang, T.Y. An, J. Qian, and M.J. Fan, Design and development ofa microwave cardio graph meter, Huadong Shifan Daxue Xuebao 4(2004), 40–47.

9. J.M. Osepchuk and R.C. Petersen, Safety standards for exposure to RFelectromagnetic fields, IEEE Microwave Mag 2 (2001), 57–69.

© 2009 Wiley Periodicals, Inc.

A WIDEBAND CIRCULARPOLARIZATION ANTENNA FORPORTABLE INMARSAT BGANTERMINAL APPLICATIONS

Shi-Qiang Fu, Shao-Jun Fang, Zhong-Bao Wang, andXiao-Ming LiSchool of Information Science and Technology, Dalian MaritimeUniversity, Dalian, Liaoning 116026, China; Corresponding author:fushq@vip.qq.com

Received 11 January 2009

ABSTRACT: A low profile, wideband, and portable antenna has beendesigned and fabricated for Inmarsat broadband global area network(BGAN) land mobile terminal applications. The purpose of the antennawas to provide a low-cost and easy-fabricated solution with wide band-width and high performance. The proposed antenna is composed of thestacked corner-truncated patches with sequential rotation oblique feedand a serial feeding network. Good antenna characteristics are achievedover the BGAN operating bands. The measurement results for returnloss, gain, axial ratio, and radiation pattern confirm the integrity of thesimulation results. © 2009 Wiley Periodicals, Inc. Microwave OptTechnol Lett 51: 2354–2357, 2009; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.24643

Key words: BGAN; singly fed circularly polarized; sequentially rotatedtechnique; oblique feed; portable

1. INTRODUCTION

Broadband satellite systems have long been in focus, but primarilyat the Ku or Ka band. After the successful launch and acquisitionof the third Inmarsat-4 satellite on August 18, 2008, a new broad-band satellite communication system called BGAN can completethe global coverage at the L-band. The BGAN is a mobile com-munications system created to transmit broadband wireless voice,video, and data communications almost anywhere on the earth’ssurface [1]. The system, developed by IMMARSAT, consists of aconstellation of geostationary satellites working in conjunctionwith portable, lightweight, surface-based terminals about the sizeof a laptop or so.

The main motivation for our work was to obtain a wide-bandand compact antenna to meet the demand for small, portable,mobile broadband satellite terminals. A commonly used antennatype in mobile satellite communications is the microstrip patchantenna. These antennas are low cost and light weight, and theyprovide fair properties regarding bandwidth and gain. A lot ofwork [2–4] in this field of microstrip antenna has been done withthe aim to enhance the bandwidth of such radiating elements.However, there are some drawbacks in those designs such asfabrication difficulty because of drilling of holes and probe sol-dering [2], poor front-to-back ratio due to the slot in the groundplane [3], and relatively low efficiency owing to the complex feednetwork losses [4].

This article describes a circularly polarized corner-truncatedsquare patch array antenna in which impedance and axial ratiobandwidths can be remarkably improved by using the stackedpatches, thick foam, and sequential rotation oblique feed. First, thesingle element is designed by using the optimization design andtuning technique [5]. Next, a serial feed network is proposedconnecting the patch by an oblique 3-D (three dimensional) mi-crostrip transition [6]. Then, using the well-known sequentialrotation feeding technique [7], a four-element array is designed.Finally, the designed four-element stacked patch antenna array was

2354 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop