Figure 6 shows a photograph of the fabricated novel parallel coupler with an area of 30 ⫻ 44 mm 2 . 4. CONCLUSIONS A novel high isolation microstrip parallel coupler with ⫻ -shaped structure has been presented in this article. With ⫻ -shaped struc- ture,the proposed couplers achieve a physical size reduction of almost 35% with the performance competed with the conventional one. Adopting RPC approach, the isolation is improved greatly. A proposed parallel coupler has been fabricated and measured at 915 MHz. The measurement of the proposed parallel coupler exhibits maximum isolation of ⫺58.4 dB and directivity of ⫺40.4 dB at 915 MHz and the isolation is over ⫺40 dB in 902–928 MHz frequency band. The proposed coupler is compact, easy for fabri- cation,which can beapplied in radiofrequency identification reader system. REFERENCES 1. L. Su,T. Itoh,and J.Rivera, Design of an overlay directional coupler by a full-wave analysis, IEEE Trans Microwave Theory Tech MTT-31 (1983), 1017–1022. 2. S. Uysal and H. Aghvami, Synthesis, design and construction of ultra- wideband nonuniform directional couplers in inhomogeneous media, IEEE Trans Microwave Theory Tech 37 (1989), 969 –976. 3. M. Dydyk,Microstrip directional couplers with ideal performance via single-element compensation, IEEE Trans Microwave Theory Tech 47 (1999), 956 –964. 4. J.-L. Chen,S.-F.Chang, and C.-T.Wu,A high-directivity microstrip directional coupler with feedback compensation, IEEE MTT-S Int Mi- crowave Symp Dig 1, Seattle, WA, (2002), 101–104. 5. W.-K. Kim and M.-Q. Lee,A passive circulator with high isolation using a directional coupler for RFID, In IEEE MTT-S Dig, San Fran- cisco,CA,2006,pp.1177–1180. 6. M.-L. Chuang and M.-T. Wu, Miniaturized ring coupler using multiple open stubs, Microwave Opt Technol Lett 42 (2004), 379 –383. © 2009 Wiley Periodicals, Inc. NONCONTACT HEARTBEAT DETECTION AT 2.4,5.8,AND 60 GHz: A COMPARATIVE STUDY Dany Obeid, 1 Sawsan Sadek, 2 Gheorghe Zaharia, 1 and Ghaïs El Zein 1 1 IETR UMR CNRS 6164 —INSA, 20 Ave. des Buttes de Coe¨ smes, CS 14315, 35043 Rennes, France; Corresponding author: dany.obeid@insa-rennes.fr 2 Lebanese University, “Institut Universitaire de Technologie,” BP.: 813, Saida, Lebanon Received 5 July 2008 ABSTRACT: The aim of this work is to provide two new schemes for human noninvasive heartbeat activity monitoring using low power mi- crowave noncontact systems and direct conversion architecture. The first system is tested at 2.4 GHz and 5.8 GHz frequencies. Another system, operating at 60 GHz, is demonstrated where higher heartbeat sensitivity detection is achieved. © 2009 Wiley Periodicals, Inc.Microwave Opt Technol Lett 51: 666 – 669, 2009; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.24110 Key words: microwave systems; Doppler effect; noncontact detection; cardiopulmonary activity; heartbeat rate 1. INTRODUCTION Noncontact detection and monitoring of human cardiopulmonary activity become a valuable tool in sleep monitoring and home health care applications. Traditional electrocardiogram (ECG) w fixed electrodes is perturbing for patients with conditions such a infants at risk of sudden infant syndrome, adults with sleep disor ders,or burn victims. To improve the quality of life forsuch patients, more attention has been given to microwave Doppler radar as a remote monitoring technique [1]. A person’s chest has a quasi-periodic movement with no net velocity, and according to Doppler theory, reflects the transmitted signal with its phase mo ulated by the time-varying chest position [2]. As shown in Eq. (1) the phase variation ⌬ ⫻ (t) of the reflected signal is directly propor- tionalto the chest position ⌬x(t) that contains information about the movement caused by heartbeat and respiration. ⌬⫻ 共 t 兲 ⫻ 4⫻ ⌬x 共 t 兲 ⫻ (1) In the above equation, ⫻ is the wavelength of the transmitted waves. The average range of the peak-to-peak chest motion caus by respiration varies from 4 mm to 12 mm, whereas the chest displacement due to heartbeat alone is about 0.3 mm [3].The measurement of this small displacement is the objective of this work and we are proposing the use of noncontact Doppler senso for the remote monitoring of such signals. Direct-conversion Doppler radars, operating at 1.6 and 2.4 GHz, have been integrated in 0.25 ⫻ m CMOS and BiCMOS technologies in 2004 [4]. The 2.4 GHz radar, placed at 50 cm range, uses a quadrature (I/Q) receiver. The use of a quadrature receiver improved the lowest accuracy form 40 to 80%. There ha been additional recent work in using existing wireless communi- cations infrastructure. A modified Wireless Local Area Network PCMCIA card and a module combining the transmitted and re- flected signals were used to detect heart and respiration activity [5].A low-power double-sideband transmission in the Ka-Band was used in 2006 [6, 7]. Two measurement systems for noncontact heartbeat detection are presented in this article.Using direct conversion Doppler radars at a distance of 1 m from the patient, the first system is tested at 2.4 GHz and 5.8 GHz, whereas the second one operates at 60 GHz. It is note fully to mention that these selected frequen cies belong to the industrial scientific medical (ISM) band and th transmitted powers do not exceed the limits specified by the federal communications commission (FCC). When breathing nor mally, the reflected signal off the target contains information ab chest displacements due to heartbeat and respiration. The utilize frequencies in this work are 2.4 GHz, 5.8 GHz,and 60 GHz. According to Eq. (1),1 mm chestdisplacement gives a phase variation of 5.76° at 2.4 GHz frequency and 13.9° at 5.8 GHz, whereas the same amount of displacements gives a phase variat of 144° at 60 GHz. For feasibility reasons, the first experiments made while holding the breath. A low power 2.4 GHz Continuous Wave (CW) signal is generated and the detection of the shifted phase between the received and the transmitted signals is per- formed. The shifted phase contains information about movement due to heartbeat. The same measurement system is used for 5.8 GHz signal. To increase the accuracy of the measured signal, another system operating at 60 GHz is also evaluated in this wor When the frequency gets high, the wavelength gets shorter and phase variation of the reflected signal increases [6, 8], as shown Eq.(1). Hence,increased sensitivity to small displacements is obtained. This willimprove the accuracy in detecting the R-R 666 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 3, March 2009 DOI 10.1002/mop