Dung Tien Pham, 1 Moon-Ki Hong, 1 Jeong-Min Joo, 1 and Sang-Kook Han 1,2. 1 Department of Electrical and Electronic Engineering, Yonsei

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1 85% scale of size reduction can be highlighted as the highest among available data. Moreover, the broadband characteristics show the efficient suppression of unwanted signals up to the sixth harmonic proving that the solutions proposed are not only extremely useful in the process of novel compact microstrip circuit development but also lead to component refinement by additional filtering effects. ACKNOWLEDGMENTS This work was supported in part by National Science Center, Poland, under grant no. 4699/B/T02/2011/40. REFERENCES 1. R. Mongia, I. Bahl, and P. Bhartia, RF and microwave coupler-line circuits, Artech House Publishers, Norwood, MA, H. Ghali and T.A. Moselhy, Miniaturized fractal rat-race, branchline, and coupler-line hybrids, IEEE Trans Microwave Theory Tech 52 (2004), W.-L. Chen and G.-M. Wang, Design of novel miniaturized fractal-shaped branch-line couplers, Microwave Opt Tech Lett 50 (2008), W.-L. Chen, G.-M. Wang, and C.-X. Zhang, Miniaturization of wideband branch-line couplers using fractal-shaped geometry, Microwave Opt Tech Lett 52 (2009), S. Dwari and S. Sanyal, Size reduction and harmonic suppression of microstrip branch-line coupler using defected ground structure, Microwave Opt Tech Lett 48 (2006), M. Maddah-Ali, H.D. Oskouei, and K. Forooraghi, A compact branch-line coupler using defected ground structures, Microwave Opt Tech Lett 50 (2008), S.-S. Liao, P.-T. Sun, N.-C. Chin, and J.-T. Peng, A novel compact-size branch-line coupler, IEEE Microwave Wireless Compon Lett 15 (2005), Y.-H. Chun and J.-S. Hong, Compact wide-band branch-line hybrids, IEEE Trans Microwave Theory Tech 54 (2006), S.-C. Jung, R. Negra, and F.M. Ghannouchi, A design methodology for miniaturized 3-dB branch-line hybrid couplers using distributed capacitors printed in the inner area, IEEE Trans Microwave Theory Tech 56 (2008), T. Jing, X.-W. Shi, Y.-C. Guo, L. Chen, and X.-Q. Chen, Design of a compact branch-line coupler using capacitance loading, Microwave Opt Tech Lett 51 (2009), K. Kim, J. Lim, K. Kim, and D. Ahn, A compact dual band branch line coupler with arbitrary power division ratio, Microwave Opt Tech Lett 52 (2010), S.-C. Jung, R. Negra, and F. M. Ghannouchi, Analysis of miniaturized 3 db branch-line hybrid couplers using distributed MIM Capacitors, Microwave Opt Tech Lett 52 (2010), S.-S. Liao and J.-T. Peng, Compact planar microstrip branch-line couplers using the quasi-lumped elements approach with nonsymmetrical and symmetrical T-shaped structure, IEEE Trans Microwave Theory Tech 54 (2006), J. Wang, B.-Z. Wang, Y.-X. Guo, L.C. Ong, and S. Xiao, A compact slow-wave microstrip branch-line coupler with high performance, IEEE Microwave Wireless Compon Lett 17 (2007), S.Y. Yuan, M.-S. Shiau, S.-S. Liao, P.-T. Sun, and C.-T. Ho, An extremely compact dual-band branch-line coupler, Microwave Opt Tech Lett 49 (2007), C.-W. Tang and M.-G. Chen, Synthesizing microstrip branch-line couplers with predetermined compact size and bandwidth, IEEE Trans Microwave Theory Tech 55 (2007), M. Nosrati and S. K. Valashani, A novel compact branch-line coupler using four coupled transmission lines, Microwave Opt Tech Lett 50 (2008), C.-W. Tang and M.-G. Chen, Miniaturized microstrip branch-line couplers with the approach of p-model, Microwave Opt Tech Lett 50 (2008), VC 19. M. Nosrati, An extremely miniaturized microstrip branch-line coupler, Microwave Opt Tech Lett 51 (2009), M.-S. Shiau, S.Y. Yuan, S.-S. Liao, P.-T. Sun, and D.-G. Liu, A miniaturized millimeter-wave branch-line coupler using nonsymmetrical T-shape structure with quasi-stepped impedance resonator, Microwave Opt Tech Lett 49 (2007), K.-S. Chin, K.-M. Lin, Y.-H. Wei, T.-H. Tseng, and Y.-J. Yang, Compact dual-band branch-line couplers with stepped-impedance-stub lines, IEEE Trans Microwave Theory Tech 58 (2010), K.W. Eccleston and S.H.M. Ong, Compact planar microstripline branch-line and rat-race couplers, IEEE Trans Microwave Theory Tech 51 (2003), K.-O. Sun, S.-J. Ho, C.-C. Yen, and D. van der Weide, A compact branch-line coupler using discontinuous microstrip lines, IEEE Microwave Wireless Compon Lett 15 (2005), F. Hosseini, M.K.-A. Hosseini, and M. Yazdany, To compact ring branch-line coupler using nonuniform transmission line, Microwave Opt Tech Lett 51 (2009), C.-W. Tang, M.-G. Chen, and C.-H. Tsai, Miniaturization of microstrip branch-line coupler with dual transmission lines, IEEE Microwave Wireless Compon Lett 18 (2008), M.K.-A. Hosseini and M. Yazdani, To compact branch-line couplers using parallel high-impedance transmission lines, Microwave Opt Tech Lett 52 (2010), J. Gu and X. Sun, Miniaturization and harmonic suppression of branch-line and rat-race hybrid coupler using compensated spiral compact microstrip resonant cell, IEEE MTT-S Int Microwave Symp Dig, 2005, C. Zhou and H.Y.D. Yang, Design considerations of miniaturized least dispersive periodic slow-wave structures, IEEE Trans Microwave Theory Tech 56 (2008), F. Zhang, Miniaturized and harmonics-rejected slow-wave branchline coupler based on microstrip electromagnetic bandgap element, Microwave Opt Tech Lett 51 (2009), P. Kurgan and M. Kitlinski, Novel doubly perforated broadband microstrip branch-line couplers, Microwave Opt Tech Lett 51 (2010), Momentum, available at Advanced Design System, available at Wiley Periodicals, Inc. HETEROGENEOUS GIGABIT ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING/RADIO OVER FIBER TRANSMISSIONS OF WIRED AND WIRELESS SIGNALS USING A REFLECTIVE SEMICONDUCTOR OPTICAL AMPLIFIER AND SINGLE-ARM MACH ZEHNDER MODULATOR Dung Tien Pham, 1 Moon-Ki Hong, 1 Jeong-Min Joo, 1 and Sang-Kook Han 1,2 1 Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea; Corresponding author: skhan@yonsei.ac.kr 2 Yonsei Institute of Convergence Technology, Yonsei University, Incheon, Republic of Korea Received 14 October 2011 ABSTRACT: We propose and experimentally demonstrate a novel radio over fiber system that provides different gigabit orthogonal frequency division multiplexing (OFDM) signals transmission for wired and wireless networks using a conventional reflective semiconductor optical amplifier and a single-arm Mach Zehnder modulator (MZM). To halve sampling speed of electronics and to simplify a radio frequency 1954 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 8, August 2012 DOI /mop

2 front-end design, the proposed scheme adopts Hermitian symmetry to generate the wireless signal. It was reported that using the proposed scheme, 5-Gbps 16-quadrature-amplitude-modulation-OFDM wired and 1.17-Gbps quadrature phase-shift keying OFDM wireless signals were successfully transmitted through 23-km standard single mode fiber link. VC 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54: , 2012; View this article online at wileyonlinelibrary.com. DOI /mop Key words: radio over fiber; orthogonal frequency division multiplexing; optical access network; optical modulator; Hermitian symmetry 1. INTRODUCTION Radio over fiber (RoF) has been a promising solution to provide effective convergence of wired and wireless access networks for the last few decades [1 3]. Among various proposed schemes based on RoF, orthogonal frequency division multiplexing (OFDM) techniques have shown great potentials in optical communications by providing superior tolerance to optical fiber dispersion [4]. Besides, OFDM signals have high spectral efficiency in combination with multilevel mapping like M-ary quadrature amplitude modulation (QAM). Thanks to this merit, OFDM-based RoF systems have been considered as an attractive approach for next-generation optical access networks to meet explosively increased bandwidth demands. Refs. 5 7 proposed heterogeneous OFDM/RoF techniques to provide a converged wired and wireless transmission network with high-bandwidth efficiency. However, they have several limitations: using different wavelengths (1.3 and 1.5 lm) to realize different types of data for the wired and wireless signals [5] and using a manually integrated external modulator module at the optical line terminal, which includes two single-arm type Mach Zehnder modulators (MZMs) and an optical phase shifter, and a specifically designed optical interleaver with narrow passband at each optical network unit [6, 7]. These make the schemes complicated and cumbersome; hence, they are infeasible in practical scenarios that should guarantee cost-effectiveness. In this article, we propose a new simple OFDM/RoF scheme to provide simultaneous different wired and wireless signal transmission using a single-arm MZM and a bandwidth-limited, cost-effective reflective semiconductor optical amplifier (RSOA) as optical modulators. In the proposed scheme, only single pair of digital-toanalog converter (DAC) and analog-to-digital converter (ADC) is needed for the wireless OFDM signal generation and recovery using Hermitian symmetry. We experimentally demonstrate heterogeneous OFDM data transmission of 5-Gbps 16-QAM-OFDM wired and 1.17-Gbps quadrature phase-shift keying (QPSK)- OFDM wireless signals over a 23-km standard single mode fiber (SSMF) link. Transmission performance of the proposed scheme is evaluated in terms of bit-error-rate (BER) less than PRINCIPLE OF OPERATION Figure 1 shows the proposed OFDM/RoF scheme for the simultaneous OFDM data transmission. In this scheme, an optical carrier from a continuous wave (CW) light source is modulated by an OFDM wireless signal, which is electrically upconverted using a radio frequency (RF) tone with a frequency of f 0,atasingle-arm MZM. This modulated optical carrier is passed through an optical circulator and fed to a RSOA. Then, an OFDM wired signal is applied to the RSOA to modulate the injected optical carrier. After the OFDM wired signal modulation, the modulated optical carrier is reflected back to the optical circulator and transmitted through a SSMF link and recovered at a base station. The wired and wireless signals are separated using RF filters. Compared to conventional methods for wireless OFDM signal generation, the proposed scheme utilizes Hermitian symmetry to generate the OFDM wireless signal as well as the OFDM wired one. Accordingly, the OFDM wireless signal has just one channel signal stream with real values. It can provide a simple electrical front-end design for the wireless signal transmission. Besides, it is able to halve the number of required electronics, such as DACs and ADCs. 3. EXPERIMENTAL SETUP Figure 2 illustrates an experimental setup of the proposed scheme. A CW light source was realized by a tunable laser source at the wavelength of 1550 nm with an output optical power of 7.2 dbm. This CW optical carrier was modulated by an upconverted 1.17-Gbps QPSK wireless OFDM signal with a 2.5-GHz intermediate frequency (IF) tone at a single-arm MZM with V p biasing for the linear operation [4]. After the wireless modulation, the optical carrier was injected into a commercially available, 1-GHz bandwidth-limited RSOA through an optical circulator. Then, this carrier was directly modulated again by a 5-Gbps 16 QAM baseband OFDM signal for wired applications. The RSOA was operated with a bias current of 27 ma and temperature of 25 C. At this point, the input optical power of the carrier was reported as 17 dbm. Polarization controller (PC) 1 and PC 2 were attached in front of the MZM and RSOA to copolarize the input polarization states of the carrier for modulation optimization, respectively. After the RSOA modulation, the optical carrier was transmitted through a 23-km SSMF link. Before the signal reception at a photo diode (PD), the input optical power of the carrier was tuned using a tunable optical attenuator (TOA) to evaluate the signal performance of the proposed Figure 1 Schematic of the proposed scheme. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] DOI /mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 8, August

3 Figure 2 Experimental setup of the proposed scheme. Inset: RF power spectrum of the OFDM signals after PD. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] scheme in terms receiver sensitivity. PD has 3 db electrical bandwidth up to 3.5 GHz. The inset of Figure 2 represents the RF spectrum of the received optical carrier for both wired and wireless OFDM signals. The OFDM baseband offline digital signal processing was performed using a MATLABVR code. Both wired and wireless OFDM signals were generated to have Hermitian symmetry with 32 and 15 data subcarriers, respectively. Consequently, each OFDM signal could be generated using a single DAC (DAC 1 or DAC 2) in an arbitrary waveform generator (AWG; Tektronix 7122B) at 5-GSa/s sampling speed and 8-bit resolution. A size of fast Fourier transform was set to 128 in generating both wired and wireless OFDM signals. Cyclic prefix and preamble ratio were set to 1/16 and 1/10, to mitigate intersymbol interference effect and to implement channel estimation and compensation, respectively. In case of the wireless application, the received wireless OFDM signal was first high-pass filtered and downconverted into baseband using the same 2.5-GHz IF tone after the PD reception. Both of wired and wireless OFDM signals were filtered by low-pass filters (LPFs), which have the passband with respect to their bandwidth. A digital phosphor oscilloscope (DPO, Tektronix 72004B) at 50-GSa/s sampling speed was used to realize ADC 1 and ADC 2, to extract the OFDM signals for offline processing. It is necessary to notice that in the experiment, both OFDM signals were generated using the same AWG, which provided DAC 1 and DAC 2, therefore the DAC sampling speed must be the same in generation of both OFDM signals. In practical scenarios, based on the proposed scheme, slower DAC sampling speed and the larger number of data subcarrier could be used to generate the wireless OFDM signal. 4. EXPERIMENTAL RESULTS AND DISCUSSION As the wired and wireless signals could be sensitive because of the MZM bias voltage condition, the relationship between the signal performance for both OFDM signals was evaluated in terms of BER with a function of the MZM bias point, and the results are shown in Figure 3(b). Figure 3(a) describes a transfer Figure 3 (a) MZM transfer function curve and (b) relationship between the MZM bias voltage and the BER performances of the wired and wireless signals. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] 1956 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 8, August 2012 DOI /mop

4 and the 23-km SSMF link transmission, is represented in Figure 5. All the performance was analyzed, when the MZM was biased at 6.0 V, and the IF tone frequency was set to 2.5 GHz. As shown in both plots in Figure 5, it was verified that the wired and wireless OFDM signals were successfully transmitted in the proposed scheme with respect to the FEC limitation. There were about 0.9- and 0.7-dB power penalties observed at BER of 10 4 after the 23-km SSMF transmission for the wired and wireless OFDM signals, respectively. The insets in Figure 5 are the signal constellations for the equalized wired and wireless OFDM symbols. The constellations were well distinguishable; it means that the equalizations had been realized successfully. Figure 4 Relationship between the RF tone frequency of the wireless signal and the EVMs of the wired and wireless signals. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] curve of the MZM we used. Among the entire bias voltage range of the MZM, we focused on the bias voltage from 4 to 8 V. All the experiments were measured with the input optical power of 5 dbm at the PD. To estimate the signal performance in terms of BER, we first evaluated the signal quality using error vector magnitude (EVM) and then converted it to BER based on the equation, reported in Ref. 8. The wireless OFDM signal had low BER, when the MZM was operated around V p /4 (4.5 6 V) bias voltage, and its performance got worse in other voltage points due to the suppression of the modulated optical carrier (mainly occurred at 4 V bias point, so-called null point ) and the modulated optical sidebands (mainly occurred at V p /2 and above range of the bias voltage). On the other hand, it was verified that in the proposed scheme, the higher bias voltage promised the better wired OFDM signal performance, because in this condition, it was able to achieve higher optical power of the modulated carrier. Therefore, the proposed scheme has a trade-off between the wired and wireless signal performance in terms of the MZM bias voltage. It was also found that the proposed scheme provided 2.8-V dynamic range of the MZM bias voltage with respect to a signal performance criterion, which should satisfy the forward error correction (FEC) limitation (BER < 10 3 ; Ref. 9). Figure 4 shows impact of the IF tone frequency for the wireless OFDM signal on the wired and wireless signal performance in terms of EVM. All the performance was measured at the input optical power of 5 dbm and the MZM bias voltage of 5 V. It is distinguishable that the performance of both signals were severely deteriorated by the IF tone with the frequency lower than 2 GHz. With respect to this frequency threshold, the signal performance could be sharply enhanced, when the IF tone frequency was further away from the wired OFDM signal (in other words, baseband signal). This phenomenon was resulted from interference between the wired and wireless signals, which was the biggest factor to lead to signal-to-noise ratio (SNR) degradations. Accordingly, both signals could have better performance as increasing the IF tone frequency by help of broader guard band between the wired and wireless OFDM signals. The transmission performance for the wireless OFDM signal was also degraded, when the IF tone frequency was increased to 3.2 GHz because of our bandwidth-limited PD up to 3.5 GHz. BER performance of the proposed scheme, for the wired and wireless OFDM signals in case of optical back-to-back (BTB) 5. CONCLUSIONS We have proposed a new simple cost-effective OFDM/RoF scheme, which can transmit different OFDM signals for wired and wireless access networks simultaneously. The wireless and wired OFDM signals were generated in a single-arm MZM and a commercially available 1-GHz RSOA, respectively. Hermitian symmetry was used to create the wired and wireless OFDM signals in a single real-valued data channel, to halve the number of needed electronics, such as DACs and ADCs, and to simplify the RF front-end design in the proposed scheme. The influence of the MZM bias voltage and the IF tone frequency were investigated experimentally with BER and EVM performance Figure 5 BER performances of the wired signal (a) and the wireless signal (b). Insets: The constellations of the equalized OFDM symbols. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com] DOI /mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 8, August

5 evaluation. The experimental results verified that the proposed scheme could accomplish both the 5-Gbps 16-QAM-OFDM wired and the 1.17-Gbps QPSK-OFDM wireless signal transmission through a 23-km SSMF link, simultaneously. ACKNOWLEDGMENTS This work was partly supported by the IT R&D Programs of MKE/ KEIT (KI002037; KI , Wired and Wireless converged access network based on OFDMA-PON with 10 Gbit/s line rate), Korea and Yonsei University Institute of TMS Information Technology, a Brain Korea 21 Program, Korea. REFERENCES 1. T.T. Pham, H.-S. Kim, Y.-Y. Won, and S.-K. Han, Bidirectional 1.25-Gbps wired/wireless optical transmission based on single sideband carriers in Fabry Perot laser diode by multi-mode injection locking, J Lightwave Technol 27 (2009), M.-K. Hong, Y.-Y. Won, and S.-K. Han, Gigabit radio-over-fiber link for converged baseband and millimeter-wave band signal transmission using cascades injection-locked Fabry Perot laser diodes, Opt Express 17 (2009), H.-S. Kim, Y.-Y. Won, and S.-K. Han, Heterogeneous optical signal transmission using re-modulation in injection-locked Fabry Perot laser diode for wired and wireless access network, Opt Commun 283 (2010), B.J.C. Schmidt, A.J. Lowery, and J. Armstrong, Experimental demonstration of electronic dispersion compensation for long-haul transmission using direct-detection optical OFDM, J Lightwave Technol 26 (2008), C.W. Chow, C.H. Yeh, C.H. Wang, C.L. Wu, S. Chi, and C. Lin, Studies of OFDM signal for broadband optical access networks, IEEE J Sel Areas Commun 28 (2010), L. Chen, J.G. Yu, S. Wen, J. Lu, Z. Dong, M. Huang, and G.K. Chang, A novel scheme for seamless integration of ROF with centralized lightwave OFDM-WDM-PON system, J Lightwave Technol 27 (2009), B. Liu, X. Xin, L. Zhang, K. Zhao, and C. Yu, Broad convergence of 32QAM-OFDM ROF and WDM-OFDM-PON system using an integrated modulator for bidirectional access networks, In: Proc OFDM/NFOEC, 2010, JThA R.A. Shafik, M.S. Rahman, and A.R.Islam, On the extended relationships among EVM, BER and SNR as performance metrics, In: Proc ICECE, 2006, pp I.B. Djordjevic. B. Vasic, and M.A. Neifeld, LDPC coded OFDM over the atmospheric turbulence channel, Opt Express 15 (2007), VC 2012 Wiley Periodicals, Inc. COMPACT CONVENTIONAL PHONE ANTENNA INTEGRATED WITH WIDEBAND MULTIPLE-INPUT-MULTIPLE- OUTPUT ANTENNA Jian-Feng Li, Qing-Xin Chu, and Zhi-Hui Li School of Electronic and Information Engineering, South China University of Technology, Guangzhou, Guangdong, China; Corresponding author: qxchu@scut.edu.cn Received 6 November 2011 ABSTRACT: A compact conventional phone antenna integrated with wideband multiple-input-multiple-output (MIMO) antenna is presented. Within operation band of the MIMO antenna, the effect of mutual coupling between the conventional phone antenna and the MIMO antenna is reduced by etching three slits into the ground plane, and this slits also can relieve the impedance matching degradation caused by the mutual coupling between the conventional phone antenna and the MIMO antenna. A wideband T-shaped neutralization line without effect on the performance of conventional phone antenna is applied to enhance the isolation for the two MIMO antenna elements. Therefore, high isolation is achieved within the operation band of the MIMO antenna. The two operation bands of the convention phone antenna with VSWR 3 are GHz and GHz, respectively, and the operation band of the MIMO antenna with VSWR 1.7 and isolation 20 db is GHz. Moreover, the conventional phone antenna has good omnidirectional radiation patterns in H-plane, and the MIMO antenna has back-radiation patterns for diversity gain. VC 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54: , 2012; View this article online at wileyonlinelibrary.com. DOI /mop Key words: MIMO antenna; diversity antenna; phone antenna 1. INTRODUCTION The rapid increasing demand for high-quality and high-data-rate mobile communication induces the development of multipleinput-multiple-output (MIMO) phone antenna, which has potentiality of increasing capacity without sacrificing additional spectrum or transmitted power in rich multipath environments. However, MIMO phone antenna covering the conventional operation band of phone antenna is difficult to design, because the room for multiple antennas is extremely limited. The multiple antennas closely spaced causes unwanted mutual coupling, and the performance of the MIMO system will be deteriorated. Some various methods have been presented to enhance the isolation of MIMO antenna, such as slits etched into the ground plane [1, 2], an LC-based branch-line hybrid coupler [3], and neutralization line [4 8]. Unfortunately, all of the methods mentioned above were only able to work within narrow bandwidth and could not cover the conventional operation band of phone antenna. To cover the conventional operation band of phone antenna and take advantage of the MIMO technology, a compact conventional phone antenna integrated with a wideband MIMO antenna is presented in this article. Within the operation band of the MIMO antenna, the effect of mutual coupling between the conventional phone antenna and the MIMO antenna is reduced by etching three slits into the ground plane, and this slits can also relieve the impedance matching degradation caused by the mutual coupling between the conventional phone antenna and the MIMO antenna elements. A wideband T-shaped neutralization line, which consists of two meandered branches and a rectangular grounded branch, is applied to enhance the isolation of the MIMO antenna, and it has no effect on the performance of the conventional phone antenna. Therefore, high isolation within the operation band of the MIMO antenna is obtained. The two operation bands of the convention phone antenna with VSWR 3 are GHz covering GSM 900 and GHz covering DCS, PCS, and UMTS, and the operation band of the MIMO antenna with VSWR 1.7 and isolation 20 db is GHz covering WLAN 2.4, WiMAX 2.5, and WiMAX 3.5. The proposed antenna with compact size can be serving as a phone antenna. 2. ANTENNA DESIGN The geometry of the proposed antenna is shown in Figure 1. The antenna is positioned on a partially grounded FR4 substrate with relative permittivity 4.4 and loss tangent 0.02, and the size of the ground plane is mm 2. The antenna consists of a conventional phone antenna (Element #1) and a MIMO antenna with two symmetric antenna elements (Elements #2 and #3), 1958 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 8, August 2012 DOI /mop