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Realization of Dual-Dipole-Antenna System for Concurrent Dual-Radio Operation Using Polarization Diversity

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The study of the mutual coupling between the two simple strip dipole antennas is first carried out and investigated. The results show that the coupling or the antenna port isolation is almost …

The study of the mutual coupling between the two simple strip dipole antennas is first carried out and investigated. The results show that the coupling or the antenna port isolation is almost separation distance independent when the two dipole antennas are arranged to be of orthogonal polarization. Following this characteristic, a novel dual-dipole-antenna system aimed for concurrent 2.4 and 5 GHz band operation and at the same time, to achieve very compact integration of two individual antennas with separate feeds is proposed. The two dipole antennas are etched on a two-layered dielectric substrate with dimensions 30 mm × 30 mm. On the front layer is put the 2.4 GHz dipole, which is perpendicular to the 5 GHz dipole located on the bottom layer. Though the two dipoles are stacked up with a distance of 0.8 mm only, port isolation can still be below –15 dB. The proposed dual-dipole-antenna system is a promising candidate for the antenna solution that enables simultaneous dual-radio operation.


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  • 1. REFERENCES 1. INTRODUCTION 1. C.Q. Scrantom and J.C. Lawson, LTCC technology: Where we are and Multiantenna design that requires high decoupling between an- where we’re going-II, IEEE Int Microwave Symp Dig, Baltimore, MD tenna ports is one of the most important tasks for multiradio (1998), 193–200. antenna system development. Many wireless devices have speci- 2. L. Xia, R.M. Xu, and B. Yan, LTCC interconnect modeling by support fications of various communications standards to provide enriched vector regression, Prog Electromagn Res PIER 69 (2007), 67–75. wireless functionality for the end user. Accordingly, many anten- 3. A. Markov, K. Orlenko, D. Heide, and P. Ruppel, Miniature fully- nas are demanded and may be closely packed inside the devices integrated WLAN front-end-modules based on LTCC technology, Radio Wireless Conf IEEE 19 –22 (2004), 139 –142. due to limited space left for antennas. Several researches on 4. J. Heyen, T. von Kerssenbrock, A. Chernyakov, P. Heide, and A.F. improving antenna port isolation have been reported, including Jacob, Novel LTCC/BGA modules for highly integrated millimeter- incorporating slits into the ground plane [1–3] or arranging the wave transceivers, MTT-S 51 (2003), 2589 –2596. shorted portions of the antennas towards each other [4 – 6]. How- 5. L.K. Yeung and K.-L. Wu, A compact second-order LTCC bandpass- ever, these designs mainly focus on multiantennas sharing a com- filter with two finite transmission zeros, IEEE Trans Microwave The- mon ground plane, and thus the decoupling between antennas is ory Tech 51 (2003), 337–341. related to ground plane currents or surface waves. In this article, 6. J.-H. Lee, N. Kidera, G. DeJean, S. Pinel, J. Laskar, and M.M. we demonstrate that the two individual antenna systems, which Tentzeris, A V-band front-end with 3-D integrated cavity filters/ include separate radiating elements and ground planes, can be duplexers and antenna in LTCC technologies, IEEE Trans Microwave placed closely (stacked-up antennas with a distance of mere 0.8 Theory Tech 54 (2006), 2925–2937. 7. G.L. Matthaei, L. Young, and E.M.T. Jones, Microwave filters, im- mm) and are still well isolated. To realize the proposed design, two pedance-matching networiks and coupling structures, McGraw-Hill simple strip dipole antennas operating in the same frequency band Book Co., New York, 1964. (2.4 GHz band in this study) are analyzed first to find out an 8. G. Ch Michail and N.K. Uzunoglu, Accurate design of coaxial cavity optimal arrangement of the two dipoles. Following the obtained resonator filter, J Electromagn Waves Appl 18 (2004), 1119 –1131. results, a novel dual-dipole-system is proposed and aimed for 9. T. Shen and K.A. Zaki, Length reduction of evanescent-mode ridge concurrent 2.4 GHz (2400 –2484 MHz) and 5 GHz [5.2 GHz waveguide bandpass filters, Prog Electromagn Res PIER 40 (2003), 71–90. 10. J.S. Hong and M.J. Lancaster, Mircrostrip filters for rf/microwave applications, Wiley, New York, 2001. © 2009 Wiley Periodicals, Inc. REALIZATION OF DUAL-DIPOLE- ANTENNA SYSTEM FOR CONCURRENT DUAL-RADIO OPERATION USING POLARIZATION DIVERSITY Saou-Wen Su,1 Jui-Hung Chou,1 and Yung-Tao Liu2 1 Network Access Strategic Business Unit, Lite-On Technology Corporation, Taipei County 23585, Taiwan; Corresponding author: susw@ms96.url.com.tw 2 Department of Electrical Engineering, R.O.C. Military Academy, Fengshan 83059, Taiwan Received 17 October 2008 ABSTRACT: The study of the mutual coupling between the two simple strip dipole antennas is first carried out and investigated. The results show that the coupling or the antenna port isolation is almost separa- tion distance independent when the two dipole antennas are arranged to be of orthogonal polarization. Following this characteristic, a novel du- al-dipole-antenna system aimed for concurrent 2.4 and 5 GHz band op- eration and at the same time, to achieve very compact integration of two individual antennas with separate feeds is proposed. The two dipole antennas are etched on a two-layered dielectric substrate with dimen- sions 30 mm 30 mm. On the front layer is put the 2.4 GHz dipole, which is perpendicular to the 5 GHz dipole located on the bottom layer. Though the two dipoles are stacked up with a distance of 0.8 mm only, port isolation can still be below 15 dB. The proposed dual-dipole- antenna system is a promising candidate for the antenna solution that enables simultaneous dual-radio operation. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1725–1729, 2009; Published on- line in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ mop.24421 Figure 1 Two 2.4 Hz dipole antennas placed distance D mm apart: (a) two parallel dipole antennas; (b) one dipole antenna perpendicular to the Key words: antennas; dipole antennas; WLAN antennas; concurrent other. [Color figure can be viewed in the online issue, which is available at operation www.interscience.wiley.com] DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 7, July 2009 1725
  • 2. (a) (a) (b) (b) Figure 2 Simulated isolation against distance D between the two dipole antennas in Figure 1: (a) for the parallel dipole antennas; (b) for the perpendicular dipole antennas. [Color figure can be viewed in the online (c) issue, which is available at www.interscience.wiley.com] (5150 –5350)/5.8 GHz (5725–5825 MHz)] band operation [7]. The 2.4 and 5 GHz dipoles are etched on a square, two-layered dielec- tric substrate. The 2.4 GHz dipole is set to be perpendicular to the 5 GHz dipole. Both dipoles are fed by mini-coaxial cables, which provide the design much flexibility in the placement inside a WLAN device. Detailed description of the proposed dual-dipole- antenna system and design consideration thereof are given, and the simulation and experimental results of a realized prototype are presented and discussed. 2. MUTUAL COUPLING OF DIPOLE ANTENNAS Figure 1 shows two simple dipole antennas placed D mm apart and configured to be of two parallel dipoles in Figure 1(a) and one dipole antenna perpendicular to the other in Figure 1(b). The two dipoles are identical in dimensions and designed to operate in the (d) 2.4 GHz band. Each dipole consists of two radiating strips (26.5 mm in length and 1.5 mm in width), which is separated by a feed Figure 3 (a) Proposed dual-dipole-antenna system with a 2.4 GHz gap (2 mm in length). With near optimal antenna size selected, the dipole on the front layer and a 5 GHz dipole on the bottom layer. (b) 10-dB return-loss bandwidth of the antenna reaches about 250 Detailed dimensions of the 2.4 GHz dipole antenna. (c) Detailed dimen- MHz (2340 –2600 MHz). The design and optimization of the strip sions of the 5 GHz dipole antenna. (d) Photo of a design prototype of a dipole antennas are realized with the aid of Ansoft HFSS [8], dual-dipole-antenna system. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] which uses the finite element method, in this study. 1726 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 7, July 2009 DOI 10.1002/mop
  • 3. arrangement of the two dipoles in Figure 1(b) results in radiation or waves of orthogonal polarization, which do not interact a lot, and thus antennas transmitting orthogonal waves are well isolated despite the fact that antennas are set closely. Following this char- acteristic, we expect that good decoupling can still exist between two dipoles set in the shaped of a cross when the antennas are operating at different frequencies, which motivates us to study and propose a very compact dual-dipole antenna system in this article. 3. PROPOSED DUAL-DIPOLE-ANTENNA DESIGN Figure 3(a) shows the proposed dual-dipole-antenna system, which includes a 2.4 GHz dipole etched on the front layer and a 5 GHz dipole etched on the bottom layer of a 0.8-mm-thick FR4 substrate with dimensions 30 mm 30 mm. More details of the two dipoles are given in Figures 3(b) and 3(c). To achieve polarization diver- sity, the 2.4 GHz dipole is first arranged to be perpendicular to the Figure 4 Reflection coefficients (S11 for the 2.4 GHz dipole, S22 for the 5 GHz dipole, similar to the shape of a cross. This orthogonal 5 GHz dipole) and isolation (S21) between the two antennas. [Color figure configuration of two dipoles allows the two antenna ports to be can be viewed in the online issue, which is available at www. easily decoupled, as has been explored in the previous section. The interscience.wiley.com] dipole arms of the 2.4 GHz dipole are further bent to have a compact structure. Each dipole arm is also of a constant width and The mutual coupling or the port isolation between the two as general rule of thumb, the wider the width is chosen, the broader dipoles against the separation distance D is presented in Figure 2. the bandwidth becomes. That is the reason why the dipole-arm In the case of two parallel dipoles, port isolation 15 dB occurs width for the 5 GHz dipole is wider when compared with that for when the separation distance D is larger than 80 mm, as seen in the 2.4 GHz dipole. In addition to the width of the dipole arms, the Figure 2(b). This distance corresponds to about 0.65-wavelength feed gap of each dipole also plays an important part in determining ( c) at the center operating frequency, 2442 MHz in the 2.4 GHz input matching of the antenna. The near optimal value of the feed band, of the antenna. In another word, to obtain isolation well gap in between the dipole arms is found to be 2 mm for the 2.4 below 15 dB between the two parallel dipoles that have good GHz dipole and 1 mm for the 5 GHz dipole. Finally, to feed the input matching of 10 dB return loss, a minimal space of 0.65 c is design prototype [see Fig. 3(d)], two short 50- mini-coaxial required between the two dipole antennas. Notice that with reflec- cables with I-PEX connectors are used. The inner conductors of tion coefficients 10 dB and isolation 15 dB in this case, the coaxial cables are connected to the feed point A and C, and the the envelop correlation can be smaller than 0.1 [9]. As for the case outer braided shielding are connected to the ground point B and D. of one dipole perpendicular to the other, the results in Figure 2(b) shows that even the two dipoles are set at very close proximity, the 4. RESULTS AND DISCUSSION port isolation is still very small and almost separation distance Measurements of the reflection coefficients (S11 for the 2.4 GHz independent too. That is, the isolation remains below 60 dB as dipole, S22 for the 5 GHz dipole) and isolation (S21) of a con- separation distance D varies. This behavior is expected because the structed prototype were taken, and the results are given in Figure Figure 5 Radiation patterns at 2442 MHz for the 2.4 GHz dipole antenna studied in Figure 4. [Color figure can be 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. 7, July 2009 1727
  • 4. Figure 6 Radiation patterns at 5490 MHz for the 5 GHz dipole antenna studied in Figure 4. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] 4. It is first seen that both measured impedance bandwidth of the 5. CONCLUSION 2.4 and 5 GHz dipoles easily satisfy the required bandwidth The mutual coupling of the two simple strip dipole antennas has specification for 2.4 and 5 GHz WLAN operation with reflection been studied first; the results show that good decoupling is ob- coefficient well below 10 dB (even below 14 dB). The isola- tained when one of the two dipoles is put perpendicular to another, tion between the two dipoles is found to be below 20 dB over the and orthogonal polarization is realized accordingly. Using this 2.4 GHz band and below 15 dB over the 5 GHz band. Notice that concept, a novel dual-dipole-antenna system has been presented, the decoupling in the 2.4 GHz band is better than in the 5 GHz constructed, and tested. It has been demonstrated that the two band, as can be observed in the sloping-up curve of S21 from the individual 2.4 and 5 GHz dipole antennas can be integrated into a simulation results (not shown here for brevity). This is probably very compact structure such that the two antennas are stacked up because the upper resonant mode of the 2.4 GHz dipole causes with a distance of mere 0.8 mm. In addition, though the antennas somewhat overlapping radiation patterns of similar polarization to are set closely, low mutual coupling with port isolation of less than those of the 5 GHz dipole. 15 dB in the bands of interest can still be achieved. Further, Figures 5 and 6 plot the far-field, 2-D radiation patterns at 2442 omnidirectional and bi-directional radiation patterns in the hori- and 5490 MHz, the center operating frequencies of the 2.4 and 5 zontal plane have been observed for the 2.4 and 5 GHz dipoles, GHz bands. For the 2.4 GHz dipole, the antenna yields dipole-like respectively. The proposed design is well suited for concurrent 2.4 radiation with omnidirectional radiation patterns in the x-y plane and 5 GHz band operation and does not lose extra gain when and nulls around the z directions. Because the two dipole arms compared with a single-feed, dual-band, dual-antenna system us- are bent and extended toward the x directions, the radiation ing an external diplexer for concurrent operation. patterns are inclined at an angle of 20 degrees in the x-z plane. For the 5 GHz dipole, due to the effect of bent dipole arms of the 2.4 GHz dipole, the radiation energy in the z directions is much less than in the y directions. In this case, bi-directional radiation patterns are created with maximum radiation (peak antenna gain) in the y directions. Interestingly notice that along the y axes, the intersection of two H-planes of the 2.4 and 5 GHz dipoles, the maximum radiation in the E field of the 2.4 GHz dipole is at the right angle to the maximum radiation in the E field of the 5 GHz dipole. This shows that the two dipoles have orthogonal waves indeed. Figure 7 presents the peak antenna gain and radiation efficiency against frequency. The peak gain over the 2.4 GHz band is seen to be at a constant level of about 2 dBi, and the radiation efficiency exceeds about 90% ( 0.5 dB). As for the 5.2 GHz band, the peak gain varies from 3.0 to 2.1 dBi with radiation efficiency larger than 74% ( 1.3 dB). Though the radiation efficiency seems to be low (usually larger than 80% for WLAN metal-plate antennas of com- Figure 7 Peak antenna gain and radiation efficiency for the two dipole parable size [10 –12]), the antenna gain is still good enough due to antennas studied in Figure 4. [Color figure can be viewed in the online high directivity of the 5 GHz dipole. issue, which is available at www.interscience.wiley.com] 1728 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 7, July 2009 DOI 10.1002/mop
  • 5. REFERENCES © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1. T. Ohishi, N. Oodachi, S. Sekine, and H. Shoki, A method to improve 1729 –1732, 2009; Published online in Wiley InterScience (www. the correlation coefficient and the mutual coupling for diversity an- interscience.wiley.com). DOI 10.1002/mop.24420 tenna, IEEE Antennas Propagation Society International Symposium Digest, Washington, DC, USA, 2005, pp. 507–510. Key words: frequency doubler; Schmitt trigger; voltage controlled de- 2. G.A. Mavridis, J.N. Sahalos, and M.T. Chryssomallis, Spatial diversity lay line two-branch antenna for wireless devices, Electron Lett 42 (2006), 266 –268. 1. INTRODUCTION 3. C.Y. Chiu, C.H. Cheng, R.D. Murch, and C.R. Rowell, Reduction of Frequency multiplier is a good candidate for high frequency signal mutual coupling between closely-packed antenna elements, IEEE generation circuit due to the generic phase noise (PN) character- Trans Antennas Propag 55 (2007), 1732–1738. istic difference between frequency multiplier and generator. The 4. K.L. Wong and J.H. Chou, Integrated 2.4- and 5-GHz WLAN antennas stability of phase locked loop (PLL) with VCO is degraded as the with two isolated feeds for dual-module applications, Microwave Opt Technol Lett 47 (2005), 263–265. operating frequency increases. Alternatively, high frequency sig- 5. S.W. Su, J.H. Chou, and T.Y. Wu, Internal broadband diversity dipole nal can be obtained by multiplying the low frequency signal that antenna, Microwave Opt Technol Lett 49 (2007), 810 – 812. has relatively high stability and low PN. Therefore, several studies 6. J.H. Chou and S.W. Su, Internal wideband monopole antenna for have been done on the design of frequency multiplier circuit [1– 6]. MIMO access-point applications in the WLAN/WiMAX bands, Mi- For example, a design technique using the nth harmonic com- crowave Opt Technol Lett 50 (2008), 1146 –1148. ponent of a transistor is most widely used [2, 3]. Because of the 7. S.W. Su, J.H. Chou, and Y.-T. Liu, Printed coplanar two-antenna periodic harmonic response of a transistor, the desired frequency element for 2.4/5 GHz WLAN operation in a MIMO system, Micro- components at integer multiple frequencies of the input fundamen- wave Opt Technol Lett 50 (2008), 1635–1638. tal signal can be obtained. By proper biasing and input/output 8. HFSS, 3D full-wave electromagnetic field simulation, Ansoft Corpo- matching network, we can obtain the desired output component ration, available at http://www.ansoft.com/products/hf/hfss/ with maximum amplitude. However, additional harmonic termi- 9. S.W. Lee, A.E. Fathy, S.M. El-Ghazaly, and V. Nair, Evaluation of optimum position and orientation of laptop MIMO antennas using nation circuits or band pass filters are required since the amount of envelope correlation coefficients and mutual coupling parameters, in undesirable harmonics, including the fundamental, are consider- IEEE Antennas Propagation Society International Symposium Digest, able due to its low bias condition. Honolulu, HI, USA, 2007, pp. 2973–2976. Time-delay technique, as shown in Figure 1, is another way of 10. S.W. Su, J.H. Chou, and Y.T. Liu, A one-piece flat-plate dipole frequency multiplication and which is most likely used in the antenna for dual-band WLAN operation, Microwave Opt Technol Lett digital circuit design [4 – 6]. However, the operating frequency is 50 (2008), 678 – 680. fairly limited due to the uneven duty cycle and time-delay mis- 11. S.W. Su and J.H. Chou, Low-cost flat metal-plate dipole antenna for matching induced by the frequency limitation of the CMOS in- 2.4/5-GHz WLAN operation, Microwave Opt Technol Lett 50 (2008), verter. 1686 –1687. In this article, we propose a group delay matched CMOS 12. S.W. Su, J.H. Chou, and Y.T. Liu, Compact paper-clip-shaped wire frequency doubler for L-band application to overcome those prob- antenna for 2.4 and 5.2 GHz WLAN operation, Microwave Opt lems and increase the frequency of operation. Design theories and Technol Lett 50 (2008), 2572–2574. principles of operation of the proposed structure are presented with © 2009 Wiley Periodicals, Inc. some simulation and experimental analysis in the following sec- tions. 2. CIRCUIT DESIGN AND SIMULATION At first, as shown in Figures 1 and 2, input continuous wave (CW) PROPAGATION DELAY MATCHED signal is converted into square wave through CMOS inverter (Inv) CMOS 0.18 m FREQUENCY DOUBLER and Schmitt trigger (ST). An input square wave is delayed T/4 by FOR L-BAND APPLICATION the delay element, which consists of an integrator and comparator circuit, where T is the period of the input signal, and is fed into an Heungjae Choi,1 Kyungju Song,1 Yongchae Jeong,1 J. S. Kenney,2 and Chul Dong Kim3 XOR gate along with the intact input signal. Finally, we can obtain 1 Department of Electronics and Information Engineering, Chonbuk the output signal with half the input period T. National University, Jeonju, Republic of Korea; Corresponding author: Figure 1 shows a block diagram of the conventional time-delay streetpoet@chonbuk.ac.kr method frequency doubler. When we tried to increase the operat- 2 School of ECE, Georgia Institute of Technology, Atlanta, GA ing frequency of the conventional frequency doubler, we were 3 Sewon Teletech, Inc., Anyang, Kyunggi, Republic of Korea confronted with two troublesome problems. First, we cannot ob- tain the square wave with 50% duty cycle from CW using a simple Received 17 October 2008 CMOS inverter structure at higher frequency. Because the rising ABSTRACT: In this article, propagation delay matched CMOS fre- quency doubler for L-band application is proposed. Schmitt trigger and voltage controlled delay line compensates duty cycle error and propaga- tion delay mismatching that are induced as the frequency of operation is increased. As a consequence, unwanted harmonic components suppres- sion is greatly improved for higher frequency of operation. CMOS frequency doubler is designed at the input fundamental frequency (f0) of 1.15 GHz and fabricated with TSMC 0.18 m CMOS process. Measured output power at the doubled frequency (2f0) is 2.67 dBm for the input power of 0 dBm. The amount of harmonic suppression for f0, 3f0, and 4f0 are 43.65, 38.65, and 35.59 dB, respectively. Figure 1 Conventional time-delay method frequency doubler DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 7, July 2009 1729