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Multiband Handset Antenna Combining a PIFA, Slots, and Ground Plane Modes Arnau Cabedo, Jaume Anguera, Senior Member, IEEE, Cristina Picher, Miquel Ribó, Member, IEEE, and Carles Puente, Member, IEEE Abstract—A multiband handset antenna combining a PIFA and multiple slots on a ground plane is presented. It is shown by means of simulations that the slots on the ground plane have a double function: to tune the ground plane resonance at low frequencies 900 MHz) and to act as parasitic radiators at high frequen(f 1800 MHz). A prototype is designed and built featuring cies (f a behavior suitable for low frequencies (GSM850 and GSM900) and for high frequencies spanning from DCS1800 to Bluetooth, and including, for instance, PCS1900, UMTS2000, and other possible systems. Reflection coefficient, efficiency, and radiation patterns are measured and compared with a design without slots to prove the advantages of the slotted ground plane. The component effect is investigated to determine critical areas where the placement is not recommended. Besides, the effect of the slot of the ground plane on SAR is investigated, by discussing the effect of the ground plane and slot modes for two phone positions. The total antenna volume of the proposed design is 40 15 6 mm3 . Index Terms—Component interaction, multiband handset antennas, PCB resonance, PIFA, SAR.

I. INTRODUCTION HE future generations of mobile phones will need to operate over as much frequency bands as possible, such as GSM850, GSM900, DCS1800, PCS1900, UMTS, WIMAX and Bluetooth, among others. In general, the PIFA determine the number of frequencies bands, while, in the absence of slots, the ground plane (also referred as PCB: Printed Circuit Board) dimensions determine bandwidth, particularly at the lower frequencies [1], [2]. Most of the work has been done on antenna design [3], but the ground plane (both its dimensions and its modification [4]–[12]) offers another design variable. The antenna design is mainly determined by the PCB dimensions, which are fixed by the size of the handset or wireless device. An important limitation is the antenna height, which should be small for the new generation of ultra-slim phones that are now appearing into the market. Moreover, the new mobile phones incorporate all kinds of extra services, such as photo-video cameras, big displays to watch television and several speakers for high-fidelity audio which reduce the available

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Manuscript received November 30, 2007; revised November 11, 2008. First published July 07, 2009; current version published September 02, 2009. A. Cabedo and M. Ribó are with the Electronics and Telecommunications Department, Universitat Ramon Llull, Barcelona 8022, Spain (e-mail: [email protected]). J. Anguera is with the Electronics and Telecommunications Department, Universitat Ramon Llull, Barcelona 8022, Spain and also with the Technology and Intellectual Property Rights Department, Fractus, 08174 Barcelona, Spain (e-mail: [email protected]). C. Picher and C. Puente are with the Technology and Intellectual Property Rights Department, Fractus, 08174 Barcelona, Spain. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2009.2027039

space to fit the antenna. Therefore new techniques are needed in order to achieve a maximum bandwidth with an antenna that occupies the smallest space possible. To enhance the bandwidth of a handset antenna, [5] and [6] propose the insertion of a slot on the ground plane of a monoband PIFA. Such a slot tunes the PCB to resonate at a frequency similar to that of the PIFA, in order to finally obtain a broadband behavior, covering the GSM850–900 band. In addition, [5] proposes an electrical model that gives a very good physical insight into the behavior of this phenomenon. In [8], the same technique is used to design a modified ground plane to achieve a dual-band PIFA with a low profile. A possible drawback of the design is the fact that the PCB is full of slots, which may interfere with the placement of electronic components such as the battery, the display, RF chips, etc. Another example of an antenna design that uses a slotted ground plane is found in [10], where it is used to improve a conventional design for a dual-band operation antenna (GSM900-DCS1800) to a quad-band design (GSM850-GSM900-DCS1800-DCS1900). In this case, the slot on the ground plane has a double function. On one hand it tunes the PCB to resonate at low frequencies1 (around 900 MHz), improving the bandwidth; on the other hand, since the slot is comat high frequencies, with enough coupling to the parable to PIFA, the bandwidth at high frequencies is improved. The slot is placed underneath the PIFA to create enough coupling with it at high frequencies and to facilitate component integration [13]–[15]. Slots on the ground plane have been used as antennas with sufficient bandwidth to cover a specific frequency band [16]. Characteristic modes [21]–[23] have been used to gain understanding of how the ground plane can be used to enhance the behavior of a handset antenna. In [11], [24] they are used to analyze a handset antenna in order to finally tune a PCB at low frequencies (900 MHz) using a slot. In [9], a handset antenna with a ground plane is modified to incorporate a parasitic patch. This patch increases the bandwidth at high frequencies. The work presented in this paper continues the research done in [10] in the sense that a slotted PCB is used to accomplish two main functions: to modify the fundamental resonant mode in order to obtain a bandwidth enhancement at low frequencies (GSM850–900) and, at the same time, to act as a parasitic element of the antenna. Thus, a bandwidth enhancement is achieved at high frequencies (DCS1800–1900). In this paper, a new slot is added to the ground plane to enhance even more the 1Hereafter, “low frequencies” refer to GSM850 (824–890 MHz) and GSM900 (880–960 MHz) and “high frequencies” include DCS1800 (1710–1880 MHz), PCS (1850–1990 MHz), UMTS (1920–2170 MHz) up to Bluetooth (2.4–2.48 GHz)

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This slot is tuned at high frequencies in order to resonate around the UMTS frequencies. In order to make the design suitable for a real handset design, this second slot is situated under the PIFA, in an area away from that where the battery and other internal components of the handset are placed, i.e., displays, RF-modules, speakers, etc. Slot #3, placed between the feed and the short-circuit to the ground plane, is used for input impedance fine-tuning purposes. III. ELECTRICAL MODEL

Fig. 1. Antenna design: (a) Front PCB view, (b) front antenna view, and (c) 3D antenna view. PCB is 100 mm 40 mm. PIFA height is 6 mm. All dimensions are in mm.

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bandwidth at high frequencies, reaching the UMTS and Bluetooth bands. This paper is organized as follows: Section II shows the new antenna structure, and Section III presents an equivalent circuit model for its input impedance. Section IV exposes a detailed study of the physical behavior of the proposed antenna. Section V discusses the measured experimental results for its input impedance bandwidth, efficiency, and radiation patterns. Component interaction is analyzed in Section VI. Its influence on SAR is investigated in Section VII. Finally, the conclusions are detailed in Section VIII. II. ANTENNA STRUCTURE Beginning from a reference antenna design proposed in [10] operating at the GSM850, GSM900, DCS1800 and PCS1900 bands, a deeper study has been performed to achieve an antenna capable to operate at the UMTS and Bluetooth bands too. The geometry of the proposed PIFA with a slotted ground plane is shown in Fig. 1. The radiating element consists of two branches: the narrower and inner one, which is tuned to operate around 900 MHz, and the wider and outer one, which is tuned to operate at frequencies around 1900 MHz. The PCB layer has ), and its size is a FR-4 composite (fiberglass substrate, 100 mm 40 mm to emulate the PCB of a typical mobile phone. The antenna support is made of ABS (acrylonitrite butadrene ). styrene, The PCB is tuned utilizing slots [10], [12], [25]. In comparison with the reference antenna design of [10], the antenna presented here has two new slots in its PCB, namely slots #2 and #3. The original slot (slot #1) has two main objectives: to tune the PCB in order to force it to resonate at GSM850–900 frequencies, improving the bandwidth of the whole structure at resonator those frequencies, and to provide an additional at the DCS1800-1900 band, enhancing the antenna bandwidth at high frequencies. The main improvement of the proposed design over the design presented in [10] is the addition of slot #2.

An electrical model, based on resonant RLC circuits is proposed to give a physical insight into the behavior of the antenna presented in this paper. The proposed electrical model is useful to perform a parametric analysis. For example, using the model it is possible to see what influence the PCB has into the bandwidth of the antenna at low frequencies or, how it affects the bandwidth at high frequencies if the coupling between the PIFA and the slot is increased (or decreased). The electrical model helps to explain how the proposed antenna structure works. It takes into account the fact that: 1) Due to its dimensions and modifications, the PCB resonates at a frequency which is very close to the lower resonant frequency of the PIFA, enhancing the bandwidth at the lower band. 2) Additional slots can contribute with their resonance to enhance the bandwidth of the structure at the higher band. The proposed electrical model is depicted in Fig. 2. It is based on the circuit model for patch antennas presented in [26], which was extended for a dual-band microstrip antenna in [27] (electrical circuit labeled as “Multiband” in Fig. 2). In [5], a similar model for single-band operation is presented. The use of an electrical model is useful to understand the behavior of this kind of antennas based on parasitic elements [26]–[30]. In the proposed model, the dual series-parallel RLC circuits take into account the single PIFA without the slots on the ground plane. To model the tuned PCB a new resonator has to be added to the first RLC circuit using a capacitive coupling. Similarly, a new resonator modeling the slot (the parallel resonator , , ) is coupled to the second resonance of the PIFA, modeled by , , . The PIFA without considering the PCB effect, that is, a PIFA on an infinite ground plane (labeled as “Reference” in Fig. 2) , , ) is modeled as follows: RLC values of the first ( and second ( , , ) resonator are calculated to match the resonant frequency as well as the antenna quality factor ( ). For the model taking into account the PCB (the “Multiband” , , model in Fig. 2), the PIFA RLC values of the first ( ) and the second ( , , ) resonator maintain the and same resonant frequency and but in this case are larger than and since the parasitic resonators force the input impedance to decrease [26]. At low frequencies the effect of the PCB is taken into account using a resonator with a lower than the one of the PIFA but having the same resonant frequency. At high frequencies the effect of the slot is taken into account: this new resonator has almost the same resonant , , ) and the same frequency as that of the PIFA ( since both antennas are practically linear resonators, and

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Fig. 3. (a) Computed current distribution on the PCB at 925 MHz and normalized E field distribution on the top of the PCB at (b) 925 MHz, (c) 1825 MHz, (d) 1990 MHz, and (e) 2170 MHz.

Fig. 2. Circuit models, and associated reflection coefficient, for the handset antenna proposed in this paper (solid line, “Multiband”) and for the PIFA without considering the effect of the PCB and slots (dashed line, “Reference”). For the Smith chart data: the PIFA without taking into account the PCB and slot, has a parallel RLC response. When the PCB and the slot are taken into account, two impedance loops appears increasing the bandwidth (the loop at 900 MHz and 1900 MHz approximately are due to the PCB and slot resonators, respectively.

therefore they may be approximated as behaving similarly in terms of . The proposed values for the resonator components are: , , ( ; ), , , ( ; ) for the PIFA when no coupling to the PCB and the slot is considered. Taking into account the PCB and , , the coupling slot, the values are: ( ; ), , , , ( ; ), , , ( ; ), , , , ( ; ). These values are illustrative since the objective of the electrical model is to analyze the trends when a PCB and the slots have similar frequencies than the PIFA antenna. From the proposed electrical model several conclusions can be obtained. • If the resonant frequency of the resonant circuit which models the PIFA and that of the coupled resonator which models the PCB are the same, an input impedance loop appears in the Smith chart (Fig. 2). The same effect is observed for the slot resonator. If the resonant frequencies are ) different, the loop moves to the inductive ( ) of the Smith chart [26]. or capacitive zone (

Similar conclusions can be obtained with the model proposed in [5]. • The size of the loop in the Smith Chart depends on the value and ). These values of the coupling capacitors ( model the coupling between the PIFA and the ground plane and slot, which can be controlled by the distance between the PIFA and the ground plane edge, and by the distance between the PIFA and the slot. If the coupling increases, the input impedance loop increases and vice versa. Depending on the SWR specification, the loop size can be adjusted by adjusting the coupling. IV. SIMULATION RESULTS Based on the conclusions extracted from the electrical model, a PIFA handset antenna on a slotted ground plane has been designed. The introduction of a slot on the PCB structure causes an alteration of the surface current distribution. Slot #1 is designed and placed to force a longer electrical path at low frequencies; thus, the resonant frequency of the fundamental mode of the PCB can be decreased. This positively affects the final frequency behavior because it results in a bandwidth enhancement [12]–[15] due to the resonance of the PCB itself at the GSM900 band. The slot length is tuned to make the PCB resonate at a frequency similar to that of the PIFA. This fact can be observed in the input impedance behavior on the Smith chart: a loop appears which improves the bandwidth in comparison with the original PIFA without slot #1. The coupling loops are similar to those obtained in [26]–[30]. Besides, the geometries of slot #1 and #2 are designed to be resonators at high frequencies, coupling their radiation to the PIFA: one slot radiates around 1.9 GHz and the other around 2.3 GHz. Thus, the antenna takes advantage of the slots as radiators that couple with the PIFA in order to enhance the bandwidth. IE3D software, based on the Method of Moments (MoM), has been used to simulate those physical behaviors difficult to observe in practice, for instance, the current distribution, which

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Fig. 4. Simulated reflection coefficient of the proposed multiband antenna in comparison with those presented in [10] (Quad-band and Dual-band PIFA).

gives a physical insight into the radiation process. To emulate a real environment, the PCB is simulated over a thin layer of FR-4 which is the substrate commonly used in most of the commercial mobile phones. Two plastic layers are also considered to simulate the antenna carrier and the back cover of the handset. The current distribution on the slotted PCB, computed at 925 MHz, is shown in Fig. 3(a). For the low frequencies it can be seen that slot #1 forces the current to bend emulating a larger electrical path. However, a different behavior can be observed at high frequencies: the slot continues to force a longer path, but its main effect is as a radiator, as shown in Fig. 3(b)-(e), where the E-field on the slot aperture is depicted. It can be seen how at high frequencies (DCS1800 to UMTS bands) the main slot #1 radiates much more efficiently than at low frequencies (GSM850-900 bands), at which it is in cut off. Fig. 4 shows the simulated reflection coefficient of the designed antenna after performing a tuning optimization, in comparison with the response of the antennas studied in [10], that is, the PIFA without slots and a PIFA having only one slot (slot #1). As can be seen, the proposed antenna is theoretically capable to operate at least at the GSM850, GSM900, DCS1800, PCS1900, UMTS2000, and Bluetooth bands. Section V shows the measured results for the proposed design.

Fig. 5. Manufactured antenna prototypes: (a) Dual-band PIFA and rear view of the (b) Quad-band PIFA and (c) the Multiband PIFA. In a) the carrier to attach the metal and the plastic cover are also shown.

V. EXPERIMENTAL RESULTS

Fig. 6. Measured reflection coefficient for the three studied prototypes. It can be seen how the proposed multiband design can operate at least over the GSM850, GSM900, DCS, PCS, UMTS and Bluetooth bands.

Prototypes of three PIFA antennas, namely, a dual-band PIFA without slots, a quad-band PIFA with one slot, and the proposed PIFA with multiple slots on the ground plane have been constructed and studied (Fig. 5). The simulation software IE3D was used for optimizing the design parameters. In the following results, the antenna geometry described in Section II is used. Minor changes have been made for fine tuning purposes. Fig. 6 shows the measured reflection coefficient for the three built prototypes shown in Fig. 5. It can be clearly seen that the multiband design achieves enough bandwidth over different bands thanks to the resonance of slot #2 at the frequency range 2.1–2.5 GHz. That is, the original PIFA without slots is matched at the GSM900 and PCS1900 bands, the second design using one slot (slot #1) improves the matching to the GSM850–900, DCS1800 and PCS1900 bands [12], and the final design proposed here enhances the former quad-band behavior including the bands from UMTS to Bluetooth, approximately.

Table I summarizes the measured total efficiency ( ) in comparison with the simulated one. Total efficiency has been measured using pattern integration employing the Satimo-Stargate 32 anechoic chamber at Fractus-Lab. The frequencies are representative of the bands covered by the multiband PIFA. The measured total efficiency takes into account the reflection losses, that , where is the radiation effiis to say, ciency. As can be seen, the results are good enough to make the antenna interesting for the upcoming generation of multiband mobile phones. of the proposed design with that of Table II compares the design without slots, that is, for an antenna that operates at 890–960 MHz and 1840–1970 MHz (its reflection coefficient is shown in Fig. 6). It is clearly observed that the new design can expand the number of bands while preserving the same antenna volume.

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TABLE I SIMULATED-MEASURED TOTAL EFFICIENCY RESULTS

TABLE II DUAL-BAND (NO-SLOTS) AND MULTI-BAND MEASURED TOTAL EFFICIENCY RESULTS

In Fig. 7, it can be seen how, at 920 MHz, the antenna presents an omni-directional radiation pattern and a gain of 0 dBi at the plane. A null at the vertical axis appears at the plane which can be explained by the fact that the behavior of dipole. In other words, at the antenna is similar to that of a this frequency, the radiation comes from the PCB rather than the PIFA-slot radiators [5]. At high frequencies the radiation pattern presents more differences between maxima and minima. VI. COMPONENT INTERACTION A handset antenna shares space with other components such as speakers, displays, battery, vibrator, camera, etc. Therefore, component interaction is an issue to take into account [31]–[33]. This section deals with the effect of a critical component, the speaker. This element is sometimes placed on the same side of the PCB where the antenna is located; in other situations, it is placed on the other side. For PIFA designs, the first case is critical if the speaker is close to the antenna as it may cause poor bandwidth and low radiation efficiency. When it is placed on the other side, the ground plane acts as a shielding, reducing the interaction between the speaker and the PIFA. For the present study, 3 cases have been considered, as shown in Fig. 8. For each case, the total efficiency has been measured, and the results have been compared with the no-component case. The speaker has a metallic part that faces the PCB. However, for the present experiment there has been no connection between the speaker and the PCB; what matters is the presence of the speaker over slot #1. Tables III and IV summarize the data obtained at selected frequencies ( is the difference between efficiencies for the no-speaker and speaker cases), revealing interesting results.

Fig. 7. Measured radiation patterns of the proposed antenna design.

Fig. 8. Speaker placed at the other side of the PIFA volume.

a) At low frequencies ( ), there is almost no change. This confirms the previous analysis: slot #1 is weakly excited at the GSM band; the slot is only forcing the current to flow along a longer path. ) the speaker can deb) At high frequencies ( grade the total efficiency as well as radiation efficiency. Since slot #1 works as an antenna at these frequencies, significant changes (about 3 dB for the total efficiency) are observed when the conductor of the speaker is over

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TABLE III MEASURED TOTAL EFFICIENCY FOR NO-SPEAKER, AND SPEAKER AT LEFT, CENTER, AND RIGHT POSITIONS

TABLE IV MEASURED RADIATION EFFICIENCY FOR NO-SPEAKER, AND SPEAKER AT LEFT, CENTER, AND RIGHT POSITIONS

the open edge of the slot, where the electric field is maximal. Half of the losses come from detuning and the other half from reduction of the radiation efficiency, approximately. c) At high frequencies, when the speaker is on the right, there are no changes, as expected. Therefore, it can share the antenna area when placed in this position. As seen, to cover the slot area is critical. The advantage of the present solution compared with other ones that use wide slots as antennas [19] is that it facilitates component integration without degradation of the antenna behavior. Obviously, there is a tradeoff between antenna volume and component integration capabilities. VII. SAR MEASUREMENTS The specific absorption rate (SAR) in passive mode has been tested using Dasy-4 at Fractus-Lab. At the GSM850-900 band the maximum transmitted power is 33 dBm; however, a user channel uses only 1/8 of a time slot. This results in a power of 24 dBm, which is the power of the continuous wave used to test SAR. A similar computation is performed at high frequencies; in this case, the maximum transmitted power is 30 dBm. Thus, SAR is tested using 21 dBm. The SAR passive test is only a preliminary measurement since SAR is finally tested with an active device which may result in a different SAR value due to extra device elements and/or other issues. However, it is interesting to test SAR in a passive way to analyze if the antenna may pose a SAR problem. The ground plane has a foam spacer of 3 mm thickness whose surface is attached to the right phantom cheek; this represents the typical separation between the PCB and the cheek. SAR is tested using two orientations: the first one, in which the antenna

Fig. 9. Measured SAR with Dasy-4 when the handset antenna is attached above the phantom ear (left column) and for a 180 rotation (right column). The inner rectangular box is the PCB footprint. The external rectangle is the tested SAR area. The bottom right part does not appear since it can not be measured because the angle of inclination for the SAR probe is out of the limits.

area is attached to the phantom ear (top position), and the other one, in which the handset is rotated 180 (bottom position, see Fig. 9). SAR distribution as well as maximum SAR values both for 1 g. and 10 g. tissue volumes are shown in Fig. 9. It is interesting to remark that at low frequencies (830–900 MHz) and for the top case, two hot-spots are observed: one is due to the slot and the other to the ground plane mode. For the bottom case the hot-spot due to the slot disappears since, for this situation, it is away from the check surface. Although for the top case the slot creates a hot-spot, the hot-spot of the ground plane

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has a larger intensity. We can also observe that the difference between SAR for the top and bottom positions is of only 0.5 dB approximately, confirming the fact that the ground plane mode is the responsible for SAR. At high frequencies, the slots create the hot-spots. Therefore, a larger difference in SAR is observed for top and bottom position (about 3 dB). Based on this passive data, SAR is a critical parameter to take into account (the most at 1 g) at stringent standard recommends high frequencies if the slots are at the top position but it can be dramatically reduced if the antenna is placed at the bottom part. Anyway, active SAR is usually lower since it takes into account all the components of a handset, which partially absorb some of the radiated power. As a conclusion, at low frequencies, where the ground plane mode dominates, SAR is mainly due to it rather than to the antenna topology [5]. On the contrary, at high frequencies the slots determine the hot-spot. An effective way of reducing SAR at high frequencies is to place the antenna at the bottom part, a technique used in some mobile phones. VIII. CONCLUSION In this paper, a built-in multiband handset antenna covering the GSM850 and GSM900 bands, and the continuous bandwidth spanning from the DCS1800 to the Bluetooth bands, has been presented. In this new antenna, a slotted ground plane is used to improve the bandwidth at both low and high frequencies without increasing the volume of the antenna. At low frequencies, the slot is below resonance, but forces the ground plane mode to be excited so as to increase the bandwidth at low frequencies; on at high frequenthe other hand, the slots are comparable to cies, and therefore they enhance the bandwidth. This new design has been compared with the same design without the slots. Results show that the bandwidth and, as a consequence, the total efficiency is improved, obtaining a radiator useful for multiband handset applications. The placement of a component (speaker) over the slot (without any metallic contact between the speaker and the ground plane) does not affect the antenna performance at low frequencies. However, it is very critical at high frequencies when the component is close to the open edge of the slot. SAR at low frequencies is dominated by the ground plane mode: the slot is mainly acting as a current path enlarger to excite the ground plane mode in an effective way as the electrical length is larger than without slots. At high frequencies, however, the slots have a big influence on the hot-spot location. An effective way of reducing SAR is to locate the antenna at the bottom edge of the PCB. REFERENCES [1] T. Y. Wu and K. L. Wong, “On the impedance bandwidth of a planar inverted-F antenna for mobile handsets,” Microw. Opt. Tech. Lett., vol. 32, pp. 249–251, Feb. 2002. [2] M. C. Huynh and W. Stutzman, “Ground plane effects on planar inverted-F antenna (PIFA) performance,” Proc. Inst. Elect. Eng. Microw. Antennas Propag., vol. 150, no. 4, Aug. 2003. [3] K. L. Wong, Planar Antennas for Wireless Communications. New York: Wiley Inter-Science, 2003. [4] K. L. Wong, J. S. Kuo, and T. W. Chiou, “Compact microstrip antennas with slots loaded in the ground plane,” presented at the 11th Int. Conf. on Antennas Propag., Apr. 2001, No. 480.

[5] P. Vainikainen, J. Ollikainen, O. Kivekäs, and I. Kelander, “Resonator-based analysis of the combination of mobile handset antenna and chassis,” IEEE Trans. Antennas Propag., vol. 50, pp. 1433–1444, Oct. 2002. [6] R. Hossa, A. Byndas, and M. E. Bialkowski, “Improvement of compact terminal antenna performance by incorporating open-end slots in ground plane,” IEEE Microw. Wireless Compon. Lett., vol. 14, pp. 283–285, Jun. 2004. [7] A. Byndas, R. Hossa, M. E. Bialkowski, and P. Kabacik, “Investigations into operation of single multi-layer configuration of planar inverted-F antenna,” IEEE Antennas Propag. Mag., vol. 49, no. 4, pp. 22–33, Aug. 2007. [8] M. F. Abedin and M. Ali, “Modifying the ground plane and its effect on planar inverted-F antennas (PIFAs) for mobile phone handsets,” IEEE Antennas Wireless Propag. Lett., vol. 2, pp. 226–229, 2003. [9] B. Sanz-Izquierdo, J. Batchelor, and R. Langley, “Multiband printed PIFA antenna with ground plane capacitive resonator,” Electron. Lett., vol. 40, no. 22, Oct. 2004. [10] J. Anguera, I. Sanz, A. Sanz, T. Condes, D. Gala, C. Puente, and J. Soler, “Enhancing the performance of handset antennas by means of groundplane design,” presented at the IEEE Int. Workshop on Antenna Technol.: Small Antennas and Novel Metamater. (iWAT 2006), New York, Mar. 2006. [11] M. Cabedo, E. Antonino, V. Rodrigo, and C. Suárez, “Análisis modal de un plano de masa radiante doblado y con una ranura para terminales Móviles,” presented at the XXI Nat. Symp. URSI’06, Oviedo, Spain, 2006. [12] J. Anguera, I. Sanz, A. Sanz, T. Condes, C. Puente, and J. Soler, “Multiband PIFA handset antenna by means of groundplane design,” presented at the IEEE Antennas Propag. Society Int. Symp., Albuquerque, NM, Jul. 2006. [13] R. Quiutero and C. Puente, “Multilevel and space-filling ground planes for miniature and multiband antennas,” Pat. App. WO 03023900. [14] C. Puente, J. Roneu, C. Borga, J. Anguera, and J. Soler, “Multilevel antennas,” Pat. App. WO 0122528. [15] C. Puente, C. Borga, and E. Rogan, “Space filling miniature antennas,” Pat. App. WO 0154225. [16] A. Ping and J. Rahola, “Quarter-wavelength wideband slot antenna for 3–5 GHz mobile applications,” IEEE Antennas Wireless Propag. Lett., vol. 4, pp. 421–424, 2005. [17] S. Kumar, L. Shafai, and N. Jacob, “Investigation of wide-band microstrip slot antenna,” IEEE Trans. Antennas Propag., vol. 52, pp. 865–872, Mar. 2004. [18] S. Latif, L. Shafai, and S. Kumar, “Bandwidth enhancement and size reduction of microstrip slot antennas,” IEEE Trans. Antennas Propag., vol. 53, pp. 994–1003, Mar. 2005. [19] C. Lin and K. L. Wong, “Printed monopole slot antenna for internal multiband mobile phone antenna,” IEEE Trans. Antennas Propag., vol. 55, no. 2, pp. 3690–3697, Dec. 2007. [20] C. H. Wu and K. L. Wong, “Hexa-band internal printed slot antenna for mobile phone application,” Microw. Opt. Technol. Lett., vol. 50, pp. 35–38, Jan. 2008. [21] R. F. Harrington and J. R. Mautz, “Theory of characteristic modes for conducting bodies,” IEEE Trans. Antennas Propag., vol. 19, pp. 622–628, Sep. 1971. [22] E. Antonino, M. Cabedo, M. Ferrando, and J. I. Herranz, “Analysis of the coupled chassis-antenna modes in mobile handsets,” presented at the IEEE Antennas Propag. Society Int. Symp., Monterey, Jun. 2004. [23] M. Cabedo, E. Antonino, A. Valero, and M. Ferrando, “The theory of characteristic modes revisited: A contribution to the design of antennas for modern applications,” IEEE Antennas Propag. Mag., vol. 49, no. 5, pp. 52–68, Oct. 2007. [24] E. Antonino, C. A. Suárez, M. Cabedo, and M. Ferrando, “Wideband antenna for mobile terminals based on the handset PCB Resonance,” Microw. Opt. Technol. Lett., vol. 48, no. 7, Jul. 2006. [25] J. Anguera, A. Cabedo, C. Picher, I. Sanz, M. Ribó, and C. Puente, “Multiband handset antennas by means of groundplane modification,” presented at the IEEE Antennas Propag. Society Int. Symp., Honolulu, HI, Jun. 2007. [26] J. Anguera, C. Puente, and C. Borja, “A procedure to design stacked microstrip patch antenna based on a simple network model,” Microw. Opt. Technol. Lett., vol. 30, no. 3, pp. 149–151, Aug. 2001. [27] J. Anguera, E. Martínez, C. Puente, C. Borja, and J. Soler, “Broadband dual-frequency microstrip patch antenna with modified Sierpinski fractal geometry,” IEEE Trans. Antennas Propag., vol. 52, pp. 66–73, Jan. 2004. [28] J. Anguera, L. Boada, C. Puente, C. Borja, and J. Soler, “Stacked H-shaped microstrip patch antenna,” IEEE Trans. Antennas Propag., vol. 52, no. 4, pp. 983–993, Apr. 2004.

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CABEDO et al.: MULTIBAND HANDSET ANTENNA COMBINING A PIFA, SLOTS, AND GROUND PLANE MODES

[29] J. Anguera, E. Martínez, C. Puente, C. Borja, and J. Soler, “Broad-band triple-frequency microstrip patch radiator combining a dual-band modified Sierpinski fractal and a monoband antenna,” IEEE Trans. Antennas Propag., vol. 54, pp. 3367–3373, Nov. 2006. [30] J. Anguera, C. Puente, C. Borja, and J. Soler, “Dual frequency broadband stacked microstrip antenna using a reactive loading and a fractalshaped radiating edge,” IEEE Antennas Wireless Propag. Lett., vol. 6, pp. 309–312, 2007. [31] C. M. Su, K. L. Wong, C. L. Tang, and S. H. Yeh, “EMC internal patch antenna for UMTS operation in a mobile device,” IEEE Trans. Antennas Propag., vol. 53, pp. 3836–3839, Nov. 2005. [32] K. L. Wong and C. H. Chang, “Surface-mountable EMC monopole chip antenna for WLAN operation,” IEEE Trans. Antennas Propag., vol. 54, pp. 1100–1104, Apr. 2006. [33] J. Anguera, I. Sanz, J. Mumbrú, and C. Puente, “Multiband handset antenna behaviour by combining PIFA and a slot radiators,” presented at the IEEE Antennas Propag. Society Int. Symp., Honolulu, HI, Jun. 2007. Arnau Cabedo was born in Barcelona, Spain. He received the B.S. (Hons) and the M.S. (Hons) degrees in telecommunication engineering from the Ramon Llull University (La Salle Universtity), Barcelona, Spain, in 2004 and 2006, respectively. From 2003 to 2006, he was with the Communications and Signal Theory Department, Ramon Llull University (La Salle Universtity). His research interests there were miniature, wideband and multiband printed antennas. He also collaborated with the R&D Department, Fractus, Barcelona, Spain, studying new techniques to miniaturize and enhance the bandwidth of PIFA antennas. Mr. Cabedo received the 2008 Best Degree Project award given by the Colegio Oficial de Ingenieros de Telecomunicación (COIT) for his degree project “Multiband Antennas for 2G, 3G, WiFi, WLAN and Bluetooth Applications on New Generation Handsets.”

Jaume Anguera (S’99–M’03–SM’09) was born in Vinaròs, Spain, in 1972. He received the Technical Ingeniero degree in electronic systems and the Ingeniero degree in electronic engineering, both from the Ramon Llull University (URL), Barcelona, Spain, in 1994 and 1997, respectively, and the Ingeniero and Ph.D. degrees in telecommunication engineering, both from the Polytechnic University of Catalonia (UPC), Barcelona, Spain, in 1998 and 2003, respectively. From 1998 to 2000, he was with the Electromagnetic and Photonic Engineering Group (EEF), Signal Theory and Communications Department, UPC, as a Researcher in microstrip fractal-shaped antennas. In 1999, he was a Senior Researcher at Sistemas Radiantes, Madrid, Spain, where he was involved in the design of a dual-frequency dual-polarized fractalshaped microstrip patch array for mobile communications. In the same year, he became an Assistant Professor at the Department of Signal Theory and Communications, Universitat Ramon Llull-Barcelona, where he is currently teaching antenna theory. Since 2000, he has been with Fractus, Barcelona, Spain, where he holds the position of R&D Manager. At Fractus he leads projects on antennas for base station systems, antennas for automotion, handset and wireless antennas. His research interest are multiband and small antennas, microstrip patch arrays, feeding network architectures, broadband matching networks, array pattern synthesis with genetic algorithms, diversity antenna systems, electromagnetic dosimetry, and handset antennas. He is Leading Engineer for the Innovation Antenna Group. From September 2003 to May 2004, he was with FractusKorea (Republic South of Korea) where he was managing projects for miniature and multiband antennas for handset and wireless applications. Since 2005, he has been leading research projects in the antenna field for handset and wireless applications in a frame of industry-university collaboration: Fractus company and the Department of Communications and Signal Theory of Universitat Ramon Llull-Barcelona, Spain. He holds more than 26 patents on fractal an other related antennas. He is author/coauthor of more than 110 journal, international, and national conference papers and he has directed more than 50 bachelor and master theses. Dr. Anguera was a member of the Fractal team that in received the 1998 European Information Technology Grand Prize from the European Council for the Applied Science an Engineering and the European Commission for the fractal-shaped antenna application to cellular telephony. He was the 2003

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Finalist of the Best Doctoral Thesis (Fractal and Broadband Techniques on Miniature, Multifrequency, and High-Directivity Microstrip Patch Antennas) on UMTS. (The prize has been promoted by “Technology plan of UMTS promotion” given by Telefónica Móviles España). He received the New faces of Engineering 2004 (promoted by the IEEE and IEEE Foundation). In the same year, he received the Best Doctoral Thesis in “Network and Broadband Services” (XXIV Prize Edition “Ingenieros de Telecomunicación”) organized by Colegio Oficial de Ingenieros de Telecomunicación (COIT) and the Company ONO. He is a reviewer for the IEEE TRANSACTIONS AND ANTENNAS AND PROPAGATION, IET Electronics Letters, and ETRI Journal (Electronics and Telecommunications Research Institute, South Korea). His biography is listed in Who’s Who in the World, Who’s Who in Science and Engineering, Who’s Who in Emerging Leaders and in the International Biographical Center, Cambridge-England (IBC).

Cristina Picher was born in Sabadell, Barcelona, Spain. She received the Technical Engineer Degree in telecommunication systems from Ramon Llull University (URL), Barcelona, where she is currently working toward the M.Eng. degree. In 2005, she began her investigation in miniature and multiband antennas when she started her final degree project in the Electronic and Telecommunication Department, URL, in collaboration with the Department of Technology and IPR in Fractus, Barcelona. She is the author/coauthor of four papers in scientific journals, international, and national conferences. Ms. Picher was awarded 3rd Place in 2008 by the Ministry of Science and Innovation Spain: VII Edition “Arquímedes” Introduction to Scientific Research program for her research in “miniature and multiband techniques combining handset antenna and groundplane design.”

Miquel Ribó (S’95–M’00) was born in La Seu d’Urgell, Catalonia, Spain, in 1970. He received the Telecommunication Engineering degree from the Polytechnic University of Catalonia (UPC), Barcelona, Catalonia, Spain, in 1994 and the Ph.D. degree in electronic engineering from Enginyeria i Arquitectura La Salle, Ramon Llull University (URL), Barcelona, in 2001. In 1997, he joined the Communications and Electromagnetics Research Group (GRECO), Enginyeria i Arquitectura La Salle (URL), where he currently teaches microwaves and electromagnetic theory, and works as a Project Manager. His research interests include the multimodal analysis of coplanar and microstrip transitions, and of EMC problems such as interference generation, propagation and mitigation. Dr. Ribó is currently Vice Chairman of the Spanish EMC IEEE Society Chapter, and was Vice Chairman of the EMC Europe 2006 International Symposium on Electromagnetic Compatibility, Barcelona.

Carles Puente (S’91–M’93) received the M.Sc. degree from the University of Illinois at Urbana–Champaign, in 1994 and the Ph.D. degree from the Polytechnic University of Catalonia (UPC), Barcelona, Catalonia, Spain, in 1997. He started researching fractal-shaped antennas while a student at the Universidad Politécnica de Catalunya (UPC) in the late 1980s. From 1994 to 1999, he worked with the faculty of Electromagnetic and Photonic Engineering at UPC on pioneering developments of fractal technology applied to antennas and microwave devices. He is a co–founder of Fractus, Barcelona, Spain, where he leads the Technology Development Team, with responsibility for IP portfolio development and antenna development. He has authored more than 30 invention patents and 50 scientific publications related to fractal antenna technology. Dr. Puente was awarded with the Best Doctoral Thesis in Mobile Communications 1997, and in 1998 he and his team received the European Information Society Technology Grand Prize from the European Commission for their work.

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