Co2Z hexaferrite T-DMB antenna for mobile phone applications. Journal: Transactions on Magnetics - Conferences

Transcription

1 CoZ hexaferrite T-DMB antenna for mobile phone applications Journal: Transactions on Magnetics - Conferences Manuscript ID: MAGCON--- Manuscript Type: Intermag Conference Date Submitted by the Author: -Mar- Complete List of Authors: Bae, Seok; University of Alabama, MINT and Electrical and Hong, Yang-Ki; The University of Alabama, MINT and Electrical and Lee, Jae-Jin; University of Alabama, MINT and Electrical and Jalli, Jeevan; University of Alabama, MINT and Electrical and Abo, Gavin; University of Alabama, Electrical and Computer Engineering; University of Alabama, MINT and Electrical and Sung, Won-mo; E.M.W. Antenna, R & D Center Kim, Gi-ho; E.M.W. Antenna, R & D Center Park, Sang-hoon; E.M.W. Antenna, R & D Center Kum, Jun-sig; E.M.W. Antenna, R & D Center Kwon, Hyuck M.; Wichita State University, Electrical Engineering and Computer Science Keywords: T-DMB, CoZ, Hexaferrite, Antenna

2 Page of FE- Co Z hexaferrite T-DMB antenna for mobile phone applications Seok Bae, Yang-Ki Hong, a, Jae-Jin Lee, Jeevan Jalli, Gavin S. Abo, Won-Mo Sung, Gi-Ho Kim, Sang-Hoon Park, Jun-Sig Kum, and Hyuck M. Kwon MINT Center and Department of Electrical and, University of Alabama, Tuscaloosa, AL, USA E.M.W. Antenna Co. Ltd., Seoul, - Republic of Korea Department of Electrical and, Wichita State University, Wichita, KS, USA We fabricated. λ miniaturized Co Z hexaferrite T-DMB antenna. T-DMB antenna was fabricated by winding turn Cu tape around the Co Z rectangular block. Antenna was mounted on the ground substrate with connection of coaxial feeding line. Fabricated Co Z antenna showed. MHz of center frequency, -. db of dimensional average gain and. % of radiation efficiency at MHz. Average gain of Co Z antenna is found to be greater than -. db in the range of ~ MHz. Index Terms T-DMB, Co Z, hexaferrite, antenna I. INTRODUCTION The frequency of digital mobile TV service, such as T- DMB (Terrestrial Digital Multimedia Broadcasting), is assigned in the range of MHz to MHz []. Currently, commercial T-DMB antennae are still based on a monopole rod antenna design. Since the length of a monopole antenna is proportional to λ/ (=. cm at MHz), the miniaturization of the T-DMB antenna is an issue to address. A dielectric chip T-DMB antenna was previously demonstrated as a potential replacement for the conventional T-DMB rod antenna []. However, volume of the dielectric chip T-DMB antenna is still larger than cm because. cm is desired for T-DMB internal antenna. The ferrite possesses permeability (µ) and permittivity (ε), and µ and ε are effective in changing of electro-magnetic (EM) wave velocity υ and wavelength λ ( υ = c / µε, λ = λ / µε ). Therefore, ferrite was proposed to miniaturize the VHF antenna [-], but the performance of electrically small magneto-dielectric antenna is not satisfied due to large magnetic loss in the range of ~ MHz. In order to further miniaturize T-DMB antenna and to achieve higher antenna gain, we developed low loss Co Z hexaferrite particles in the T-DMB frequency range [, ]. In this paper, we report performance of Co Z hexaferrite T-DMB antenna. A. Design II. EXPERIMENT We used an inverted L antenna (ILA), which is one type of electrical small antenna. Figure (a) shows a helical turn ILA which was fabricated by winding the Co Z block with a. mm wide Cu tape with mm wide interval. The ground of ILA was x x. mm in size, is approximated motherboard size of mobile phone, and of double side CCL (Cu Clad Laminate) FR substrate. The fabricated antenna is Digital Object Identifier inserted by IEEE shown in the Fig.. An additional matching device or circuit is not used for tuning of frequency and impedance. B. Measurement Fig. HERE Fig. HERE Anechoic chamber system (volume: x x m ; shielding: - db; ripple < ± db in. ~ GHz) as shown in the Fig. (b) and network analyzer (Agilent ENA B) were used to evaluate antenna performance. III. RESULTS AND DISSCUSION The synthesis of Z-type hexaferrite has been reported by the authors [, ]. We used the Z-type hexaferrite block for our antenna fabrication. The magnetic properties and frequency dependence of permeability and loss tan δ of the Co Z are shown in Fig. and. Fig. HERE Fig. HERE The real part of permeability and loss tan δ of Co Z are. and. % at MHz, respectively, as shown in Fig.. We used the design in which Cu radiator is wound on the surface of ferrite block. With regard to antenna performance, we located the Co Z hexaferrite antenna in anechoic chamber which is connected to network analyzer. Figure shows VSWR (voltage standing wave ratio) for the Co Z ferrite antenna. Bandwidth (BW) was estimated to be MHz between and MHz at VSWR of. The VSWR at and MHz are. and., respectively. Even though these VSWR values are high, we obtained reasonable antenna gains of -. and -. db at and MHz, respectively. The center frequency (f c ) was

3 Page of FE-. MHz as marked by an open arrow in Fig.. This frequency exactly meets the requirement of T-DMB application. This is attributed to the high inductance per volume of helical radiator with high permeability of Co Z hexaferrite. Fig. HERE The average gains of antenna were measured in anechoic chamber system as shown in Fig. (b). Four average gains for xy, yz, xz-planes and dimension were estimated by S ij parameters in terms of frequency ranging from to MHz. The results are presented in Fig.. The average gains increase up to about MHz and then followed by a gradual decrease. We calculated radiation efficiency (RE) by the following relationship: log RE = D average gain [db] The D average gain and radiation efficiency (RE) are -. db and. % at MHz, respectively. Maximum D average gain and RE are -. db and. % at MHz. This small RE is attributed to the Chu s limit []. The lowest D average gain is. db at MHz as shown in Fig.. Figure shows D average gain patterns at MHz. Gain patterns of xy- and xz-planes are omni-directional. The insignificant gain for yz-plane at degree is attributed to the position of measurement cable in the DUT (Device Under Test) system. Fig. HERE Fig. HERE Summary of antenna dimension, material, and characteristics is given in table I. We used dielectric and conventional rod antennas [] for comparison. The dielectric antenna is shown in Fig., which consists of two spiral radiators to meet T-DMB frequency. The Co Z hexaferrite antenna shows superior performance to dielectric and conventional rod antennas. Furthermore, the Co Z antenna volume is % smaller than the dielectric antenna and rod antenna is longer than the Co Z hexaferrite antenna. Electrical and physical antenna sizes of Co Z antenna are. λ (Cu tape length/wavelength at MHz) and. λ (Antenna length/wavelength at MHz), respectively. Table I HERE Fig. HERE IV. CONCLUSION The miniaturized. cc Co Z hexaferrite T-DMB antenna was fabricated for mobile phone applications. The maximum D gain and radiation efficiency were found to be -. db and. %, respectively, at MHz, while. db and. % at MHz. The Co Z hexaferrite antenna size is % smaller than the dielectric antenna. It is noted that the Co Z hexaferrite is an excellent candidate material for. λ miniaturized T-DMB antenna. REFERENCES [] Final Acts of the Regional Radiocommunication Conference for the Revision of the ST Agreement, RRC--Rev.GE, ITU, June. [] H. P. Jeon, J. H. Seo, T. J. Yang, J. P. Kim, and W. M. Sung, Design of terrestrial DMB internal antenna for mobile handset, Proc. Korean Microwave and Propag. Technology Fall Conf., vol.,, Gangneung, Korea. [] H. Mosallaei, and K. Sarabandi, Magneto-dielectrics in electromagnetics: concept and applications, IEEE Trans. Antennas Propag., vol., pp.-,. [] S. Bae and Y. Mano, A small meander VHF & UHF antenna by magneto-dielectric materials, Asian Pacific Microwave Conf., vol.-, pp.-, Suzhou, China. [] S. Bae, Y. K. Hong, and S. H. Gee, IEEE Intermag Conf., DU-, San diego CA, May -,. [] S. Bae, Y. K. Hong, and A. Lyle, Effect of Ni-Zn ferrite on bandwidth and radiation efficiency of embedded antenna for mobile phone, J. Appl. Phys., vol., E, (). [] I. Y. Kim, S. Bae, and J. R. Kim, Effect of ferrite substrates on antenna miniaturization, J. the Korean Physical Soc., vol., pp. -, [] S. Bae, Y. K. Hong, J. J. Lee, J. Jalli, G. S. Abo, A. Lyle, W. M. Seong, and J. S. Kum, Low-loss Z-type ferrite (Co Z) for T-DMB antenna application, J. Appl. Phys., vol., A, (). [] S. Bae, Y. K. Hong, J. J. Lee, J. Jalli, G. S. Abo, A. Lyle, W. M. Seong, J. S. Kum, and S. H. Park, New synthetic route of single-phase Z-type (Ba Co Fe O ) hexaferrite particles, IEEE Trans. Magn., In press, May. [] L. J. Chu, Physical limitations of omni-directional antennas, J. Appl. Phys., vol., pp. -, May Manuscript received March,. Corresponding author: Yang-ki Hong ( ykhong@eng.ua.edu).

4 Page of FE- (a) Fig.. Fabricated Co Z hexaferrite antenna (b) Fig.. (a) The designed Co Z hexaferrite antenna, and (b) anechoic chamber system for antenna gain pattern measurement. σ [emu/g] BaFe O (M-type) - Ba Co Fe O (Y-type) - Ba Co Fe O (Z-type) -k -k k k Applied Field [Oe] Fig.. Magnetizations of synthesized M, Y and Co Z powders by MCP. Permeability µ' µ" Tan δ Frequency [MHz]..... Tan δ Fig.. Frequency dependencies of permeability and tan δ of Co Z hexaferrite.

5 Page of FE- Average gain [db] xy-plane (H) yz-plane (E) xz-plane (E) dimensional Total - Frequency [MHz] Fig.. Frequency dependencies of average gain of ferrite antenna. Average gain [db] (c) xy-plane (H) yz-plane (E) xz-plane (E) at MHz Fig.. Frequency dependencies of average gain patterns of ferrite antenna at MHz. Fig.. Frequency dependencies of VSWR (Voltage Standing Wave Ratio). Table I. Comparison on size, material, and D gains for ferrite, dielectric, and conventional rod antenna. Size Material Gain at MHz RE at MHz Ferrite antenna mm (= mm ) Co Z ferrite (µ =., ε =.) Dielectric antenna [] mm (= mm ) Dielectric composite (µ =, ε =) Fig.. Structure of dielectric antenna for T-DMB application []. Conventional rod antenna [] Length: mm Steel -. db -. db -. db. %. %. %