UWB SLOT ANTENNA IN THIE 3-9 GHZ BAND Jose Manuel Pidre Mosquera*, Maria Vera Isasa. Dpto. Teoria de la Sefial y Comunicaciones. Universidad de Vigo. Spain. http://www.grp.tsc.uvigo.es Introduction Recently an emerging ultra-wide band (UWB) technology is on development. It requires hard design specifications for antennas over a very wide bandwidth. U.S. Federal Communication Commission (FCC) defines UWB as higher than 20% fractional instantaneous bandwidth. Short-pulse UWB technology is applied in communication, radar and precision radiolocation [I ]. One of last applications for UVWB technology is breast tumor detection [2]. In this detection system, the antenna has to work in frequencies ranging from 3 to 9GHz. In addition, the impulse response has to be short, constant radiation pattem over the band and low return losses. One of the most promising antennas that can meet these design goals is the ultra- wideband magnetic antenna [3] [4]. The behavior of this antenna in the 3-9 GHz range is presented in this paper. An V-model and the use of a back-absorber layer in order to improve its performance is analyzed. A prototype has been built and measured. UWB Magnetic slot antenna The antenna consists of a leaf-shaped slot, excited across the gap as can be seen in figure 1. The radiated fields are orthogonally polarized to the longitudinal slot axis. Figure 1. UWB Magnetic slot antenna. Original flat configuration (right ) and proposed configuration. (in the left) 0-7803-8883-6/05/$20.00 ©2005 IEEE 508 Authorized licensed use limited to: Phan Phuong. Downloaded on January 14, 2010 at 03:11 from IEEE Xplore. Restrictions apply. In [3] is defined the width of the slot w as we move across longitudinal slot axis 1: w= cos( [l-c ] I <) (1) where Xo is the wavelength in the center frequency. A deeper analysis of equation 1, reveals this ratio between maximum slot width W and slot length L: W 1 - = - = 0.0625 (2) L 16 The antenna was evaluated using the software packages IE3D and XFDTD. IE3D is a commercial method of moments code [5]. XFDTD is a commercial code based on FDTD algorithm [6]. Both can deliver radiated fields and input impedance of simulated devices. IE3D is very fast evaluating planar slots. So we have employed it to study how the slot input impedance changes with dimensions. XFDTD is a powerful tool to simulate 3D devices in time domain. It was very useful to analyze the antenna with different bending angles. Starting with slot dimensions obtained from (1) for 6GHz, several simulations were made changing the W/L ratio. We found that increasing slot dimensions the matching bandwidth increases and the frequency band where radiation pattem does not change decreases. In order to get an ultra-wide matching band maintaining the broadside maximum radiation, a longer slot bent across H-plane is proposed, as figure I shows. After studying several angles, we have found an optimal bending of 58° when L=2X0 and W=X/2 (W/L=1/4, Xo=50mm). Figures 2 and 3 show the simulated radiation pattern of this configuration in E-plane and H-plane. The pattern still needs some corrections: sidelobes and back radiation can be suppressed with absorber sheets. 13 Ghz-4 Ghz -5 Ghz .6 Ghz-7 Ghz-6 Ghz*9 Ghz I 9= . \ - - I- - T I- 8 4 ~~~~ \i- i I ' 7 5- -L \-, i / 0 1 0 20 30 40 50 60 70 80 90 Theta [Grados] para Phi = 0° Figure 2. Simulated E-plane Gain Magnitude. 509 Authorized licensed use limited to: Phan Phuong. Downloaded on January 14, 2010 at 03:11 from IEEE Xplore. Restrictions apply. 7 i- , Ii ~0 0 20 40 60 80 100 120 140 160 Theta [Gradosi pata Phi - 900 Figure 3 Simulated H-plane Gain Magnitude. Results and Discussion A prototype with the mentioned dimensions was built and measured. The prototype was built in 0.5mm brass, and a sheet of eccosorb [7] was employed as absorber. Figure 4 shows the measured and simulated input impedance. The measurement is comparable to the simulation result. Therefore, if we feed the antenna with a suitable matching network the antenna would be well matched over the entire desired frequency band. Measured and simulated gain in broadside direction is plotted in figure 5. Measurement '4 SirTulation Figure 4. Input impedance from 3GHz to 6GHz. Simulation and Measurernent. Ga.in i. Bmdrdd dheti 0 1~~~~~~~~~~~~~ 385 485 585 6885 75 Frr.qu0ny (G3I) Figure 5. Gain in broadside direction. Simulation and Measurement. 510 Authorized licensed use limited to: Phan Phuong. Downloaded on January 14, 2010 at 03:11 from IEEE Xplore. Restrictions apply. Conclusions and Future Work The UWB magnetic slot antenna can be designed in order to meet challenging specifications over a very wide frequency band. The patented design of [3] was analyzed, and some changes are proposed in order to get better return losses without radiation pattern deterioration. We built a prototype increasing the dimensions published in [3] and bending the antenna 580. An absorber sheet was added in order to correct undesired sidelobes and back radiation. Measurements were very similar to simulation results, and both comply with proposed objectives Acknowledgment This work was supported by Xunta de Galicia (PGDITOITIC32201PR) and FEDER-CYCIT (TIC2003-01432). References: [1] R.J. Fontana "Recent System Applications of Short-Pulse Ultra-Wideband (UWB) Technology". IEEE Trans. Microwave Theory and Techniques. Vol. 52 N 9. September 2004. Pp. 2087-2104. [2] E.J. Bond, X. Li, S.C. Hagness, "Microwave Imaging via space-time beamforming for early detection of breast cancer". IEEE Trans. on Antennas and Prop. Vol. 51.N°8. August 2003. Pp. 1690-1705. [3] M. Barnes "Ultra-Wideband Magnetic Antenna" US Patent 6091374. July 2000. [4] H.G. Schantz, M. Barnes "The COTAB-UWB magnetic slot antenna". IEEE APS Int. Symposium 2001, Vol.4, July 2001. Pp. 104-107. [5] Zeland Software Inc. "IE3D User's Manual". January 2001. [6] "XFDTD Reference Manual. Version 6.0". Remcom Inc. 2003 [7] Emerson&Cuming Microwave Products. http://www.eccosorb.com 511 Authorized licensed use limited to: Phan Phuong. Downloaded on January 14, 2010 at 03:11 from IEEE Xplore. Restrictions apply. . In [3] is defined the width of the slot w as we move across longitudinal slot axis 1: w= cos( [l-c ] I <) (1) where Xo is the wavelength in the center frequency. A deeper analysis of equation 1, reveals this ratio between maximum slot width W and slot length L: W 1 - = - = 0.0625 (2) L 16 The antenna was evaluated using the software packages IE3D and XFDTD. IE3D is a commercial method of moments code [5]. XFDTD is a commercial code based on FDTD algorithm [6]. Both can deliver radiated fields and input impedance of simulated devices. IE3D is very fast evaluating planar slots. So we have employed it to study how the slot input impedance changes with dimensions. XFDTD is a powerful tool to simulate 3D devices in time domain. It was very useful to analyze the antenna with different bending angles. Starting with slot dimensions obtained from (1) for 6GHz, several simulations were made changing the W/L ratio. We found that increasing slot dimensions the matching bandwidth increases and the frequency band where radiation pattem does not change decreases. In order to get an ultra-wide matching band maintaining the broadside maximum radiation, a longer slot bent across H-plane is proposed, as figure I shows. After studying several angles, we have found an optimal bending of 58° when L=2X0 and W=X/2 (W/L=1/4, Xo=50mm). Figures 2 and 3 show the simulated radiation pattern of this configuration in E-plane and H-plane. The pattern still needs some corrections: sidelobes and back radiation can be suppressed with absorber sheets. 13 Ghz-4 Ghz -5 Ghz .6 Ghz-7 Ghz-6 Ghz*9 Ghz I 9= . - - . UWB SLOT ANTENNA IN THIE 3-9 GHZ BAND Jose Manuel Pidre Mosquera*, Maria Vera Isasa. Dpto. Teoria de la Sefial y Comunicaciones. Universidad de Vigo. Spain. http://www.grp.tsc.uvigo.es Introduction Recently an emerging ultra-wide band (UWB) technology is on development. It requires hard design specifications for antennas over a very wide bandwidth. U.S. Federal Communication Commission (FCC) defines UWB as higher than 20% fractional instantaneous bandwidth. Short-pulse UWB technology is applied in communication, radar and precision radiolocation [I ]. One of last applications for UVWB technology is breast tumor detection [2]. In this detection system, the antenna has to work in frequencies ranging from 3 to 9GHz. In addition, the impulse response has to be short, constant radiation pattem over the band and low return losses. One of the most promising antennas that can meet these design goals is the ultra- wideband magnetic antenna [3] [4]. The behavior of this antenna in the 3-9 GHz range is presented in this paper. An V-model and the use of a back-absorber layer in order to improve its performance is analyzed. A prototype has been built and measured. UWB Magnetic slot antenna The antenna consists of a leaf-shaped slot, excited across the gap as can be seen in figure 1. The radiated fields are orthogonally polarized to the longitudinal slot axis. Figure 1. UWB Magnetic slot antenna. Original flat configuration (right ) and proposed configuration. (in the left) 0-7803-8883-6/05/$20.00 ©2005 IEEE 508 Authorized. In [3] is defined the width of the slot w as we move across longitudinal slot axis 1: w= cos( [l-c ] I <) (1) where Xo is the wavelength in the center frequency. A deeper analysis of equation 1, reveals this ratio between maximum slot width W and slot length L: W 1 - = - = 0.0625 (2) L 16 The antenna was evaluated using the software packages IE3D and XFDTD. IE3D is a commercial method of moments code [5]. XFDTD is a commercial code based on FDTD algorithm [6]. Both can deliver radiated fields and input impedance of simulated devices. IE3D is very fast evaluating planar slots. So we have employed it to study how the slot input impedance changes with dimensions. XFDTD is a powerful tool to simulate 3D devices in time domain. It was very useful to analyze the antenna with different bending angles. Starting with slot dimensions obtained from (1) for 6GHz, several simulations were made changing the W/L ratio. We found that increasing slot dimensions the matching bandwidth increases and the frequency band where radiation pattem does not change decreases. In order to get an ultra-wide matching band maintaining the broadside maximum radiation, a longer slot bent across H-plane is proposed, as figure I shows. After studying several angles, we have found an optimal bending of 58° when L=2X0 and W=X/2 (W/L=1/4, Xo=50mm). Figures 2 and 3 show the simulated radiation pattern of this configuration in E-plane and H-plane. The pattern still needs some corrections: sidelobes and back radiation can be suppressed with absorber sheets. 13 Ghz-4 Ghz -5 Ghz .6 Ghz-7 Ghz-6 Ghz*9 Ghz I 9= . - -