Author: Shaker, Ahmed
Date published: December 1, 2012
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Among short-range wireless communication systems, Ultra-wideband (UWB) technology, with a frequency allocation of 3.1 10.6 GHz, has gained a lot of popular-ity from researchers and the wireless industry alike due to the high data transfer rate (110 200 Mb/s) and low power consumption. The design of UWB antennas is one of the major factors affecting the progress of UWB technology. As a result, UWB antenna design has been studied much in recent years [1-4]. UWB antennas must be electrically small and inexpensive without compro-mising on performance. Omnidirectional radiation pat-tern is desired in order to be well suited for ad hoc net-works with arbitrary azimuthal orientations. However, over the designated frequency band, there exist some narrow bands for other communication systems, such as WiMAX operating in the 3.3 3.7 GHz band, WLAN operating in the 5.15 5.825 GHz band, and C-band sat-ellite communication systems at 7.2 GHz. They may cause communication interference with the UWB system. To solve this problem, it is desirable to design antennas with band notched characteristic at these bands to mini-mize potential interference. Several UWB antennas with frequency band notched function have been reported re-cently [5-9].
The reported antennas are generally embedded with a half-wavelength structure such as a U-shaped slot, a C-shaped slot or an arched slot. But most reported an-tennas were designed with only one notched band, mainly discussed on WLAN frequency band 5.15 5.825 GHz. Many UWB antennas with dual notched bands were recently reported in [5-7]. In , the dual notched bands were formed by two nested C-shaped slots em-bedded in the beveled patch. A U-slot defected ground structure (DGS) and an arched slot were used to achieve dual notched band in . A compact ultra-wideband an-tenna with tri-band notched characteristic is presented in . An ultra-wide band printed monopole antenna with four band notches are investigated in .
Moreover, a planar integrated antenna working on both Bluetooth and UWB has been recently introduced for systems operating in those two communication sys-tems [10,11]. In  a compact 5 GHz WLAN notched Bluetooth/UWB antenna is depicted by adding inverted L-shaped strips to both sides of a conventional rectangu-lar UWB monopole antenna to avoid interference with 5 GHz WLAN band. The Bluetooth frequency band is achieved by using a coupling-fed meander line on the backside of the UWB patch antenna. A simple compact, microstrip fed printed dual band antenna for Bluetooth and UWB applications with WLAN band notched char-acteristics is presented in . The antenna is composed of a fork shaped radiating element and a rectangular shaped ground plane. A pair of L-shaped slots and a pair of symmetrical step slots are etched on the ground plane to obtain the 5.15 5.825 GHz band-notched characteris-tic.
In this paper, a small-sized, low-profile, and planar in-tegrated Bluetooth and notched UWB antenna that satis-fies the performance requirements of both technologies is presented. This antenna configuration was initially stud-ied in  but without band notched characteristics.
Two compact printed notched UWB/Bluetooth anten-nas with double and tri-band notched characteristic are proposed. A U-shaped slot etched on the radiating patch and a U-slot defected ground structure (DGS), dou-ble-bands notched characteristic are achieved in antenna A .A H-shaped slot etched on the radiation patch and a U-slot defected ground structure (DGS), tri-bands notched characteristic are achieved in antenna B. Details of the antennas design are presented and simulation results us-ing the FEM [13,14] and FIT [15,16] are given.
2. Antennas Design
2.1. Antenna A Design
Figure 1 shows the geometry of the antenna A which is fed by a microstrip line and built on a FR-4 substrate with 42 × 46 mm2 surface area, 1mm thickness with rela-tive permittivity of 4.4 and loss tangent of 0.02. There is no ground metallization underneath the radiator for proper operation.
The antenna provides a dual-band operation due to two different radiating elements. The UWB element of rhomboidal geometry is responsible for the 3.1 10.6 GHz UWB band and exhibits tapered smooth transitions for the wideband response and improved matching at higher frequencies.
The design of the UWB rhomboid antenna starts with choosing L1, L2, and W1. L1 and L2 are critical parameters associated with the upper and lower operating frequen-cies of the antenna. W1, on the other hand, is a key pa-rameter to maintain good input impedance matching for the frequency range of 2.4 11 GHz. Accordingly, L1 and L2 are selected to have a reasonable return loss at fmin = 3.1 GHz and fmax = 10.6 GHz, which are the lower and upper ends of the UWB band . A good starting point for these dimensions is as follows:
The geometrical parameters have been optimized by using two commercial EM simulators based on Finite Element Method (FEM) and the second simulator based on Finite Integration Technique (FIT). Table 1 shows the dimensions of antenna A.
2.2. Antenna B Design
Figure 2 shows the second proposed antenna B. It has the same basic structure of antenna A to give the operat-ing frequency range of 2.4 11 GHz with a U-shaped slot in the ground plane and a H-shape slot in the radiating patch. The geometrical parameters have been optimized by using two commercial EM simulators based on Finite Element Method (FEM) and the second simulator based on Finite Integration Technique (FIT) as shown in Table 2.
3. Numerical Results
3.1. Numerical Results of Antenna A
Figures 3 and 4 show the simulated return loss (RL) and voltage standing wave ratio (VSWR) of the proposed antenna before and after adding slots using FEM and FIT simulators versus the operating frequency. Good agree-ment is obtained. A U-shape slot is embedded at the cen-ter of the ground plane forming DGS which can notch the WLAN frequency band at 5.2 5.8 GHz. On the other hand, the U-shaped slot etched on the radiating patch can notch the 3.3 4 GHz band for WiMAX. The figures show that RL < -10 dB and VSWR < 2 in the operating bands of Bluetooth and UWB except the notched bands for WiMAX and WLAN. Figure 5 shows the radiation patterns at 2.4, 3.5, 5.5 and 9 GHz. It is found that, the antenna gives nearly omnidirectional pat-tern in xz-plane as required at Bluetooth and UWB bands. Figure 6 present the antenna gain versus the frequency. The gain has acceptable flatness in the operating bands and it decreases at the notched bands where the gain is -2.2 dB at 3.6 GHz and -9.8 dB at 5.7 GHz.
3.2. Numerical Results of Antenna B
Figures 7 and 8 show the simulated return loss and voltage standing wave ratio (VSWR) of the antenna B before and after adding slots using FEM and FIT simulators. Good agreements are obtained. The -10 dB band in-creased from 3.1 GHz to 13.5 GHz. The U-shape slot is embedded at the center of the ground plane forming DGS which can notch the WLAN frequency band at 5.2 5.8 GHz. The H-shaped slot etched on the radiation patch may be regarded as two slots: an upper U-shaped slot and a lower C-shaped slot. The upper U-shaped slot can notch the 3.3 4 GHz band for WiMAX, and the lower C-shaped slot can notch the 7.2 GHz for some C-band satellite communication systems. Figure 9 shows the radiation patterns at 2.4, 4.2, 7.2 and 9 GHz. The antenna gives nearly omnidirectional pattern in xz-plane required at Bluetooth and UWB bands.
The antenna gain in the entire operating band for An-tenna B is shown in Figure 10. The gain has acceptable fitness in the operating bands and it decreases at the notched bands the gain is -2.2 dB at 3.6 GHz, -9.8 dB at 5.7 GHz and -2.2 dB at 7.2 GHz.
Figure 11 shows the return loss versus the frequency for antenna B with varying the length Ls3 of the H-shape slot. The central WiMAX band and central of C-band rejection can be tuned by changing the dimensions of H-shape slot by changing the parameter LS3 which changing the dimension of the upper U-shaped slot and a lower C-shaped slot without changing WLAN band notch and the bandwidth of the antenna.
Finally the comparison between antenna A and antenna B is shown in Figure 12. Double notched bands at 3.3 4 GHz for WiMAX and 5.2 5.8 GHz for WLAN are achieved in antenna A by using U-shape slot in the radiating patch and U-shape slot in the ground plane but in antenna B tri-notched bands at 3.3 4 GHz, 5.2 5.8 GHz and 6.7 7.8 GHz for C-band satellite communica-tion are achieved by using H-shape slot in radiating patch and U-shape slot in the ground plane. Antenna B has wider bandwidth from 2.4 GHz to 13.6 GHz.
Two compact printed Bluetooth and UWB antennas with dual band and tri-band rejection characteristic are presented. Two different types of slots, a U-shaped slot and a H-shaped slot etched on the radiating patch plus the U-shape slot in the ground plane, are used to obtain two and three notched bands respectively, which means ex-emption from interference with existing WiMAX, WLAN, and C-band satellite communication systems. The pro-posed antennas yield an impedance bandwidth of UWB (3.1 10.6 GHz) and at the Bluetooth frequency band with Return loss < -10 dB and VSWR < 2, except the notched bands. The omnidirectional radiation patterns are very stable across the Bluetooth and UWB bands.
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Ahmed Shaker1, Saber Helmy Zainud-Deen2, Kurany Ragb Mahmoud1, Sabry Mohamed Ibrahem1
1Faculty of Engineering, Helwan University, Helwan, Egypt; 2Faculty of Electronic Engineering, Menoufiya University, Menouf, Egypt.
Received October 1st, 2011; revised November 10th, 2011; accepted November 27th, 2011.