A Compact Dual-Band Microstrip-Fed Monopole Antenna Hua-Ming Chen', Yi-Fang Lin, Chin-Chun Kuo and Kuang-Chih Huang Department of Physics National Kaohsiung University of Applied Sciences Kaohsiung, Taiwan 807, R.O.C. Introduction The rapid developments in the wireless communications industry demand novel antenna designs that can be used in more than one frequency band. Recently, dual-band cellular phones capable of operating in two different cellular systems are increasing. A cellular phone operating at both frequencies (900 MHz and 1800 MHz) requires the antenna to operate equally well at both frequency bands. Dual-band antenna are not used in cellular networks alone, in fact, they are widely used for dual-band ISM applications. As an example, many laptop computers use 900 MHz or 1800 MHz band for wireless printer and modem connections. The 2400 MHz band is used by laptops in wireless local area network (LAN) applications and the Bluetooth is being considered as a cable replacement between portable and fixed electronic devices. Dual-band antennas with one feed have some advantages over multi-feed antennas and were proposed in [1]-[4] for cellular applications. The antenna in [I] consists of a straight radiating element and a helically wound element, while the antenna in [2] uses a non-uniform helix radiating element. An internal dual-band mobile phone antenna [3 J is derived from a quarter-wave planar inverted F-type antenna (PIFA), which has compact size and good performance. All the above antennas are designed to operate at 900 MHz (GSM) and 1800 MHz (DCS). In reference [4], a dual-band strip-sleeve antenna is described for use on a laptop computer, which is designed to resonate at 0.85 and 1.9 GHz. In this paper we will extend the antenna design to be used for dual-band ISM applications. In this application there is a particular interest to obtain an increased operational bandwidth of the antenna. The effects of design parameters of the microstrip-fed uniplanar monopole antenna on its operational frequency and impedance bandwidth are presented and discussed. Antenna Configuration and Results The configuration of the microstrip-fed uniplanar monopole antenna is shown in Fig. 1, which is printed on a microwave substrate of thickness 0-7803-7070-8/01/$10.00 02001 IEEE 124 h and relative permittivity zr. Two printed strip monopoles of different lengths, printed on the same side of an electrically thin substrate, are connected through a series microstrip line with a tuning stub. It is noted that the presence of the dielectric substrate lower the fundamental resonance frequency of the antenna with air substrate and can provides mechanical support. The parallel symmetrical strip monopoles with z-axis have the same width of W,,, and a length of L, and L2, respectively. A coupled gap of width W, between the parallel strip monopoles is chosen in the proposed design. A 504 microstrip line with a tuning stub is used for feeding the proposed antenna at the center of the two monopoles. The truncated ground plane on the backside of the substrate is used as reflector element. The distance between the end of monopole and the terminal of the microstrip line is denoted as monopole height Lo. The tuning stub has a length of L, and a distance S from the edge of the truncated ground plane. The section of the tuning stub has a width of W’the same as the width of the microstrip line. The tuning stub length L, was found to be very effective in controlling the coupling of the electromagnetic energy from the microstrip feed line to the strip monopole antenna, and good impedance matching for the dual-band antenna can be obtained. By observing the influence of various parameters on the antenna performance, it can be seen that there is no single design parameter that affects only one of the frequency bands. In order to reduce experimental cut-and-try design cycles, simulation software [5] is used to guide fabrication and measured results were compared against the simulation ones. A dual-band uniplanar monopole antenna operating at 1800 MHzl 2400 MHz has been designed using a dielectric substrate of thickness h = 1.6 mm and relative permittivity = 4.2. Optimal design has been designed by choosing Lo = 2 mm, L, = 34 mm, L2 = 20.5 mm, W,= 3.0 mm, W,,, = 5 mm, W, = 1 mm, S = 0 mm and L, = 5.0 mm. The antenna was fabricated, tested, and compared with simulated results. In Fig. 2 the simulated values of input return loss of the final design are compared with measured data, showing good agreement. It can also be seen that the optimal antenna has more than 9% bandwidth at two design frequency bands. The measured E-plane (x-z cut) and H-plane (x-y cut) radiation patterns of the proposed antenna at 1800 MHz and 2450 MHz are plotted in Fig. 3. As shown from this figure, the maximum radiations are on the same directions for the both bands. For the elevation plane radiations, the maximum radiation directions are in the horizontal directions as expected. And for the azimuth plane radiations, the radiation patterns are basically omnidirectional. This phenomenon is similar to that of typical monopole antenna. Conclusions 125 A parameter study of a microstrip-fed uniplanar monopole antenna has been performed with respect to its several design parameters. It has been found that the design frequency and the operational bandwidth are affected by the changes of these parameters. The proposed antenna has adequate operational bandwidths and suitable radiation patterns so that it is commercially good for use in wireless communications applications. Although the DCS and ISM bands are used here, similar design procedure can be obtained for the 900 MHz and 1800 MHz DCS bands. References [l] B. Winter and V. Stoiljkovic, \"A novel dual antenna for mobile IEEE Antennas Propagut. Soc. Int. Syrnp. communications,\" in 1998 Dig., Atlanta, GA, June 1998, pp. 778-78 1. [2] I. Egorov and Z. Ying, \"A non-uniform helical antenna for dual-band cellular phones,\" in 2000 IEEE Antennas Propagat. Soc. Int. Symp. Dig., Salt Lake City, UT, July 2000, pp. 652-655. [3] S. Tarvas and A. Isohatala, \"An internal dual-band mobile phone antenna,\" in 2000 IEEE Antennas Propagat. Soc. Int. Symp. Dig., Salt Lake City, UT, July 2000, pp. 266-269. [4]M. Ali, M. 0. Wski, M. A. Stuchly and S. S. Stuchly, \"A dual-frequency strip-sleeve monopole antenna for a laptop computer,\" in 1998 IEEE Antennas Propagat. Soc. Int. Symp. Dig., Atlanta, GA, June 1998, pp. 794-797. [5] IE3D release 5.0, Zeland Software Inc., August 1998. Fig. 1 Configuration of the microstrip-fed uniplanar monopole antenna. 126 e. -351 -30 1 -40 \"\"1600 measured simulated h2MHz \"'\"'\"\"\"'\"'\" 1800 2000 frequency, MHz 2200 2400 2600 2800 Fig. 2 Measured and simulated results for the return loss of the optimized uniplanar monopole antenna. E-plane(x-z cut) H-plane(x-y cut) Fig. 3 Measured elevation plane and azimuth plane radiation patterns of the proposed antenna. (a) 1800 MHz. (b) 2450 MHz. 127