Tuning a Bowtie Slot Antenna with an Equation Based Curve for 900 and 2400 MHz ISM Bands Layne A. Berge * ,Michael T. Reich * Masud A. Aziz † , Benjamin D. Braaten † * Center for Nanoscale Science and Engineering, North Dakota State University 1805 Research Park Dr. Fargo, ND 58102 USA † Electrical and Computer Engineering, North Dakota State University 1411 Centennial Boulevard, Room 101U Fargo, ND 58102 USA layneberge@ieee.org Abstract—A dual-band bowtie slot antenna is proposed and designed for the 900 and 2400 MHz ISM bands. Using Rogers 4003C substrate (r = 3.55) with a thickness of 1.6 mm, the antenna is produced and tested. A comparison is made between measured and simulated data from both a Method of Moments and Finite-Element method software packages. By using a parabolic curve to form the sides of the bowtie slot, the new antenna integrates features from a Vivaldi antenna into its design. Using these features, the antenna achieves dual-band operation while maintaining an omni-directional pattern similar to a normal bowtie slot. The parabolic sides of this bowtie slot antenna offers an additional design element for other CPW fed slot antenna designs. I. I NTRODUCTION Printed planar antennas today present an attractive option for wireless applications. Using low cost equipment such as a rapid-prototyping machine, a person can create unique designs satisfying specific and demanding needs. A properly designed planar slot antenna, such as a bowtie slot, provide stellar efficiency while exhibiting an omni-directional pattern. Using a coplanar waveguide (CPW) furthers the planar slot antenna’s functionality since it does not require a balun. Also, a CPW eases the matching process by allowing simple placement of components in either a shunt or series fashion. Inherent to the slot antenna geometry is the ability to tune the antenna structurally with stubs, patches, resonant structures or other suitable devices [1]. A. The Bowtie Slot Antenna The bowtie slot antenna, as outlined in [2], demonstrates the characteristics of a CPW fed slot antenna. The bowtie slot antenna used in [2] achieved a bandwidth of 40% between 3 and 5 GHz. It accomplished this by using centrally located tuning stubs, varying their width and height accordingly. The antenna design presented in [1] expanded on the design in [2] by lowering the frequencies of operation to between 1.8 and 2.4 GHz. This modified design obtained a bandwidth of 55%. The overall design of the antenna in [1] differed little from that of the design in [2] except for enlargements in dimensions to obtain a lower operating frequency. Fig. 1. Bowtie Slot Antenna with the following dimensions: H=140 mm, W =240 mm, Bw=100.2 mm, Bi=8 mm, Bo=70.3 mm, g=0.4 mm, d=4.6 mm, S=7.5 mm. II. DESIGN OF THE BOWTIE SLOT ANTENNA A traditional Vivaldi antenna is a traveling-wave antenna. When used in a planar configuration, it takes the form of a tapered slot, where the minimum and maximum distances between the slot edges correspond to its operating frequency range [3]. While normally used in an end-fire configuration with high-directivity, a Vivaldi antenna’s broad-bandwidth characteristics prove desirable in many designs [4]. To improve the bowtie slot antenna, we replaced the straight sides of the slot presented in [2] with a parabolic curve. Using this modified bowtie slot antenna, we determined its ability to tune to the 900 and 2400 MHz ISM bands. Figs. 1 and 2 display the results of integrating a Vivaldi style design into a bowtie slot. Fig. 1 also displays the dimensions used in the manufactured antenna. The CPW’s dimensions in Fig. 1 optimize the antenna for a 50Ω source load. To accomplish this, the transmission line width d is 4.6 mm and the gap g is 0.4 mm. We determined these parameters using a passive circuit design utility [7]. In designing the antenna, the width of the slot Bw de- termines the operating frequency. The overall height of the antenna, H, greatly affects both resonant points in a comple- mentary manner. With this design, increasing the tuning stub