Tuning a Dual-Band Bow-Tie Slot Antenna with Parabolic Radiating Slots for the 900 Mhz and 2400 Mhz Bands Layne A

Tuning a Dual-Band Bow-tie Slot Antenna with Parabolic Radiating Slots for the 900 MHz and 2400 MHz Bands Layne A. Berge Michael T. Reich Masud A. Aziz Benjamin D. Braaten Department of Electrical and Computer Engineering North Dakota State University Fargo, ND, USA Overview • Introduction and background information

• Purpose of research

• Simulated and measured results

• Discussion

• Conclusion Introduction

•Planar, bow-tie, CPW fed, slot antenna

•Original design maintained broadband operation between 3 and 5 GHz M. Miao, B. Ooi, and P. Kooi, “Broadband CPW-fed wide slot antenna,”Microwave and Optical Technology Letters, vol. 25, no. 3, pp. 206– 211,2000. Background

•Planar antennas are simple to fabricate in-house

•CPW (coplanar waveguide) feed allows balanced excitation

•Bow-tie antenna design has a dipole like gain pattern

Purpose of Research

•Create an antenna design using a lower permittivity substrate (original ɛr = 10.1)

•Dual-band operation at lower, consumer-band frequencies •900 MHz •2400 MHz

Design

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 Design

•Rogers 4003C

•Ɛr = 3.55

•Thickness = 1.6 mm

Design

•Parabolic curves emulate a Vivaldi antenna design

•Broadband

•Greater slot perimeter = longer path taken by currents J. Mandeep and M. Nicholas, “Design An X-Band Vivaldi Antenna,” Microwaves & RF, vol. 47, no. 8, 2008. Measurement and Simulation Results

•Compared both Method of Moments and Finite- Element Method

•Good correlation between simulated and measured results

•Dual-band operation at 900 MHz and 2400 MHz Measurement and Simulation Results

•Gain at 900 MHz in the y-z plane (left) and x-z plane (right) •Gain pattern similar to a dipole antenna •Simulated gain excursion caused by ideal assumptions (infinite substrate layer) Measurement and Simulation Results

•Gain at 2400 MHz in the y-z plane (left) and x-z plane (right) •Gain pattern deviates from that of a dipole at high frequencies •Caused by too large of a slot (electrically large dipole antenna → favors side-lobes) Measurement and Simulation Results

•Surface currents at 900 MHz (left) and 2400 MHz (right) •Too large of slot evident in “odd” surface currents in 2400 MHz plot (right) Measurement and Simulation Results

•Field strength at 900 MHz in the y-z plane (left) and x-z plane (right) •Low cross-polarization in both plots •Correlates well with gain plots Measurement and Simulation Results

•Field strength at 2400 MHz in the y-z plane (left) and x-z plane (right) •Non-negligible cross-polarization evident in each plot •Reinforces distorted gain patterns Discussion • Deviation from simulated and measured gain results at 900 MHz occurred because of ideal assumption by software (infinite substrate) • Poor gain plots at 2400 MHz – Asymmetries partly caused by radiation losses through the substrate – Main cause was found to be the slot width being near 1.5λ – Large slot results in prominent side lobes – Similar to results for electrically long dipole antennas Discussion • Maintained large bandwidth at both operating frequencies (Return Loss > 10 dB) – 602 MHz bandwidth at 900 MHz – 229 MHz bandwidth at 2400 MHz • Used a lower permittivity substrate – Less loss • Curved slot sides presented a longer path to currents than a comparable straight side Conclusion • Created a dual-band bow-tie slot antenna operating at 900 MHz and 2400 MHz • Used a lower permittivity substrate than previous designs • Used curved slot sides in order to reduce size of antenna • Gain pattern at 2400 MHz was distorted – Slot width too wide

Questions?

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