The objective of the work is to design a dual frequency microstrip antenna for small frequency ratio applications. The proposed geometry comprised of suspended truncated circular microstrip antenna, with double U slot etched on the radiating element. The design parameters are radius of circular patch, width and length of slot, height of air gap. The proposed design of the antenna has enough freedom to control the dual design frequencies/frequency ratio by varying the above design parameters. FR4 substrate with dielectric constant 4.4 is chosen for design and fabrication. The dual design frequencies are 1.93 GHz and 2.17 GHz, covering the applications such as WCDMA, 3G mobile data terminals, and 4G LTE applications. The antenna is fed by a 50 Ω coaxial probe. The simulation of the antenna is performed using ANSOFT HFSS and analyzed for return loss, VSWR and radiation pattern. The antenna is fabricated and tested for impedance matching and radiation characteristics. The simulation and experimental results show that the antenna worked well at desired dual frequencies. The impedance matching is well at both frequencies (VSWR <2). Though, the measured radiation pattern is unidirectional in co-polarisation, nearly omnidirectional (butterfly) pattern is obtained in cross-polarisation and gain is about 5.54 dB at 1.93 GHz and 8.23 dB at 2.17 GHz. Also, the design is well suited for small frequency ratio dual frequency applications.
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