A wideband unidirectional bowtie antenna with stable radiation patterns is proposed and investigated. It is fed by a wideband microstrip balun, using a coupling triangular structure to induce more balanced currents. Particularly, the corners of the conventional triangular bowtie dipole are rounded to achieve an impedance BW of 106.9% for |S11| ≤ -10 dB ranging from 1.97 GHz to 6.49 GHz. Additionally, a special small circular reflector between the ground plane and the bowtie dipole is used to stabilize the radiation patterns. The antenna achieves a stable gain of around 9.5 dBi with a little variation of 1.4 dBi and unidirectional radiation patterns over the whole operating band.
2. Lai, H.-W. and K.-M. Luk, "Design and study of wideband patch antenna fed by meandering probe," IEEE Trans. on Antenna and Propag., Vol. 54, No. 2, 564-571, Feb. 2006.
3. Lai, H.-W. and K.-M. Luk, "Wideband stacked patch antenna fed by meandering probe," Electron. Lett., Vol. 41, No. 6, 297-298, Mar. 2005.
4. Hazdra, P. and M. Mazanek, "Wideband shorted backfire antenna with L-probe fed microstrip patch," Proc. 4th Eur. Conf. Antennas Propag., 1-3, 2010.
5. Li, R., D. Thompson, M. M. Tentzeris, J. Laskar, and J. Papapolymerou, "Development of a wideband short back¯re antenna excited by an unbalance-fed H-shaped slot," IEEE Trans. on Antenna and Propag., Vol. 53, No. 2, 662-671, Feb. 2005.
5. Ehrenspeck, H. W., "The short-backfire antenna," Proc. IEEE, Vol. 53, 1138-1140, Aug. 1965.
7. Keen, K. M., "Log-periodic antenna with unidirectional radiation characteristics," Electron. Lett., Vol. 12, No. 19, 498-500, 1976.
8. Qu, S.-W., J.-L. Li, Q. Xue, and C. H. Chan, "Wideband and unidirectional cavity-backed folded triangular bowtie antenna," IEEE Trans. on Antenna and Propag., Vol. 57, No. 4, 1259-1263, Apr. 2009.
9. Sagnard, F. and F. Rejiba, "Wide band coplanar waveguide-fed bowtie slot antenna for a large range of ground penetrating radar applications," IET Microw. Antennas Propag., Vol. 5, No. 6, 734-739, 2011.