An analytical model for a frequency reconfigurable rectangular-ring microstrip antenna is proposed. The resonant frequencies and input impedance of the reconfigurable antenna are analyzed using a lossy-transmission-line (LTL) model. By making use of -admittance matrices, a formulation for the input impedance is analytically derived. The structure of the frequency reconfigurable antenna consists of a rectangular-ring shaped microstrip antenna which is loaded with a rectangular patch in the middle of the rectangular-ring antenna and fed by a microstrip line. RF switches are applied to connect the load to the antenna in order to reconfigure the operating frequencies. By modeling the antenna into a multiport equivalent circuit, the total input impedance is analytically derived to predict the resonant frequencies. To verify the analysis, the model input impedance and reflection coefficient calculation have been compared with the full-wave simulation and measurement results. The proposed model shows good agreement with full-wave simulated and measured results in the range of 1–3？GHz. 1. Introduction Frequency reconfigurable antennas are receiving higher attention in line with the development of advanced communications system. Different techniques have been presented to achieve reconfigurability of the antenna operating frequencies, but mostly the reconfigurability is controlled by means of RF switches, such as PIN diodes, FETs, varactor diodes, and RF-MEMS switches [1]. Recently, with the urge to integrate various types of wireless communication systems such as UMTS, LTE, WiFi, and WiMAX into a single device, the need for novel multiband frequency reconfigurable antenna is even more important. A lot of reconfigurable antenna structures have been widely reported, such as slot [2–4], monopole [5, 6], square-ring [7–9], and rectangular-ring antenna [10–12]. However, there are only few design procedures or theories of operation for the reconfigurable antennas that allow designers to create their own antennas using the same principles. The reconfigurable antennas are commonly designed and characterized using full-wave solver. Reconfigurable slot antenna in [4] was one that has been discussed in detail covering analytical model using transverse resonant technique, full-wave characterization, and design procedure, whilst square/rectangular-ring shaped reconfigurable antennas in [7–12] have reported the full-wave characterization and experimental validation but did not include the analytical model representation. Transmission line model (TLM) is commonly used to
References
[1]
J. T. Bernhard, Reconfigurable Antennas, chapter 4, section 4.2, Morgan & Claypool, 2007.
[2]
L. Pazin and Y. Leviatan, “Reconfigurable slot antenna for switchable multiband operation in a wide frequency range,” IEEE Antennas and Wireless Propagation Letters, vol. 12, pp. 329–332, 2013.
[3]
H. F. Abutarboush, R. Nilavalan, S. W. Cheung et al., “A reconfigurable wideband and multiband antenna using dual-patch elements for compact wireless devices,” IEEE Transactions on Antennas and Propagation, vol. 60, no. 1, pp. 36–43, 2012.
[4]
D. Peroulis, K. Sarabandi, and L. P. B. Katehi, “Design of reconfigurable slot antennas,” IEEE Transactions on Antennas and Propagation, vol. 53, no. 2, pp. 645–654, 2005.
[5]
C. Zhang, S. Yang, S. El-Ghazaly, A. E. Fathy, and V. K. Nair, “A low-profile branched monopole laptop reconfigurable multiband antenna for wireless applications,” IEEE Antennas and Wireless Propagation Letters, vol. 8, pp. 216–219, 2009.
[6]
R. Gon？alves, P. Pinho, and N. B. Carvalho, “Compact, frequency reconfigurable, printed monopole antenna,” International Journal of Antennas and Propagation, vol. 2012, Article ID 602780, 6 pages, 2012.
[7]
J.-F. Tsai and J.-S. Row, “Reconfigurable square-ring microstrip antenna,” IEEE Transactions on Antennas and Propagation, vol. 61, no. 5, pp. 2857–2860, 2013.
[8]
Y. J. Sung, “Frequency and polarisation reconfigurability from an open-loop square ring antenna,” IET Microwaves, Antennas and Propagation, vol. 6, no. 5, pp. 505–509, 2012.
[9]
M. A. Alkanhal and A. F. Sheta, “A novel dual-band reconfigurable square-ring microstrip antenna,” Progress in Electromagnetics Research, vol. 70, pp. 337–349, 2007.
[10]
B. S. Nugroho, F. Y. Zulkifli, and E. T. Rahardjo, “Simple frequency reconfigurable antenna by changing the number and position of the switches,” in Proceedings of the 12th International Conference on Quality in Research (QiR '11), pp. 428–433, Bali, Indonesia, 2011.
[11]
B. S. Nugroho, F. Y. Zulkifli, and E. T. Rahardjo, “PIN diodes slotted microstrip antenna as frequency reconfigurable antenna,” in Proceedings of the 17th International Symposium on Antennas and Propagation, pp. 814–817, Nagoya, Japan, November 2012.
[12]
E. T. Rahardjo, F. Y. Zulkifli, and B. S. Nugroho, “Multiband reconfigurable microstrip antenna,” in Proceedings of the Asia Pacific Conference on Antennas and Propagation, Chiang Mai, Thailand, 2013.
[13]
R. Garg and V. S. Reddy, “Edge feeding of microstrip ring antennas,” IEEE Transactions on Antennas and Propagation, vol. 51, no. 8, pp. 1941–1946, 2003.
[14]
D. M. Pozar, Microwave Engineering, chapter 3, sec. 3.8, John Wiley & Sons, New York, NY, USA, 3rd edition, 2005.
[15]
R. W. Dearnley and A. R. F. Barel, “Broad-band transmission line model for a rectangular microstrip antenna,” IEEE Transactions on Antennas and Propagation, vol. 37, no. 1, pp. 6–15, 1989.
