The two resonant frequencies approach each other when the (Lee & Nalbandian, 1993) air gap length increases.
The resonant behavior can be considered as a coupling between two resonating modes in the dielectric regions through the air gap.
Many techniques have been proposed to design microstrip patch antennas with multiband characteristics.
In the proposed antenna design, a combination of dual U-slot and multiple layers is used to get multiple bands and wide bandwidth.
Low dielectric constant is used in the prototype design because it gives better efficiency and higher bandwidth (Balanis, 2005; Ramesh, Prakash, Inder, & Apisak, 2001; Wong, 2002) and it increases the fringing field at the patch periphery and thus increases the radiated power.
The small loss tangent was neglected in the simulation.To design coaxial probe feed rectangular patch antennas, there are some essential parameters to be considered.Firstly, the resonant frequency () and loss tangent equal to 0.002.Multiband antennas (Lee, Luk, Mak, & Yang, 2011) can cover multiple wireless technologies; however, in microstrip patch antennas, the U-slot was mainly used for bandwidth enhancement rather than introducing a band notch and it has been shown that the U-slot technique can be used to design patch antennas with dual and multi-band characteristics.The studies reported (Lee, Steven Yang, Kishk, & Luk, 2010; Singh, Ali, Singh, & Ayub, 2013) on U-slot patch antenna showed that, it can be intended not only for wideband applications, but also for multiband (dual and triple-band) applications.It is even more complex to integrate multiple bands for wireless technologies (Vedaprabhu & Vinoy, 2010) such as AWS (Advanced Wireless Services), GSM (Global System for Mobile) and various Wi MAX and WLAN bands operating at several frequency ranges.Design of multi-band microstrip patch antennas even with narrow bandwidths is challenging.The techniques such as multilayer microstrip antennas using low dielectric constant substrate improve the impedance bandwidth and multiple (Ghassemi, Neshati, & Rashed-Mohassel, 2007) frequency band of operation.Design of multilayer stacked patch antennas provides bandwidths for broadband applications (Hoorfar, 1992).Many works had reported on the design of low-profile multiband antennas.In this paper design of triple-layer double U-slot patch antenna is proposed to get multiple bands and wide bandwidth.