The paper describes the effect of with and without dielectric superstrates on bandwidth, beamwidth, gain, resonant frequency, input impedance, return loss, Voltage Standing Wave Ratio (VSWR) and radiation pattern of rectangular microstrip patch antenna. It is found that there is a slight degradation in the performance of the antenna when the superstrate is touching the patch antenna. In particular, the resonant frequency decreases with increase in the dielectric constant of the superstrate thickness. In addition, it has also been observed that return loss and VSWR increase, however, bandwidth and gain decrease with the dielectric constant of the superstrate thickness. The microstrip patch antenna without dielectric superstrate achieves an impedance bandwidth of 0.203 GHz (SWR < 2) at 2.4 GHz, compared to microstrip patch antenna with dielectric superstrate, which shows that the resonate frequency is decreased to 2.31 GHz from 2.40 GHz, impedance bandwidth to 0.040 GHz from 0.200 GHz (SWR < 2) at 2.30 GHz and the gain to 2.80 GHz from 7.30 GHz. The optimum gain is obtained at r2 = 2.2. This type of antenna is mainly used in wireless and Bluetooth applications.

A microstrip antenna consists of a radiating patch on one side of a dielectric substrate, which has a ground plane on the other side. The patch conductors, normally copper or gold, can assume virtually any shape, but regular shapes are generally used to simplify analysis and performance prediction. Ideally, the dielectric constant of the substrate should be low (r < 2.5) to enhance the fringing fields that account for the radiation (Bahl and Bhartia, 1980; and Balanis, 2007). The dielectric superstrate (cover or radome) protects the patch from climatic conditions and environmental hazards and improves the antenna performance (Bahl and Bhartia, 1980; Bahl et al., 1982; Ramahi and Lo, 1992; Afzalzadeh and Karkar, 1994; Bhattacharyya and Tralman, 1998; and Balanis, 2007). Researchers (Bahl et al., 1982; Ramahi and Lo, 1992; Afzalzadeh and Karkar, 1994; and Bhattacharyya and Tralman, 1998) have investigated the input impedance of rectangular patch with dielectric superstrate (radome). The effects of different methods on the rectangular patch microstrip antennae have been investigated by many researchers. Luk et al. (1989) reported the investigation of the effect of dielectric cover on a circular microstrip patch antenna. The resonant frequency of patch is decreased, while bandwidth is slightly varied. Hammas (2009) discussed the microstrip antenna performance covered with dielectric layer. They found from the simulated results that the antenna resonant frequency is reduced as the dielectric layer thickness is increased; however, the gain is decreased as dielectric layer thickness is increased. Yadav and Yadava (2011) observed that the resonant frequency lowers and shift in resonant frequency increases with the dielectric constant of the superstrates; in addition, it was also observed that return-loss and Voltage Standing Wave Ratio (VSWR) increase, however, bandwidth and directivity decrease with the dielectric constant of the superstrates. Attia et al. (2011a) found that a microstrip patch antenna can be designed to achieve the highest possible gain when covered with a superstrate at proper distance in free space. The transmission line analogy is used to deduce the resonance conditions required to achieve the highest gain. Gupta and Singh (2012) found that the design of multi-dielectric layer, based on different thickness and permittivity of the superstrate layer, has significant effect on gain and efficiency. The proper choice of thickness of substrate and superstrate layer significantly increases gain.

Telecommunications Journal, Bandwidth, Beamwidth, Dielectric superstrate, Resonant frequency.