In this paper, three millimeter wave antennas are presented for 60 GHz. Each antenna is an array of 2 x 2 microstrip antennas. All three antennas utilize thin substrate of RT Duroid 5,880 having permittivity Er = 2.2. The basic design of 2 x 2 array antenna utilizing RT Duroid is extended for two superstrate loaded antennae designs. The first design uses foam and the other design uses RT Duroid with air gap as superstrates. 2 x 2 array patch engraved on RT Duroid above ground plane acts as driven patch, while the patch incised upon the superstrate acts as a parasitic patch. Optimization of the basic design achieves highest gain in millimeter wave region, whereas the superstrate loaded design results in a much wider bandwidth. A comparison of all design configurations is carried out through the sensitive study of the simulation results, including return loss, polarization and radiation patterns, which validates the designs for millimeter wave region.

With the development of wireless device technology, the demand for large bandwidth is rapidly increasing. Since the lower frequency bands are unable to cater to the needs of high bandwidth, researchers are showing deep interest and are motivated by the 7 GHz unlicensed frequency band available around 60 GHz (Nesic et al., 2001; Smulders, 2003; and Prasanna, 2008). Millimeter-wave technology is one solution to provide up to several Gbps wireless connectivity for short distances between electronic devices. A 60 GHz link can potentially replace various cables used in the offices/home, including gigabit Ethernet (1,000 Mbps), USB 2.0 (480 Mbps) or IEEE 1394 (~800 Mbps). An outstanding and significant phenomenon at millimeter-wave band is the O2 absorption, which results in atmospheric attenuation of about 10-15 dB per km. Due to this high attenuation, the signal is unable to propagate beyond a specific propagation range that makes 60 GHz a naturally secure communication band suitable for WLANs, WPANs, etc. As is already known, new systems need compact and highefficiency millimeter front-ends and antennas. For antennas, printed solutions are always demanding for the researchers because of their small size, weight and ease of integration with active components (Lau et al., 2006; and Zhang and Wang, 2006). It is reported that conventional antenna arrays are used for high-gain applications, but in all these cases, for achieving high gain, arrays of large number of elements are used, which not only increases the size of the antenna, but also decreases the efficiency (Navarro, 2002; Oh et al., 2004; and Liu et al., 2009). It has been reported that for high gain, superstrate layer can be added at a particular height of 0.50 above the ground plane (Choi et al., 2003; and Meriah et al., 2008).

Telecommunications Journal, Bandwidth Enhancement, Stacked Configuration, Microstrip Antenna Array, Millimeter Wave Applications, Microstrip antenna array, Millimeter wave, Bandwidth enhancement, Miniaturization.