performance is evalu- ated by a number of different specifications. In general, a switch must have a low insertion loss, high linearity, high port-to-port isolation, high-power handling, and a fast switching time. In mmWave systems, broadband frequency operation becomes increasingly important. To facilitate the transition to mmWave, switches must be able to support multiple bands, such as dual bands (28 and 39 GHz) or even triple bands (24, 28, and 39 GHz). In addition to multiple bands, each band has rigorous requirements on frequency-response variation. For example, a 28 GHz mmWave application will have a wide bandwidth and the system fre- quency response (gain) may not meet the flatness requirement. Furthermore, a true wideband support implies minimum variation across the supported frequency bands [26]. 5.9 Large Antenna Array Design and Implementation in Sub-6 GHz and mmWave Bands It is desirable for an antenna system to be able to focus its radiated energy in a particular direction in order to maximize the signal power toward a particular user device. Using a simple X/2 dipole as an example, the gain can be increased using two methods [18,19]: Antenna aperture: By increasing the aperture (or size of the antenna), the (larger) antenna becomes more directive due to the periodic current distribution across the antenna. Although this method does not require external circuitry for control, the direc- tion of the beam is fixed and the number of sidelobes increases. Antenna array: If the single dipole element is repeated according to the periodicity of the current distribution, an antenna array is created. The amplitude and phase of the sig- nals to individual elements can be adjusted to control both the beam direction and side- lobe levels, creating a phased-array. This results in a significantly more complex feeding network with relatively higher losses. 738 Chapter 5 The beam steering capabilities of an antenna array can create both a high-gain beam toward a specific direction as well as creating a null in a spe