Nuts and Volts - September/October 2018

These modules can be packaged together as an array as needed. Today, semiconductor technology lets you put one or more modules on a single semiconductor chip.

A good example of a commercial product available to implement phased arrays is the Anokiwave family of millimeter wave phased array front-ends. The AWMF- 0139 operates in the 24 to 26 GHz band allocated to the coming 5G cellular networks It encapsulates four modules per IC. Figure 6 shows how 64 of these chips can be used to make a 4 x 64 = 256 element array. Another similar IC is Analog Devices ADAR1000.

MIMO

Phased array antennas can also be used for multiple input multiple output (MIMO). MIMO is a technique that transmits the same data with multiple antennas over the same path in the same bandwidth. This does two things.

First, each signal takes a slightly different route to the receiving antennas. The result is less fading and greater data reliability. Second, MIMO multiplies the data rate by a factor that is determined by the number of transmit and receive antennas. Common configurations are 2 x 2, 4 x 2, 4 x 4, and 8 x 8, where the first number is the number of transmit antennas and the second number is the number of receive antennas.

A multi-element phased array can be partitioned into sections making it suitable for some MIMO applications.

For example, the 256-element array could be arranged to provide four 64-element arrays or sixteen 16-element arrays. With beam steering capability, the signal path can be optimized for best performance.

Also, 5G cellular radios operating in the millimeter wave bands will use MIMO to give gigabit data rates. The big hurdle is putting a phased array into a smartphone handset. Initially, two antennas will be used and later will be increased to four. MIMO is also widely used in Wi-Fi routers. NV