This works, but is inflexible – it can only handle one data stream and therefore it can only generate one signal beam. If the system needs to handle multiple data streams and generate multiple beams from one array, we need to move to digital beam forming, as shown in Figure 2, in which each element of the antenna array has its own transceiver and set of data converters.
Greater complexity leads to greater power consumption, which needs to be controlled to reduce the environmental impact and operating-cost implications – and the cooling challenge.
Estimating the cooling needs of an antenna array
Take a 4x4 antenna array panel operating at 30 GHz, in which the antenna elements are placed half a wavelength apart – that is, 5 mm. To use digital beam forming means each element needs 2 DACs (for I and Q), 2 ADCs, 1 PLL, 1 LNA, 1 PA, 1 transmit/receive switch and some amplifiers and other electronics, including filters. The circuits for each element should ideally be on one chip, for cost and size reasons. The antenna is then assembled by laying out 16 chips evenly across a panel, so that they have short connections to the antenna elements they are driving and the heat they produce can be evenly distributed, as in Figure 3.