Page 14 - EngineerIT February 2022 UPDATED

ICT – MILLIMETRE WAVE TECHNOLOGY

using active phased array antennas that
offer beam forming and beam steering
capabilities.

Antenna arrays in mmWave 5G
Antenna arrays are not a new concept.
Passive arrays have been used in cellular
base station antennas since the early
years of the GSM deployment, and
radar systems have been using them
for several decades. As stated in the
previous section, the solution to larger
path loss and lower power per PA in
mmWave frequencies is to use active
phased array antennas. This is achieved Figure 1: A 256-element antenna array with dual polarised radiating elements.
by placing many antenna elements in an
array, while each element is driven with receive channels with associated PAs typically smaller than 10 mm . Therefore,
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a low power PA. Using more elements and low noise amplifiers (LNAs), as well many antennas can be placed in a
increases the total radiated power as per path phase and gain controls, relatively small area to enhance the gain.
output of the array and at the same time and TDD switch functionality. All this Let’s assume a 256 element antenna array
enhances the array gain and narrows integrated on a single piece of silicon! with eight rows and 16 columns of dual
the resulting beam. The phased array The first generation of these devices polarised radiating elements, as shown in
antenna theory is beyond the scope of were implemented using SiGe BiCMOS Figure 1. The red and blue lines indicate
this article. For further information on technology (ADMV4821). To further +45° and –45° polarised elements,
the topic please refer to the three-part improve the power efficiency and cost, respectively.
Analog Dialog series, “Phased Array the second generation uses the SOI The total area of such antenna
Antenna Patterns.” 1-3 CMOS process (ADMV4828). These array, assuming λ/2 distance between
The high cost of active phased array highly integrated and power efficient antenna elements, is 8(λ/2) × 16(λ/2)
antennas has limited their application beam formers, along with mmWave = 32λ . Comparing a 900 MHz and a 28
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mostly to aerospace and defence up/down converters (ADMV1017/ GHz antenna, the total area of a 900
applications. More recent advances in ADMV1018) and frequency synthesisers MHz array is 3,55 m , whereas the 28
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semiconductor technology, combined (ADF4371/ADF4372), enable a complete GHz array is only 3,67 × 10 m – almost
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with high levels of integration, have RF front-end solution for mmWave 5G 1000 times smaller! While the size of a
made it possible for active phased array base stations. 256-element antenna array at 900 MHz
antennas to become commercially At mmWave frequencies, the is quite prohibitive, a similar array at 28
viable in 5G applications. ADI offers antenna elements have a small physical GHz can be implemented on a printed
active beam-former devices that footprint. For example, a simple circuit board (PCB) in an area less than
integrate 16 complete transmit and microstrip patch antenna at 28 GHz is 40 square centimetres.
A 256-element dual polarised
mmWave antenna array at 28 GHz was
developed on a multi-layer PCB, using
ADI beam formers and mmWave up/
down converters. To reduce the cost
and avoid expensive/lossy interconnect
between antenna and radio, active
components were mounted on one side
and the antenna elements on the other
side of the PCB. A picture of this board,
which is called AiB256 (AiB stands for
antenna in board), is shown in Figure 2.
There are 16 ADMV4828 SOI beam
former chips on AiB256, each providing
16 transmit and 16 receive channels,
connecting to 128 antenna elements in
Figure 2: The component side of AiB256 (16 beam formers and four mmWave up/down converters). each polarisation, covering a frequency

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