the lower frequencies, the antennas are just too large to
be practical. For example, at 30 MHz, a half wavelength is
about 16. 4 feet long. A multiple array would be enormous.
However, at 5 GHz or 5,000 MHz, a half wavelength is
only:
λ/2 = 150/5000 = 0.03 meters or 1.18 inches
Bigger arrays at the higher frequencies are smaller and
more practical.
Many of the new 5G cellular systems will operate in
the millimeter wave bands; 28 GHz is an example. One
half wavelength at this frequency is only:
λ/2 = 150/28000 = 0.00536 meters or 0.21 inches
A half wavelength at 60 GHz (a popular unlicensed
frequency band) is only:
λ/2 = 150/60000 = 0.0025 meters or roughly 0.1 inches
At these frequencies, large arrays can be packaged in a
small space. The antenna array may even be small enough
to integrate on a semiconductor chip along with the
related circuitry. This translates into phased arrays inside
smartphones and other portable equipment.
Figure 2a shows the radiation pattern of a basic dipole.
Its figure 8 pattern causes most power to be radiated
broadside from the antenna element and also some in
other directions, except in those directions at the ends of
the antenna elements. By using multiple antennas in an
array, the radiation pattern can be shaped into a narrower
beam as shown in Figure 2b. This pattern or lobe is
made up of multiple signals from multiple antennas in the
array. The signals are focused, making them stronger and
allowing the beam to be pointed in a desired direction.
Phased Array Defined
A phased array is two or more antennas used together
to provide some desired characteristic or feature not
available with a single antenna. An array is usually a
collection of multiple antennas arranged in a matrix of rows
and columns or some other pattern.
Figure 3 shows an example using 16 square patch
antennas on a PCB. The antennas in the matrix are
individually fed units, but collectively they work together
as a single antenna. The backside of the PCB has a copper
backplane that acts as a reflector. Feed lines are not shown.
The whole idea of the phased array is to achieve some
needed features. These key features are:
• Gain – Gain is like amplification. Some types of
antennas boost the signal level or effective radiated
power (ERP) as if greater signal power is used. Gain
applies to both transmitting and receiving.
• Directivity – Directivity implies that the antenna
is more effective in one direction or another.
Directivity means that the signal is narrowly focused
in one direction. This focusing of the signal is what
creates the antenna gain. Figure 2 showed the
broad radiation pattern of a standard dipole and the
radiation pattern (or lobe) of a phased array.
• Interference Minimization – Pointing the antenna
in a particular direction means that it’s less effective
in the other directions. This feature helps eliminate
or reduce interference for signals coming in from
other directions. Nulls can be created to take out
undesirable signals.
• Steerable – Phased arrays can be adjusted to
reposition a lobe on-the-fly. The direction of the signal
can be changed electronically to optimize the gain.
This allows them to scan horizontally and/or vertically.
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THE LATEST IN NETWORKING AND WIRELESS TECHNOLOGIES
Figure 2. The radiation patterns of a dipole (a) and a patch (b).
Figure 3. A 16-patch array on a PCB. The back of the
board is a solid copper backplane that serves as a
reflector. Feed lines are not shown.
86 September/October 2018
