Introduction to beamforming antennas

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Introduction to Beamforming Antennas
This document describes basic functional blocks of the Beamforming Antennas, how they
work and can be tested.
1. Beamforming Antennas
2. Difference between 5G passive and active antennas
3. Basic principles of Beamforming
4. Analog and Digital beamforming
5. Smart Antennas
6. Beamforming Antennas testing
Beamforming Antennas
Beamforming is the most commonly used method by a new generation of smart antennas.
In this method, an array of antennas is used to transmit radio signals in a specific direction,
rather than simply broadcasting energy/signals in all directions inside the sector in
conventional antennas. Multiple smaller antennas control the direction of the combined
transmitted signal by appropriately weighing the magnitude and phase of each of the
smaller antenna signals. In Beam forming technique, the phase and amplitude of the
transmitted signal of each component antenna are adjusted as needed, resulting in a
constructive or destructive effect, concentrating the total transmitted signal into targeted
beam/ beams.
Beamforming antennas are becoming increasingly common and have many applications. in
radars, and especially in the field of telecommunications by the evolvement of 5G.
Beamforming as a technology has been around since well before 5G, since of the early days
of mobile broadband. The method by which beamforming is achieved is growing
increasingly more sophisticated, partly thanks to contemporary Massive MIMO antennas.
Used since 3G, MIMO technology lets the radio signals to be sent and received using several
antennas. Massive MIMO antennas have many more component antennas (around 100)
that allow them to transmit radio signals more efficiently. This allows for very high data
rates.

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Difference between 5G passive and active antennas
Passive antennas are built with entirely out of passive elements, whereas active
antenna systems contain active components that control the amplitude and phase of each
antenna elements to improve the overall antenna performance, to maintain the best
possible operation for any field conditions. While passive antennas play a role in 5G
networks, it is active antennas that enable beamforming through Massive MIMO
technology. Active antennas support many different use cases with a need for increased
signal strength or configurable antennas. This ensures high throughput with active
antennas.
5G has established new standards for wireless communications, expanding the frequency
ranges above the frequencies used by previous generations. The technology developed for
5G includes FR1, which operates below 6 GHz, and FR2, which includes bands above 24 GHz
and extremely high frequency range above 50 GHz.
Basic principles of Beamforming
A beamforming antenna uses multiple antenna elements to control the direction of a wave-
front. By changing the phase of the individual signals in an antenna array the beam can be
formed at an angle. The plane wave can then be directed in the desired direction.
When pointing the resulting beam at a target receiving antenna in the far-field, the distance
from each element of the array to the target is slightly different. Also, the path length
difference for each signal is d*cos(θ), where is the angle of arrival for the individual signal.
To offset this difference, so that each signal arrives at the same phase, phase shifters are

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applied to each element, resulting in a coherent beam in the far-field. This is called coherent
combining.
Due to the constructive and destructive effects of the combining individual signals in a
directional antenna, the resulting radiation pattern will have many lobes of differing field
strengths at various angles. In this case, the signal strength reaches a maximum, separated
by nulls, angles at which the radiation falls to zero. The main lobe with the highest power is
the intended beam, while the other, smaller side lobes are usually unwanted as they radiate
undesired radiation in unnecessary directions.
Analog and Digital beamforming
There are many methods to implement antenna beamforming. The three main categories of
analogue, digital and hybrid beamforming are briefly introduced below
Digital beamforming: In this method, each antenna element has its own transceiver and
data converters. This makes it possible to generate several sets of signals and apply them to
the antenna elements. The antenna array is able to handle multiple data streams and form
multiple directed beams at the same time. With the ability to form multiple beams, this
antenna type can transmit data simultaneously to multiple receivers, serving multiple users
in a highly efficient manner. Digital antenna beamforming requires more hardware and
signal processing resources but is generally a more adaptable approach.
Analog beamforming: Using the analogue method, there is only a single set of data
converters for the entire antenna, and only a single data stream is handled. This means only
one beam per set of antenna elements can be formed. The data stream is split into several
signal paths, as many as there are antenna elements, and each signal path is fed through a
phase shifter and sent to the individual antenna element. Analog beamforming increases
the gain of the antenna array, providing additional coverage. Downside of the analogue
beamforming is that the whole frequency band has same beam direction.
Hybrid beamforming: This approach combines the two methods above. The antenna array
has subarrays of analogue beamforming, as well as digital combining of the subarray signals.
This reduces energy consumption and design complexity, making it more generally cost-
effective.

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Smart Antennas
Smart antennas are able to analyse their operating environment and alter their antenna
pattern, adjusting their functions appropriately to changing conditions. This enables smart
antennas to achieve improved performance. The development of smart antenna technology
is supported by the deployment of new applications such as software-defined radio,
cognitive radio, MIMO, and many others.
Smart antennas include artificial intelligence, capable of signal processing, and can detect
the direction of incoming and outgoing signals. They also use beamforming to change
transmitted antenna pattern as well as the direction of the transmitted signal. With the
extensive amount of functionality that is required from smart antennas, two major methods
of smart antenna technology have been developed. Both systems have the same basic
function and can provide directivity. However, they differ in cost and complexity, and suited
to different applications:
Switched beam smart antennas: Switched beam smart antennas are designed to combine
the signals of multiple antennas to create several predetermined fixed beam patterns.
These beams are then steered towards one or several specific directions. The SBA can select
the most suitable one for the given situation. This method is not as flexible, but it is a
simple, robust design that is suitable for a lot of uses.
Adaptive array smart antennas: An adaptive antenna array can continuously steer the
beam in any direction and has a more adaptable radiation pattern. Adaptive arrays require
more intelligence and can better determine the surrounding environment. They are usually
more accurate and efficient compared to SBAs since they can better suppress unwanted
beams. In comparison to multi-user MIMO networks, massive MIMO is using a high number
of antennas in the base station. It can be seen as a direct extension of Multi-user MIMO.
Read more about multi-user MIMO and massive MIMO.
How are Beamforming Antennas tested
He we considered testing of large beamforming antenna arrays is considered. Typical
example is a 4G or 5G base station utilizing a beamforming active antenna array. Testing the
OTA performance of beamforming antennas can be divided into two main classes, namely
passive and active antenna testing.
Several Software based OTA test stations are available for testing Beam forming Antennas.

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1. Passive Antenna Testing
Passive antenna testing uses an OTA test method where the test signal is fed directly to the
antenna array, and the outputted RF signal is then measured. The DUT is typically only the
passive antenna array without any active radio unit. This makes passive antenna testing
straightforward and delivers easily comparable results. Passive antenna performance
measurements mainly entail measuring characteristics such as gain, directivity, efficiency,
side lobe ratios etc. Typically, either 2D cross sections or full 3D pattern is measured. Each
antenna port is measured either separately and the beam is formed in postprocessing using
mathematical port weights, or a beamforming combiner device is used to produce the
desired beam at measurement time.
2. Active Antenna Testing
For testing active antennas, a similar environment is used. However, in an active antenna,
the antenna ports are embedded in the device. Most of the RF signal generation steps are
performed in the radio unit itself. The testing has to be performed in active mode, so that
the DUT is in signalling mode, with the radio unit and antenna array operating as it would in
the real network. Due to the tight integration of the radio unit and active antenna array,
more and more parameters that were traditionally measured in a conducted test setup
must be tested in radiated conditions. On the FR1 frequency range, typical parameters
measured over the air include the transmitted power and sensitivity of the base station. In
addition to this, on FR2 all the RF parameters must be evaluated over the air. These include
parameters such as EVM, ACRL, blocking, selectivity, spurious emissions, among many
others.
3GPP Test Methods
At this time, there are multiple OTA measurement system types described in 3GPP (3rd
Generation Partnership Project) test standard for testing beamforming active antennas. The
standards defining conformance evaluation of beamforming active antennas are 3GPP TS
38.141-2 and 3GPP TS 37.145-2. These standards refer to 3GPP TR 37.941, which gives
definitions for the test system types, procedures and uncertainty calculation methods. The
main test system types are indoor anechoic chamber, compact antenna test range (CATR)
and plane wave synthesizer.
1. Indoor anechoic chamber
The indoor anechoic chamber refers to a chamber in which the measurement distance is
sufficiently large so that the DUT is tested in a far field condition, defined by the Fraunhofer
distance. The size of the required test chamber can be quite large, depending on the
frequency and DUT size.

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2. Compact antenna range
The compact antenna test range (CATR) test system utilized a radio frequency reflector. The
radiated signals are reflected from a parabolic reflector to create the far-field condition at
distance shorter than required by the Fraunhofer criterion.
3. Near to far-field method
An alternative approach is antenna near-field measurements using a near-field to far-field
(NF-to-FF) conversion, where the far-field characteristics are calculated using software and
necessary transformation algorithms. This approach considerably reduces the required
distance to measure far-field characteristics. This allows test labs to reduce the size of their
anechoic chambers without losing measurement accuracy.
4. Plane Wave Synthesizer
In a test system utilizing plane wave synthesis, the far field is produced at the test zone
using a plane wave converter. A plane wave converter is a phased antenna array, which acts
as a replacement for a traditional test system antenna. The test signals are fed through the
antenna elements of the converter, and are the amplitude and phase of each element in the
array is controller so that a plane wave field is produced at the test zone.
Beamforming in a nutshell
Beamforming has become a standard technology in boosting the data rates of wireless
communication. It forms the basis of massive MIMO technology and is in use in 5G base
stations and client devices. Beamforming enables adjusting the antenna pattern shape on
the fly, and thus increased adaptivity to the network conditions.
The testing of beamforming antennas brings new challenges, due to increase in integration
between the radio unit and antenna, due to which more and more of test cases that were
traditionally done in a conducted test setup are being done in OTA conditions. Testing of
large antennas requires far field condition capability from the test system, and specialized
test equipment and methods are required to achieve it, especially in active antenna testing.

Introduction to beamforming antennas

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Introduction to beamforming antennas