In a communication system or radar system, the antenna model needs to be closely combined with the communication channel or the radar usage scene to work together. This paper studies the communication and radar system simulation compares the antenna models in the two types of systems and summarizes several methods for considering the antenna performance in the current communication terminal and radar system simulation design.

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What is the antenna model in the communication
terminal and the radar system?
By Calio Huang of C&T RF Antennas Inc
Abstract: In a communication system or radar system, the antenna model needs to be closely
combined with the communication channel or the radar usage scene to work together. This paper
studies the communication and radar system simulation compares the antenna models in the
two types of systems and summarizes several methods for considering the antenna performance
in the current communication terminal and radar system simulation design.
1. Introduction
For communication or radar systems, the antenna plays the role of transmitting and receiving
electromagnetic waves. The performance of the antenna will have a great impact on system
performance. Traditional theory and simulation techniques rarely put antennas into
communication/radar systems for overall consideration. Antenna designers focus on the
directionality, efficiency, volume and other indicators of the antenna. The antenna and
transmission channel are rarely considered. It is even more difficult to consider how the antenna
characteristics can affect the system.
This paper summarizes the differences in antenna models and the focus of simulation in two
different systems by studying the methods and system simulation examples of antenna and
transmission channel model modeling in communication terminals and radar systems.
2. Antenna model in the communication terminal
The mobile communication channel mainly has the following characteristics: open
variable-parameter channel, which is susceptible to various interferences; the geographical
environment of the receiving point is very complex and diverse, such as roughly divided into
three categories: urban, suburban and rural; users have random mobility.
Due to the characteristics of the above mobile communication channel, the electromagnetic
wave propagates compared with the free space. In addition to the direct wave, there are many
diffracted waves and scattered waves, and there are different types of losses: path propagation
loss, slow fading loss, and fast fading. Loss. In order to obtain the best reception effect in
different environments, the antenna of the communication terminal is designed as an
omnidirectional antenna as much as possible.
2.1 Single antenna terminal antenna model
For communication system terminals, the antenna model is usually defined by its coordinates and
gain; and the channel model is defined by parameters such as noise, fading, and multipath. For
different types of communication systems, the antenna and channel models are often put
together for comprehensive consideration.
The figure below refers to the most common antenna and channel usage patterns described in
the ADS software. The channel (PropGSM) is located between the base station (AntBase) and the
mobile antenna (AntMobile). The mobile antenna indicator only has information such as gain,
position, and height, speed, etc. The antenna type defaults to an omnidirectional antenna and
the contribution to system performance are mainly gain and multipath effect, Doppler shift.

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Figure 1. GSM system antenna and channel model
2.2 Antenna model in the MIMO system
In mobile communication, the quality of the received signal is degraded due to factors such as
multipath fading and Doppler shift. In order to improve the quality of mobile received signals, the
use of dual antenna diversity reception technology significantly improves the received signal
quality on the premise of low cost and low implementation difficulty. The use of diversity
antennas is to receive more than two uncorrelated signals in order to find the strongest signal or
vector signal synthesis in subsequent processing. Therefore, the lower the correlation between
the antennas, the better. The electromagnetic environment in which the antenna operates varies,
so the wireless environment must be taken into account when measuring the relevance of the
antenna. The transmitter and obstacle total effects can be described by a probability density
function PDF, which characterizes the probability distribution characteristics of the antenna
receiving the strongest signal from different directions.
In addition to spatial diversity, there are polarization diversity cases. The spatial wave polarization
can be described using Cross-Polarization Discrimination (XPD). The larger the XPD is, the larger
the polarization component in the phi direction is. On the contrary, the smaller the XPD, the
smaller the polarization component in the theta direction.
Complex Correlation is used to describe the similarity average received by two antennas under
certain electromagnetic conditions and polarization.
Using some commercial software, such as EMPro, it is possible to set PDF and XPD for a specific
diversity antenna model and consider the effect of dual antenna diversity reception.In the
wireless communication system simulation software, the antenna and channel of the
communication system can be modeled by introducing a three-dimensional pattern of the
transmitting and receiving antennas and their relative positions, combined with a typical channel
model (such as WINNER), thereby simulating system indicators. The following figure shows the
WINNER II channel model in the system simulation software SystemVue, which supports the
introduction of simulation or test multi-antenna pattern, and can set the two-dimensional
relative position of the transmitting and receiving antenna array.

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Figure 2. WINNER channel MIMO antenna model setting
By introducing a simple mobile phone far-field pattern and considering the mobile phone
direction of the SAM human head model, two-channel models are created, which can compare
the ideal working scene and the system capacity under the actual working scene. In this way, the
true antenna pattern and antenna layout can be integrated into the channel model to obtain the
influence of antenna performance on system indicators.
The antenna and channel model can be used not only in the simulation software but also as a
necessary test condition to participate in the standard test. A typical case is Keysight's Radiation
Two-Step Method (RTS).
The two-step method of radiation is to divide the test of MIMO OTA into two steps: the first stage
is to measure the direction of the terminal in the darkroom, and the radiation pattern of the test
piece is measured by the reporting function of the terminal; the second stage is in the first stage.
The detected direction information is loaded into the channel emulator to simulate a wireless
channel containing the characteristics of the antenna of the device under test. The downlink
signal output by the base station simulator is convolved with the wireless channel loaded with
the direction information of the device under test and is transmitted by the measurement
antenna to perform performance test of the receiver.

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Figure 3. Radiation two-step test
The consistency of the two-step measurement and the multi-probe method (MPAC)
measurement that has become the CTIA MIMO OTA measurement standard has been recognized
by 3GPP. The conclusion was formally approved at the 3GPP RAN4 meeting that ended in May
2017.
3. Antenna model in radar system
Unlike the omnidirectional antenna of a mobile terminal, the antenna beam width of the radar
system is generally several degrees to ten degrees. When the radar system works in the search
and tracking modes, the beam direction needs to be accurately modeled.
In the traditional simulation system, the main focus is on the simulation of the signal flow level of
the radar system, that is, considering the signal transmission path and the signal processing result,
and does not consider the influence of the antenna pattern and directivity on the radar system.
For example, in VSS, considering the distance and speed of the target, the transmitting and
receiving antennas are simplified to a gain model, which only affects the signal level obtained by
the receiver. In this system simulation architecture, only some of the antenna's specifications
(such as reflection coefficient, impedance, etc.) can be associated with the cascaded RF system.
For complex application scenarios, it is necessary to consider the position information of the
moving platform (such as a ship, aircraft or chariot) and the antenna. The system simulation
software SystemVue provides a hierarchical design solution, in addition to the signal level analysis,
the position of the moving platform where the phased array radar system is located (such as the
geocentric inertial coordinate system) and speed information, antenna The location information,
etc. are included in the analysis. In this platform, multi-target, multi-station radar can be set, and
multiple antenna settings can be performed.
Figure 4. Three-layer simulation setup of the radar system
In the signal layer, set the basic mode of the antenna's working mode (search or tracking),
antenna pattern, etc. In the antenna layer, set the radar target position, and the roll angle, pitch
angle, and yaw angle of the radar platform. The antenna is in the radar. The roll angle, pitch angle
and yaw angle of the platform; in the track layer, the radar receiving and transmitting platform

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and the position (longitude, dimension, height), pointing, speed, acceleration, motion track and
other information of the target are respectively set. Through the conversion in different
coordinate systems, the antenna pattern and the radar platform, the target's motion trajectory
and other information are comprehensively considered.A complex application scenario for the
radar can be illustrated with an example of an EW receiver test. In the scene, the EW receiver
(EW Rx) is used to monitor four radar stations in space. The mission of the EW receiver is to
detect all of these signals, identify each signal, and organize the position, velocity, time waveform
and frequency content of each radar station.
Figure 5. EW receiver test scenario
In order to test the EW receiver, a test signal must be generated, which does not mean simply
superimposing multiple time waveforms. Since the EW receiver may be mounted on an aircraft,
car or warship, the tool used to generate the test signal must allow the user to specify the
position, speed, trajectory, etc. of the EW Rx station. In addition, for each radar station, the tool
must allow the user to specify its position, speed, time waveform, frequency, antenna operating
mode, etc.
If you need to accurately model the environment, the signal layer simulation software Simulink,
SystemVue, etc. will not be able to do it. Using professional scene simulation software, such as
STK, to model the target pose and environment, you can get more realistic target characteristics.
As shown in Figure 6, the system frequency is generated by using SystemVue, and the
nonlinearity and noise of the RF device are added to the RF transmission path. The time domain
signal enters the STK software through the interface. The STK pre-defines the external site shape
and the aircraft trajectory and flight attitude. The radar is in tracking mode, trying to illuminate
the beam onto the aircraft, while the aircraft makes various maneuvers to evade radar detection.
The time domain signal of the entire scene is returned to the SystemVue software, and the
post-processing program is used to obtain the detection probability of the radar.

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Figure 6. STK joint simulation diagram
4. Conclusion
It can be seen that in the communication or radar system, the antennas no longer appear in an
independent posture, but closely combine with the communication channel, the radar use scene,
and the like, and work together. Antenna designers and communication/radar system designers
can use the existing commercial software and mature theory to integrate the characteristics of
the antenna into the system design, which can greatly reduce the risk of joint adjustment and
speed up product design.