Eravant offers Doppler Radar Target Simulators for Radar manufacturers and developers to test and evaluate their Radar systems’ performance in an economic way by replacing expensive and time-consuming field tests. The standard models are offered to cover common radar frequency bands of 24.125 GHz, 35 GHz, 77 GHz, 79 GHz and 94 GHz with an operating bandwidth from ±100 to ±250 MHz, respectively. The actual operating bandwidth can be extended to ±500 MHz and up to ±1,000 MHz for 77 GHz, 79 GHz and 94 GHz models. While the level setting series is a lower cost version more geared up for production “go or no go” testing, the direct reading series is for R&D project setups, where the quantified Radar sensitivity information is the interest. It can give exact sensitivity information by reading the dB difference from the attenuator directly after calibration, for instance, a 6 dB attenuation reading increase on the direct reading attenuator indicates that the DUT Radar detection distance is increased by 100%. Figure 1 and Figure 2 shows the level setting and the direct reading 77 GHz Radar simulators, respectively. Various antennas, such as Eravant's SAR series can be selected from Eravant’s standard antenna offerings and added to the antenna port. These Radar Target Simulators are designed and fabricated for Doppler Radar Target Simulation, which will simulate the Radar Target Size, the Speed of the Radar Target and Moving Direction of the Radar Target.
Figure 1. Level Setting Series
Figure 2. Direct Reading Series
The core technology implemented in the Doppler radar simulators are single sideband modulator-based with the following working mechanism. The radar signal emitted by the Radar (Device) Under-Testing (DUT) is received through the antenna port and fed into the single sideband modulator through a diplexer. The single sideband modulator modulates the incoming signal and sends either upper or low band signal back to the diplexer. The frequency shifted signal is transmitted back to the antenna as Doppler signal for the DUT to receive. The amount of frequency shifting equals the input modulation frequency, i.e., the intermediate frequency (IF). By adjusting the intermediate frequency (IF), the phase of the IF’s “I” and “Q” channels and the routing attenuation, the speed, direction and radar cross-section of the Radar target can be simulated. The amplitude of the input modulation frequency is ±10 Vp-p.
The simplified block diagram of the simulator with the signal flowing is shown in the Figure 3.
Figure 3. The Simplified Block Diagram with the Signal Flow of the Radar Simulator
It is well known that the relationship between the Doppler frequency and target speed is governed by the following equation:
Where:
FRF is the frequency of the transmitted frequency from DUT Radar in Hz
C is the speed of light (3 x 108 meter/sec.)
V is the target speed in travel in meters/sec.
ϴ is the angle between the moving target and the radar beam. The two extremes are 1) no Doppler shift Fd = 0 when the moving target direction and radar beam are perpendicular (ϴ=90°) and 2) Fd = 2 V FRF / C when the moving target direction and radar beam are parallel or ϴ is very small (0 to 10°).
Some Doppler Shifts (Intermediate Frequency) in common microwave and millimeterwave bands are listed in the table below if the Radar is aiming the target directly, i.e., ϴ=0°.
To operate the simulator, a function generator capable of delivering two orthogonal output signals (IF-I and IF-Q) in the frequency range of Doppler shift of the DUT due to the target speed and the 10 VP-P equal amplitude is required.
Once the function generator is located and set up for operation, follow the steps below to operate the Doppler Target Simulator.
1. Use a function generator which can deliver two orthogonal sine wave signals (IF-I and IF-Q) in the frequency range of the TBD target speed and ±10 Vp-p amplitude level. For example, if the interested target speed is at 80 kilometers per hour and your radar under testing is at 24.125 GHz (Fo), the IF-I and IF-Q frequency is 3,575 Hz.
2. Connect the output of the function generator to the IF inputs of the simulator.
3. Select a proper antenna, such as, SAR series, from Eravant’s standard offerings and install it onto the antenna port.
4. Emit the radar signal from the DUT radar system towards the simulator antenna port (ANT). The returned Doppler shifted frequency Fo+IF or Fo-IF is received by the Radar and the Radar will display the speed of the target.
5. Vary the frequency of the function generator to simulate the speed of the target.
6. Vary the phase of the function generator (the phase difference of the IF-I and IF-Q signal, 90 or –90 degrees) to simulate the direction of the moving target, i.e., approaching and receding target.
7. Vary the path attenuation by adjusting the attenuator value to simulate the target radar cross section or the distance. While the level setting attenuator can only give relative ranging (distance) information, the direct reading attenuator can give the exact ranging information directly after system calibration by using the Radar Equation.
To measure the relative sensitivity of the DUT Radar, a variable attenuator is added to the antenna port of the simulator. From the famous Radar Equation shown below, one can estimate the Radar detection range by reading the attenuation value from the attenuator.
Where:
Pr is returning power to the receiving antenna
Pt is the transmitting power
Gt is the gain of the Radar antenna
Rt is the distance from the Radar to the target
Click Here to watch Eravant's Doppler Radar and Basics and Setup video.