In this test, the SNR of a target object is measured in a radiated Tx-Rx loopback and validated against the link budget analysis. This test combines the Tx output power and Rx Noise Figure into one test and helps to correlate the sensor to the calculated link budget. Any issues in transmitter gain, output power, or receiver gain can be detected by this test. Additionally, this test helps to verify the two-way path losses and noise figure of the system.

Procedure: The corner reflector is placed at a far-field distance inside the anechoic chamber as shown in Figure 2-2. The chirp parameters are chosen appropriately so that it generates an IF of around 1 MHz. The RF sweep is chosen to be within the specified operating range of Radar. One transmitter and all receivers are selected first. The SNR of the FFT signal corresponding to the target is measured for each receiver. This is repeated for all the transmitters. The expected SNR can be calculated from the Radar equation below.

P_t = TX output power

R = Range of object

G_Rx, G_Tx = RX and TX antenna gain

σ = RCS of the object

f_c = Center frequency of the chirp ramp

N = Number of chirps

T_r = Chirp ramp time in seconds

NF = Noise figure of the receiver

SNR = Signal to noise ratio

k = Boltzman constant

T = Effective noise temperature

The Radar equation helps to estimate the expected SNR for a given an object of a given RCS. The RCS of the corner reflector used in the test must be known correctly. Any variables that can impact the SNR such as a radome enclosure or a car bumper should be considered in the calculation. The temperature also impacts the performance of the radar, thus testing should be performed in a controlled environment.

The SNR test should be done for different RF frequencies to cover all the frequencies of operation. The calculated SNR based on the link budget analysis and the measured SNR should be compared to confirm that the radar is operating within the specified bounds.