Application Briefs

Radar cross section (RCS) is the measure of an object's ability to reflect radar signals in the direction of the radar receiver, i.e. it is the measure of the ratio of backscatter per steradian (unit solid angle) in the direction of the target radar to the power density intercepted by the target. RCS measurements help ensure the design of commercial and military aircraft and radar systems, as well as to maintain their performance once they are deployed.

Figure 1. Radar range equation diagram.
Accuracy in measuring RCS can have a direct result on safety and successful aviation operations. In military, stealth technology is used to reduce RCS and make it difficult to detect aircraft. For commercial planes, a large RCS is necessary, so air traffic radar systems can easily locate aircraft and help guide them during take-offs and landings. For reference, tactical jets typically have RCS ranging from 5 to 100 m2, whereas bomber jets usually have an RCS from 10 to 1000 m2. By contrast, stealth aircraft exhibit RCS under 0.1 m2, with some advanced designs under 0.0002 m2.

Figure 2. Simple block diagram describing the physical representation of a radar.
Vector Network Analyzers (VNAs) have become the instrument of choice when measuring RCS because of their speed and accuracy in making S-parameter measurements. Advances in handheld VNAs have allowed them to deliver the necessary performance, as well as features such as time domain gating, to simplify RCS testing on the flight line or in the field.

Radar Range Equation

Figure 3. Circuit diagram of the radar depicted in Figure 2.
The radar system in Figure 1 transmits a pulse of energy through the transmit antenna of gain (Gt). Signal amplitude at the output of the transmit antenna is reduced by the free space propagation loss. At the target, some of the power (backscatter) is reflected back towards the radar. The ratio of the backscatter power to the incident power is the RCS (σtgt) of the target. Amplitude is further reduced by the free-space propagation loss. Then, the signal is received by the receive antenna with gain (Gr) and detected in the receiver.