Mi-Wave radar target simulatorRadar Target SimulatorRTStrihedral corner reflector

Radar Test: Target Simulation and Calibration Reflectors

No real targets and no field trips: synthesize range, velocity and RCS echoes electronically, then calibrate the whole radar back with a trihedral reflector of known RCS.

Mi-Wave millimeter-wave components and production facility

In short

The most time-consuming part of radar development and production verification is not the algorithm but the target: real vehicles, aircraft and obstacles are neither repeatable nor movable into a lab. A radar target simulator (RTS) receives the radar's transmitted signal, applies attenuation, phase delay and I/Q modulation, and re-radiates it from an antenna so the radar interprets it as a real echo at a chosen range, velocity and RCS. A trihedral corner reflector provides a theoretically calculable, known RCS as the calibration reference for the measurement chain. This article covers how an RTS works and its signal flow, how to choose and place corner reflectors and their limits, and the millimeter-wave components used in the test setup: 18–110 GHz standard gain horn antennas, 8–110 GHz variable attenuators and directional couplers, 18–325 GHz isolators, 7–110 GHz low noise amplifiers and waveguide-to-coax adapters. The simulator and reflector units themselves can be quoted and supplied through Mi-Wave.

Why physical targets are not enough

A radar has to be verified on three axes: does it read range, velocity and target strength correctly. In a real environment those three can almost never be controlled independently. Making a target approach at a fixed speed, turn back at a fixed range and keep a constant RCS is not achievable in a field trial, and nobody can schedule a road test for every automotive radar on a production line. Unrepeatable targets make results impossible to compare, and when something fails, nobody can tell whether the radar, the algorithm or the site is at fault.

Frequency band is the other problem. Automotive, industrial sensing and aerospace radars now commonly operate in the K, V, E and W millimeter-wave bands, where the wavelength is a few millimeters. Indoor multipath and people walking past change the echo, and an anechoic chamber is expensive to build and maintain, so most development teams cannot book chamber time for every firmware revision. What the lab needs is a device that turns the target into a set of parameters, so CW, FMCW and pulsed radars can all be tested repeatably on a bench.

How a radar target simulator works

Radar target simulator main unit — Radar target simulator

An RTS does not create distance in space. It receives the radar's transmitted signal, applies controlled changes to its amplitude, phase and I/Q characteristics inside, and re-radiates it toward the radar receiver. The radar treats the processed signal as the echo of a real target. The whole device is a hardware-in-the-loop system and needs an external I/Q waveform generator (AWG or DSP), scenario software, and a synchronization trigger interface for coherent operation with the radar.

The signal flow breaks into seven steps: the radar transmits toward the simulator antenna; a circulator routes the signal into the internal RF chain; an attenuation stage represents target strength and range; I/Q modulation introduces Doppler and motion; the processed signal returns through the circulator and a directional coupler; the antenna re-radiates it to the radar receiver; and the coupled port provides a sampled copy for monitoring and calibration. Every element in that chain is a standard millimeter-wave component from the Mi-Wave catalog.

What controls range, velocity and RCS

RCS versus angle curve of a trihedral corner reflector — RCS versus angle

Range is expressed by phase delay and signal strength together: a strong signal with a short phase delay reads as a near target, a weak signal with a long delay as a distant one. Velocity is synthesized from the baseband I/Q signal through the Doppler relation fd = 2v/λ. The phase difference between I and Q sets whether the target approaches or recedes, the I/Q frequency sets the speed, and time-varying I/Q profiles represent acceleration, micro-motion and multi-target scenarios. The maximum simulated velocity is limited mainly by system bandwidth and configuration.

Target size and RCS are controlled purely by attenuation: more attenuation gives a weaker echo, which the radar sees as a smaller or more distant target, and less attenuation the reverse. This is why the repeatability and frequency-response flatness of the attenuator directly set the simulator's credibility. If the attenuation drifts with frequency, an FMCW radar sweeping across the band sees the target strength change with it, which a real target would not do. Likewise, the stability of the phase-delay stage sets the repeatability of the range reading. Both must be verified together during system calibration.

Trihedral corner reflectors: a known-RCS calibration reference

Trihedral corner reflector geometry — Trihedral corner reflector

The target strength a simulator produces needs an absolute reference to calibrate against, and that reference is usually a trihedral corner reflector. Three mutually perpendicular conducting plates return an incident wave precisely along its arrival direction after multiple reflections, so a small body has a very large RCS, and the theoretical value follows directly from edge length and wavelength (RCS scales with the fourth power of edge length and inversely with the square of wavelength). Compared with a dihedral reflector, the trihedral has a wider half-power response angle, tolerates misalignment better and is faster to set up in the field.

A few limits apply in use. The theoretical formula assumes free space; the ground and other nearby reflectors shift the real value. RCS falls sharply as the incidence angle approaches parallel to a plate. If the reflector is tilted forward so the direction of maximum RCS makes a shallow grazing angle with the ground, ground-lobe effects ruin the accuracy of the calculation. Manufacturing precision matters most: the three plate pairs must meet at exactly 90°, and a very small angular error degrades the response severely, so calibration reflectors should not be shop-made.

Millimeter-wave components in the test setup

The antenna is the only interface between simulator and radar. The Mi-Wave 261 series standard gain horn antennas cover 18–110 GHz with several gain options in each of the V, E and W bands; the gain is precisely calibrated and the pattern stable, so the horn itself serves as a calibration standard for antenna measurement. Attenuators cover 8–110 GHz in manual dial, micrometer and electronically programmable versions, the last of which suits direct RCS control from the scenario software. Directional couplers offer 10/20/30 dB coupling with directivity above 30 dB and provide the monitoring tap in the signal flow.

Isolators protect amplifiers and sources from reflected signals: the 115 series Faraday-rotation type covers 18–325 GHz with 20–25 dB isolation, and the 178 series Y-junction type has insertion loss as low as 0.4 dB. Low noise amplifiers cover 7–110 GHz and compensate link loss in the receive front end. Waveguide-to-coax adapters (8–110 GHz, with 2.4 mm, 2.92 mm and 1.85 mm interfaces) connect the waveguide chain to instruments and cables. The whole chain assembles on standard waveguide flanges, so once the band is chosen the components mate directly with no extra allowance for adapter loss or VSWR mismatch.

From components to a complete system

A radar test setup usually starts from three questions: which band the radar operates in, how wide the simulated range and velocity spans must be, and whether multi-target and dynamic scenarios are required. The first sets the waveguide size and the band of every component; the other two set the bandwidth of the I/Q waveform generator and the dynamic range of the attenuator. If only the receive chain and antenna need verification, one horn antenna plus one corner reflector of known RCS completes a basic calibration; a full RTS is needed only for algorithm and production-line testing.

Evencat is the authorized Mi-Wave distributor in Taiwan and can help select antennas, attenuators, couplers, isolators, amplifiers and waveguide parts by band and flange specification, with component measurement data and technical support. Radar target simulators and trihedral corner reflectors are not in the standard catalog; they can be quoted and supplied through Mi-Wave on request.