As a proof of concept, we investigate the possibility of designing a secondary Frequency-Modulated Continuous-Wave radar for ranging at 5.8 GHz by only employing Commercial Off-the-Shelf (COTS) components. The primary objective is modularity, whilst ensuring required signal quality for ranging. Those components can be replaced later with Application Specific Integrated Circuits (ASICs), on the one hand, to test them and, on the other hand, to optimise the radar regarding specific performance metrics. Thus, we evaluate transmitter and receiver architectures. Besides that, research encompass system simulations, Radio Frequency (RF) component selection, filter design, and layout of the Printed Circuit Board. Overall, we propose direct Voltage-Controlled Oscillator modulation with a Phase-Locked Loop for the transmitter and a direct-conversion I/Q receiver. Measurements confirm 22 dBm transmit power and distance-dependent beat frequency, validating operability. One limitation is reference oscillator frequency instability being addressed in future.