A testing apparatus includes one or more trace banks. Each trace bank includes (1) an input switch operable to couple an input port to one of multiple output ports, (2) an output switch operable to couple one of multiple input ports to one output port, and (3) transmission lines of different lengths coupled between the output ports of the input switch and the input ports of the output switch. The trace banks can be cascaded using cables to connect their output and input ports. The input and output switches in the trace banks are controlled to provide a transmission path of the desired length.