## 2 Radar System and Measurement Setup  
The Soprano radar system was developed at University College London (UCL) in 2014. The radar uses a FMCW architecture operating at C-band with a central frequency of 5.8 GHz. This system was manufactured using commercial off-the-shelf (COTS) surface mount components on an in-house designed PCB [35; 36]. A basic block diagram of the system design can be seen in Figure 1 along with the RF parameters in Table 1. The Direct Digital Synthesiser (DDS) chip used within the system is capable of a bandwidth of 200 MHz but is limited to 83.5 MHz to meet ISM bandwidth regulations in the UK. The system is capable of operating in monostatic or bistatic mode, using an over-the-air deramping (OTAD) technique unique to this radar [35]. However, for all the results presented here the system was only operated in a monostatic configuration.  
Digitization of the output baseband signal was performed using a USB external audio card controlled using Matlab (Natick, MA, USA) on a standard laptop. This is possible due to the low output frequency of the deramped FMCW signal. An external sound card is a good candidate for an Analogue to Digital Converter (ADC) in this case as it is low cost, small, easy to setup, and the data can be read by most programming languages. The sound card has 24-bit dynamic range and is capable of measuring signals up to 98 kHz. As the exact start of a chirp period was challenging to sample, with the slow ADC used, a second channel of the audio card was used to sample the output from a pulse stretching device which elongates the instance of the beginning of the chirp to a duration that can be sampled by the audio card. Through the use of interpolation, it was then possible to break down the long string of data samples into individual chirps which were first windowed using a hanning window to reduce range side-lobes and then filtered using a high-pass Finite Impulse Response (FIR) filter across multiple chirps of data. The FIR filter was applied as part of the Moving Target Identification (MTI) processing on the data to enhance only moving targets within the scene. This data was then Fourier transformed in order to obtain range-time profiles which could be used to identify where a moving target was within the scene.  
The experiments were performed at a UCL test site in Shenley, UK. The building used was a residential house with a brick wall that was approximately 33 cm thick, with a central air gap. The radar system was setup outside of the property with the antennas at a distance of 43 cm from the exterior wall. The room had a floor to ceiling height of approximately 2.4 m and no furniture was present within the area of interest. This represented a very challenging real world scenario for a through wall radar; features such as the chimney-breast, electrical wires, and pipes within the walls all contributed to a complex cluttered environment. The geometry of the building and radar location can be seen in Figure 2, along with an image of the Soprano radar deployment in Figure 3.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Central Frequency & 5.8 GHz \\ Bandwidth & 83.5 MHz \\ Base-bandwidth & 125 kHz \\ Transmit Power & 13 dBm \\ Noise Figure & 2.5 dB \\ Antenna Beamwidth & 30\({}^{\circ}\) Azimuth 30\({}^{\circ}\) Elevation \\ Antenna Gain & 12 dBi \\ \hline \hline \end{tabular}
\end{table}
Table 1: Soprano radar parameters.  
Figure 1: Soprano radar block design.