# Experimental Seaborne Passive Radar
## 2 Materials and Methods  
### System Setup and Signal Acquisition  
A block diagram of the considered PCL receiver is depicted in Figure 1. The hardware setup consists of two dual-channel software-defined radio (SDR) receivers (RSPduo [14])connected to a host PC, a receiving antenna array, and a training signal generator. All tuners in the receivers are tuned to the same frequency of a DAB or DVB-T broadcast station selected for the illumination of a radar scene. The RSPduo devices are connected to the host PC via distinct USB ports used for data transfer and power supply. The training signal generator is controlled and powered from another USB port. It is responsible for the periodical generation of pilot signals that are later employed in the synchronization of the channels [15]. The pilot signals are combined with RF signals from the receiving antennas using a set of directional couplers. After filtering, downconversion, and digitalization in the RSPduo devices, the received complex baseband signals are finally stored in the SSD drive of the host PC for further offline processing. The receiving antenna array installed for PCL experiments on the port side of the ship is shown in Figures 2 and 3 with the proviso that only part of the antennas were used in the experiments described in this paper. Four commercial-grade VHF antennas (Yagi-Uda, 800 \(\times\) 100 \(\times\) 750 mm, 4-element, 6... 8 dBi gain, vertical polarization) were employed to acquire RF signals from the DAB frequency band; three of them in the surveillance path and one in the reference path--installed in the opposite direction. Another set of four antennas (dipole, 200 \(\times\) 700 \(\times\) 100 mm, 2 dBi gain, horizontal polarization) was installed for DVB-T reception. An additional vertically polarized VHF antenna was installed on the front of the ship as a reference, as shown in Figure 3. The surveillance antenna set and the reference antenna were selected individually for each signal acquisition, depending on the experiment's scenario. A DAB transmitter (218.64 MHz, 1.536 MHz bandwidth, 3.2 kW ERP, vertical polarization, 54\({}^{\circ}\)12\({}^{\prime}\)15\({}^{\prime\prime}\) N, 16\({}^{\circ}\)13\({}^{\prime}\)42\({}^{\prime\prime}\) E) and a DVB-T transmitter (191.5 MHz, 7.6 MHz bandwidth, 15 kW ERP, horizontal polarization, 54\({}^{\circ}\)00\({}^{\prime}\)15\({}^{\prime\prime}\) N, 16\({}^{\circ}\)44\({}^{\prime}\)27\({}^{\prime\prime}\) E) were selected as the sources of illumination, both located near Koszalin, Poland (ca. 15 km from the coast). Those transmitters were chosen because of their vicinity to the measurement area. An interesting fact is that DVB-T transmitters usually operate in the UHF band (approximately 400-800 MHz). In Poland, however, some DVB-T transmitters also operate in the VHF band (around 200 MHz), which provided an interesting and unusual opportunity for measurement. Between consecutive signal acquisition sessions, the PCL receiver was alternately tuned to either the DAB or DVB-T channel. In each case, a set of antennas with polarization consistent with the illuminating transmitter was employed. Figure 1: Four-channel receiver used in the experiments. The RF signals were downconverted and digitized in two RSPduo devices (shown in Figure 4), which are compact dual-tuner SDR receivers from SDRplay [14], intended for general purpose SDR applications in the frequency range from 1 kHz up to 2 GHz [16]. The sampling rate was set to \(F_{\mathrm{s}}\) = 2 MHz, which allows it to receive the whole bandwidth of the DAB signal. In the case of the DVB-T signal, only a part of the bandwidth is acquired in this way. The remaining out-of-band components are filtered out through the RSPduo tuner, thanks to internal oversampling and anti-aliasing filters. Figure 3: Top view of the antenna array (**a**) and additional reference antennas on front of ship (**b**) (some parts of the picture are masked for security and privacy reasons). Figure 2: Receiving antenna array installed on the side of the ship.