## 4 Results
### Calculation of C-PCL System Performance  
For purposes of the calculation of the C-PCL system performance and derivation of the requirements for system components, the following C-PCL structure was assumed (Figure 9). The system consists of two separate transmitters of two sounding signals at f1 and f2 of equal power PT, transmitting antenna and receiving antenna. The antennas are described by the gain parameter, GT for transmitting one and GR for the receiving one. The transmitting antenna is the part of the C-PCL system and the value of the gain GT may be high due to a dedicated design and high directivity. The receiving antenna for the sounding signals is the PCL radar own receiving antenna. The gain GPCL of this antenna depends on the design of the PCL; however, in real-world scenarios there are two solutions used most frequently: first is a conformal array of half-wave dipole antennas (usually eight dipoles) with a digital synthesis of the receiving beam, second is the log-periodic antenna with a gain equal to about 8 dBi used in the additional reference receiver in the PCL structure [2,16,17]. In some solutions, there are linear arrays of unit antennas [18]. In the case of the circular array of dipoles and digital beamforming of the baseband signals in the radar processing, each dipole followed by a LNA amplifier may be treated as a separate PCL receiver. Then, the process of sounding signal reception may be described by a single dipole directive gain. Further, the IMD generation may be analyzed as for a single transistor. The reverse situation becomes more complex. Each of the LNAs in every sub-receiver in the array produce their own IMD signals and emit them back through the dipole. Because of the fact that the dipoles are spatially distributed in a circular way, the incoming sounding signals arrive with different phase shifts depending on the array dimension and the value of sounding frequencies. Then, the IMD products are generated in every LNA and they have different relative phase shifts due to the frequency conversion of phase-shifted sounding signals. Moreover, when the IMDs are emitted back from the dipoles, they are additionally phase-shifted between each other due to the spatial distribution of the dipoles. Therefore, the equivalent transmitting beam of the dipole array with respect to the IMD wave has a directivity depending on the IMD frequency and the direction of the sounding signals arrival. Thus, it is difficult to evaluate the PCL antenna directive gain value by a simple formula to use in a radio link range equation. A further analysis of predefined cases should be performed, where the dimensions of the PCL antenna array, range of frequencies and different angles of arrival of sounding signal are assumed. This analysis should be conducted in order to design a dedicated C-PCL system based on real tactical requirements. For the purposes of further consideration, in this paper the PCL transmitting antenna gain for IMD was assumed to be equal to 2.14 dB - in the worst case with only one dipole and about 5 dB - in the case of a cumulative gain of the array. The reference channel antenna in the PCL, used to direct receive the opportunity signal, is usually of log-periodic \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Power at Input of DUT at f1 and f2 (dBm)**} & **Power of 2f1 – f2 IMD Product at DUT Input (dBm)** & **Analytical Characteristic of Power of 2f1 – f2 IMD Product at DUT Input (dBm)** & **Conversion Loss for 2f1 – f2 IMD Product (dB)** \\ \hline –26.8 & –79.9 & –90.8 & 64.0 \\ –23.9 & –80.2 & –83.0 & 59.2 \\ –20.8 & –75.8 & –75.8 & 55.0 \\ –17.9 & –68.9 & –68.9 & 51.0 \\ –14.8 & –59.0 & –59.0 & 44.2 \\ –11.8 & –49.1 & –49.1 & 37.3 \\ –8.86 & –41.8 & –41.8 & 33.0 \\ –5.88 & –35.8 & –35.8 & 29.9 \\ –2.90 & –30.7 & –30.7 & 27.8 \\
0.14 & –27.4 & –27.4 & 27.5 \\
2.99 & –26.0 & –26.0 & 29.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Measurement results for R820T DVBT USB dongle. or Yagi-Uda type and may be described by a gain equal to about 8 dB.