Six-Port Radar

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1 General Information

The Six-Port radar is a kind of radar that utilizes a specific principle (the so-called additive mixing property) of the Six-Port network. The Six-Port network was at the beginning developed to be used in a homodyne receiver. However, the principle can be applied to radar applications as well. The Six-Port network is a passive network consisting of six terminals, which are two input ports and four output ports. At the inputs, the two input signals are superimposed with each other under four different relative phase shifts. Depending on the phase difference and the amplitudes of the two input signals, constructive and destructive interaction takes place at the four output ports. A basic diagram of the Six-Port network is shown in Figure 1 [1]. Detailed mathematical analyses can also be found in [1]. A power divider is used to split the input power I1 to the two couplers, where the other inputs of them come from the other coupler that is interfaced with the input I2. The four DC voltages B3 to B6 are extracted from the four outputs O3 to O6 using envelope detectors. When plotted, the DC voltages B3 to B6 become quadrature function of the phase difference between I1 and I2, as shown in Figure 2.

Figure 1: Basic Six-Port Structure Diagram
Figure 2: Four basic Six-Port DC Output Voltages

2 Six-Port Network in Radar

For radar applications, the Six-Port network is normally utilized in monostatic radar configuration, as shown in Figure 3. A voltage-controlled oscillator (VCO) is usually used as I1, while the antenna used at the same time for transmitting and receiving signal is used as I2 (via a coupler or circulator). It is important for the operation of the Six-Port network, that the power levels of I1 and I2 are similar. Therefore a variable-gain amplifier is normally used to amplify the power level of I2 to be similar to that of I1 which is from the VCO. It can be noted in the Six-Port radar that, the frequency from the VCO does not need to be swept, as in the case of FMCW radar.

Figure 3: Monostatic Radar employing Six-Port Network

3 References

  1. 1.0 1.1 Stefan Lindner, dissertation 2017, FAU University Press.