# First SIMO Harmonic Radar Based on the SFCW Concept and the HR Transfer Function
## 4 First Measurements Performed with the SIMO HR Setup  
For the first measurement using the SIMO HR setup presented here, the interrogator antenna was placed at distance of 1 m on a scaffold above a wooden table surface. The mixed frequency switched reflection matrix (see Figure 9) was placed below the table surface and propped up using an empty shipping box at a distance of approximately 10 cm below the lower table surface. A picture of this setup is presented in Figure 11. The matrix cell bias optimization routine was executed, with the results shown in Figure 12 and an initial reference measurement was performed to capture the undisturbed propagation paths to all individual cell elements of the matrix. A small metal plate was then inserted into the propagation path on top of the table's surface. Sequential measurements of the propagation paths to each cell element were then performed for different positions of the metal plate. A simple visualization of the measurement results was performed by plotting the change in magnitude for each propagation path normalized to the reference measurement as a change in color for a 3-by-5 pixel bitmap. The setup and general location of the metal plate and the results for the two measurements are shown in Figure 11 on the right and left of the laptop. The relative change in path magnitude is visualized in the color change from blue (equivalent to 1) to a more reddish color (representing values close to 0) in a color gradient. The position of the metal plate can easily be inferred from these plots. The visualization results for a larger metal plate are shown in greater detail on the left side of Figure 13, while the right side shows a visualization of the obstruction imposed by the metal plate upon the matrix as seen from the interrogator antenna's beam boresight in a planar top-down projection during this measurement. Figure 10: Scheme of the digital transponder matrix control circuit. Figure 11: **(Left,right)**: Measurements of the scenario set up for various MUT measurements. **(Middle)**: Ray-casting visualization of the propagation paths in the setup to a row of five cell elements when a metal plate is placed upon the table surface, highlighting the RHCP-polarized 2.45 GHz transmit signal, and the return from three switched tag elements with the LHCP-polarized 4.9 GHz harmonic return signal. Figure 12: Tuning results obtained for each of the HR matrix tag cell elements during the initial element calibration, measured quantity VNA receiver IF power in dBFS over-tuning voltage. The final measurement results presented here are shown in Figure 14 to demonstrate the propagation phase sensitivity of the system. For these measurements, only a single HR tag cell array was used in CW mode at 2.45 GHz, and a small plastic bowl was inserted into the propagation path (blue line in Figure 14). The bowl was then filled to a height of 9 mm with tap water (red line) and finally filled up to the height of 15 mm (yellow line) to avoid a 2 \(\pi\) phase rollover. The DC bias voltage of the cell element was varied during the measurement to demonstrate the dynamic range and phase variability over bias voltage of one HR-cell. Peak conversion gain occurred at a DC bias voltage of 0.45 V, and the plastic bowl and different water height can easily be  
Figure 14: Diagram of the measured harmonic magnitude and phase response of a single HR cell of the array in CW mode (2.45 GHz) when a plastic bowl and subsequent addition of water were added to the propagation path over the DC voltage bias applied to the matrix cell element. Figure 13: Side by side visualization of the relative magnitude change observed by introducing a metal plate in the propagation path. **Left side**: 3-by-5 pixel bitmap color gradient visualization of the magnitude change, blue equivalent to 1, red equivalent to 0.