# First SIMO Harmonic Radar Based on the SFCW Concept and the HR Transfer Function
## 5 Upcoming Measurements with the SIMO HR System and Outlook  
The authors are currently in the process of developing and building an automated test setup to move materials and objects under test precisely and repeatable in one dimension through the electronically switched propagation paths of the system to facilitate the development of imaging generating harmonic SAR signal processing algorithms or to train neuronal networks for object recognition and/or feature extraction from the obtained data.  
The mechanical scanning in one dimension was chosen to emulate a much larger mixed frequency switched reflection matrix for the time being until additional funding is acquired. While a 1D-cell line array would be sufficient in this setup, the electronic switching between three rows of lines reduces the measurement time by reducing the amount of precise mechanical movement needed to scan a given number of positions and/or propagation paths.  
It is planned to put the first measurements performed in this setup on the web by the time this article is published. A description of the experimental setup, an explanation of the data format, and the links to the measurement data will be available at the link [[https://www.researchgate.net/project/Mixed-frequency-S-parameter-measurements](https://www.researchgate.net/project/Mixed-frequency-S-parameter-measurements)]([https://www.researchgate.net/project/Mixed-frequency-S-parameter-measurements](https://www.researchgate.net/project/Mixed-frequency-S-parameter-measurements)) from August 2022. These measurements are intended for signal processing oriented scientists who want to perform MUT material analysis and/or MUT/object visualization using this new SIMO HR system without going through all the troubles associated with developing and building a SFCW HR system, as no commercial off the shelf turn-key solution systems are available.  
The SIMO HR system shown here can also be employed in a multitude of configurations otherwise not feasible for transmission based radar and material analysis systems, as no RF cables are required on the far side of the MUT and no mechanical scanning of the radar antenna is necessary. An exemplary massive SIMO setup consisting of several mixed frequency switched reflection matrices oriented throughout a scene is shown in Figure 15. When a sufficient amount of MFSRM units are positioned throughout the scene, a multitude of RF propagation effects such as diffraction, refraction, knife-edge diffraction reflection, and plane wave reflection can be used for feature extraction.  
In larger radar scenes, it would also be feasible to use individual HR tag cells fitted with an independent power source and with a radio data link for switching control to perform complex measurement tasks, such as wall material composition, structure and moisture analysis radar [32; 33; 34], and precise position monitoring of assets such as glacier movement or bridge vibration analysis [35; 36] in harmonic CW doppler radar mode without impairment by clutter.  
Furthermore, the cells used in this first implementation of the mixed frequency switch reflection matrix only employed as passive nonlinear element in its design even though a power supply is available--while suitable for short distances and lower GHz frequencies--this principle can also easily be extended to longer ranges by using cell design based upon an active low power frequency doubler based upon SiGe BJTs [18] or other various active nonlinear elements (see the very good overview presented in [37]) or even extended into the millimeter wave regions for much higher range resolution by using the method shown in [38], which would even allow such applications as millimeter wave body scanners to use a massive MIMO setup.