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Novel system for terahertz power measurements


Photo of the novel 300 GHz detector (1) with an optimized amplifier (2), both manufactured by SLT Sensor- und Lasertechnik GmbH. A radio-frequency system with external frequency doubling from 75 GHz to 150 GHz (3) and then to 300 GHz (4) from Lytid SAS is connected to the detector via the emitting antenna, which is mounted in a special antenna socket (5) of the detector.

Until now, it has not been possible to measure the radiated power of millimeter waves in the terahertz spectral range in the so-called H-band with frequencies from 220 GHz to 330 GHz traceable to the International System of Units. The solution to this problem is a new type of terahertz detector, which was developed as part of a Franco-German cooperation project. The partners in this project called SCAFT (Safe communication at 6G frequencies enabled by precise THz power measurements) were Lytid SAS on the French side and SLT Sensor- und Lasertechnik GmbH and PTB on the German side. This international research and development project was funded on the German side by the Central Innovation Program for SMEs (ZIM). Following the successful completion of the project, the developed prototype was presented to an international audience of experts for the first time at the 11th International Workshop on Terahertz Technology and Applications 2024 in Kaiserslautern.

The rapidly increasing data rates for wireless communication at inevitably ever higher transmission frequencies require precise measurements of the power emitted by an antenna in order to comply with the corresponding safety limits. For frequencies in the H-band, rectangular waveguides are used for transmission from the transmitter to the transmitting antenna. However, due to the tiny dimensions of such waveguides, a power measurement within the waveguide is not possible. The solution is to measure the total radiated power directly at the output of the antenna. Without imaging optics, this measurement must be carried out in the near field of the antenna. A specially developed arrangement of the detector elements ensures that interfering back reflections into the antenna are avoided. Measurements of the spatial distribution of the radiation emitted by the antenna at PTB and corresponding simulations by Lytid SAS made this solution possible. Thus, the uncertainty budget of a calibration of the spectral power responsivity of the prototype detector at 300 GHz manufactured by SLT with the THz laser of PTB can now be determined. In this way, PTB makes a crucial contribution to close the global metrological gap in detector radiometry before new high-technology developments at 6G frequencies are launched on the market.

B. Röben, 7.34, benjamin.roeben(at)ptb.de