Hybrid design approach for the design of high-frequency components in MID technology

The digitalisation of industry and especially the IIoT (Industrial Internet of Things) requires ever more powerful and smaller devices, such as sensors and actuators. These are more and more battery-powered and communicate in a wireless way. The MID technology enables easy integration into existing systems and machines due to the free shaping. This is particularly important for retrofit applications, where the installation spaces are fixed and can not be modified.The integration of antennas and microstrip lines on the surfaces of the MID bodies enables a high degree of miniaturisation of these components, as costly assembly and adjustment of the antennas is not necessary. However, it is essential that the dimensions of the antennas and microstrip lines are precisely matched to the matter parameters in order to function correctly. Otherwise, the resonance frequency of the antenna is detuned or the line impedances do not match. This would significantly impair the transmission and receiving characteristics of the IIOT device and thus significantly restrict its operability by reduction of the antenna radiation efficiency. For the designer of the circuit, the challenge is that often the dielectric material parameters of the used substrate material are not available or not specified in the required frequency range. Especially by adding additives and aggregates, the electrical material parameters permittivity, permeability and loss angle tan(delta). The determining of the electrical material parameters is a complex measuring procedure and requires special measuring equipment. In addition to a vector network analyser, special material fixtures and a measurement software tool are required. Furthermore, the material samples must be precisely fitted to the test fixture used. Then the material samples must be prepared, polished flat, in order to avoid measurement errors due to air pockets. This makes electrical material characterisation very complicated and cost-intensive. The following article describes the procedure for determining the electrical material parameters by means of an MID cavity resonator. Here, the principle of mode excitation is applied. Where the resonance frequency is determined by the known dimensions of the resonator and the unknown material parameters. By means of the network analyser, the S parameters of the resonator are acquired. Here, different spatially placed ports are used to avoid local zeros. Subsequently, an exact 3D model of the resonator including the SMA connectors is created and a corresponding fullwave simulation is carried out over the previously measured frequency range. This eliminates the complex de-embedding process of the SMA connectors. In an optimisation process, the characteristic impedance of the material model is adapted to the characteristic behaviour of the measurement. If these match, the permittivity and the loss factor can be derived directly from the material model.