Signal «crosstalk» effect in the structure of the polarization attenuator channels

An ideal model of a polarization attenuator implies the full absorption of the tangential component of the electric field both in the resistive layer of rotor plates and those of stator plates. In a real attenuator, however, due to the incomplete absorption in the resistive layer of plates the so called “crosstalk” occurs. In most cases the “crosstalk” results in diminished attenuation values of a polarization attenuator. Furthermore, with the high frequencies and especially when the attenuation is high, it significantly affects the attenuation error of a polarization attenuator. This paper analyzes the effect of a series of geometric and electric parameters of the structure of a polarization attenuator’s channels on the “crosstalk” value. As distinct from the well-known calculation methods based on the calculation of separate elements of a polarization attenuator, an algorithm of point-to-point calculation from input to output ports of the entire device is offered. From the general principles of classical electrodynamics, in order to calculate the attenuation of electromagnetic wave in the longitudinal direction of the channel of the attenuator’s conduction system, a formula derived from the method of perturbation theory has been applied. This was possible thanks to an assumption about the weak perturbation of a conducted electromagnetic wave. This condition proves true in the said system thanks to choosing certain correlations between longitudinal and transverse dimensions of the polarization attenuator’s structural channels when the length of a plate with a resistive film is several times greater than the expanding electromagnetic wave as well as to choosing certain upper range values of a film’s surface resistance. From the general correlation of the perturbation theory method a precise expression aimed at defining the attenuation value in a polarization attenuator which is regarded as a result of functioning of geometric and electric parameters with consideration of frequencydependence of attenuation, is obtained. For numerical calculations an algorithm of reprojecting the electric field onto two orthogonal components with respect to a plate from the resistive film followed by defining with the help of the superposition principle the resulting field has been used. This procedure has been fulfilled with respect to each single unit every time the structure in the cross section of the polarization attenuator’s channels appeared heterogeneous. The authors performed the numerical calculations of characteristics of a polarization attenuator with operating frequency range from 53.57 to 78.33 GHz. A diagonally structured graph reflecting the changes of “crosstalk” in function of surface resistance of the film Rп in the range from 300 Оhm/m2 to 700 Оhm/m2 is offered. It graphically explains the physical process of transition from linear region of attenuation to saturation region. Recommendations on choosing Rп are provided. The authors demonstrate how with the use of the widely known in the literature results and the data on calculations provided in this paper one can evaluate the effect, which the heterogeneity of the plate with a film, in the form of out-of-flatness “fractures”, in particular, may have on the “crosstalk”. The numerical evaluations of the effect a diameter of the polarization attenuator channel has on the “crosstalk” are provided in the paper with the help of a double graph illustrating the “crosstalk” value being “expanded” on the attenuation deviations scale. The numerical calculation of the effect of a distortion of the plate with films in input/output ports of the polarization attenuator has been carried out. The paper proves the possibility of linearizing the characteristics and reducing the attenuation errors both by separate regulation of distortion wall in input/output ports and their common interaction. The physical interpretation of the calculation results of the polarization attenuator is provided. It describes the general principles and can be applied to any other operating frequency range of the polarization attenuator.