Comparing the Measured Frequency Characteristics of PCBs with Modal Reservation Before and After Failure at Different Temperatures

Abstract

Introduction . Modal reservation (MR) is a new way of reserving electrical circuits by means of strong electromagnetic coupling between their conductors, which not only increases their reliability, but also ensures their electromagnetic compatibility. Although showing much promise for critical radio electronic devices, MR has so far been studied exclusively at room temperature, without taking climatic conditions into account. Aim . Presentation of the results of an experimental study into the frequency characteristics of printed circuit boards (PCBs) with MR based on coupled microstrip lines under climatic impacts in the form of low and high temperatures to evaluate the MR effectiveness before and after failures. Materials and methods . PCB prototypes based on a microstrip line from a domestic material of the STF brand without and with MR (before and after two types of failure) were manufactured at the Polyus research and production center, Tomsk, Russia. These prototypes simulated the device operation before and after two types of failures. Using a vector network analyzer, frequency dependences of S-parameters of the prototypes were experimentally investigated in a heat-cold climatic chamber at temperatures ranging between minus 50 and 150 °С. Transmission and reflection coefficients in both directions of signal propagation were measured. Results . It is shown that for the working circuit of PCBs with MR, before and after failures, an increase in temperature from room temperature to 150 °С leads to a decrease in the transmission and reflection coefficients in both directions (to a maximum of 2 dB and 29 dB, respectively). Conversely, a decrease in temperature results in an increase in these coefficients (to a maximum of 0.8 dB and 23 dB, respectively). At low and high temperatures, a shift of resonances (up to 500 MHz) towards high and low frequencies, respectively, is observed. Conclusion . The MR effect is shown to remain after failure, having almost no influence on the useful signal, except at high temperatures, at which the operating frequency range of the useful signal can be significantly reduced. Future research should be aimed at reducing the sensitivity of the characteristics to temperature changes by means of selecting other PCB materials, as well as at investigating the radiated emissions from PCBs with MR before and after failures under the impact of climatic conditions.