Adjustable frequency-selective microwave structures based on heterogeneous microstrip transmission line

In this research, the possibility of creating frequency-selective structures in excess of the high-frequency range on the basis of inhomogeneous segments of microstrip lines was investigated. The calculation of a quarter-wave short-circuited resonator on the basis of microstrip line segments with a stepwise inhomogeneity is presented, on the basis of which a two-resonator microwave filter on the basis of microstrip line segments with a stepwise inhomogeneity was calculated. Using the calculations, bandpass filters on the basis of microstrip line segments with a stepwise inhomogeneity with central frequencies of 900 MHz and 1800 MHz were designed and experimentally tested for use in conjunction with GSM modules. Various methods of filter on the basis of microstrip line segments with a stepwise inhomogeneity control were considered: capacitance control by means of an electric field (for example, using varactors); control of dielectric permittivity by means of an electric field (for example, using ferroelectric films); control the effective permeability of the system by changing its geometry (for example, changing the mutual arrangement of parts of the structure using electromechanical transducers); optical control of dielectric permittivity; control of magnetic permeability with the help of a magnetic field; combined magneto-electric control; controlling the conductivity of the material by means of an electric field, lighting, etc. To control the resonant frequencies of the filters on the basis of microstrip line segments with a stepwise inhomogeneity, we chose two methods: controlling the effective permeability of the system by changing its geometry and controlling the conductivity of the material by means of an electric field and illumination. In first case, the control is realized by changing the width of the gap between the substrate and the earth electrode. The air discontinuity (gap) introduced in this way interrupts the lines of force of the electric field of the system, which leads to a strong perturbation. As a consequence, there is a significant shift in the resonant frequency of the system, even with small changes in the width of the air gap. In the second case, optical control was realized by changing the mobility of charge carriers under illumination of a semiconductor GaAs substrate. Experimental samples with these types of controls were created and investigated. The results of measurements are also presented in this paper. An experimental study of the proposed designs showed that in the case of electromechanical control, the frequency change is 10% when the air gap between the substrate and the earth electrode varies from 10 to 100 μm. At the same time, the quality factor of the system remains almost unchanged. For the optical control method, a resonance frequency tuning of 1% was obtained at a Q-factor of 240, which is sufficient for practical use. The shift of the phases of the controlled filter on the basis of microstrip line segments with a stepwise inhomogeneity was investigated. The phase shifter on the basis of microstrip line segments with a stepwise inhomogeneity was calculated and constructed on the previously designed filters. All the results of the phase shifter on the basis of microstrip line segments with a stepwise inhomogeneity studies are also presented in this paper. References 13, figures 6.