Physical principles of the design of electrically controllable microstrip devices

Abstract

Electrically controllable microstrip microwave devices are investigated in which liquid crystals, hightemperature superconducting films, or varactors are used as active media. It is demonstrated that comparatively large controllable phase shifts can be obtained using resonant liquid crystal or varactor phase shifters; however, in this case, the working frequency band of the devices become significantly narrower. The possibilities of obtaining maximum frequency tuning of filters whose bandwidth in the tuning frequency range remains unchanged or changes by a preset law are demonstrated. Varactor designs of two-channel power dividers with a smoothly varying division coefficient between the channels are considered. An original device protecting from a radio pulse based on a superconducting film in which total pulse reflection is observed when the pulse power exceeds a preset threshold is investigated.Controllable devices based on microstrip resonators (MSR) with varactor frequency tuning differ by their simplicity, miniature dimensions, and adaptability to manufacture. They are used to design not only filters [1, 2] but also tunable phase shifters [3] and power dividers [4]. Among the advantages of these devices are fairly good agreement of experimental data with the results of high-speed numerical analysis of microstrip devices in the quasi-static approximation. This fact allows effective automated design systems to be developed [5]. It is important to note that specially formed MSR irregularities not only improve the frequency selection properties of the filters, but also considerably expand their frequency tuning range [6]. Therefore, investigation of systems based on the irregular resonators aimed at obtaining extremely high performance of electrically controllable filters is an important and urgent problem. To this end, a dependence of the natural oscillation spectrum on the design parameters of the resonator comprising two microstrip lines with different wave impedances was investigated (Fig. 1а). The high-impedance end of the resonator was connected to a screen through capacity C x . The behavior of the amplitude-frequency characteristics (AFC) in the process of varactor frequency tuning for the two-pole filter based on these irregular resonators attendant to variations of the character of MSR interactions was also investigated.Theoretical investigations of the resonator and filter were performed by numerical calculations for onedimensional models comprising regular sections of coupled and single lines connected in series. The parameters of these lines were calculated in the quasi-static approximation. Figure 1b shows dependences of the natural frequencies for the first and second oscillation modes on the relative length of the high-impedance section of the irregular resonator drawn for w 1 = 5 mm, w 2 = 0.5 mm, l 1 + l 2 = 20 mm, and dielectric permittivity of the substrate ε = 80. Solid curves are drawn for C x = ∞, and dashed curves are drawn for C x = 0. Obviously, these curves correspond to the minimum an...

Magnetically Tunable Resonant Phase Shifters for UHF Band

“…1 the solid line denotes the typical frequency and phase responses of a bandpass filter with central frequency f 0 and bandwidth Δf. If one changes the central frequency of the filter by an offset δf, which does not exceed the bandwidth Δf (dash line Fig.1 The expression for estimating the value of tunable phase shift for resonant structure was presented in [7]:…”

“…So, new approaches in designing tunable phase shifters are desirable. One of them, named resonant, was proposed in [6,7] and developed in a number of works [8][9]. The approach is based on a simple idea that in the filter's passband its phase response is linear and by filter tuning this response shifts along the frequency axis without changing its slope.…”

Split striplines with adjustable parameters and devices based on them

“…There are two main methods to change the parameters of striplines and coupled strip transmission lines. The first method is based on control of dielectric parameters, magnetic or magneto-dielectric medium [1][2][3][4][5]. The second method is based on the introduction of lumped heterogeneities, creating the effect of changing parameters in a limited frequencies range, as this heterogeneity creates a frequency-selective circuit [6].…”

Note: Phase-locked loop with a voltage controlled oscillator based on a liquid crystal cell as variable capacitance

“…[5][6][7][8] However, only a few applications for non-optical applications have been described until now and mainly related to microwave region. [9][10][11][12] As it is well known, the capacitance value for a plane capacitor is given by the following expression:…”