Abstract : We report on the development of an electrically controllable superconducting phase shifter suitable for operation in a terahertz heterodyne receiver. The key physical principle of operation, and that of nonlinear kinetic inductance, is developed into a device theory and also appropriate design rules. Critical figures of merit are then identified and optimized designs presented. Experimental tests of prototypes are described that were used to help further refine the design rules. Although a practical phase shifter was not produced, the prospects for the device concept appear good. Terahertz, Phase-Shifter, Nonlinear, Kinetic Inductance, Superconducting.
A Terahertz Imaging Radar System which exploits superconductive electronics for all of its major components is described in this report. In particular, the importance of the superconducting millimeter(mm)-wave phase shifter in the development of such systems was fully investigated. The experimental and theoretical results presented are better than the authors expected to achieve under Phase I of the project. Conventional technology is unable to provide the high frequencies required to obtain small apertures for target acquisition. Superconducting technology offers a high-performance, very broadband and low-power, mm- and sub-mm wave phase shifter based on superconducting microstrips. The physics of the non-equilibrium superconductivity underlying the operation of the superconducting microstrip phase shifter has been studied. Theoretical analysis and numerous experimental results show that superconducting stripline modulation leading to phase velocity reduction and subsequent phase shift is achievable by quasi-particle injection. A digital N-bit phase shifter based on the superconducting microstrip transmission line is proposed for development. The implementations of such a mm and sub-mm wave phase shifter will fulfill a crucial need in the development of the Terahertz Imaging Radar.
Abstract : A Terahertz Imaging Radar System which exploits superconductive electronics for all of its major components is described in this report. In particular, the importance of the superconducting millimeter (mm) wave phase shifter in the development of such systems has been fully investigated. The experimental and theoretical results presented here are better than we expected to achieve under Phase I of the project. Conventional technology is unable to provide that high frequencies required to obtain small apertures for target acquisition. Superconducting technology offers a high performance, very broadband and low power, mm and sub-mm wave phase shifter based on superconducting microstrips. The physics of the non-equilibrium superconductivity underlying the operation of the superconducting microstrip phase shifter has been studied. Theoretical analysis and numerous experimental results show that superconducting stripline modulation leading to phase velocity reduction and subsequent phase shift is achievable by quasi-particle injection. A digital N-bit phase shifter based on the superconducting microstrip transmission line is proposed for development. The implementations of such a mm and sub-mm wave phase shifter will fulfill a crucial need in the development of the Terahertz Imaging Radar.
The W-Band (
75−110GHz) sky contains a plethora of information about star formation, galaxy evolution and the cosmic microwave background. We have designed and fabricated a dual-purpose superconducting circuit to facilitate the next generation of astronomical observations in this regime by providing proof-of-concept for both a millimeter-wave low-loss phase shifter, which can operate as an on-chip Fourier transform spectrometer (FTS) and a traveling wave kinetic inductance parametric amplifier (TKIP). Superconducting transmission lines have a propagation speed that depends on the inductance in the line which is a combination of geometric inductance and kinetic inductance in the superconductor. The kinetic inductance has a non-linear component with a characteristic current,
I∗, and can be modulated by applying a DC current, changing the propagation speed and effective path length. Our test circuit is designed to measure the path length difference or phase shift,
Δϕ, between two symmetric transmission lines when one line is biased with a DC current. To provide a measurement of
Δϕ, a key parameter for optimizing a high gain W-Band TKIP, and modulate signal path length in FTS operation, our
3.6×2.5cm chip employs a pair of
503mm long NbTiN inverted microstrip lines coupled to circular waveguide ports through radial probes. For a line of width
3μm and film thickness
20nm, we predict
Δϕ≈1767rad at
90GHz when biased at close to
I∗. We have fabricated a prototype with
200nm thick Nb film and the same line length and width. The predicted phase shift for our prototype is
Δϕ≈30rad at
90GHz when biased at close to
I∗ for Nb.
The authors report on a novel microwave phase shifter featuring rapid electronic adjustment, continuous phase control true time delay operation, high device fault tolerance, and very broadband operation. By coupling a large number of superconducting quantum interference devices (SQUIDs) to a superconducting microstrip transmission line, a variable magnetic medium in which the wave velocity is controlled electronically is created. The authors have measured 60 degrees phase shift at 10 GHz, and wideband operation from 5 to 15 GHz for an 8-cm-long Nb transmission line coupled to 1600 SQUIDs, each containing a single Nb/AlO/sub x//Nb tunnel junction. The observed phase shift corresponds to a change in wave velocity of about 1 part in 60.>
We implement a broadly tunable phase shifter for microwaves based on superconducting quantum interference devices (SQUIDs) and study it both experimentally and theoretically. At different frequencies, a unit transmission coefficient, |S21| = 1, can be theoretically achieved along a curve where the phase shift is controllable by the magnetic flux. The fabricated device consists of three equidistant SQUIDs interrupting a transmission line. We model each SQUID embedded at different positions along the transmission line with two parameters, capacitance and inductance, the values of which we extract from the experiments. In our experiments, the tunability of the phase shift varies from 0.07 × π to 0.14 × π radians along the full-transmission curve with the input frequency ranging from 6.00 GHz to 6.28 GHz. The reported measurements are in good agreement with simulations, which is promising for future design work of phase shifters for different applications.