The millimeter-wave properties of superconducting microstrip lines

We have developed a novel technique for making high quality measurements of the millimeter-wave properties of superconducting thin-film microstrip transmission lines. Our experimental technique currently covers the 75-100 GHz band. The method is based on standing wave resonances in an open ended transmission line. We obtain information on the phase velocity and loss of the microstrip. Our data for Nb/SiO/Nb lines, taken at 4.2 K and 1.6 K, can be explained by a single set of physical parameters. Our preliminary conclusion is that the loss is dominated by the SiO dielectric, with a temperature-independent loss tangent of 5.3 ± 0.5 x 10^(-3) for our samples

High-Frequency Microstrip Cross Resonators for Circular Polarization EPR Spectroscopy

In this article we discuss the design and implementation of a novel microstrip resonator which allows for the absolute control of the microwaves polarization degree for frequencies up to 30 GHz. The sensor is composed of two half-wavelength microstrip line resonators, designed to match the 50 Ohms impedance of the lines on a high dielectric constant GaAs substrate. The line resonators cross each other perpendicularly through their centers, forming a cross. Microstrip feed lines are coupled through small gaps to three arms of the cross to connect the resonator to the excitation ports. The control of the relative magnitude and phase between the two microwave stimuli at the input ports of each line allows for tuning the degree and type of polarization of the microwave excitation at the center of the cross resonator. The third (output) port is used to measure the transmitted signal, which is crucial to work at low temperatures, where reflections along lengthy coaxial lines mask the signal reflected by the resonator. EPR spectra recorded at low temperature in an S= 5/2 molecular magnet system show that 82%-fidelity circular polarization of the microwaves is achieved over the central area of the resonator.Comment: Published in Review of Scientific Instrument

High-Q bandpass resonators utilizing bandstop resonator pairs

A high-Q bandpass resonators utilizing composite bandstop resonator pairs is reported. The bandstop resonator pairs are formed of composite series or parallel connected realizable transmission line elements. The elements are exclusively either quarter-wavelength lines or half-wavelength lines

On the resonances and polarizabilities of split ring resonators

In this paper, the behavior at resonance of split ring resonators SRRs and other related topologies, such as the nonbianisotropic SRR and the broadside-coupled SRR, are studied. It is shown that these structures exhibit a fundamental resonant mode the quasistatic resonance and other higher-order modes which are related to dynamic processes. The excitation of these modes by means of a properly polarized time varying magnetic and/or electric fields is discussed on the basis of resonator symmetries. To verify the electromagnetic properties of these resonators, simulations based on resonance excitation by nonuniform and uniform external fields have been performed. Inspection of the currents at resonances, inferred from particle symmetries and full-wave electromagnetic simulations, allows us to predict the first-order dipolar moments induced at the different resonators and to develop a classification of the resonances based on this concept. The experimental data, obtained in SRR-loaded waveguides, are in agreement with the theory and point out the rich phenomenology associated with these planar resonant structures.MEC (España)-TEC2004-04249-C02-01 y TEC2004-04249-C02-02Comunidad Europea (programa Eureka)-2895 TELEMACAgencia de Subvenciones de la República Checa-102/03/044

Charge Transport Processes in a Superconducting Single-Electron Transistor Coupled to a Microstrip Transmission Line

We have investigated charge transport processes in a superconducting single-electron transistor (S-SET) fabricated in close proximity to a two-dimensional electron gas (2DEG) in a GaAs/AlGaAs heterostructure. The macroscopic bonding pads of the S-SET along with the 2DEG form a microstrip transmission line. We observe a variety of current-carrying cycles in the S-SET which we attribute to simultaneous tunneling of Cooper pairs and emission of photons into the microstrip. We find good agreement between these experimental results and simulations including both photon emission and photon-assisted tunneling due to the electromagnetic environment.Comment: 4 pages, 4 figures, REVTeX

Dynamic pinning at a Py/Co interface measured using inductive magnetometry

Broadband FMR responses for metallic single-layer and bi-layer magnetic films with total thicknesses smaller than the microwave magnetic skin depth have been studied. Two different types of microwave transducers were used to excite and detect magnetization precession: a narrow coplanar waveguide and a wide microstrip line. Both transducers show efficient excitation of higher-order standing spin wave modes. The ratio of amplitudes of the first standing spin wave to the fundamental resonant mode is independent of frequency for single films. In contrast, we find a strong variation of the amplitudes with frequency for bi-layers and the ratio is strongly dependent on the ordering of layers with respect to a stripline transducer. Most importantly, cavity FMR measurements on the same samples show considerably weaker amplitudes for the standing spin waves. All experimental data are consistent with expected effects due to screening by eddy currents in films with thicknesses below the microwave magnetic skin depth. Finally, conditions for observing eddy current effects in different types of experiments are critically examined

Numerical synthesis of filtering antennas

Dizertační práce je zaměřena na kompletní metodiku návrhu tří a čtyř prvkových flíčkových anténních řad, které neobsahují žádné filtrující části a přesto se chovají jako filtrující antény (filtény). Návrhová metodika kombinuje přístup pro návrh filtrů s přístupem pro anténní řady a zahrnuje tvarování frekvenčních odezev činitele odrazu a normovaného realizovaného zisku. Směr hlavního laloku přes pracovní pásmo je kontrolován také. S cílem kontrolovat tvary uvedených charakteristik, nové gi koeficienty jsou představeny pro návrh filtrujících anténních řad. Návrhová metodika byla ověřena na tří a čtyř prvkové filtrující anténní řadě přes frekvenční pásmo od 4,8 GHz do 6,8 GHz, pro šířku pásma celé struktury od 7 % do 14 % a pro požadovanou úroveň činitele odrazu od –10 dB do –20 dB. Celá metodika byla podpořena výrobou a měřením šesti testovacích vzorků filtrujících anténních řad s rozdílnými konfiguracemi. Ve všech případech se simulované a naměřené výsledky dobře shodují.The dissertation thesis is focused on a complete design methodology of a three and four-element patch antenna arrays which are without any filtering parts and yet behave like a filtering antenna (filtenna). This design combines filter and antenna approaches and includes shaping the frequency response of the reflection coefficient and the modelling of the frequency response of the normalized realized gain. The frequency response of the main lobe direction is controlled as well. In order to control the shape of these responses, a set of gi coefficients for designing the filtering antenna array are obtained. The design methodology was verified on the three-element and four-element filtennas over the frequency range from 4.8 GHz to 6.8 GHz; for fractional bandwidth from 7 % to 14 % and for level of the reflection coefficient from –10 dB to –20 dB. The whole design methodology was supported by manufacturing and measuring six test cases of the filtering antenna array with different configurations. Simulated and measured results show a good agreement in all cases.

Low-noise 1 THz niobium superconducting tunnel junction mixer with a normal metal tuning circuit

We describe a 1 THz quasioptical SIS mixer which uses a twin-slot antenna, an antireflection-coated silicon hyperhemispherical lens, Nb/Al-oxide/Nb tunnel junctions, and an aluminum normal-metal tuning circuit in a two-junction configuration. Since the mixer operates substantially above the gap frequency of niobium (nu >~ 2 Delta/h ~ 700 GHz), a normal metal is used in the tuning circuit in place of niobium to reduce the Ohmic loss. The frequency response of the device was measured using a Fourier transform spectrometer and agrees reasonably well with the theoretical prediction. At 1042 GHz, the uncorrected double-sideband receiver noise temperature is 840 K when the physical temperature of the mixer is 2.5 K. This is the first SIS mixer which outperforms GaAs Schottky diode mixers by a large margin at 1 THz