A. Karbassi

Linear tunable phase shifter using a left-handed transmission line

We demonstrate a compact, linear, and low loss variation hybrid phase shifter using a left-handed (LH) transmission line. For frequencies from 4.3 to 5.6 GHz, this phase shifter gives a nearly linear phase variation with voltage, with a maximum deviation of /spl plusmn/7.5/spl deg/. Within this frequency range, the maximum insertion loss is 3.6 dB, and the minimum insertion loss is 1.8 dB over a continuously adjustable phase range of more than 125/spl deg/, while minimum return loss is only 10.2 dB. Furthermore, this phase shifter requires only one control line, and it consumes almost no power.

Quantitative scanning near-field microwave microscopy for thin film dielectric constant measurement.

We combine a scanning near-field microwave microscope with an atomic force microscope for use in localized thin film dielectric constant measurement, and demonstrate the capabilities of our system through simultaneous surface topography and microwave reflection measurements on a variety of thin films grown on low resistivity silicon substrates. Reflection measurements clearly discriminate the interface between approximately 38 nm silicon nitride and dioxide thin films at 1.788 GHz. Finite element simulation was used to extract the dielectric constants showing the dielectric sensitivity to be Deltaepsilon(r)=0.1 at epsilon(r)=6.2, for the case of silicon nitride. These results illustrate the capability of our instrument for quantitative dielectric constant measurement at microwave frequencies.

Wave propagation in nonlinear left-handed transmission line media

Using a one-dimensional system, we demonstrate a wide variety of wave propagation phenomena possible in nonlinear left-handed media. These include effective second-harmonic generation where the fundamental wave and the second-harmonic wave are badly mismatched. We also observe parametric instabilities accompanying intensive harmonic generation.

Compact Left-Handed Transmission Line as a Linear Phase–Voltage Modulator and Efficient Harmonic Generator

We construct a synthetic left-handed transmission line with cascaded varactors and shunt inductors. By modulating dc bias, the capacitance of the varactors can be changed and modulation of the output phase state is possible. For frequencies from 4.7 to 6.4 GHz, a very linear phase variation versus voltages of over 200deg phase variation with low insertion-loss variation (plusmn0.5dB) is demonstrated. This circuit can also act as an efficient harmonic generator when a large signal is applied. Since the left-handed transmission line shows high-pass filter response, harmonics generated are not seriously attenuated. However, because this synthetic transmission line is a very dispersive medium, strong dispersions and instabilities may arise. The circuit size is determined by the diode size and lumped-element inductor, allowing it to be compact

Quadraxial probe for high resolution near-field scanning rf/microwave microscopy

The authors propose and demonstrate a miniaturized quadraxial probe that employs a differential feed technique for use in near-field rf/microwave transmission microscopy. Their quadraxial probe’s electric field measurements show higher electric field localization than a conventional coaxial (monopole) probe. The improved spatial resolution and more sensitive phase measurement of the quadraxial probe versus coaxial probe are further validated by a metal line scan experiment.

Microfabricated Left-handed Transmission Line Operating at 50 GHz

We report a mushroom-type left-handed transmission line constructed using a microfabrication method, which also yields new opportunities to reduce the structure dimensions, and consequently, increase the operating frequency. Comprehensive characterization using both S-parameter measurement and full wave electromagnetic simulation shows a wide left-handed pass band between 37 and 60 GHz.

Higher harmonic generation and parametric instabilities in left-handed nonlinear transmission lines

Negative-index materials (NIM), also known as left-handed (LH) media, are becoming an exciting reality, Here we present experimental results for harmonic generation and parametric generation in a short left-handed nonlinear transmission line (NLTL) that confirms the general predictions of Kozyrev et al. (2005).

Atomic Force Microscopy Probe with Integrated Loop and Shielded Leads for Micromagnetic Sensing

The effort to produce an instrument that can achieve high spatial resolution, nondestructive, surface and sub-surface imaging for a variety of materials comes with many challenges. One approach, magnetic resonance-force microscopy (MRFM), lies at the nexus of two sensitive technologies: magnetic force microscopy (MFM) and magnetic resonance imaging (MRI). MFM uses a magnetic tip in a standard atomic force microscope (AFM) to obtain magnetic information about a surface. A difference in the magnetic moments of surface atoms in different regions on the surface varies the cantilever resonance. MRI, on the other hand, uses the spin states of magnetically biased atoms to differentiate between chemical species.

Localized microwave measurement using AFM-compatible scanning nearfield microwave microscope cantilever with ultra-tall coaxial probe

We have demonstrated localized microwave measurements using SNMM cantilevers integrated with ultra-tall coaxial tips. Our results demonstrate improved electromagnetic field confinement with enhanced immunity to the parasitic capacitive coupling that is typically associated with SNMM imaging using cantilever based probes. Dielectric spectroscopy capabilities at microwave frequencies are currently being pursued for material characterization in nanometer scale.