Antonio Morini

Constraints to the optimum performance and bandwidth limitations of diplexers employing symmetric three-port junctions

This work addresses the problem of the fundamental limitations to the optimum performance of diplexers employing three-port junctions and preassigned branching filters. In this situation it is a common misconception that optimum results are achieved by utilizing a good power divider closed by two good branching filters. From the properties of the S-matrix of a three-port junction, we show this not to be the case and derive a set of necessary conditions to be satisfied in order that the junction be successfully employed in the realization of diplexers. We derive explicit expressions for the positions at which the filters must be placed in the junction arms for optimum diplexer performance, resulting in considerable simplification of the difficult diplexer synthesis problem. A theorem on the maximum achievable bandwidth is proved and validated by means of two practical examples.

Hybrid modes, substrate leakage, and losses of slotline at millimeter-wave frequencies

Guided, hybrid propagation in a slotline at microwave and millimeter-wave frequencies is discussed. The analysis is carried out rigorously in the space domain, involving the variational solution of a singular integral equation for an E, field tangential to the slot. Data are obtained for field distributions, dispersion, and characteristic impedance, and are compared with data available in the literature. Results are reported on power lost by the propagation mode in the conductors and in the dielectric substrate. The analysis highlights the onset of leakage into a sufficiently thick substrate due to the excitation of a TM (transverse magnetic) surface wave. This sets a high-frequency limit for lossless operation. >

Accurate full-band equivalent circuits of inductive posts in rectangular waveguide

Inductive posts of finite dimensions are currently employed for the precise realization of millimeter-wave filters in waveguides. Although this structure constitutes a classical problem, no true wideband equivalent circuit seems to be available, that is, with elements dependent only on post geometry and, at the same time, capable of describing higher-order mode interaction. The availability of such an equivalent circuit is prerequisite for efficient CAD. A rigorous wideband model, including near-neighbor interaction, that is suitable for accurate filter synthesis and CAD by means of a desk-top computer is developed. Three applications to the design of multipost filters are presented with practical results in excellent agreement with computer predictions. Computation times are such that the analysis can be effected in real time. >

Calibration Protocol for Broadband Near-Field Microwave Microscopy

In this paper, we describe how to define and build a set of known loads to be used in near-field microwave microscopy. Such loads are necessary to set up a microwave calibration kit, enabling local quantitative measurements by the microscope. The proposed protocol is validated through the microscopy system we have recently developed that combines a scanning tunneling microscope and a 70-GHz vector network analyzer.

Analysis and applications of 'microstrip-loaded inset dielectric waveguide' (mig)

The authors investigate analytically and experimentally the properties of the mig (microstrip inset guide), highlighting its features with respect to microstrip and its applications to antenna circuitry. The method used in the analysis is the transverse resonance diffraction (TRD) method in the space domain. The authors discuss dispersion of the first three modes, field distribution, characteristic impedance, and losses of the fundamental mode. They report the experimental antenna characteristics of an array of longitudinal strips, designed as a cascade of mig sections alternating with idg (inset dielectric guide) sections, showing good gain input match and pure polarization. >

Tomographic effects of near-field microwave microscopy in the investigation of muscle cells interacting with multi-walled carbon nanotubes

In this work, we introduce a hybrid atomic-force/near-field scanning microwave microscope, exploiting the tomographic capabilities of the microwave microscopy to explore structures of relevant interest, namely, samples involving both biological and non-biological materials at the same time. In particular, we show imaging of C2C12 muscle cells grown in the presence of bundles of multi-walled carbon nanotubes: here, the microwave microscopy, by virtue of its tomographic potentiality, highlights how cells incorporate some nanotubes in their fibers.

High Resolution Scanning Microwave Microscopy for Applications in Liquid Environment

In this work, we demonstrate a hybrid scanning tunneling microscope/near field scanning microwave microscope featuring nanometric resolution in liquid environment. The system performs an ultra-broadband microwave analysis, since the frequency is swept (up to 50 GHz) for each spatial point of the sample under measurement. A conversion in time-domain allows to disentangle near-field and far-field probe-sample interactions. Results are reported for highly oriented pyrolitic graphite immersed in water, and demonstrate microwave nanometric resolution in spite of the presence of the losses induced by the aqueous environment.

Analysis of compact E-plane diplexers in rectangular waveguide

Photolithographic techniques permit the realization of complex circuits totally confined to the E-plane of millimetric rectangular guides with high precision and low cost. This work contains a detailed analysis of an E-plane diplexer configuration recently introduced. Its main feature is the matching section of the three port junction, a simple abrupt E-plane one tuned by means of an inductive post realized on the same mask as the branching filters. On the basis of this analysis, we also demonstrate the application of a recently developed diplexer synthesis technique. Many prototypes, in K/sub a/-band were designed and tested, showing good performances and good agreement between theory and experiment. >

Broadband Scanning Microwave Microscopy investigation of graphene

In this work we describe the application of a dual-channel scanning probe microscope performing simultaneously Scanning Tunneling Microscopy (STM) and wide-band Near Field Scanning Microwave Microscopy (wide-band SMM) - developed by ourselves- to a graphene flake. In our system we introduce a conversion in Time-Domain to discriminate the desired information, achieving high quality microwave images with nanometric resolution. The graphene sample is deposited on a substrate of SiO2 with an additional deposition of gold (a contact finger). The preliminary measurements seem to show evidence of localized change of impedance near the edge of the flake.

A new adaptive prototype for the design of side-coupled coaxial filters with close correspondence to the physical structure

This paper presents a novel kind of circuit prototype suitable for modeling of coaxial cavity filters, where all cavities are coupled sidewise. Initially, the parameters of the prototype are explicitly derived from those of the classical Cohns inline filter, which is assumed as the starting point. The main feature of the proposed adaptive model is its one-to-one correspondence to the physical structure, making design feasible without additional optimizations or expensive tuning. Another feature lies in that the prototype is adapted to the structure along the way in the synthesis process. A practical example shows the merits and the accuracy of the proposed prototype. The relationships between the proposed method and existing techniques are also discussed.