Armin Parsa

Group-Delay Engineered Noncommensurate Transmission Line All-Pass Network for Analog Signal Processing

A group-delay engineered noncommensurate transmission line two-port all-pass network for analog signal-processing applications is presented, analytically modeled, and experimentally demonstrated. This network consists of transversally cascaded C-sections, which are distributed implementations of the bridged-T equalizer lumped circuit. It is obtained by interconnecting the alternate ports of adjacent lines of a 2N -port coupled transmission line network with transmission line sections, and it is modeled using multiconductor transmission line theory with per-unit-length capacitance matrix C and inductance matrix L. By allowing the different C-sections of the network to exhibit different lengths, a generalized group-delay engineering procedure is proposed, where quasi-arbitrary group-delay responses are achieved by combining the group-delay responses of C-sections with different lengths. A computer design approach based on genetic algorithms is applied for synthesis, which consists of determining the structural parameters of the different C-section groups. Using this approach, noncommensurate networks are group-delay engineered in edge-coupled stripline technology, and Gaussian, linear and quadratic group-delay responses are realized. The theoretical results are validated by experiment. Finally, two application examples of analog signal processing-a tunable impulse delay line and a real-time frequency discriminator-using the proposed dispersive noncommensurate all-pass networks are presented.

Power-Recycling Feedback System for Maximization of Leaky-Wave Antennas' Radiation Efficiency

A novel power-recycling feedback scheme is proposed for systematic maximization of the generally poor radiation efficiency of leaky-wave antennas (LWAs). In this scheme, the nonradiated power at the end of the LWA structure, instead of being lost in the terminating load, is fed back to the input of the LWA through a power-combining system, which constructively adds the input and feedback powers while ensuring perfect matching and isolation of the two signals. As a result, the radiation efficiency of the isolated (or open-loop) LWA η0 is enhanced by the systems gain factor Gs (Gs > 1) to the overall radiation efficiency of ηs = Gsη0, which may reach 100% for any value of η0 in a lossless system. The design of the power-recycling system depends on η0 , which typically results from a tradeoff between required directivity and restricted size. The paper derives, for a rat-race-based implementation, the exact design equations, which determine both the rat-race impedance ratios and the feedback phase conditions of the system. The build-up of the steady-state regime from the transient regime at the onset of the system is explicated by transient circuit and electromagnetic simulations. Finally, an experimental power-recycling LWA system, including naturally ohmic and dielectric losses in addition to other imperfections, is demonstrated, where the isolated antenna efficiency η0 is enhanced from 38% to 68%, corresponding to a system efficiency enhancement of Gs = 1.8 . The proposed power-recycling feedback system applies to all LWAs and solves their fundamental efficiency problem in practical applications involving a tradeoff between relatively high directivity (higher than half-wavelength resonant antennas) and small size (smaller than open-loop LWAs or complex phased arrays).

Ferrite Based Non-Reciprocal Radome, Generalized Scattering Matrix Analysis and Experimental Demonstration

A non-reciprocal antenna radome based on the Faraday rotation effect in a ferrite slab is proposed and analyzed. This radome allows transmission in one direction and attenuates the signal in the opposite direction. It includes two layers of strip gratings on each side of the ferrite slab, consisting of highly conductive strips for proper reflection, and thin highly lossy strips for reflection/dissipation, and three dielectric layers for matching. The radome is analyzed rigorously by the generalized scattering matrix (GSM) method and its performance experimentally demonstrated between two broadband antennas. The measured results show 21 dB and 0.85 dB loss in the isolation and transmission directions, respectively.

Recent advances in micro-structured electric and nano-structured magnetic microwave metamaterials

Some recent advances in wire-type micro-structured electric metamaterials and nano-structured magnetic metamaterials are presented. It is shown that both exhibit rich macroscopic properties leading to novel microwave concepts and devices. The micro and nano scales may be combined in multi-scale metamaterials with unprecedented functionalities.

Novel power recycling schemes for enhanced radiation efficiency in leaky-wave antennas

Two novel power recycling schemes for enhancing the radiation efficiency of leaky-wave antennas are proposed and demonstrated both theoretically and experimentally. The first scheme enhances the radiation efficiency of a single leaky-wave antenna by feeding the energy remaining at the output of the antenna back into its input terminal via a rat-race hybrid coupler. In this manner, the power associated with each information symbol loops several times along the structure until all its energy has been fully radiated, leading ideally to a 100% radiation efficiency. This is the self-recycling scheme. The second scheme enhances the radiation efficiency of a leaky-wave antenna array by re-injecting the energy remaining at the output of the excited element into the adjacent elements of the array via a series feeding network, and possibly including phase-shifters for full-space pencil-beam scanning. This is the cross-recycling scheme.

Comparison of vertically and horizontally polarized radar antennas for target detection in sea clutter — An experimental study

An experimental study of small target detection in sea clutter using vertically and horizontally polarized radar antennas is presented. The experimental study is performed to detect a person in water (PIW) and a fast rescue craft (FRC). The vertically and horizontally polarized X-band radar data were recorded simultaneously from a mobile radar platform located at Cape Spear, Newfoundland, Canada. Two commercial marine radars with grazing angles less than 1° were used. The analysis of the experimental data shows that the vertically polarized antenna is equally effective for detecting small targets at close range and low sea states as a horizontally polarized antenna.

Non-reciprocal ferrite antenna radome : The faradome

A non-reciprocal Faraday effect based radome, or faradome, has been introduced. The generalized scattering matrix (GSM) method has been used to model this faradome. The transmission and isolation of the structure have been verified numerically when excited by a patch antenna. The results have revealed a 7 dB isolation. The proposed faradome may find applications in providing immunity to scattering and interferences. The problem of the currently required magnet may be solved by self-biased nanostructured magnetic materials currently under development in our group.

A fast modeling of the wave propagation inside a rectangular room

A fast modeling of the wave propagation inside a rectangular room surrounded by walls of arbitrary thickness was presented. The solution was based on derivation and evaluation of the Greens function for the separable rectangular room, obtained by separation of variables method. The results for the test cases showed a good agreement when compared with the results obtained by the ray tracing technique.

Edge Diffraction Suppression in Rectangular Dielectric Resonators for Quality Factor Enhancement Using Artificial Plasma

The concept of quality factor enhancement in a two dimensional rectangular dielectric resonator (RDR), based on the phenomenon of edge diffraction suppression by a plasma, is presented. This phenomenon occurs when the plasma exhibits the specific negative permittivity, which makes the RDR separable, i.e., analytically solvable by means of the separation of variables. The Rotman plasma, constituted of metal thin wires is proposed as a practical implementation of this ideal plasma, and the diffraction suppression concept is demonstrated with this plasma by an SIE/MoM approach verified by using a finite element method solver, HFSS. It is shown that a relatively small number of wires (4 times 4) in the plasma is sufficient to mimic a close-to-ideal plasma medium, which suggests a potential for practical applications. This study reveals that the utilization of this plasma allows a strong (high-Q) resonance even for low-permittivity dielectrics otherwise improper to act as resonators.

Double-Band Tunable Magnetic Conductor Realized by a Grounded Ferrite Slab Covered With Metal Strip Grating

The property of a perfect magnetic conductor (PMC) boundary is achieved at two frequency bands by using Faraday rotation in a grounded ferrite slab covered with a metal strip grating. The PMC boundary condition is obtained for the wave polarized perpendicularly to the strips. The two frequency bands correspond to 45° and 90° Faraday rotation across the slab, respectively. In the former case, the strip grating traps the incident rays inside the slab after one round trip in the slab. As a result, the incident ray performs two round trips inside the slab before exiting it. This provides the maximum possible Faraday rotation with the smallest possible slab thickness. The concept is demonstrated experimentally by placing the PMC structure along the sidewalls of a rectangular waveguide so as to produce a TEM wave.