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The detection of buried targets has been a problem of significant interest for decades, with microwave-based sensing constituting an important tool. In this paper, we review the basic issues that characterize microwave-based subsurface sensing. Issues considered include the use of microwaves in the context of an airborne synthetic aperture radar, as well for radars deployed close to the air-soil interface. Rough-surface induced clutter is also discussed. Particular examples are presented for detection of land mines and unexploded ordnance. Index Terms--Ground penetrating radar, synthetic aperture radar, ultra-wide-band.

RF micromachining and microelectromechanical structure (MEMS) technology promise to provide an innovative approach in the development of effective and low-cost circuits and systems. This technology is expected to have significant application in the development of low-cost antenna arrays and reconfigurable apertures, due to its potential to support novel systems architectures. This paper presents a brief history and the state-of-the-art in the development of RF MEMS devices, with primary emphasis on switches and Si-micromachined circuit components for use in high-performance high-density on-water packaged circuits. Index Terms--High-frequency circuits, on-water packaging, RF MEMS, Si micromachining, three-dimensional integration.

The two-dimensional (2-D) hybrid dielectric slab-beam open and closed waveguide systems are suitable for the design of planar quasi-optical integrated circuits and devices. An open system consisting of an active E-plane amplifier array consisting of Vivaldi-type antennas with MESFET and monolithic microwave integrated circuit (MMIC) devices was investigated. The 4 x 1 MESFET amplifier array generated 11 and 4.5 dB of amplifier and system gain, respectively, at 7.12 GHz, and the cascade MMIC Vivaldi-type antenna produced 24 dB of amplifier gain at 8.4 GHz. Also, experiments on a new 2-D H-plane parallel-plate closed system with a stripline slot antenna is introduced, and the wavebeam-mode theory is presented. The new system minimizes scattering and isolation losses associated with open structures. The amplifier gain of the closed system based on slot antennas is compared to the open system based on Vivaldi antennas. Index Terms - Power combining.

In this paper, a preliminary study is carried out to demonstrate the application of wavelets for improving the computation time and reducing computational memory required for evaluating the statistics of the scattered field from rough surfaces using the method of moments (MOM) in conjunction with a Monte Carlo simulation. In specific, Haar and the first order B-spline wavelet basis functions are applied to the MoM formulation of one-dimensional rough surfaces in order to compare the computation time and sparsity for wavelets in the same family but of higher order. Since the scattering coefficient (the second moment of the backscatter field per unit area) is a gentle function of the surface parameters and the radar attributes, it is demonstrated that a relatively high thresholding level can be applied to the impedance matrix, which leads to a sparser impedance matrix and faster computation time. It is also shown that applying a high threshold level the coefficients of the high-order wavelets would increase out of proportion, however, the effect of these current components averages out when computing the scattering coefficients. The resulting sparse impedance matrices are solved efficiently using fast search routines such as the conjugate gradient method. A systematic study is carried out to investigate the effect of different threshold levels on the accuracy versus computing speed criterion. The computed scattering coefficients are compared to previous results computed using a conventional pulse basis function as well as the existing theoretical solutions for rough surfaces. It is shown that wavelet basis functions provide substantial reductions in both memory requirements and computation time. Index Terms--Electromagnetic scattering by rough surfaces, wavelet transforms.

The recently developed multiresolution time-domain technique (MRTD) is applied to the modeling of open microwave circuit problems. Open boundaries are simulated by the use of a novel formulation of the perfect matching layer (PML) absorber. PML is modeled both in split and nonsplit forms and can be brought right on the surface of the planar components. The applicability of the MRTD technique to complex geometries with high efficiency and accuracy in computing the fields at discontinuities is demonstrated through extensive comparisons to conventional finite difference time domain (FDTD). In addition, the numerical reflectivity of the PML absorber is investigated for a variety of cell sizes, some of which are very close to the Nyquist limit ([Lambda]/2). Index Terms--Absorbing boundary conditions, electromagnetic transient analysis, multiresolution methods, open waveguides, perfectly matched layer.

The stability and dispersion performance of the recently developed Battle - Lemarie multiresolution time-domain schemes is investigated for different stencil sizes. The contribution of wavelets is enhanced and analytical expressions for the maximum allowable time step are derived. It is observed that larger stencils decrease the numerical phase error, making it significantly lower than finite.difference time domain for low and medium discretizations. The addition of wavelets further improves the dispersion performance for discretizations close to the Nyquist limit, though it decreases the value of the maximum time step, guaranteeing the stability of the scheme.

Microwave and millimeter-wave systems have generally been developed from a circuit perspective with the effect of the electromagnetic (EM) environment modeled using lumped elements or N-port scattering parameters. The recent development of the local reference node concept coupled with steady-state and transient analyses using state variables allows the incorporation of unrestrained EM modeling of microwave structures in a circuit simulator. A strategy implementing global modeling of electrically large microwave systems using the circuit abstraction is presented. This is applied to the modeling of a quasi-optical power-combining amplifier. Index Terms - Circuit field interaction, circuit theory, electromagnetic analysis, global modeling, method of moments, microwave circuits, nonlinear analysis.

Focuses on the concept of three-dimensional (3-D) circuit integration using silicon bulk micromachining. Integration and packaging of radio frequency systems; Components for 3-D integration and on-wafer packaging.