Wideband Millimeter Research Articles

High resolution imaging of objects at Ka band

A coherent wideband millimeter wave (mmW) imaging radar which operates in two different imaging modes is briefly described. The principles of two-dimensional (2-D) high resolution imaging are introduced. The image reconstruction algorithm together with image enhancement techniques are discussed. Some experiments imaging on both scaled aircraft model and full-size large scale vehicle are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-electron-mobility-transistor gain stability and its design implications for wide band millimeter wave receivers

Advances in the noise performance and frequency range of high-electron-mobility-transistor devices have led to an increase in their usage in systems below ∼100 GHz. In light of these developments, the effects of low frequency noise upconversion on the performance of the current GaAs device generation are investigated. A spectrum of gain fluctuations characterized by δg2(f)=δg21/(f/1 Hz)α, with α≂0.9 and a spectral density at 1 Hz of δg21≂12 GHz−1 is observed in 45 GHz low noise cryogenic amplifiers. The measured level of fluctuations is in agreement with theoretical device scaling stability predictions. The presence of these fluctuations will limit continuum receiver performance with bandwidths greater than ∼1 GHz under typical operating conditions. The implications of these measurements on the design of wide band receivers and means of reducing sensitivity to gain fluctuations are discussed.

Copolarized and cross‐polarized enhanced backscattering from two‐dimensional very rough surfaces at millimeter wave frequencies

Wideband millimeter wave experiments from 75–100 GHz on the scattering from two‐dimensional very rough conducting surfaces are presented. The two‐dimensional very rough surfaces are manufactured using a computer‐numerical‐controlled milling machine so that the surface statistics are precisely controlled. The surfaces have both Gaussian roughness statistics and Gaussian surface correlation functions. Bistatic scattering experiments on surfaces with either isotropic or anisotropic correlation functions are performed. Copolarized and cross‐polarized bistatic scattering cross sections are measured for both transverse electric and transverse magnetic incidence at 20°. For isotropic surfaces, backscattering enhancement exists for both copolarized and cross‐polarized returns and is found to be a function of the surface rms slope. In addition, a strong frequency dependence is observed across the 25‐GHz bandwidth in the cross‐polarized returns. To investigate the effect of surface correlation anisotropy, scattering experiments on anisotropic rough surfaces are also performed. It is found that the bistatic scattering cross section for an anisotropic surface is a function of the effective correlation length projected along the plane of scattering. Results on the bistatic scattering experiments presented here serve as a motivation to further pursue more elaborate and complete scattering experiments in order to advance research on scattering from very rough surfaces.