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Backscatter signatures of multiyear sea ice (MYI) during the late summer and early fall season before the fall freeze-up in the Canadian Arctic Archipelago (CAA) have been obtained through the use of a ship-based polarimetric scatterometer. The device operates in C-band, and measurements were conducted in swaths from incidence angles of 20[degrees]-60[degrees]. Three characteristic sites on MYI floes were investigated in the high Arctic and the central Arctic regions. In situ snow and sea-ice thermophysical data were collected at each site in conjunction with local scatterometer measurements. The thermophysical data were subsequently analyzed using dielectric modeling techniques and coupled with the backscattering measurements ([sigma][degrees]). Observed backscatter values and ratios were found to be in agreement with literature data, with volumetric scattering as the dominant scattering mechanism. Index Terms--Canadian Arctic, multiyear sea ice (MYI), polarimetric radar, remote sensing, snow.

The polarization characteristic of unloaded and loaded square-ring microstrip antennas is investigated. Several different loading types like single-stub, dual-stub, notch, gap and shorting-pin are considered and their effects are studied. Loading enables feeding using a 50-[OMEGA] probe. The simulation and measurement results show that the loading techniques excite a loaded [TM.sup.y.sub.11] mode that is orthogonal to the unloaded [TM.sup.x.sub.11] mode. This indicates that by loading the ring antenna its polarization can be switched adaptively. However, the purity of the loaded and unloaded modes depends on the loading type. For some loading types like gap and shorting-pin, the excitation of the unloaded mode seems negligible in comparison to the loadings by stub and notch. For the stub and notch loaded antennas the unloaded mode is also present, and its excitation efficiency is frequency dependent. Thus, their polarization plane, which is due to both loaded [TM.sup.y.sub.11] and unloaded [TM.sup.x.sub.11] modes, also becomes frequency dependant. The results of this investigation can be useful in selecting the loading methods for high-impedance microstrip ring antennas, and control of their impedance and polarization. The knowledge of the antenna polarization is essential in communications, and its dependence on the loading type can be used as an important parameter in design of adaptive antennas and sensors. Index Terms--Microstrip antennas, polarization, square-ring antennas.

A new application for reflector antennas is proposed and developed. Using the aperture theory, a phase center on the reflector aperture is determined and shown that, its location is dependent on the field distribution. The proposed concept is, initially, verified by using a symmetric reflector. It is shown that the phase center is located at the aperture geometric center, when the reflector is illuminated symmetrically about its principal planes. Then, a dual mode feed, employing [TE.sub.11] and [TM.sub.01] modes, is used for generating different reflector illuminations, and causing displacement of its phase center. The concept is then extended to offset reflectors, and the influence of the reflector geometry on the phase center displacement and other reflector electrical parameters is investigated. Based on the established feed radiation pattern requirements, a feed horn is designed using circular waveguide that can propagate both modes. By modifying the amplitude and phase of the modes in the horn, a controlled asymmetric reflector aperture field is achieved. A prototype feed horn is fabricated and tested for its dual mode radiation patterns. The results are in good agreement with simulations. The reflector phase center properties are then investigated, by using the designed feed. A reflector-feed assembly, with its dual phase center capability, was developed for improving the performance of the ground moving target indicator radars. The concept allows the conversion of a single reflector to two or more reflectors, simply by modifying the mode excitation amplitudes and phases, in the feed alone. Index Terms--Beam shift, dual mode, feed horn, ground moving target indicator (GMTI) radar, multiple phase center, reflector antenna.

In this paper, the far-field phase shift properties of microstrip patch antennas are investigated. It is shown that, similar to reflectarrays, the resonant nature of microstrip patches can be used to change the phase of the radiated field. This phase change can be caused by the dimensional change of the microstrip patch, or by a reactive loading of its cavity such as an aperture on its ground plane. However, the available phase shift is limited by the antenna impedance bandwidth. The problem is initially investigated for conventional patch antennas, determining the available phase shift range. It is then studied for a wideband E-slot microstrip antenna, showing a considerably larger phase shift range. Then, a micro-electro-mechanical (MEM) based ground plane membrane, activated by an electrode from below, is proposed to adaptively generate and control the required phase shifts. It provides a low loss, continuously variable phase shifter that can be used at high frequencies for beam scanning in small arrays. Index Terms--Far-field phase shift, frequency tuning, microstrip antenna, microstrip array, phased array.

This paper presents the investigation results on the beam focusing properties of a wire circular monopole array (CMA) antenna consisting of six-elements on a finite ground plane, by exciting more than one monopole at a time. The excitation of more than one element provides enhanced horizontal and vertical plane peak directivities, and a reduced 3 dB beamwidth for the horizontal pattern. The effect of varying the number of monopole elements in the array is also discussed, when only one element is excited, and the remaining ones are shorted to the ground. The antenna was fabricated and tested for its impedance and radiation characteristics for one of the excitation schemes, and the results were found in reasonable agreement with the simulations. Index Terms--Beam focusing properties, circular monopole array (CMA), finite ground, multiple excitations.

Reduced size microstrip monopole slot antennas with different slot shapes--straight, L and inverted T, and placed on a small ground plane, are investigated. The ground plane size is 50 mm x 80 mm, which is about the size of a typical PC Wireless card. Detailed simulation and experimental investigations are conducted to understand their behavior and optimize for broadband operation. It is shown that, the variation in the slot shape, from straight to L and T shapes, helps in generating additional resonances, which when coupled to the original resonances of the slot, further increases impedance bandwidths. The bent shapes of the L and T slots reduce their height and provide more space on the ground plane for electronics. A mirror image dual L-slot antenna, placed at two adjacent corners of the ground plane, is also investigated and optimized for the polarization diversity. They provide an impedance bandwidth of 87%, with near orthogonal radiation characteristics. The measured impedance bandwidths ([S.sub.11] = -10 dB) of up to 60%, 84%, and 80% are achieved for these straight, L and inverted T slots respectively, by suitably selecting their design parameters. The simulation results are in good agreement with the experimental data considering several practical issues. Index Terms--Dual slot antenna, finite ground plane, microstrip line feed, microstrip slot antenna, monopole, polarization diversity, wide bandwidth.

This paper presents the investigations on a miniaturized vertically polarized traveling wave antenna for operation in the high frequency band (3-6 MHz), with a specific requirement of keeping its height near 1/8th of a wavelength. The antenna is desired to have a good endfire gain and front to back ratio, and small radiation levels in the vertical direction at broadside angle. A log-periodic Zigzag antenna (LPZA) has acceptable performance in both gain and polarization. Its height however is large, at about one wavelength (1[[lambda].sub.L]). The concept of fractal antenna is employed in this antenna to achieve the necessary height reduction to [[lambda].sub.L]/8, while keeping its radiation characteristics nearly constant. Both single and dual arm quasifractal log-periodic zigzag antenna (QFLPZA) configurations are investigated, with a maximum antenna height of only 1/8th of a wavelength, showing the desired radiation characteristics, and a wide impedance bandwidth of 67%. This type of antenna may find applications in surveillance radar. Index Terms--Miniaturized wire antenna, vertically polarized, log-periodic (LP), zigzag (Z), backfire radiation, quasi-fractal (QF).

This paper presents the simulation and experimental investigations of a printed microstrip slot antenna. It is a quarter wavelength monopole slot cut in the finite ground plane edge, and fed electromagnetically by a microstrip transmission line. It provides a wide impedance bandwidth adjustable by variation of its parameters, such as the relative permittivity and thickness of the substrate, width, and location of the slot in the ground plane, and feed and ground plane dimensions. The ground plane is small, 50 mm x 80 mm, and is about the size of a typical PC wireless card. At the center frequency of 3.00 GHz, its width of 50 mm is about [lambda]/2 and influences the slot impedance and bandwidth significantly. An impedance bandwidth ([S.sub.11] = -10 dB) of up to about 60% is achieved by individually optimizing its parameters. The simulation results are confirmed experimentally. A dual complementary slot antenna configuration is also investigated for the polarization diversity. Index Terms--Dual slot antenna, finite ground plane, microstrip line feed, microstrip slot antenna, monopole, polarization diversity, wide bandwidth.

A prime focus low sidelobe parabolic reflector antenna with self-supported feed is designed for low sidelobe applications. The parabolic reflector diameter is between nine and 12 wavelengths. A simple design is achieved to satisfy the required first sidelobe level. The design is performed numerically using a computer code for bodies of revolutions (AKBOR2). The measured radiation patterns of the 18-in reflector system are presented. Good agreement between computed and measured radiation patterns is obtained. Index Terms--Reflector antenna, rear end feed.

A novel approach for analyzing the quasi-optical offset Large Adaptive Reflector (LAR) Cassegrain system is described. In this system a Feed-Reflector is used to illuminate a reconformable hyperboloid subrefiector with 5 ~ 10 m diameter, located 500 m above the ground. An exact equation for the offset LAR surface is given in this paper. To scan the beam up to 60[degrees] which is one of the LAR requirements, the concept of the dual offset LAR with the Feed-Reflector is introduced. In this design the cross polarization is eliminated by a proper orientation of the subrefiector. The parameters of the configuration are obtained by utilizing generalized Gauss-Laguerre beam modes and matrix representation of beam mode transformation factor. In this design the blockage effect due to the Feed-Reflector is totally removed. Index Terms--Antenna feeds, antenna radiation patterns, Gaussian beam, reflector antenna.

This paper describes the development of a rigorous transmission-line matrix-based modal-extraction approach to analyze discontinuities in guided-wave structures in general, with particular attention to the nonradiative dielectric waveguide (NRD). The motivation for this paper arose from the need to ascertain the admittance of a slot in the ground plane of an NRD without relying on experimental data. These data enabled one to design an NRD-based slot array following the methodology of Malherbe, Malherbe et al., and Ghosh et al.. Previous work in this area relied on placing observation points sufficiently remote from the discontinuity in order to ensure the decay of scattered evanescent modes to appreciably low levels. The method discussed here obviates this requirement and allows the evaluation of generalized scattering-matrix coefficients arbitrarily close to the discontinuity, thus significantly reducing the computational overhead. Results pertaining to discontinuities in the NRD and the rectangular waveguide have been presented and shown to give good agreement with those in the literature and with measurements. The perfectly matched layer has been used as an absorbing boundary condition in our simulations. Finally, the results have been verified using the power-conservation and Poynting's theorems. Index Terms--Discontinuities, modal extraction, NRD, PML, TLM.

Two techniques based on electric and magnetic field integral equation (EFIE and MFIE) formulations of surface equilalent principle and multiple network theory (SEMN) method are developed for the analysis of finite microstrip structures. Using pulse surface basis functions, the surface of each homogeneous dielectric body is modeled by small flat segments of arbitrary geometry and constant electromagnetic field. Using the surface equivalence principle and the Green's functions of the homogeneous space, the admittance and impedance matrices are computed. Then, the boundary conditions and multiple network theory are applied to determine the overall characteristic of the entire space. Several radiation and scattering examples are numerically analyzed and their calculated near and far fields are presented. The numerical results of the two formulations are then compared with measurement and those of HFSS and ENSEMBLE. Index Terms--Integral equations, microstrip antennas, method of moments (MOM).

A full wave moment method is applied for the analysis of aperture coupled microstrip antennas, in which all components of electric and equivalent magnetic surface currents are considered. Electric current distributions on the rectangular patch for different coupling aperture positions are presented with their radiation patterns. Effects of the coupling aperture shape and size on the input impedance and radiation performances are also discussed. As an example of new radiators, slotted patches are studied, and it is shown that they can be used to achieve dual-frequency operation.

A dual‐band dual‐mode microstrip antenna design is presented, with the application of adaptive interference cancellation in global positioning system at the L1 and L2 bands. The antenna consists of two stacked TM11 rings and two stacked TM21 shorted rings all fed by coaxial probes. By properly combining the two modes and utilizing both polarization components of each mode, up to three nulls can be steered at each frequency band to cancel interferers close to horizon. The concentric structure of the radiating patches in the proposed design allows for a compact antenna, which for a substrate of dielectric constant of 10 is only 0.33 λ in diameter at its lowest frequency of operation and can be further miniaturized on a higher dielectric constant substrate. [ABSTRACT FROM AUTHOR]