Shaya Karimkashi

Invasive Weed Optimization and its Features in Electromagnetics

A new numerical stochastic optimization algorithm, inspired from colonizing weeds, is proposed for Electromagnetic applications. This algorithm, invasive weed optimization (IWO), is described and applied to different electromagnetic problems. The linear array antenna synthesis, the standard problem used by antenna engineers, is presented as an example for the application of the IWO. Compared to the PSO, The features of the IWO are shown. As another application, the design of aperiodic thinned array antennas by optimizing the number of elements and at the same time their positions is presented. By implementing this new scenario, thinned arrays with less number of elements and lower sidelobes, compared to the results achieved by genetic algorithm (GA) for the same aperture dimensions, are obtained. Finally, the IWO is applied to a U-slot patch antenna to have the desired dual-band characteristics.

Focused Microstrip Array Antenna Using a Dolph-Chebyshev Near-Field Design

A new concept in designing large array antennas to focus the microwave power in the radiation near-field region is presented. A small focused array antenna using microstrip patch elements to achieve the desired sidelobes levels in the Fresnel region based on Dolph-Chebyshev design is implemented. This array is built to verify the concept, and then the measured and computed near fields are compared to verify the accuracy of the design. Larger arrays are designed by using the knowledge of the mutual admittances between the elements of smaller arrays. Several computed examples are presented in order to show some properties of focusing arrays. It is shown that the maximum intensity of the electric field along the axial direction is displaced from the focal point towards the antenna aperture. This displacement decreases as the aperture size increases.

Focusing Properties of Fresnel Zone Plate Lens Antennas in the Near-Field Region

Some focusing properties of Fresnel zone plate (FZP) lens antennas in the near-field region are presented at the ka-band. Simulated and measured results of the FZP antenna show displacement of the maximum intensity of the electric field along the axial direction from the focal point toward the antenna aperture. This displacement increases as the antennas focal length increases. In addition, the focused beam scanning of the FZP lens antennas in the radiation near-field is examined.

A Dual-Polarized Series-Fed Microstrip Antenna Array With Very High Polarization Purity for Weather Measurements

The design and analysis of a dual-polarization frequency scanning array antenna, operating in a frequency band of 2.7-3.0 GHz, for weather measurement applications are presented. Stacked patch elements are coupled to feed lines through slots etched on the ground plane. A wall of plated holes in the middle of the antenna column is designed to improve the isolation between the two input ports. Both simulation and measurements results confirm that very high polarization purity is achieved.

Atom based RF electric field sensing

Atom-based measurements of length, time, gravity, inertial forces and electromagnetic fields are receiving increasing attention. Atoms possess properties that suggest clear advantages as self calibrating platforms for measurements of these quantities. In this review, we describe work on a new method for measuring radio frequency (RF) electric fields based on quantum interference using either Cs or Rb atoms contained in a dielectric vapor cell. Using a bright resonance prepared within an electromagnetically induced transparency window it is possible to achieve high sensitivities, <1 μV cm−1 Hz−1/2, and detect small RF electric fields μV cm−1 with a modest setup. Some of the limitations of the sensitivity are addressed in the review. The method can be used to image RF electric fields and can be adapted to measure the vector electric field amplitude. Extensions of Rydberg atom-based electrometry for frequencies up to the terahertz regime are described.

Antenna Array Optimization Using Dipole Models for MIMO Applications

A very fast and efficient method for designing compact antenna arrays preserving the maximum channel capacity of multi input multi output (MIMO) systems using infinitesimal dipole model (IDM) theory is presented. Using this method each antenna element is replaced by a set of infinitesimal dipoles producing the same electric fields of the antenna. The recently introduced Invasive weed optimization (IWO) algorithm is employed to find the infinitesimal dipole models. The algorithm is applied to a planar inverted F-antenna designed as an element of a compact array for MIMO applications. Using the obtained IDMs, self and mutual admittances between the antennas are predicted. Therefore, correlation coefficients of the MIMO array system are achieved using S-parameters. Having the correlation of the system, the location and orientation of each antenna are optimized to find the minimum correlation value for the MIMO antenna system. Using the optimization technique, very low cross correlation coefficient is obtained for very close antennas over a finite ground plane.

Comparison of Theoretical Biases in Estimating Polarimetric Properties of Precipitation With Weather Radar Using Parabolic Reflector, or Planar and Cylindrical Arrays

Planar or cylindrical phased arrays are two candidate antennas for future polarimetric weather radar. These two candidate antennas have distinctly different attributes when used to make quantitative measurements of the polarimetric properties of precipitation. Of critical concern is meeting the required polarimetric performance for all directions of the electronically steered beam. The copolar and cross-polar radiation patterns and polarimetric parameter estimation performances of these two phased array antennas are studied and compared with that obtained using a dual-polarized parabolic reflector antenna. Results obtained from simulation show that the planar polarimetric phased array radar has unacceptable polarimetric parameter biases that require beam to beam correction, whereas biases obtained with the cylindrical polarimetric phased array radar are much lower and comparable to that obtained using the parabolic reflector antenna.

Dual-Polarization Frequency Scanning Microstrip Array Antenna With Low Cross-Polarization for Weather Measurements

The design of a dual-polarization frequency scanning array of microstrip patch antennas is presented. The coupling between the patch elements and the transmission lines is realized using microstrip directional couplers. Cross polarization suppression is achieved by applying a differential feed configuration to each element for the vertical polarization and an imaged feed arrangement with respect to the columns for the horizontal polarization. The antenna has been fabricated and test results are provided verifying the accuracy of the simulated results. In addition, the imaged feed configuration is used for two neighboring columns of the array to compensate for the spurious radiations and achieve a lower cross polarization level.

Antenna array synthesis using Invasive Weed Optimization: A new optimization technique in electromagnetics

The applicability and efficiency of the invasive weed optimization, recently invented optimizer, for linear antenna array synthesis were investigated. It was shown that this new optimization method outperforms the PSO in the convergence speed and final error level.

Dual-polarization challenges in weather radar requirements for multifunction phased array radar

This paper summarizes the challenges in achieving (and even specifying) the antenna polarization accuracy requirements for the Multifunction Phased Array Radar (MPAR) and the progress that has been made towards meeting these requirements through demonstrations and theoretical investigations.