Aerodynamic Characteristics of Radar Antenna in Stationary and Azimuthal Rotational Motion

To study the effects of aerodynamic loads on the aerodynamic characteristics of stationary and azimuthally rotating antennas, wind tunnel force tests are conducted using solid and porous plate antennas. The variation of aerodynamic coefficient with azimuth angle is obtained when the antenna is stationary and azimuthal rotation, and the results are compared with those from numerical simulations. The variation in the aerodynamic coefficients with respect to the azimuth angle is found to be sinusoidal for both the solid and porous plate antennas rotating in azimuth. Compared with the antenna stationary, quantitative analysis indicates that the rotational motion increases the maximum value and root mean square of the aerodynamic coefficient. For solid plate antenna, |Cx|_max, |Cmy|_max, and |Cmz|_max increase by 41.6%, 15.0%, and 47.3%, respectively; Cx_rms, Cmy_rms, and Cmz_rms increase by 19.0%, 20.0%, and 19.1%, respectively. For porous plate antenna, |Cx|_max, |Cmy|_max, and |Cmz|_max increase by 30.6%, 71.4%, and 40.9%, respectively; Cx_rms, Cmy_rms, and Cmz_rms increase by 22.9%, 50%, and 20%, respectively. The wind tunnel tests verify the feasibility of using numerical simulations to obtain the flow field results. By analyzing the surface pressure coefficient and vortex core track distribution, the effects of azimuthal rotation on the aerodynamic characteristics of the antenna are further clarified.

Measurement of Negative Lightning Return Strokes Using a Proposed Small-Scale Parallel Plate Antenna at the Central Region in Peninsular Malaysia

Lightning can occur between the clouds (intra-clouds), ground-to-cloud (CG), and inside the clouds. The lightning strike hazards can be managed appropriately using a lightning detector system consisting of an antenna, buffer amplifier circuit, and a measurement device. In this study, the development and fabrication of small-scale parallel plate antenna were carried out by reducing the physical height and antenna dimension to measure the generated electric fields. The experimental work was conducted at the rooftop of the College of Engineering, Universiti Tenaga Nasional (UNITEN), Selangor, Malaysia, from August 2019 to March 2020. The total number of 115 return strokes (RS) of negative lightning events were recorded during the measurement period. Characterization of seven types of criteria for negative return stroke has been analysed and compared to the existing parallel plate antenna with a similar climate condition and different countries. Based on the comparative study, the proposed and the existing parallel plate antenna shows a good agreement. Hence, the proposed small-scale parallel plate antenna can be used as a portable, lightweight, and easy to install device for the lightning measurement system.

Unsteady Aerodynamic Characteristics of Antenna Rotating in Different Elevation Angles

The aerodynamic characteristics of radar antennas should be considered in computing their wind resistance and designing pedestal servo systems. In this paper, the aerodynamic characteristics of a flat plate antenna with azimuthal rotation are explored using a wind tunnel, and the effects of the antenna elevation angle and reduced frequency on the aerodynamic coefficients are analyzed. The corresponding results of numerical simulation are given to compare with the experimental results. The variation of aerodynamic coefficients with respect to the azimuth angle is found to depend on the reduced frequency and the antenna elevation angle. When the increase in antenna elevation angle is slight, the mean and root mean square values of the aerodynamic coefficients are not monotonic with respect to increases in elevation angle and may increase at individual elevation angles. When the elevation angle increases significantly, the mean, maximum, and root mean square values of the aerodynamic coefficients all significantly decrease. The simulation results are in good agreement with the experimental results, which verify the feasibility of using unsteady numerical simulations to obtain the flow field structure when the antenna is rotating. This approach allows the influence mechanism of the elevation angle change on the aerodynamic characteristics of the rotating antenna to be identified.

Suspended plate antenna with circular polarization and configurable sense of rotation

Introduction: Circular polarization antennas (CPA) are able to reduce the “Faraday rotation” effect due to the ionosphere, which causes a significant power losses compared to the case of using linear polarization antennas (LPA) [1]-[2]. Therefore, these antennas are widely used for space telemetry applications of satellites, space probes and ballistic missiles among others [2]. Furthermore, suspended plate antennas (SPA) offer the possibility to obtain largest levels of maximum gain and impedance bandwidth compared to those obtained with conventional technologies. Likewise, it is useful to be able to select the most appropriate sense of rotation, depending on the propagation conditions in the up/down links. Objective: To design a CPA with configurable sense of rotation for small satellite applications, using SPA technology, such that it has gain and bandwidth levels higher than those obtained with conventional technologies. Method: The antenna design is based on models proposed in the literature, through which an initial geometry consisting of a suspended patch with an L-shaped feeder and a hybrid coupler is designed. Subsequently, geometry optimization by parametric analysis is carried out with appropriate electromagnetic simulators. Results: The proposed design has an impedance bandwidth of 34.39% and a maximum gain of 8.75 dBi at a frequency of 2.35GHz. Conclusions: The L-shaped feeder technique for suspended patches improves the behavior of the antenna in axial ratio, impedance and maximal gain.