Jorge L. Salazar

Dual-polarization performance of the phase-tilt antenna array in a casa dense network radar

In this paper the evaluation of dual-polarized scanning performance of a large planar array antenna for a solid state radar for weather is discussed. The antenna array is designed to operate at 9.36 GHz ±50 MHz, and the transmission and reception mode is configured to work alternatively. The antenna array architecture based on a series-fed array configuration of Dual-Polarized Aperture Coupled Patch Antennas (DP-ACPA) was designed and implemented to achieve the required radar polarimetric performance at low cost. Measured patterns of the array in the elevation and azimuth plane are used to evaluate the two principal polarimetric radar parameters (Zdr and LDR) over the scanning range in azimuth plane. It is shown that the biases in the differential reflectivity due the cross-polarization of this antenna configuration are negligible in comparison with the biases produced for the mismatch antenna patterns (H and V).

CASA Phased Array Radar System description, simulation and products

This paper discusses the systems architecture of the CASA Phased Array Radar System, the Phase-Tilt Escan Radar System, for deployment in a CASA DCAS network of low power, solid-state phased array radars. The paper highlights the high-level systems architecture accompanied by measured data from the subsystems.

Coverage comparison of short range radar networks vs. conventional weather radars: Case study in the northwestern United States

The West Coast of Washington and the NE and SW comers of Wyoming are regions of the contiguous United States where NEXRAD coverage is incomplete. One approach to addressing these gaps is to install additional NEXRAD-class radars. Another potential approach is to install small radar networks of the type being investigated in the CASA project. This paper compares these two approaches. We provide a meteorological and user-need assessment of present radar coverage in these regions (based on a recent feasibility study led by J. Brotzge [1]) as well as an objective assessment of the radar-coverage that would be achieved using the large radar and small radar approaches. For this evaluation we consider two classes of radar: long-range radars having similar attributes to the WSR-88D (i.e., 10 cm wavelength, >250 km maximum range, 1 degree beamwidth, −500 kW peak power); and short-range radars having attributes similar to those operating in CASAs Oklahoma prototype network (i.e., 3 cm wavelength, 40 km maximum range, 2 degree beamwidth). We first establish the number of both types of radar that would be needed to provide coverage over a given rectangular ground-domain. Next, we quantify the coverage-versus-altitude for both weather-event detection and precipitation estimation over these regions, considering the blockage caused by both the curved earth and the local terrain.

Design trade-offs for airborne phased array radar for atmospheric research

This paper discusses the design options and tradeoffs of the key performance parameters, technology, and costs of dual-polarized and two-dimensional active phased array antenna for an atmospheric airborne radar system. The design proposed provides high-resolution measurements of the air motion and rainfall characteristics of very large storms that are difficult to observe with a ground-based radar system. Parameters such as antenna size, wavelength, beamwidth, transmit power, spatial resolution, along-track resolution, and polarization have been evaluated. The paper presents a performance evaluation of the radar system. Preliminary results from the antenna front-end section that corresponds to a Line Replacement Unit (LRU) are presented.

T/R modules for active phased array radars

This paper presents a summary of the three T/R modules developed for weather active phased array radars. Critical factors that influence the system performance are discussed in terms of the technology and tradeoffs that includes cost. Performance is considered for deployable dual-polarized PAR radar systems. The three T/R modules and antenna aperture Line Replacement Units (LRU) have been designed, integrated and tested. Performance and cost are derived from affordability constraints imposed by the latest technology is presented.

A dual-polarized cross-stacked patch antenna with wide-angle and low cross-polarization for fully digital multifunction phased array radars

In the following contribution, the design of a high performance antenna element with dual-polarization, wide scan angle, and low cross-polarization levels for phased array radars is reported. The antenna was optimized to operate in the federal radio navigation and meteorological band (2.7–2.9 GHz). Cross-polarization levels for E-, D-, and H-plane ≤ −45 dB based on Ludwigs 3rd definition were obtained. Scanning performance of ± 60° for all scanning ranges in the frequency band was achieved. Isolation greater than −40 dB and bandwidths greater than 10 % were reached at the array level.

Cylindrical Polarimetric Phased Array Radar: Beamforming and Calibration for Weather Applications

Future weather radar systems will need to provide rapid updates within a flexible multifunctional overall radar network. This naturally leads to the use of electronically scanned phased array antennas. However, the traditional multifaced planar antenna approaches suffer from having radiation patterns that are variant in both beam shape and polarization as a function of electronic scan angle; even with practically challenging angle-dependent polarization correction, this places limitations on how accurately weather can be measured. A cylindrical array with commutated beams, on the other hand, can theoretically provide patterns that are invariant with respect to azimuth scanning with very pure polarizations. This paper summarizes recent measurements of the cylindrical polarimetric phased array radar demonstrator, a system designed to explore the benefits and limitations of a cylindrical array approach to these future weather radar applications.

Current polarization impact on cross-polarization definitions for practical antenna elements

With the growing interest in polarization diversity in communications and radar systems, the use of Ludwigs second and third definitions have become controversial among scientists and antenna engineers. Therefore, this paper is an attempt to clarify some of the ambiguity and confusion caused by these definitions. A detailed comparison of Ludwigs 2nd and 3rd definitions of cross-polarization, as applied to linearly polarized antennas, was performed. The results show that, in the diagonal plane, Ludwigs 2nd definition leads to a lower cross-polarization level than the 3rd definition for x- or y-polarized current sources. For a Huygens source, by Ludwigs 3rd definition, the radiation pattern has a lower cross-polarization level than that obtained by Ludwigs 2nd definition.

A novel near-field robotic scanner for surface, RF and thermal characterization of millimeter-wave active phased array antenna

This work describes the concept and current development of a novel automated system to characterize active phased array antennas. The proposed system, called an RF Scanner, has been conceptualized and developed by the Advanced Radar Research Center (ARRC) at the University of Oklahoma (OU). This system enables the full characterization of electromagnetic, surface, and thermal properties of an active phased array antenna. An industrial 6-axis articulated robot is used to move a sensor suite to perform near-field measurements as well as surface and thermal inspection of the antenna under test (AUT). The sensor suite consists of a mechanical fixture supporting an infrared camera, a high-precision laser, a high-definition camera, and an antenna array probe. The AUT, the robotic manipulator, and the sensor suite are located inside of an environmental chamber. This environmental chamber enables characterization of the AUT under controlled temperature and humidity. The combination of the high precision robot, sensor suite, environmental chamber, and vector network analyzer (VNA), along with a software interface, allows fully automated characterization of an active phased array antenna from 1 GHz to 18 GHz, up to 60 GHz if the VNA is upgraded, over a temperature range of 0° C to 50 ° C.

Edge diffractions impact on the cross polarization performance of active phased array antennas

This paper examines the impact of diffracted fields on the cross-polarization performance of finite array antennas. The investigation included the calculation, simulation and measurement of several antenna prototypes with different element positions and different ground planes sizes. Characterization of the induced cross-polarization in a finite array with discontinusities in the ground plane was also performed. Excellent agreement between simulations and the actual measurements of eight antenna prototypes were obtained. The results demonstrated that the cross-polarization of the antenna elements in the array can be significantly impacted by the diffracted fields of the external and internal edges or discontinuities.