Eric J. Knapp

Salient features of radar nodes of the first generation NetRad System

The recently established National Science Foundation Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) will be deploying the first generation of an automated network of four low-power, short-range, X-band, polarimetric, Doppler radars, known as NetRad, in central Oklahoma in late 2005. This network is developed with the goal of tracking tornadoes with high spatial and temporal resolution as well as mapping severe weather events in the lowest 2 km of the troposphere. Each radar node has been developed to accomplish this system goal through the coordinated interaction with other radars in the network via a real-time, closed-loop software control system. This paper will describe the characteristics of the individual radar nodes in the system, with emphasis on those aspects of the design that lend themselves toward operation as a coordinated network. Calibration results and performance characteristics of the single node radar of the first generation system will also be presented.

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).

A Dynamically-Reconfigurable Phased Array Radar Processing System

Digital beam forming is an important radar processing technique used in many communication and radar sensing applications. This paper presents a low-cost digital beam forming system which takes advantage of four eight channel analog-to-digital (A-to-D) converter chips and dynamic FPGA reconfiguration. A full digital beam forming algorithm capable of forming up to 24 beams from 64 antenna input signals is described. FPGA reconfiguration is performed in 400 ms allowing for FPGA ret asking of the associated radar for weather and aircraft tracking. Beam forming performance of 64.2 GOPs per second for weather tracking and 72.2 GOPs per second for aircraft tracking is reported. The complete low cost digital beam forming board, including parts and assembly, costs less than

CASA Phased Array Radar System description, simulation and products

3,000.

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

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.

Phase Shifter System Using Vector Modulation For Phased Array Radar Applications

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.

Scalable Multifunction Dense Radar Network

This paper presents the design and implementation of a complete phase shifter system using vector (polar) modulation, suitable for solid-state phased array radar applications, providing a cost effective solution which overcomes the main constraints involved with traditional systems. The performance characteristics for an intermediate frequency (150 MHz) are shown. Finally a four channel prototype was built to evaluate the network connectivity of the phase shifter.

Phase shifter system using vector modulation for xband phased array radar applications

This paper discusses an approach to evaluating network topologies of scalable, low power, solid-state phased array radars that improve the coverage of the lower troposphere (<3 km), which is absent in coverage available with current weather sensing networks.

A concept for evaluating the performance of wet radomes for phased-array weather radars

This paper presents the design and implementation of a complete phase shifter system using vector (polar) modulation, suitable for solid-state phased array radar applications, providing a cost effective solution which overcomes the main constraints involved with traditional systems. The performance characteristics for three intermediate frequencies were measured. In addition, measurements at X- band were performed using frequency up-converters. Finally a four channel prototype was built to evaluate the network connectivity of the phase shifter.

Phase-Tilt Weather Radar: Calibration and preliminary results

A novel analytical method for evaluating the electrical performance of a flat, tilted radome for a dual-polarized phased-array antenna under rain conditions is presented. Attenuation, reflections and induced cross-polarization are evaluated for different rainfall conditions. A new radome model is presented which takes into account the properties of the skin surface, area, inclination, radome structure, and rainfall rate. The radome is modeled as consisting of multiple layers, including a wet layer. Attenuation and propagation effects through the radome are characterized using a transmission line equivalent circuit model. Knowledge of the rainfall rate and surface properties of the radome is used to determine the radome performance. Calculated results are compared with radar data obtained with the NEXRAD and CASA systems, where good agreement between measurements and simulations was found.