1. Overview

In 2013, the weather‑monitoring radar was upgraded to a dual‑polarization configuration. The dual‑polarization variables it processes enable differentiation among various types of hydrometeors, identification of non‑meteorological scatterers such as insects, birds, and debris, and improved accuracy in rainfall estimation. In a typical volume‑coverage scan, there are… 5000 Different pointing directions; to achieve acceptable data quality, an average of approximately… is required. 0.05 seconds The continuous processing interval, completed A volume scan takes a quarter of an hour or longer. 。

Accordingly, several research institutions specializing in radar have increased the volume‑scan rate per minute, which—by improving detection probability, reducing false‑alarm rates, and extending lead time for warnings—can help minimize casualties and deliver quantifiable societal benefits. The U.S. National Severe Storms Laboratory has spearheaded a major research effort to determine whether PPAR systems can support faster volume scans while maintaining high data quality. This initiative leverages a key experimental asset (ATD), developed by Lincoln Laboratory, General Dynamics, NSSL, the University of Oklahoma, and others, to address critical performance challenges and demonstrate the operational advantages of highly digitized PPARs. The foundational architectural module for next‑generation PPAR development is an 8×8‑element, dual‑polarized, phased‑array panel, whose scalable, digitized element architecture can accommodate features envisioned for future weather radars.

2. Requirements for Next-Generation Digital Phased-Array Radars

To achieve faster volumetric scanning times, next-generation radars must support multiple, simultaneous, agile beams with excellent beam‑to‑beam isolation. For planar phased‑array architectures, this can be realized by generating and processing several concurrent beams on a single array surface—whether the array is fixed, rotatable, or some combination of both.

Simultaneous beam reception requires a certain frequency or beam‑steering separation to achieve high isolation. To maintain low receive sidelobes when producing multiple beams with wide separations, it is preferable to employ an all‑digital array—or at least a digitally controlled array in one dimension—rather than a subarray‑based or overlapping‑subarray radar. In subarray systems, beams must be coherently combined to match the subarray pattern; however, digital beam steering within the subarray pattern introduces systematic phase irregularities in the receive phase gradient, leading to elevated sidelobes.

For maximum power efficiency, the array should operate the power amplifier in saturation. Beamwidth can be broadened (or degraded) by applying only phase tapering to the array, thereby enabling multiple receive beams—at the cost of reduced effective isotropic radiated power (EIRP) and increased bidirectional sidelobes. Alternatively, a “shotgun” approach can be employed, using multiple closely spaced transmit pulses directed toward widely varying angles.

Either of the two methods described above requires that the transmit power be increased proportionally to the number of concurrent beams in order to maintain sensitivity.

To provide high-quality data for polarimetric measurements, radar systems must maintain excellent polarization isolation and superior beam pattern matching between the H‑ and V‑polarization channels. To keep sidelobes low and ensure robust isolation of receive beams with wide separation within the same aperture, the antenna’s phase and amplitude must be precisely calibrated.

3. System Overview

The DPPAR consists of a “fast‑build” panel that incorporates 64 stacked patch antennas arranged in an 8×8 grid with a 2‑inch (5‑cm) pitch, covering the frequency range from 2.7 GHz to 3.1 GHz. The panel can operate independently or be combined with other panels in an array.

The PPAR architecture places certain signal-processing functions—such as beamforming and pulse compression—directly behind each antenna element. This approach maximizes degrees of freedom by digitizing both received and transmitted signals at the individual element level. Furthermore, PPAR employs a liquid-cooling architecture to manage the thermal load introduced by increased processing complexity and higher transmit power levels in the array.

As shown in Figure 1, the DPPAR panel employs the same dual‑board design as the ATD panel, with a series of connectors linking the aperture board to the backplane printed circuit board assembly. This simplifies assembly and minimizes the panel’s overall thickness. The aperture assembly comprises 64 dual‑polarized patch antennas, each paired with a dedicated transmit/receive module.

Figure 1. DPPAR panel with a double-plate design, featuring perforations and a backplate.

The backplane PCB serves three purposes: 1) providing localized power regulation; 2) synchronizing to a larger array via Distributed Signal Bus (DSB); and 3) utilizing eight processing chips for off‑array data transmission.

Figure 2: Double-plate design of the DPPAR panel, featuring a perforated plate and a back panel.

Figure 3: High-density RF connector linking the perforated plate and the backplane

Figure 4: DPPAR panel—on the radiation side (left), the panel features an antenna grid; on the electronics enclosure side (right), it includes a rigid mechanical mounting and a handle.

Figure 4 illustrates the design of the DPPAR panel. On the left side is the radiating surface, featuring an array of patch radiators; on the right is the electronic equipment housing. To dissipate the heat generated by the system, the two panels are cooled via a common cold plate, as shown in Figure 5.

Figure 5: DDAR panel—on the radiation side (left), the panel is equipped with an antenna mesh, while the electronic equipment enclosure features rigid mechanical mounting and a handle.

4. All-digital RF system

Figure 5: DPPAR Panel Design

Figure 6: DPPAR Panel Design (Exploded View)

A fully digital architecture simplifies RF design by eliminating the need for several analog components. Element weights are computed in the digital domain, enabling beam steering and beamforming at each element without requiring analog attenuators or phase shifters. The signals from each element are digitally summed, obviating the need for costly microwave beam‑forming networks. Furthermore, the use of high‑speed direct‑sampling converters eliminates the requirement for analog frequency‑mixing circuits. The block diagram of a single‑channel RF chain is shown in Figure 7.

Figure 7: Block diagram of a single-channel RF chain

Figure 8: Block diagram of the TR section

The RF circuit is responsible for transmitting and receiving signals, multiplexing these signals onto the radiating elements, and implementing bandpass filtering to prevent aliasing. The signal converter and signal conditioner are mounted on the backplane PCB, while the T/R module and the radiator are located on the aperture PCB. The two boards are sandwiched together with a water-cooled aluminum heat sink for thermal management.

Figure 9: Conceptual design of a cold plate sandwiched between the aperture and the backplane.