Figure 1 A summary of the evolution of radar.
Radar plays a critical role in a variety of aerospace and defense applications. As the mission types evolve, fully digital phased array technology that can handle multiple radar, electronic warfare and communications functions with different frequency and bandwidth requirements is emerging. A fully digital phased array is software-defined, meaning each element can be controlled and tuned independently, making it possible to configure compact multi-mission radar systems. But there are new complexities, especially related to ensuring proper filtering in these increasingly tight spaces, that must be overcome when implementing a fully digital antenna design. This article explores how radar designers can overcome the complexities of using fully digital beamforming and how to address the new filtering challenges related to this evolving radar technology.
A Brief Review of the Evolution of Radar
Since the beginning of the 20th century, radar has rapidly evolved from a fairly simplistic device only capable of short-range object detection to the sophisticated systems of today that can stealthily provide detailed imaging and real-time data for objects thousands of miles away. As a result, radar systems have transitioned from passive detection to active detection techniques that use analog signal processing methods to the active digital technology we are familiar with today. Figure 1 shows an overview of the evolution of radar systems.
Figure 2 (a) Representative passive phased array radar system block diagram. (b) Representative active phased array radar system block diagram. (c) Representative subarray digital phased array radar system block diagram. (d) Representative element-level digital phased array radar system block diagram.
Radar system architectures are also evolving to support the radar system transitions shown in Figure 1. These architectures give system designers a wide range of solutions that can be optimized to meet system requirements. Figure 2a shows a passive phased array. Figure 2b shows an active phased array. Figure 2c shows a subarray digital phased array and Figure 2d shows an element-level digital phased array.
The industry is experiencing a technological shift. It is evolving from subarray digital phased arrays to element-level digital arrays. In subarray digital phased arrays, antennas are divided into smaller subarrays that share common signal processing components and perform beamforming in the subarray at the RF or intermediate frequency (IF) level. Element-level digital arrays perform digital beamforming at the individual antenna element level. Element-level arrays, which are also known as fully digital phased arrays, have an analog-to-digital converter (ADC) connected directly to each antenna. As a result, this technology offers unparalleled flexibility, performance and scalability for radar systems.
The Benefits and Challenges of Fully Digital Phased Arrays
In a fully digital configuration, the functions of each antenna are software-defined. Each element can be controlled and tuned independently, allowing users to implement more complex beamforming algorithms that can split beams in multiple directions or detect and transmit beams at different frequencies simultaneously. Additionally, since the ADC is closer to the antenna element, the dynamic range is improved and more signals can be detected. With so many capabilities, one radar system can now be used for multiple missions; this saves space, which is crucial for tight environments such as on a ship.
However, like most applications, compact size and additional capabilities come with challenges. Locating devices closer to the antenna element imposes physical size constraints for the electronics and passive components needed behind every radiating element. Second, fully digital receivers pick up all signals from all directions since the antenna cannot be pointed away from a specific signal. Additionally, there is also the potential for the antenna to jam itself if the signal from one transmit beam impacts the reception of another, for example. Together, these challenges make it crucial to have high performance yet compact filters for these systems.
