The Importance of RF Interconnects in Phased-Array Systems

What you’ll learn:

Trends in phased-array radar.
RF losses and mitigation strategies.
Millimeter-wave phased-array challenges.
Key design considerations for RF interconnects.

The latest advances in phased-array radar and communication systems for applications like active electronically scanned arrays (AESAs), 5G, and tactical communications are pushing boundaries in frequency operation and physical densification. As these systems integrate increasing numbers of antenna elements, transmit/receive modules, and analog or digital beamforming components, the importance of optimized RF interconnects becomes evident. Engineers must address challenges of size, weight, cost, and installation complexity while ensuring system performance and reliability.

This article investigates key considerations for designing RF interconnects in next-generation phased-array radar and communication systems, focusing on emerging trends and practical solutions.

Trends in Phased-Array Radar

Phased-array radar systems leverage electromagnetic principles to enable higher-frequency operation with reduced antenna sizes. As operating frequencies increase, antenna elements can be smaller, yielding compact, efficient systems.

However, higher frequencies also introduce more significant losses, including RF attenuation and atmospheric absorption. These challenges necessitate additional antenna elements and advanced phase and amplitude control to maintain performance.

Actively controlled phased arrays, such as AESA radars, provide precise beamsteering, which is essential for jamming, low-probability-of-intercept (LPI) communications, and tactical operations. Narrower beam widths at millimeter-wave (mmWave) frequencies enhance directivity, making mmWave phased arrays attractive for radar, communications, and 5G applications. Such advances drive the need for high-density, high-performance RF interconnect solutions capable of withstanding the demands of these compact, complex systems.

RF Losses and Mitigation Strategies

Operating at higher frequencies introduces challenges, including increased RF losses and attenuation. Effective mitigation strategies involve:

High-quality interconnects: Using low-loss coaxial cables and connectors minimizes insertion loss and maintains signal integrity.
Phase control: Ensuring a stable and predictable phase across signal paths requires phase-stable and phase-matched coaxial cables.
Robust materials: Advanced materials help manage environmental factors such as temperature changes, vibration, and mechanical stress.

These considerations are particularly critical in dense phased-array systems, where minor losses or inconsistencies can impact overall performance.

Millimeter-Wave Phased-Array Challenges

At mmWave frequencies, phased-array antennas benefit from reduced size and weight but also face challenges related to densification. Increasing the number of antenna elements demands tighter integration of transmit/receive modules, beamforming components, and signal processors. High-density RF interconnects must support this integration without compromising performance.

Emerging mmWave systems, including industrial 5G applications, often adopt ruggedized designs initially developed for military and aerospace use. These designs prioritize reliability and resistance to environmental stress, ensuring durability under challenging conditions. The same principles are expected to extend to automotive, infrastructure, and industrial applications, reinforcing the need for robust interconnect solutions.

The Phased-Array Signal Chain

Phased-array antenna systems rely on interconnected components, including amplifiers, phase shifters, and antenna elements. Advances in integration have led to the development of transmit/receive (TR) modules, which consolidate power amplifiers and low-noise amplifiers into compact units. These modules reduce overall system size and weight, but they require high-density RF interconnects to connect seamlessly with the rest of the system.

Hybrid and digital beamforming architectures further shrink phased-array designs by incorporating system-on-chip (SoC) and system-in-package (SiP) technologies. These systems reduce reliance on RF connections between components, instead utilizing high-speed digital links. However, they still require tight-pitch RF interconnects for critical signal paths, particularly in high-frequency and high-power applications like jamming and radar.

Key Design Considerations for RF Interconnect

Phase Stability and Matching

The performance of phased arrays depends on precise phase control across signal paths. Two critical factors include:

Phase stability: RF interconnects must resist environmental influences such as temperature fluctuations, shock, and vibration. Phase-stable cables are essential for maintaining consistent performance.
Phase matching: Systematic phase errors can arise from inconsistencies in cable production. Phase-matched cables ensure uniform phase response, improving system predictability and performance.

Mechanical Robustness

Military and aerospace applications demand mechanically robust interconnects capable of withstanding shock, vibration, and thermal cycling (Fig. 1). These requirements often extend to automotive and industrial applications, where reliability is critical. High-reliability (Hi-Rel) interconnects, certified to meet stringent standards, are essential for mission-critical systems.

Compact and High-Density Interconnects

Due to size and performance limitations, traditional RF connectors like N-type and SMA may no longer suffice at mmWave frequencies. More miniature connectors, such as 2.92 mm, 2.4 mm, and SMPM, offer higher-frequency operation and compact form factors (Fig. 2). Blind-mate and ganged connectors enable efficient assembly and disassembly, reducing pitch requirements and simplifying system integration.

2. Traditional RF connectors may no longer suffice at mmWave frequencies. Miniature connectors offer higher-frequency operation and compact form factors.

Board-to-Board and Component-to-Board Interconnects

Modern phased arrays increasingly use printed circuit boards (PCBs) with surface-mounted components. This trend necessitates:

Surface-mount connectors: Compact, solderless connectors reduce RF path loss and support high-density layouts.
Stacking solutions: Mezzanine-style connectors provide reliable interconnects for stacked PCB configurations, minimizing interference and enhancing system reliability.

Addressing Supply-Chain Challenges

Sourcing RF interconnects for phased-array systems can be complex, involving numerous vendors and stringent quality requirements. Military and aerospace applications often require MIL-SPEC compliance, necessitating careful material selection and manufacturing oversight. Partnering with experienced suppliers familiar with these standards simplifies procurement and ensures consistent quality, benefiting defense and commercial applications.

As phased-array systems evolve, so do the demands placed on RF interconnects. Upcoming technologies like mmWave AESA radar, 5G, and advanced tactical communications will rely on innovative solutions that balance performance, integration, and reliability. High-density interconnects, robust materials, and advanced manufacturing techniques will be critical to meeting these demands.

Moreover, as industries like automotive, industrial automation, and telecommunications adopt phased-array technologies, the importance of standardized, scalable interconnect solutions will grow. Engineers and designers must stay informed about emerging trends and technologies to ensure the success of next-generation systems. By addressing the challenges of RF interconnect design, engineers can unlock the full potential of phased-array antennas, paving the way for advances in radar, communications, and beyond.