Supporting RF Systems Using the CDL Protocol

Common Data Link (CDL) is a secure U.S. military communications protocol. Established by the Department of Defense (DoD) in 1991, CDL is the primary standard for intelligence, surveillance, and reconnaissance (ISR) data transmission, enabling full-duplex, jam-resistant digital communications between airborne platforms, ground stations, and naval vessels. CDL supports real-time distribution of video, imagery, and sensor data critical for modern military operations.

While CDL is considered a mature technology, it is continuously evolving to meet changing operational demands. Early standard CDL systems focused on full-duplex, jam-resistant communication in the Ku-band, with data rates scaling up to 274 Mbps. In the early 2000s, Tactical CDL (TCDL) was released for unmanned aerial vehicle (UAV) applications, while the 2017 deployment of Bandwidth Efficient CDL (BE-CDL) marked a major leap in spectral efficiency, enabling high data throughput with lower bandwidth requirements. Figure 1 provides a summary of the evolution of the CDL protocol.

Figure 1. Timeline of CDL protocol evolution from 1979 to 2024

CDL Frequency Bands

To ensure operational flexibility and spectrum efficiency, CDL operates across multiple frequency bands including:

• Ku-band: CDL primarily operates in the 14.4 – 15.35 GHz range, with specific allocations for uplink (15.15 – 15.35 GHz) and downlink (14.4 – 14.83 GHz) operations.
• X-band: Operating in the 9.75 – 10.425 GHz range, the X-band provides secondary allocation status for CDL operations requiring non-interference with primary allocated systems. This band offers good atmospheric penetration characteristics and is used for backup communications.
• Ka-band: The 26.5 – 40.0 GHz range represents future expansion capabilities, with potential for significantly higher data rates as technology advances. Ka-band offers larger bandwidth availability but faces greater atmospheric attenuation challenges.

Common Military Applications Using CDL

CDL technology is deployed across a diverse range of military platforms, each optimized for specific operational requirements. Below are a variety of examples of how CDL can be used in different types of military applications.

Unmanned Aerial Systems

• CDL supports basic ISR missions and can be adapted to meet evolving communication standards over time.

• CDL enables secure control of payloads and supports high-bandwidth data dissemination from airborne platforms to ground stations.

• Miniaturized CDL terminals allow integration into smaller UAVs that are constrained by size, weight, and power (SWaP) requirements. 

Manned Aircraft

• CDL technology can be integrated into tactical aircraft to enable faster, more secure communications and enhanced interoperability.

• Modern CDL systems reflect the progression from legacy data links to advanced, multi-band communication solutions within manned flight platforms.

Surface Platforms

• Naval vessels use the Network Tactical Common Data Link (NTCDL) for real-time exchange of voice, data, imagery, and full-motion video between aircraft carriers, amphibious assault ships, and next-generation platforms.

• Fixed and mobile ground stations provide command and control capabilities for CDL networks, supporting all CDL variants and waveforms.

Targeting and ISR Systems

• CDL enables secure, two-way, multi-band communication in targeting systems for transmitting video, imagery, and metadata.

• Integrated into advanced sensor platforms, CDL supports real-time ISR operations for both reconnaissance and targeting applications.

The Push for Miniaturization and Multi-Band Agility in Modern CDL-Capable Systems

As military communications systems evolve, two clear trends are shaping the future of CDL technology: Miniaturization through SWaP optimization and the adoption of multi-band, software-defined radio (SDR) architectures. This means today's CDL terminals must deliver high performance in increasingly compact packages. However, at the same time, emerging systems are also demanding support for a wide range of frequencies within a single, modular architecture. These requirements are driving the need for RF components that can operate reliably at high frequencies while occupying minimal space.

Knowles microstrip filters can provide RF system designers with options to meet these seemingly conflicting demands. Built using high-performance ceramic materials and designed for operation at microwave and mmWave frequencies, these filters offer a compact footprint without sacrificing signal integrity.

With low insertion loss, excellent rejection, and the ability to be customized for specific bandpass requirements, our microstrip filters are ideal for SDR systems operating across multiple bands. Additionally, our microstrip filters deliver the ruggedness and thermal stability needed for harsh defense environments, helping engineers meet SWaP goals without compromising on performance.

As CDL applications continue to demand smaller, more capable systems, Knowles’ advanced filtering solutions can provide the precision and scalability needed to stay ahead of evolving platform requirements.

To learn more about microstrip filter technology download our white paper Microstrip Filter Topologies or visit our Microwave Products Page.