The electromagnetic spectrum is a finite and fiercely contested resource in modern defense operations. The historical separation between radar sensing and communications functions — each with dedicated hardware, antennas, and spectrum allocations — is increasingly unsustainable on platforms where size, weight, power, and cost (SWaP-C) are tightly constrained. The convergence of radar and communications into integrated sensing and communication (ISAC) systems promises to reduce the RF footprint while enhancing both functions. This article examines the communications interface challenges and solutions for radar-dominated platforms.

Shared Aperture Architectures

The most SWaP-C efficient approach to radar-communications integration is to share the antenna aperture. An AESA radar, with its hundreds or thousands of individually controlled elements, can form simultaneous beams for radar surveillance and communications — a directional data link beam toward friendly forces, for example, while maintaining a search pattern. The key technical challenge is isolation: the radar transmitter can produce peak powers exceeding tens of kilowatts, while the communications receiver must detect signals at the noise floor. Circulators, filters, and careful frequency planning provide the necessary isolation, typically exceeding 100 dB.

Digital beamforming at the element level enables even more flexible aperture sharing. Different sub-arrays can be allocated to radar and communications functions dynamically, and nulls can be steered toward interference sources — including the platform’s own high-power radar transmissions.

Dual-Function Waveforms

An elegant approach to ISAC embeds communications data directly into the radar waveform. Information can be modulated onto the radar pulse through phase modulation of the LFM chirp, index modulation of frequency-hopping patterns, or amplitude modulation of sidelobe levels in a way that is transparent to the radar’s primary sensing function. The radar receiver naturally strips the communications modulation as part of the matched filtering process, while partnered communications receivers extract the embedded data.

Orthogonal frequency-division multiplexing (OFDM) waveforms, widely used in 4G/5G communications, have been adapted for radar sensing. OFDM radar offers inherent separation of subcarriers, facilitating simultaneous sensing and communications on different subcarrier groups. Range-Doppler processing is performed via a two-dimensional FFT on the received OFDM symbol grid, providing direct compatibility with standard communications hardware.

Tactical Data Link Interfaces

Beyond the physical and waveform layers, radar systems must interface with standard tactical data links — Link 16, Variable Message Format (VMF), and emerging wideband networking waveforms. These interfaces require protocol conversion between the radar’s internal data formats (tracks, detections, raw video) and the standardized messages exchanged across the tactical network. Latency, reliability, and security (encryption at the link and message levels) are paramount, particularly when radar tracks are used for weapon engagement decisions.

The trend toward networked, distributed sensing — where multiple platforms share radar data to create a fused, resilient tactical picture — places further demands on communications interfaces. High-bandwidth, low-latency, jam-resistant data links are the essential enabler of distributed coherent radar operations, where physically separated radars operate as a single virtual array through precise time and phase synchronization across the communications link.