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Ruggedized RF Payloads for Autonomous Aircraft

Georgia Tech Research Institute · Spectrum Warfare Operations & Research

Role
Mechanical Engineering Intern
Group
Spectrum Warfare Operations & Research Division (SWORD), SEAL
Location
Atlanta, GA
Dates
January – May 2024

Owned mechanical design and integration for a suite of SDR-based electronic warfare payloads, from packaging through fabrication, test, and field trials.

Built and integrated multiple UAV payloads: custom enclosures, RF and power wiring, and modular hardware. Ran RF path, antenna isolation, and system-level checkout before each payload went onto a platform.

Field-tested the payloads on autonomous UAVs. The units survived multiple UAV crashes.

Background

I worked in SWORD, the Spectrum Warfare Operations and Research Division of GTRI's Sensors and Electromagnetic Applications Laboratory. SWORD conceives, develops, assesses, and fields advanced radio frequency and electromagnetic warfare capabilities for defense sponsors.

On an airborne platform the envelope is fixed long before the electronics that go inside it. The payloads had to package RF electronics, antennas, power, and data connections inside that envelope and still survive flight vibration, and in some cases impact.

Timing diagram of a false-target jamming technique. A threat emitter pulse sits at the end of a prediction time-of-arrival gate. Above it, a synthesized pulse train of false targets FT1, FT2 and FTn, annotated with pulse width, mean delay, and delay jitter.
01How radar jamming worksRadar spoofing works by intercepting a radar's transmitted radio frequency wave, altering its characteristics, and broadcasting a modified signal back to the receiver to feed it false information.

Structural design of RF up-down converter (UDC)

I designed the mechanical structure for a multi-channel RF up-down converter. It had to hold 50+ g impact loads inside a fixed size and weight budget. I cut part count to get the weight down, which also shortened the tolerance stack. The assembly went through several design iterations and reviews in SolidWorks. I then drew 20+ machined 6061 parts with tolerances and material callouts. The unit was machined from billet and integrated with the RF and electrical hardware.

I ran a topology study to find where material could come out of the housing without giving up strength, and used it to guide the shape.

I sourced vendor CAD where it existed and modeled the rest myself, then designed the housing around the finished internal assembly. The electronics and connectors have fixed geometries, so their positions set the housing, not the other way around.

Downconversion mixes an RF signal with a local oscillator down to an intermediate frequency. Upconversion mixes an intermediate frequency up to two RF products, one below the local oscillator and one above. Under each, a mixer symbol with its RF, LO, and IF ports.
02RF up-down converterDownconversion mixes an RF signal with a local oscillator down to an intermediate frequency. Upconversion mixes an intermediate frequency up to two RF products, one below the local oscillator and one above.
An orange subscale target drone in flight over open water, carrying a white pod under each wing. Air-force markings are visible along the fuselage.
03Subscale target drone platformA subscale target drone, included for scale. NOT a photo from this project.

Assembly, harness, and fit-up

I assembled the unit and, working with the lab technicians, built a custom wiring harness carrying 100+ external power and data connections. Bend radii and strain relief compete with service access for the same volume, so I laid the harness runs out in the model while the housing was still open to change.

Hot-swappable RF filter bay

I designed and fabricated a modular bay housing ten commercial off-the-shelf cavity filters. Any one filter can be pulled without disturbing the other nine.

Hot-swap was a hard requirement. Each filter needed its own mechanical retention and its own RF access, so I built the bay as ten identical single-filter bays inside one chassis.

Render of a cavity filter: a long rectangular aluminum body with two rows of tuning screws across its top and side faces, a threaded coaxial connector at each end, and a mounting foot at each corner.
04Commercial off-the-shelf RF cavity filterGeneric RF bandpass cavity filter. NOT my model.

SDR radar hardware and checkout

I worked across several applied research groups building hardware for SDR-based radar systems, then ran functional checkouts on the assembled units to verify each build matched its design before integration.

Writing the checkout procedures turned up errors in the system chain. Faults visible at the receiver usually originated upstream of it, so I traced each one back through the chain: connectors, firmware register settings, then the design assumptions themselves.

Block diagram of a software-defined radio. An antenna feeds an RF front end. The front end connects to an analog-to-digital converter and a digital-to-analog converter, and both connect to a baseband processing block. A dashed outline groups the two converters with the baseband processing.
05SDR signal chainSDR system diagram: antenna, RF front end, converters, baseband. The dashed outline is typically implemented on a system-on-chip.
A software-defined radio board photographed from directly above. A system-on-chip sits at the center, six coaxial connectors run down the right edge, and Ethernet, USB, DisplayPort, SFP, and power connectors run down the left.
06SDR boardA software-defined radio of the class these payloads were built around. This board is one of many on the payload, including microcontrollers / IO boards.

RF cabling and connectors

I modeled the internal RF cabling in CAD to work out the run lengths before anything was ordered, so cables arrived at length and did not have to be routed by guess during assembly.

I also standardized the data and power connector interfaces across the unit. That cut the number of distinct parts to stock and made the harness quicker to build and easier to service.

Field test and integration

I integrated the payload hardware with the firmware and took the units out for field testing on autonomous UAVs.

The units came back from multiple UAV crashes still working.

A twin-boom fixed-wing UAV climbing over treetops against a clear sky. The wing is high-mounted with a pusher propeller turning behind it, the landing gear is down, and a pale cylindrical pod is mounted under the fuselage on the centerline. NASC and Georgia Tech Research Institute markings run along the fuselage side, and the tail carries the registration N433GT.
07GTRI TigerShark UAV testbedThe airframe class these payloads flew on, carrying a centerline pod in the position a payload occupies. NOT a photo from this project. The field test itself is described above.

Skills applied

Mechanical design
  • SolidWorks, part and assembly modeling
  • Design under size, weight, and impact-load constraint
  • Part-count reduction and load-path design
  • Topology study for material removal
  • Tolerance stack-up
  • Modular and hot-swappable packaging
  • Thermal simulation of sealed enclosures
Manufacturing
  • Detailed part drawings for machining
  • Knee milling
  • CNC milling
  • Sheet-metal fabrication
  • Press brake
  • Anodizing and plating
  • Water jet cutting
  • 3D printing
RF and electronics
  • SDR-based radar hardware and firmware checkout
  • Oscilloscope and spectrum analyzer use for signal verification
  • Function generation and signal injection for testing
  • IP network configuration and testing
  • RF cable routing and length modeling in CAD
  • Connector interface standardization
  • Custom wiring harness, 100+ connections

Note on redaction

This entry stays inside the boundary of publicly available and approved material. Sponsor names and images of the hardware I built are not public and do not appear here. The entry is otherwise complete and accurate.

Sources