KRIZIK — A Complete Radio Payload on One CubeSat Board

KRIZIK_H00 top side — AD9361 transceiver and RF baluns bottom left, RF ports on the left edge, system-on-module connectors in the centre.

The Problem

Communications is where most CubeSat missions get expensive. The radio is mission-specific — a different band, a different modulation, a different data rate for every mission — but the flight-qualified options on the market are fixed-function boxes. Change the requirement and you change the supplier.

A software-defined radio solves that in principle, but only if the processing sits next to the transceiver. Splitting the analogue front end and the baseband processor across two boards costs a slot in a satellite that has very few, and pushes a wideband digital interface across a connector where it does not belong.

What We Built

KRIZIK puts the whole signal chain on one board in the standard 90 × 96 mm CubeSat outline. An Analog Devices AD9361 agile transceiver gives two receive and two transmit channels anywhere from 70 MHz to 6 GHz, with channel bandwidths from 200 kHz to 56 MHz. Each of the four ports leaves through a 1:1 wideband balun to its own 50 Ω MMCX connector on the board edge.

The digital side is a Trenz TE0820 system-on-module carrying an AMD Zynq UltraScale+ ZU4EV MPSoC — a quad-core Arm Cortex-A53 application processor, a dual-core Cortex-R5F real-time processor and 192,150 logic cells of programmable fabric on one die. The transceiver reaches the fabric over LVDS, six data pairs in each direction. Filtering, modulation and forward error correction run in logic; the protocol stack and mission software run on the A53 cores; deterministic housekeeping runs on the R5F cores.

Designed for the Orbit, Not the Bench

Two design decisions separate this from a terrestrial SDR carrier.

Latch-up gets interrupted, not survived. Both switched supply rails carry a current-sense comparator. When either trips, it pulls the enable and under-voltage node of the input e-fuse, dropping the board's input rail. A single-event latch-up is cleared by a power cycle instead of being left to cook the device holding it.

Mission state does not live in flash. Configuration and state sit in 16 Mbit of STT-MRAM on the carrier. MRAM is byte-alterable with no erase cycle and no wear-out mechanism, which takes flash write endurance out of the mission-design budget entirely.

Around that: an e-fuse-protected 5–15 V input with inrush limiting and over- and under-voltage lockout, low-noise LDOs feeding the transceiver's analogue rails separately from the digital supplies, two I²C temperature sensors, and TVS protection on every externally exposed line including the RF ports.

Bottom side — USB bridge, CAN and RS-485 transceivers, ESD protection arrays.

Talking to the Spacecraft

Two identical board-edge interfaces each carry a UART, a four-wire SPI, I²C, CAN, RS-485 and four bidirectional GPIO with per-line direction control. Payload data goes out over gigabit Ethernet. A USB-C port exposes JTAG and a serial console for ground testing, and a separate expansion header drives and powers an external RF front end — a power amplifier, an LNA, a filter bank or an antenna switch — over I²C plus eight GPIO.

Two CAN controllers and the console UART are hard peripherals in the processing system. Everything else is wired to programmable-logic pins and instantiated in the fabric by the reference design, which means the interface mix can be changed without touching the hardware.

At a Glance

RF tuning range	70 MHz – 6.0 GHz
Channels	2 RX, 2 TX (2×2 MIMO), 12-bit converters
Channel bandwidth	200 kHz – 56 MHz
Processor	Zynq UltraScale+ ZU4EV, 192,150 logic cells, 728 DSP slices
Memory	2 GB DDR4, 8 GB eMMC, 128 MB QSPI, 16 Mbit STT-MRAM
Interfaces	1000BASE-T Ethernet, 2× (UART, SPI, I²C, CAN, RS-485, GPIO), USB-C JTAG and console
Supply	5–15 V, e-fuse protected, latch-up interrupters
Board	90.17 × 95.89 mm, 8 layers, FR-4, 1.6 mm

Key Takeaway

The interesting part of a software-defined radio is not that it can be reprogrammed. It is that the reprogramming happens next to the antenna, on the same board, inside the power and thermal budget of a CubeSat. Getting there is a layout and power-integrity problem as much as an RF one — wideband LVDS and a 6 GHz front end sharing eight layers with switching regulators, in a footprint the size of a postcard.