Multipaction Testing

ATEC Solutions

Multipaction testing is used to evaluate how RF components respond to high-frequency signals in vacuum environments. This testing is critical for aerospace applications, where RF-induced breakdowns can cause performance degradation or failure. People sometimes refer to the phenomenon as the multipactor effect, a term common in European aerospace standards.

Understanding the Multipactor Effect

Under the right RF conditions, free electrons in a vacuum can strike surfaces with enough force to release additional electrons. This can trigger a cascading avalanche known as multipaction, leading to RF noise, arcing, and component damage.

Multipaction most often affects space-based systems and components such as:

Waveguides and coaxial lines
Filters, diplexers, and couplers
Antennas and connectors
Microwave and RF passive components

Types of Multipaction

Single-Surface: Occurs on dielectric surfaces where electrons build locally.
Two-Surface: Involves electrons bouncing between two metal surfaces in close proximity.

When Does Multipaction Occur?

Vacuum environment with low pressure
Presence of free electrons (from radiation or electron sources)
RF power and frequency tuned to cause resonance
Electron travel time aligns with half-period multiples of the RF waveform

Multipaction Testing Methods

Global Testing: Evaluates complete systems for signs of breakdown such as harmonics and power loss.
Local Testing: Focuses on individual components to determine threshold conditions for multipaction onset.

Test Equipment Categories

ATEC rents high-performance equipment to support multipaction testing, including:

Multipaction Test Setup

This block diagram shows a typical multipaction test setup, including a signal generator, pulsed amplifier, directional couplers, vacuum chamber, and downstream RF analysis equipment.

How to Check Conditions for Multipaction Testing

Test set-up calibrated prior to testing
Multipaction standard used to verify the test set-up
Power level ramped from 1600 Watts peak, 315 Watts average to 3000 Watts peak, 600 Watts average, in 200 Watts intervals with 5 minutes dwell at each level. 30 minutes dwell at maximum power of 3000 Watts peak, 600 Watts average
Forward, reflected and output powers continuously monitored and recorded
Third harmonic signals at input and output continuously monitored and recorded
Current probes (Pico ammeters) placed at all ports through the vent holes to detect possible anomalies
Several thermocouples placed on DUT and base plate to continuously monitor and record the temperature
Thermal vacuum chamber pressure continuously monitored
Visual inspection after multipaction testing using a microscope

Vacuum Chamber Configuration

Pictured above is a physical multipaction test environment, featuring Cs-137 electron sources, temperature sensors, and current probes inside a thermal vacuum chamber simulating orbital RF exposure.

Test Parameters

Parameter	Setting	Notes
Frequency	7.0 GHz	Primary RF carrier
Power	3000 W peak	600 W average
Pulse Width	100 µs	5% duty factor
Pressure	<1.0e-5 Torr	Vacuum environment
Temperature	-10 to +23 °C	Test chamber conditions
Electron Source	Cs–137	3 sources, 10 µCi each
Sample Rate	50 kHz	Signal monitoring rate
Detection Methods	Return loss, harmonics, picoammeters	Used to detect anomalies and thresholds
Samples Tested	20	Number of components evaluated

Related Testing

ATEC also provides Radiated Immunity Testing services, which evaluate how devices withstand external RF interference in compliance with EMC regulations.

Simulation Software Tools

CST Studio Suite: 3D EM simulation and RF modeling
Spark3D: RF vacuum breakdown prediction software
Fest3D: Passive RF component simulation

Contact ATEC

ATEC provides rental equipment and expert support for multipaction and RF breakdown testing. Contact us today to find the right equipment for your mission-critical project.