This study investigates multipactor mitigation techniques in X-band geometries, focusing on surface modifications, surface conditioning, and additive manufacturing. Surface modifications include geometric alterations such as dimpled surfaces. Experimental results demonstrate that 3D-printed copper test pieces can achieve a multipactor onset threshold comparable to traditionally machined test pieces with appropriate sample preparation. Surface conditioning, involving rapid successions of pulses, is explored for its mitigative potential. Among assessed techniques, dimpled configurations demonstrated superior multipactor hold-off compared to non-modified components. Additionally, the conditioning of test pieces significantly increased the single-pulse threshold.

Rectangular waveguides are susceptible to avalanche-style breakdown via the multipactor phenomenon. The growth in secondary electron density produced via multipactor can damage and destroy RF components. A pulse-adjustable, hard-switched modulator powering an X-band magnetron was utilized to drive a modular experimental setup that enables testing different surface geometries and coatings. Power measurements, taken via diodes, and phase measurements, facilitated via a double-balanced mixer, were integrated into the overall apparatus enabling multipactor detection with high sensitivity and nanosecond temporal resolution. The utilized 150 kW peak microwave source with 2.5 μs pulse width and 100 Hz repetition frequency allows for threshold testing without the need for initial electron seeding. This paper includes the initial results of surface conditioning of the test multipactor gap via electron bombardment.

Multipactor (MP) suppression is essential as more powerful signal sources in smaller form factors are needed. This study utilizes a high-power X-band system with plug-and-play features allowing for quick testing of different surface modifications.’ The presented work uses phase and power diagnostics to detect the onset of MP.

The increased need for multi-carrier signals and higher power requirements has made it essential to study the multipactor (MP) phenomenon in practical structures. A 3-stage rectangular waveguide filter has been designed and implemented in a plug-and-play test fixture for X-band frequencies. The test source for this system is a coaxial magnetron, which yields a peak power output of 150 kW at a frequency of 9.4 GHz and a pulse width ranging from 0.25 to 2.5 μs. Global power diagnostics and phase detection methods were employed to detect MP in the system.

To investigate multipactor, we designed a testbed for S-band frequencies with geometries akin to the standard WR-284 waveguide geometry. Narrowing the waveguide height from WR-284 dimensions to 5.5 mm for a suitable frequency-gap product left the waveguide cutoff frequency unaffected and the RF signal propagating in the dominant TE10 mode. A coaxial magnetron provides the test input power at 2.85 GHz with a peak power output of 4 MW and a 3.5 μs pulse width, and an RF solid-state source using gallium nitride high-electron-mobility transistors delivers a pulse width of 100 μs with a test input power of 2 kW for comparison of threshold power. Local (electron multiplier tube) and global (phase/power) diagnostic methods are implemented to detect multipactor within the test setup. At power levels tested (MW) and a 5.5 mm gap, low multipactor orders (N = 1) are observed. Prior numerical studies demonstrated that structures with grooves in the waveguide broadside wall reduced multipactor susceptibility. Such grooves run along the direction of propagation to avoid continuous impedance mismatching. The efficacy of this mitigation technique was experimentally evaluated. Differences over a smooth broadside wall are noticeable, however limited.

The multipactor effect is detrimental in space-based RF systems through detuning, heating, and causing permanent component damage. Studying thresholds and suppression of multipactor utilizing surface geometries in structures akin to WR-90 waveguide are of specific interest in the presented work. Operating in the dominant TE10 mode, a copper stepped impedance transformer transitions the waveguide to a 1.5 mm height, providing a frequency-gap product conducive for multipactor ignition. The stepped impedance transformer housing is designed as a plug-and-play system, allowing for quick swapping different stepped impedance transformer heights or materials. Input power is injected into the test gap from a coaxial magnetron, operating at 9.4 GHz with a peak power of 250 kW and 2.5 µs pulse width.The setup will enable the measurement of base thresholds for a machined and polished copper surface (material that has undergone a simple cleaning process only), as well as thresholds for multipactor suppression geometries. The testing apparatus details, including the phase-sensitive diagnostics, are presented