Scientific Microwave Corporation (SMC) has been at the forefront of microwave technology, specializing in designing and developing high-power, wideband circulators and isolators. These components play a critical role in various applications, including telecommunications, satellite communications, and military radar systems. They have introduced two new products for high-power microwave applications - the WRD350 high-power isolator and the WRD200 high-power circulator. These components are designed to handle substantial RF power levels while maintaining high isolation and low insertion loss, making them essential for applications that require reliable and efficient performance.
WRD350 High-Power Isolator
The WRD350 high-power isolator operates within the 4-8 GHz frequency range and is based on a Double-Ridge waveguide design. This design provides a 2:1 bandwidth ratio, making it suitable for a wide range of applications. The isolator utilizes a ferrite with a saturation magnetization of 1300 Gauss (G) and a large linewidth, which ensures immunity to resonance under high-power conditions.
The design includes a four-matching transformer to transfer the signal from the center section to the standard waveguide opening, along with tuning screws to allow for post-fabrication adjustments. The isolator is externally biased using Samarium cobalt DC magnets, which enhances its performance. The WRD350 isolator achieves a matching level of over 17 dB at the input port, with 17 dB isolation across the 4-8 GHz range. The insertion loss is minimal, varying from -0.3 ± 0.1 dB over the entire operating range.
Measured S-Parameter of the WRD350 High-Power Isolator
During testing, DC magnets were positioned on both the top and bottom sides of the isolator, and tuning screws were adjusted to optimize return loss and isolation. The selected ferrite, with a saturation magnetization of 1230 Gauss and a linewidth of 390 Oersted (Oe), contributes to the component's high-power capabilities.
WRD200 High-Power Circulator
The WRD200 high-power circulator operates in the 2-4 GHz frequency range and is designed to handle an average power of 500W in continuous wave (CW) mode. This circulator features a 7/16(f) coaxial interface on all three ports, making it suitable for high-power applications where a coaxial design is preferred.
The WRD200 circulator achieves a matching level of over 14 dB at the input port, with 13.5 dB isolation across the 2-4 GHz range. The insertion loss is -0.7 ± 0.2 dB, which, while slightly higher than waveguide interfaces, is still within acceptable limits for coaxial designs. Similar to the WRD350 isolator, the circulator's design includes DC magnets for external biasing and tuning screws to optimize performance.
Measured S-Parameter of the WRD200 High-Power circulator with coaxial interface
SMC has also developed several prototypes of high-power circulators and isolators that support various applications. For example, the WRD250S/WRD600 models are specially designed Double-Ridge waveguide structures that cover an extremely wide band of 3:1. The WRD600P is another model designed to handle very high power, demonstrating SMC's capability to develop customized solutions for specific requirements.
Design Considerations for High Power Isolators & Circulators
Designing high-power circulators and isolators involves addressing several critical parameters to ensure reliable performance. These parameters include:
- Frequency and Waveguide Dimensions: The design process begins by determining the operating frequency and corresponding waveguide dimensions, including width, height, and gaps between the ridges in the Double-Ridge waveguide.
- Ferrite Selection: The choice of ferrite is crucial, particularly for high-power applications. The selected ferrite must have appropriate magnetic properties, including large linewidth and high saturation magnetization, to handle the required power levels and achieve the desired return loss, isolation, and insertion loss.
- Power Handling: High-power circulators and isolators must be capable of handling significant RF power without damage. This requires careful material selection, including the use of high-thermal epoxy glue for the ferrite base and consideration of alternative designs if a single junction cannot handle the power level. Power-handling analysis through Electromagnetic (EM) simulations is essential to verify the component’s ability to handle high power without breakdown.
- Impedance Matching: Proper impedance matching is critical to minimize reflected power and maximize power transfer. Techniques such as multi-section stepped transformers are commonly used for impedance matching in waveguide assemblies.
- Pressurization: For applications such as satellites and space missions, pressurization is used to protect components from environmental factors like moisture and to enhance peak power handling capabilities.
- Testing and Post-Fabrication Tuning: Components undergo rigorous testing using vector network analyzers (VNA) and spectrum analyzers to ensure they meet performance specifications. Post-fabrication tuning is often required to optimize matching levels and improve overall performance.
- Cooling and Thermal Management: High-power components generate heat, necessitating cooling solutions such as heat fins to dissipate heat and prevent overheating.
- Size and Weight Considerations: The physical size and weight of the circulator or isolator must be appropriate for the intended application, taking into account space constraints and integration requirements. Proper weight balancing and support structures are also important for ensuring mechanical stability.
SMC continues to explore new developments in high-power microwave technology. Future work includes more complex designs, such as Dual-junction Double-Ridge waveguide isolators, capable of handling even higher power levels.
Click here for more information on the WRD350 high-power isolator and the WRD200 high-power circulator.
