Microwave Journal
www.microwavejournal.com/articles/33760-kw-solid-state-microwave-generator-for-ism-applications

6 kW Solid-State Microwave Generator for ISM Applications

April 13, 2020

RFHIC’s 6 kW, solid-state microwave generator provides enhanced performance for 2.4 GHz industrial, scientific and medical (ISM) applications, such as CVD reactors for artificial diamond growth, PVD thin film deposition equipment for semiconductor films and drying/sterilization for industrial food processing.

Using GaN power amplifiers (PA), the compact and lightweight RIU256K0-40T generator operates from 2.4 to 2.5 GHz, combining four, 1.6 kW GaN PAs into a stand-alone, rack mounted solid-state power amplifier (SSPA) that is modular and fault tolerant (see Figure 1). The SSPA supports both CW and pulse operation and can be customized to application requirements. With an adjustable power range from five to 100 percent of rated output, the RIU256K0-40T utilizes RFHIC’s technology enabling high system efficiency at both low and high power levels (see Figure 2).

Figure 1

Figure 1 SSPA head.

Figure 2

Figure 2 System efficiency vs. output power.

Each of the four GaN PAs in the generator uses RFHIC’s high performance GaN on SiC transistor technology, which provides wide bandwidth, high efficiency, high breakdown voltage and reduces the overall size of the system. The RIU256K0-40T uses 200 W transistors (IE24200P), which have a saturated output power of 230 W and 74 percent drain efficiency at 50 V bias. The fully matched transistors are integrated with DC blocking capacitors on both RF ports to simplify SSPA integration.

SSPA vs. TUBE

Many historic RF energy applications use vacuum tubes or magnetrons as the core power source. Such systems have significant disadvantages controlling the frequency, power and phase. The RIU256K0-40T includes RFHIC’s drive and control module to precisely set the output frequency and power, and the generator delivers a clean signal with low noise and spurious compared to a magnetron (see Figure 3). Another advantage is the capability to generate full power without any warm-up time.

Tubes have short lifetimes - often less than 6,000 hours - causing down time and increasing operating cost. The RIU256K0-40T’s lifetime is between 50,000 and 100,000 hours, depending on the operating conditions, which yields significant cost savings. Unlike magnetrons and other tube-based systems with a single power source, the RIU256K0-40T combines four rugged GaN SSPAs, enabling the system to degrade gracefully if one of the PAs fails. Tube-based systems require high voltage power supplies inside the generator, which are susceptible to arcing. The SSPA operates at a safer voltage of 50 V.

Figure 3

Figure 3 Signal purity of the SSPA head (SH) compared to a magnetron head (MH).

The RIU256K0-40T uses water cooling to eliminate large metal heat sinks and reduce generator size. With water cooling, the SSPA can be compatible with the existing cooling infrastructure for a tube-based system, which reduces installation and operating costs for the customer. The system has multiple sensors to detect water flow rate, SSPA temperature and VSWR. In case of abnormal operation, the system will automatically shut down and alert the user, ensuring the generator is not damaged. The RIU256K0-40T has an LCD touchscreen and jog wheel, providing full access to the system controls, sensors and alarms; full monitoring and control is also accessible using a laptop or remote PC. Controlling the system remotely via PLC, CAN or Bluetooth is available as an option.

MODULAR DESIGN

The RIU256K0-40T is a stand-alone, rack mounted system with two parts:

  • SSPA head with isolator, which is 42.4 cm wide, 74.7 cm long, 25.6 cm high and weighs 41 kg.
  • Power supply, which is 48.3 cm wide, 43.2 cm long, 17.7 cm high and weighs 29 kg. The power supply uses three-phase, 380 V AC and generates the 50 V bias for the GaN transistors. The power supply contains six, 3 kW rectifier modules designed to load share, be hot-swappable and n+1 redundant, meaning the SSPA will continue to operate if one of the power modules fails. The failed module can be replaced without replacing the entire generator.

Four 1.6 kW SSPAs are combined to produce the 6 kW CW output, using RFHIC’s four-way waveguide combiner. From 2.4 to 2.5 GHz, the WR340 combiner has a maximum insertion loss of 0.1 dB with 1.1:1 VSWR and less than 3 degrees imbalance among the ports. The generator is scalable, meaning users can add RFHIC’s commercial off-the-shelf PAs without manual phase synchronization. This flexibility maximizes amplifier utilization, reduces capital expense and shortens development time.

RFHIC Corp. is semi-vertically integrated, the only company with a portfolio from GaN transistors and PAs to full systems, from commercial off-the-shelf products to custom module and sub-system designs with output power to multi-megawatts. RFHIC’s extensive capabilities ensure low cost and quality products, with fast lead times and after-care service.

RFHIC Corp.
Anyang, South Korea
www.rfhic.com