While the focus today is primarily on devices, subsystems and systems for wireless frequencies, there are still many systems that operate within the HF band from 1 to 50 MHz. They include long-range radar, commercial and military communications, and scientific and industrial equipment, many of which require a combination of high RF output power and high linearity. As with their higher frequency counterparts, HF power amplifiers must be as small as possible to accommodate space constraints, while delivering rated performance with minimal cooling. The VEGA Series of RF power amplifier modules is designed to meet these requirements, delivering more than 1 kW CW in enclosures typically measuring only 4" × 2" × 1.2" and weighing about 1 lb.
The VEGA Series can be used either as stand-alone amplifiers or as building blocks in a higher power amplifier system controlled via RS-422, RS-232 or Ethernet. Delta-Sigma has used amplifiers in this series to create systems that deliver CW output power up to 4 kW over portions of the HF region and wider bandwidths.
The amplifiers achieve small size through a combination of very efficient, rugged LDMOS RF power transistors, low loss combiningnetworks and precise impedance matching, using design techniques to achieve full rated RF output power with minimum heat sinking and external convection cooling. The amplifier’s efficiency is between 65 and 68 percent depending on frequency, and it draws 27 A from a +50 V DC supply.
Over-temperature protection is integrated in the amplifier, and other protection circuits can be supplied depending on the requirements of the application. Key amplifier specifications include 26 dB gain, harmonic rejection up to -37 dBc, spurious rejection of -70 dBc and third-order intercept point of +69 dBm. More detailed specifications are shown in Table 1. The gain, efficiency and return loss of a VEGA Series 1 kW RF power amplifier from 5 to 25 MHz are shown in Figure 1.
Although they are specified for Class AB CW operation, the VEGA Series amplifiers are suitable for pulsed modulation, AM or FM and digital modulation schemes. Specifications can be modified to meet requirements from the standard broadband design to narrower or wider frequency ranges up to 230 MHz, RF output power, and mounting and connector types. The amplifiers can be specified to meet a variety of military specifications. One example is airborne operation, with an operating temperature range of -40° to +55°C, altitudes up to 10,000 ft., and shock and vibration per MIL STD-810F Method 516.5.
Other models in the series include:
- VEGA6 driver amplifier, delivering 6 W CW from 20 to 88 MHz or 20 W CW from 30 to 150 MHz or 1.7 to 30 MHz
- VEGA50, providing 50 W CW from 100 to 500 MHz
- VEGA100, with 100 W CW from 10 to 175 MHz
- VEGA150, delivering 150 W CW from 20 to 150 MHz
- VEGA200, providing 200 W CW from 30 to 88 MHz
The company has designed and manufactured solid-state RF power amplifiers that deliver extremely high power levels required for scientific and radar applications with RF outputs as high as 350 kW. A recent example is an amplifier system that powers the Doppler radar wind profiler (DRWP), recently deployed at the Kennedy Space Center. It consists of 20, 16 kW subsystems, each consisting of 10 hot-swappable
Figure 1 Gain, efficiency and return loss of a VEGA Series 1 kW RF power amplifier.
The DRWP power amplifier has a soft fail capability that allows it to continue to operate if one of the modules fails, after which a new module can be “hot swapped” for the failed one while the system is running. This quickly returns the system to full-power. Efficiency of the DRWP amplifier is about 75 percent, 45 percent from AC to RF output. The total combining losses for the entire amplifier system is only 0.3 dB, including the 40 final-stage transistors, absorptive lowpass filters, and a patented transmit/receive solid-state switch.
Delta-Sigma Inc.
Riverside, Calif.
www.111rfpower.com