A 10 to 20 GHz Solid-state Amplifier
AR RF/Microwave Instrumentation is introducing a new 5 W solid-state microwave amplifier (SSMA) that operates from AC power. The model 5S10G20 amplifier features high gain, low noise and good linearity making it an excellent replacement for traveling wave tube amplifiers (TWTA). It provides instant power with the press of a button and requires no warm-up time.
The 5S10G20 solid-state amplifier’s block diagram is shown in Figure 1. The design utilizes numerous GaAs FETs and MMICs in a balanced configuration. All devices are biased class A using an active bias circuit. The output stages are combined using AR proprietary technology.
The instrument features a minimum of 5 W output power, 40 dB of gain and a typical noise figure of 6 dB (a significant improvement over a typical TWT amplifier). Gain flatness is within ±1.5 dB across the band, as shown in Figure 2. All second harmonics are better than 20 dBc and the third-order intercept is typically +46 dBm. In addition, the broadband amplifier is protected with an overdrive circuit at the input. Figure 3 shows the amplifier’s typical power output characteristics.
The model 5S10G20 amplifier is selfcontained, air-cooled and designed for applications where instantaneous bandwidth and high gain are required. Housed in a stylish contemporary cabinet, the unit is designed for benchtop use, but can be removed from the cabinet for equipment rack mounting. When used as a sweep generator, it will provide a minimum of 5 W of RF power. A front panel gain control is included that permits the operator to conveniently set the desired output level.
The new amplifier is protected from RF overdrive by an RF input leveling circuit that controls the input level applied to the first stage of amplification when the RF input is increased above 0 dBm. In addition, the individual RF amplifier stages are protected from over temperature by removing the DC voltage applied to them if an over temperature condition occurs due to a cooling blockage or fan failure. There is a digital display on the front panel to indicate the operational status and fault conditions when an over-temperature or power supply fault has occurred. The unit can subsequently be returned to normal operation when the condition has been cleared.
The 5S10G20 amplifier includes a digital control for both local and remote control of the amplifier. This eight-bit RISC microprocessor-controlled board provides both IEEE-488 (GPIB) and asynchronous, full duplex RS-232 control of all amplifier functions. Table 1 lists the model 5S10G20 amplifier’s electrical specifications.
Advantages over TWTAs
AR RF/Microwave Instrumentation manufactures high grade microwave and millimeter-wave amplifiers based on a hybrid thin film and GaAs chip technology. Compared to TWT amplifiers, solid-state amplifiers offer significant advantages over TWTAs in similar applications. As the tube in a typical TWTA ages, the output power continually decreases and readjustment is required. Eventuallythe tube will need to be replaced. On the contrary, solid-state microwave amplifiers do not require readjustment. The SSMA will outlast the TWTA. The average mean time between failure (MTBF) for a SSMA is greater than 20 years, while the MTBF for a TWT has an average of eight years.
The SSMA is more cost effective than a TWTA. The amplifier provides good linearity for low power levels up to P1dB. Meanwhile, the dynamic range of a TWT amplifier is less than the SSMA because of its noise floor at low power levels, and its harmonics and spurious outputs at high power levels. In conclusion, the SSMA provides a much cleaner, more stable output and better intermodulation performance.
AR RF/Microwave Instrumentation
Souderton, PA (215) 723-8181