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HIGH LINEARITY SSPAs FOR THE 2.3 – 2.7 GHz MARKET

SM1720-48L Microwave Journal Article

The demand for high speed data transmission is on the rise. Thanks to the world-wide-web, data transmission has become the fastest growing segment of the telecommunications market. Fiber optics and high speed copper, DSL and T1, have satisfied many of the urban areas, but suburban and rural America continue to crawl at 28 and/or 56 kbps. Since cable TV companies have been slow to capture the growing market, a large window of opportunity has been opened.

Many wireless operators are currently performing trials in wireless local loop and fixed point broadband access using new techniques such as orthogonal frequency division multiplexing (OFDM). Several frequency bands have become popular for these trials, including Wireless Communication Services (WCS) at 2.305 – 2.360 GHz, Industrial, Scientific and Medical (ISM) at 2.385 GHz and Multichannel Multipoint Distribution Systems (MMDS) at 2.500 – 2.686 GHz.

These trials demand ultra linear RF subsystems with very low intermodulation products (IMDs). Since the high power amplifier is typically the leading cause of IMD products, it usually dictates the linearity of the entire transmitter. Another hurdle system providers face is rough environmental conditions since the subsystems are typically placed on telephone poles and/or rooftops to maximize RF coverage. With this type of deployment, a large, feedforward basestation amplifier can not be used since its power consumption and cooling requirements are too difficult to satisfied under the aforementioned conditions. A small, high efficiency, ultra linear amplifier is the only solution.

To address this market, Stealth Microwave has completely redesigned its 2.3 – 2.7 GHz high power amplifier line. By incorporating the latest GaAs technology, the amplifiers deliver similar performance to their predecessors, while consuming 20 to 40 percent less DC power! Exterior dimensions of 7.5 x 4.0 x 0.8 inches, remain unchanged. The units operate in frequency bands between 2.3 GHz and 2.7 GHz, and range in output power (P1dB) from 12 Watts to 25 Watts. Power levels to 100 Watts (SM2527-50 & 50L) are also available. The line-up also consists of models incorporating Stealth’s proprietary predistortion linearization, which improves the output intercept point (OIP3) by 6 to 7 dB. The following specifications are for the SM2325-41L:

Electrical CharacteristicsSM2325-41L
1.1 Frequency Range2.3 – 2.5 GHz
1.2Pout (P1dB)+ 41 dBm
1.3Third Order Intercept Point+ 60 dBm
1.4 Linear Gain55 dB ± 2 dB
1.5Gain Flatness over Full Band± 0.5 dB
1.6Input/Output VSWR1.4:1/1.3:1
1.7 DC Input Voltage+ 12 Volts
1.8 DC Input Current, typ.4.3 Amps (Varies per application)


The pre-distortion circuitry uses amplitude and phase correction to the reduce the IMDs created in the amplifier. For the SM2325-41L, IMD levels are 60 dBc, at an average output power of 35 dBm, vs. 40 dBc for a non-linearized unit. See Figure 1.

Figure 1


Similar performance can be produced in the 2.5 –2.7 GHz band with the SM2527-41L. If more power is needed, 20W non-linearized (SM2527-43) and 25W linearized (SM2527-44L) versions are also available. Specifications for the SM2527-44L are shown below:

Electrical CharacteristicsSM2527-44L
1.1Frequency Range2.5 - 2.7 GHz
1.2Pout (P1dB)+ 44 dBm
1.3Third Order Intercept Point+ 63 dBm
1.4Linear Gain55 dB ± 1 dB
1.5Gain Flatness over Full Band± 0.5 dB
1.6Input/Output VSWR1.4:1/1.3:1
1.7DC Input Voltage+ 12 Volts
1.8DC Input Current, typ.10 Amps (varies per application)


All units have several built in features, including a single DC power supply, over/ reverse voltage protection, and thermal protection, which automatically turns the unit off if the baseplate temperature exceeds +70 o C and will reset once the temperature returns to operating conditions. Logic On/Off control is also standard, allowing the user to turn the unit on and off via a TTL signal. Optional features include Forward/Reverse Power Detection, an RF Sample port for analog monitoring, and for the first time, a TTL pin for high speed switching at rates up to 10 uS.