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RF Components: Power Amplifiers

SM1720-48L Microwave Journal Article

As PCS systems are deployed, many service providers are finding that conventional base stations do not always provide satisfactory service over the entire cell. This is typically caused by two issues: first is coverage holes, which are caused by obstructions like those found in urban areas and indoor locations; second is dropped calls, due to over-capacity.

To effectively address these issues, providers are selecting smaller, less expensive repeater stations which simultaneously fill coverage holes and increase capacity. However, as wireless communications increase in popularity, more powerful repeaters are needed to help PCS systems maintain high quality service.

One of the main challenges repeater manufacturers face, as they try to increase their output power, is the performance of the power amplifier. Requirements for these units include multi-carrier capabilities, low power consumption, small size and an affordable price.

Stealth Microwave, Inc. has established itself as a leading manufacturer of compact, high quality, ultra-linear amplifiers. Their latest model, SM1720-48L, offers a new solution to higher power repeater requirements. Using the latest GaAs FET technology, in conjunction with Stealth’s proprietary predistortion circuitry, the SM1720-48L boasts an output third order intercept (OIP3) of +66 dBm. This performance is equivalent to a conventional 400 Watt amplifier.

The SM1720-48L provides +48 dBm (P1dB) of output power, and can transmit 17 Watts of CDMA (single channel) or >12 Watts for 4 FA CDMA systems. Working in 100 MHz bands from 1.7 to 2.0 GHz, the SM1720-48L requires 16 Amps. (typ.) at +12V. Linear gain is 56 dB, gain flatness is ± 0.4 dB, and input VSWR is better than 1.4:1.

The amplifier has several built in features including single supply operation (+12V), over/reverse voltage protection, and thermal shutdown (with automatic reset). Logic On/Off control, which is also standard, allows the end user to turn the unit on or off with a TTL signal. An optional Forward Power detector is also available; this allows for monitoring or the transmitted power. All of the forementioned is available over a temperature range from 0 to +75° C (baseplate).

Stealth’s predistortion approach offers a lower parts count, smaller size and higher reliability than typical feedforward designs. With thousands of units already in the field, Stealth’s proven technology can fulfill the requirements of repeater designers. Stealth’s ultra-linear performance, low power consumption, and affordable price, make Stealth the obvious choice.