An Ultralinear Amplifier for PCS Applications

Stealth Microwave, a division of SSB Technologies Inc.
Trenton, NJ

As PCSs are being deployed, many service providers are discovering that conventional base stations do not always provide satisfactory service over the entire cell area. This deficiency typically is caused by two factors: coverage holes due to obstructions similar to those found in urban areas or indoor locations, and dropped calls due to over capacity.

To effectively address these issues, service providers are selecting smaller, less expensive repeater stations that simultaneously fill coverage holes and increase capacity. However, as wireless communications increase in popularity, more powerful repeaters are required to help the systems maintain a high quality of service. One of the main challenges repeater manufacturers face as they attempt to increase their systems' output power is the performance of the power amplifier. Requirements for these amplifiers include multicarrier capabilities, low power consumption, small size and an affordable price.

Table I
Key Specifications

Frequency range (GHz)
(100 MHz bands)

1.7 to 2.0

Power output (dBm) (PldB)

+ 48

OIP3 (dBm)

+ 66

Linear gain (dB)

56 ± 1

Gain flatness over full band (dB)

± 0.5

Gain change over temperature (dB)

± 0.5

Input/Output SWR


DC Input voltage (V)


The model SM1720-48L solid-state PCS amplifier offers a new solution to these higher power repeater requirements. The amplifier uses the latest GaAs FET technology in conjunction with proprietary predistortion circuitry and features an output third-order intercept point (OIP3) of +66 dBm. This level of performance is equivalent to a conventional 400 W amplifier.

Table 1 lists the amplifier's performance specifications applicable over a 0° to 75°C base plate operating temperature range. The new high power amplifier provides an output power of +48 dBm at the 1 dB compression point (P1dB) and is able to transmit 17 W of CDMA (single channel) average power or greater than 12 W with four frequency assignment (4-FA) CDMA carriers, as shown in Figure 1 . Operating in 100 MHz frequency bands from 1.7 to 2.0 GHz, the amplifier features a linear gain of 56 dB, gain flatness of ±0.4 dB and input SWR of better than 1.4, as shown in Figure 2 .

The SM1720-48L amplifier is powered from +12 V DC and has several built-in features, including single-supply operation, over- and reverse-voltage protection and thermal shutdown (with automatic reset). In addition, a standard logic on/off control permits the end user to turn the unit on or off with a TTL signal. An optional forward power detector also is available for monitoring the transmitted power. The amplifier weighs 4.3 lb and is supplied in a 7.5" x 4.0" x 3.3" housing that includes a finned heat sink. The RF connectors are SMA female (type N on the output is optional).

The new amplifier's predistortion approach offers a lower part count, smaller size and higher reliability than typical feedforward designs. This proven technology allows the SM1720-48L amplifier to fulfill the requirements of today's repeater designers and provide ultralinear performance and low power consumption at an affordable price.

Stealth Microwave, a division of SSB Technologies Inc.,
Trenton, NJ
(609) 538-8586.