Columbia, MD

Today's wireless base stations operate in a duplex mode and require a duplexer at the antenna to provide low insertion loss and high power capabilities in the transmit mode and low noise amplification and steep attenuation close to the passband in the receive mode. A new duplexer assembly has been developed that is aimed at these stringent requirements and makes use of the considerable performance advantage of high Q ceramic resonators. The model 80163 duplexer/combiner/receive distribution amplifier (RXDA) is designed for 900 MHz wireless data two- or four-channel operation. The two-channel system comprises the company's models 80212 duplexer, 80189-937 combiners, 80119-2 power divider and 80251 low noise amplifier (LNA). The integrated subsystem is capable of expanding from two-channel to four-channel operation with the appropriate changes in internal components and contains duplex filtering that has been optimized for hostile RF environments.

Fig. 1 The duplexer/ combiner/RXDA's block diagram. t

The subsystem makes use of high Q ceramic resonators to form the filtering and offers very low insertion loss and steep attenuation to the neighboring AMPS transmit band (894 MHz) and paging frequencies (902 MHz). Featuring greater than 90 dB of RX-to-TX isolation, this duplexer offers excellent channel-to-channel isolation. In addition, the transmit path includes an integrated second-harmonic notch filter.

Figure 1 shows the unit's block diagram in a four-channel configuration. The duplexer is designed to operate over an 896 to 901 MHz RX frequency band and a 935 to 940 MHz TX band, and utilizes the latest in ceramic resonator technology to obtain maximum performance. The proprietary resonator and support design simplifies manufacture and enables production of a consistent-quality product.

The two-channel hybrid combiner comprises a microstrip design with an internal load and integrated heat sinking, allowing it to handle 60 W per channel. The design also includes two dual-stage ferrite isolators that offer –50 dB of antenna-to-TX isolation. That level combined with the isolation of the hybrid provides –80 dB of TX-to-TX isolation over the 935 to 940 MHz TX range. The two-channel combiner is available as a separate standard unit (model 80189-937), which covers the 912 to 963 MHz frequency range and can be easily modified to shift higher or lower in frequency depending on the requirement.

Fig. 2 The amplifier's performance with the two-way power divider in the (a) active and (b) bypass operating modes.

The power divider is a shielded microstrip design composed of standard Wilkenson divider circuits. The unit is available in two-, three- and four-channel configurations as separate products (models 80119-2, 80119-3 and 80119-4, respectively). The individual units cover the 800 to 900 MHz frequency range, and a PCS version is also available.

The pre-amplifier is a low noise, high dynamic range amplifier designed for ultralinear receiver applications in the 925 to 960 MHz range. The circuit is matched to 50 W and employs a single-stage GaAs FET with internal matching to provide exceptional noise figure in combination with a high +36 dBm IP3 typ. The LNA requires +12 V DC for operation and has an integrated current monitoring circuit with TTL output and light-emitting diode status indicators. The design also includes an RF bypass switch in case of power supply or device failure. Figure 2 shows the amplifier's performance with the two-way power divider in both active and bypass operating modes.

Fig. 3 Typical duplexer performance; (a) RX only and (b) RX and TX.

Specifications for the 80163 duplexer include an 896 to 901 MHz RX frequency passband with an insertion loss of < 1.75 dB and a return loss of > 15 dB. Attenuation in the 825 to 894 and 935 to 940 MHz bands is > 82 dB and > 90 dB, respectively. Attenuation at 902 MHz is > 40 dB. The TX passband is 935 to 940 MHz with an insertion loss of < 1 dB and return loss of > 18 dB. Attenuation at 896 to 901 MHz is > 90 dB and second harmonic suppression at 1870 to 1880 MHz is > 80 dB. Figure 3 shows typical duplexer performance vs. frequency.

The combiner features isolation of > 80 dB TX to TX and > 50 dB antenna to TX. Maximum power handling is 60 W per channel and insertion loss per channel is < 4 dB.

The two-channel RXDA has a specified gain of 9.5 dB ±1 dB and a noise figure of < 2.7 dB. Third-order intercept is +33 dBm typ. Maximum current consumption is 250 mA at +12 V DC and the TTL output is low with an amplifier failure. The 80163 unit is housed in two stacked 19-inch rack-mounted decks and operates from &ndash;30° to +60°C. Additional information may be obtained from the company's Web site at www.fsymicrowave.com or via e-mail at sales@fsymicrowave.com.

FSY Microwave Inc., Columbia, MD (410) 381-5700.

Circle No. 303