WMAN RADIO A 2 . 5 GHz WMAN Radio Demonstration Circuit

W ireless Metropolitan Area N e t w o r k s (WMAN) using the IEEE 802.16/ETSI HyperMAN standard will soon be ready for deployment to deliver broadband wireless access. WMAN development is spearheaded by the WiMAX Forum of telecommunications operators and equipment suppliers, with trial deployments planned for later this year. Industry analysts expect network deployments to accelerate during 2006. The 802.16 standard is an adaptive protocol that covers applications in the 2-11 GHz frequency range, and is meant to complement the Personal Area Network standards such as Bluetooth (802.15), and Local Area Network standards such as WiFi (802.11a/b/g). The 802.16 standard supports fixed, portable, and " nomadic " users, and is envisioned to provide a number of services, such as backhaul connection for WiFi " hotspots, " broadband connec-tivity for industrial and educational campuses , and as an alternative to digital cable or DSL for " last mile " broadband service to businesses and residences. The standard offers non–line-of-sight (NLOS) service, and can deliver up to 280 Mbps service to base stations using a very spectrally efficient modulation (3.8 bit/Hz). The air interface standard combines high-data-rate QAM (quadrature amplitude modulation) with multi-tone OFDM (orthogonal frequency division multiplexing), and consequently the transmitter power amplifier must be very linear to avoid distortion due to the RF carrier's peak-to-average envelope variation. This presents new challenges to the radio design engineer. A 2.5 GHz WMAN radio demonstration circuit was designed, fabricated and tested using Filtronic Compound Semiconductors' pHEMT process technology. A 2-stage linear power amplifier is combined with a single-stage low noise amplifier and a pHEMT-based broad-band packaged SPDT switch to validate design procedures and demonstrate the basic performance specifications for a radio trans-mit/receive front-end. The power amplifier is designed to provide a linear 28.5 dBm output power, with less than 2.5% EVM (error vector magnitude) when an 802.16 modulation is applied. The receive path was designed to provide at least 13.5 dBm of input intercept point (IIP3) performance, referenced to a standard 2-tone measurement technique. A block diagram of the demonstration radio is shown in Figure 1. The Filtronic model FPD1000AS packaged pHEMT device was selected for the transmit (TX) path driver stage, and the FPD4000AF as the output stage, with the radio designed to provide at least +28.5 dBm linear power with less than 2.5% EVM using standard 802.11/802.16 modulations. Experience has shown that amplifiers need to be operated 7-8 …