Building a 3.3 to 3.8 GHz 802.16a WiMAX LNA on FR4 Material

Fig. 1 ATF-54143 low noise amplifier’s (a) circuit schematic and (b) ADS simulation.

This article presents the design of a 3.3 to 3.8 GHz LNA, suitable for IEEE 802.16a WiMAX customer premise equipment (CPE) and base transceiver stations (BTS), built on inexpensive FR4 copper laminate epoxy glass board material using the Agilent Technologies ATF-54143 E-pHEMT (enhancement-mode pseudomorphic high electron mobility transistor).

The high loss tangent (tan ?) and relatively variable dielectric constant (?r) of the FR4 copper laminate epoxy glass material (tan ? = 0.04, ?r = 4.6) generally limits its use to applications below 3 GHz.1 For higher frequencies, designers usually use more expensive materials such as the Rogers RO4350B glass-reinforced hydrocarbon/ceramic laminate2 with tan ? = 0.003 and ?r = 3.48. Normally, the insertion loss for the FR4 board will increase rapidly when the operating frequency goes above 3 GHz, and designing 3 GHz circuits using FR4 material is usually not recommended. When using high performance devices such as the ATF-54143, however, circuits designed on FR4 material can meet the customer’s requirements for noise figure, gain and linearity. The biggest benefit to customers is the lower cost of the FR4 material. This is a critical concern for customers’ main production. With the increasing acceptance of WiMAX as a substitute for the existing broadband wire-line infrastructure in the last mile, people are now designing and testing WiMAX CPE and BTS operating at around 3.5 GHz. Properly designed circuits on a FR4 board can help to reduce the transceiver cost. Based on theoretical analysis and ADS simulation, this article presents a successful WiMAX LNA built on a FR4 board using the ATF-54143 E-pHEMT.

Fig. 2 Input S* 11 and Γopt for the ATF-54143 transistor.

Target Analysis

With a single 3.6 V supply, the E-pHEMT LNA delivers a measured 0.82 dB noise figure (NF), 12.8 dB gain, +19 dBm output power at 1 dB gain compression (P1dB), 36.7 dBm third-order output intercept point (OIP3), –20 dB input return loss (IRL) and –12 dB output return loss (ORL) at 3.5 GHz.

To arrive at a balance between noise figure, gain and linearity, the device drain source current (Ids) was chosen to be 60 mA with a 3 V drain-to-source voltage; the gate-to-source voltage was 0.59 V. According to the ATF-54143 data sheet,3 this transistor has the following typical features at 3.5 GHz: Fmin = 0.65 dB, Ga = 14.5 dB, OIP3 = +37.2 dBm, S11=0.608< 149.60 (VSWR?4.1), ?opt = 0.32<-1700.