This application bulletin describes the use of the ATF-36077 in a 5.7 GHz application. The ATF-36077 amplifier uses microstripline matching circuitry to obtain a low noise stable amplifier with good input and output return loss. Design The input microstripline network matches the ATF-36077 for low noise and reasonable input return loss. The output microstripline network provides a conjugate impedance match for maximum associated gain.

Some resistive loading is used to improve stability. Quarterwave bias decoupling lines with low frequency resistive terminations are used to couple in the gate and drain voltage. For best overall performance including stability, it is suggested that both source leads be dc grounded. The somewhat customary low frequency LNA design approach of using a source resistor to bias the FET would require a source bypass capacitor with extremely low series inductance. Even a tenth of a nanohenry of source inductance can cause very high frequency stability problems with HEMT devices. The Figure 1. Artwork for 5.7 GHz Low Noise Amplifier for ER = 2.2 and PCB thickness 0.031 inches use of dc grounded source leads necessitates the use of a negative voltage to be applied to the gate to set the desired drain current. The artwork for the 5.7 GHz amplifier is shown in Figure 1. The amplifier was originally designed for the amateur radio band at 5760 MHz and provides very low noise performance over the 5725 to 5800 MHz ISM band with no additional tuning. With minimal tuning the amplifier can be used anywhere in the 5 to 6 GHz frequency range. A schematic diagram and component parts list is shown in Figure 2. The nominal gate bias is -0.2 volts for a drain current of 10 mA. Vds is set to 1.5 volts. Measured noise figure is approximately 0.75 dB at 2.0 INCHES ATF-36077 WB5LUA 03/96 ER = 2.2 T = 0.031 Vdd Vgg INPUT OUTPUT 5.76 GHz. A graph of noise figure and gain versus frequency is shown in Figure 3. Input and Output return loss are shown in Figure 4. For technical assistance or the location of your nearest Hewlett-Packard sales office, distributor or representative call: Americas/Canada: 1-800-235-0312 or (408) 654-8675 Far East/Australasia: Call your local HP sales office. Japan: (81 3) 3335-8152 Europe: Call your local HP sales office. Data Subject to Change Copyright © 1997 Hewlett-Packard Co. Printed in U.S.A. 5966-1277E (12/97) Freq. Gain Noise (MHz) (dB) Figure (dB) 5000 13.2 1.10 5050 13.4 1.06 5100 13.6 1.02 5150 13.7 0.99 5200 13.8 0.96 5250 13.8 0.92 5300 13.8 0.90 5350 13.7 0.86 5400 13.6 0.83 5450 13.4 0.82 5500 13.2 0.79 5550 13.1 0.79 5600 12.9 0.78 5650 12.7 0.76 5700 12.6 0.76 5750 12.3 0.75 5800 12.1 0.77 5850 11.6 0.78 5900 11.4 0.80 5950 11.1 0.81 6000 10.6 0.86 Figure 3. Gain and Noise Figure Figure 4. Input and Output Return Loss Figure 2. 5.7 GHz Low Noise Amplifier Schematic Diagram