This repository presents the complete design and simulation workflow of a single-stage Low Noise Amplifier (LNA) developed to amplify weak RF signals in the 1.8–2.6 GHz band. The amplifier was designed using standard microwave design methodology and simulated using Keysight Advanced Design System (ADS).
The objective of the design was to achieve high gain, low noise figure, and unconditional stability while maintaining practical biasing and matching networks suitable for hardware implementation.
The LNA was designed to:
- Amplify low-power RF signals with minimal added noise
- Maintain unconditional stability across the operating band
- Achieve an optimal trade-off between gain, noise figure, and stability
| Parameter | Value |
|---|---|
| Center Frequency | 2.0 GHz |
| Small Signal Gain (S21) | ≈ 14 dB |
| Minimum Noise Figure | ≈ 0.83–0.93 dB |
| Input Return Loss (S11) | ≈ −14 dB |
| Output Return Loss (S22) | ≈ −22 dB |
| Stability Factor (μ, μ′) | > 1 across band |
The amplifier uses the ATF-21170 GaAs FET, chosen for its:
- Low intrinsic noise
- High gain at microwave frequencies
- Accurate S-parameter models available for simulation
A stabilization network consisting of:
- Gate damping resistor
- Source inductive degeneration
was implemented to ensure unconditional stability, verified using Mu (μ) and Mu-prime (μ′) stability factors.
The transistor was biased at:
Vds = 3 V
Ids ≈ 20 mA
RF chokes and DC blocking capacitors were used to isolate the RF and DC paths while maintaining proper biasing conditions.
Both Input Matching Network (IMN) and Output Matching Network (OMN) were designed using the Smith Chart Utility in ADS.
The matching networks were implemented using lumped elements:
- Inductors for impedance transformation
- Capacitors for DC blocking and reactive tuning
This ensured the source and load impedances were transformed close to their optimal reflection coefficients (Γs and ΓL).
The LNA was developed using the following RF design workflow:
The ATF-21170 transistor model in ADS was verified against the datasheet to ensure accurate simulation behavior.
A bias point of Vds = 3 V and Ids ≈ 20 mA was selected to balance gain and noise performance.
Stability was analyzed using:
- Mu (μ) factor
- Mu-prime (μ′) factor
A stabilization network was introduced until μ > 1 across the frequency band, ensuring unconditional stability.
Input and output matching networks were synthesized using the Smith Chart utility, aligning the circuit with: Γs ≈ Γopt (for low noise operation) ΓL optimized for power gain
Multiple simulation passes were performed to optimize:
- Gain (S21)
- Noise Figure (NF)
- Input/Output Return Loss
- Stability
The final LNA achieved:
- ~14 dB small-signal gain at 2 GHz
- Noise figure below 1 dB
- Good input and output impedance matching
- Unconditional stability across the band
This demonstrates an effective balance between low noise performance, gain, and stable operation.
- Gonzalez, G. Microwave Transistor Amplifiers: Analysis and Design
- Keysight Advanced Design System (ADS) Documentation
- ATF-21170 Datasheet
- IEEE ICMRSISIT 2019 Conference Paper
Achutha Thyagaraju
Electrical Engineering
NIT Rourkela
+91 82961 71669
achuthathyagaraju@gmail.com
