Antennas, Antenna Cables, Wireless Products: Technical Articles
Antenna Testing with Vector Network Analyzers (VNAs)
Table of Contents
- VNA testers: Indispensable tools in the design, testing, and optimization of antennas.
- Why Use a VNA for Antenna Testing?
- Typical VNA Testing Setup for Antennas
- Example Use Cases
- Advantages of Using a VNA for Antennas
- Practical Tips
- Common Vector Network Analyzer (VNA) models, their frequency ranges, ports, typical use cases, and price tiers:
- Conclusion
- FAQs
VNA testers: Indispensable tools in the design, testing, and optimization of antennas.
VNA testers provide a precise and versatile method for analyzing how antennas perform across their intended frequency ranges and under real-world conditions.
In the world of RF and microwave engineering, Vector Network Analyzers (VNAs) are essential instruments for evaluating the behavior of radio frequency components—including one of the most critical components in any wireless system: The antenna: From simple whip antennas to complex phased arrays.
A Vector Network Analyzer is an electronic instrument used to measure the network parameters of electrical networks, primarily in the RF, microwave, and millimeter-wave frequency ranges. VNAs assess how RF signals transmit and reflect through a device under test (DUT), typically presenting data in the form of S-parameters (scattering parameters).
Key Capabilities of VNAs:
S11 (Return Loss / Reflection Coefficient) – How much signal is reflected back from the antenna.
S21 (Insertion Loss / Forward Gain) – How much signal passes through from one port to another.
Phase and magnitude of signal responses.
Impedance matching diagnostics.
Real-time Smith Chart, VSWR, and gain visualization.
Why Use a VNA for Antenna Testing?
Antennas are passive components designed to radiate or receive electromagnetic signals efficiently at specific frequencies. Testing with a VNA helps ensure that the antenna:
Is properly matched to its feed line (typically 50 ohms).
Performs within its advertised bandwidth (frequency range).
Minimizes return loss (reflections that waste energy).
Operates with desired VSWR levels (ideally ≤ 2:1).
A poorly tuned antenna can result in:
Reduced range
Lower signal quality
Heat generation in transmitters
Increased battery drain in mobile devices
Common VNA Tests for Antennas:
| Measurement | Purpose |
|---|---|
| S11 / Return Loss | Shows how well the antenna is matched to the transmission line |
| VSWR (Voltage Standing Wave Ratio) | Measures reflection efficiency; VSWR of 1.5:1 or lower is often desirable |
| Impedance Plot | Confirms the antenna’s feed-point impedance across frequency |
| Bandwidth Verification | Ensures antenna maintains performance across its intended band |
Typical VNA Testing Setup for Antennas
Components:
VNA (e.g., Keysight, Rohde & Schwarz, NanoVNA)
Calibration kit (Open, Short, Load standards)
RF test cables and adapters
Antenna under test (AUT)
Anechoic chamber or open test environment (for far-field measurements)
Basic Steps:
Calibrate the VNA at the end of the test cable using SOLT (Short, Open, Load, Through) or equivalent.
Connect the antenna to Port 1 of the VNA (single-port S11 test).
Measure and analyze:
S11 curve
Smith Chart impedance trace
VSWR across frequency range
Optionally compare to datasheet specs or known standards.
Example Use Cases
Antenna development labs test new designs for embedded wireless modules (LoRa, GPS, Wi-Fi, LTE).
Field engineers use portable VNAs to verify and tune antennas on installed systems (base stations, IoT devices, UAVs).
Manufacturing QA ensures each antenna batch meets return loss and impedance specs.
Advantages of Using a VNA for Antennas
High precision vs simpler tools like SWR meters or spectrum analyzers
Wide frequency range (many VNAs support MHz to GHz)
Visual diagnostics (e.g., Smith Charts help with tuning)
Real-time feedback for adjusting antenna elements or matching networks
Practical Tips
Always calibrate close to the DUT to eliminate cable effects.
Use flexible, low-loss RF cables to maintain signal integrity.
Avoid nearby conductive objects when testing—especially at high frequencies.
For far-field radiation pattern testing, pair the VNA with a turntable and test antenna in an anechoic chamber.
Common Vector Network Analyzer (VNA) models, their frequency ranges, ports, typical use cases, and price tiers:
| Model | Frequency Range | Ports | Use Case | Price Tier |
|---|---|---|---|---|
| NanoVNA V2 Plus4 | 50 kHz – 4.4 GHz | 2 | Hobbyist/field | Lower (~$170–$300) |
| NanoVNA‑H4 | 50 kHz – 1.5 GHz | 2 | Entry-level antenna testing | Lower (~$70–$110) |
| RigExpert AA‑230 ZOOM | 100 kHz – 230 MHz | 1 | HF/VHF antenna & cable | Lower (~$300–$400) |
| Siglent SVA1015X + VNA | 9 kHz – 1.5 GHz | 2 | Budget bench measurements | Mid (~$1,800–$2,500) |
| Anritsu ShockLine MS46122B | 1 MHz – 6 GHz | 2 | Production testing | Mid (~$7,000–$10,000) |
| Keysight FieldFox N9912A | 30 kHz – 6.5 GHz | 2 | Rugged field use | Higher (~$10,000+) |
| Copper Mountain S5065 | 9 kHz – 6.5 GHz | 2 | Lab/microwave R&D | Higher (~$12,000+) |
| Rohde & Schwarz ZNL3 | 5 kHz – 3 GHz | 2 | Lab‑grade precision | Higher (~$15,000–$20,000) |
| Keysight E5071C ENA | 9 kHz – 20 GHz | 2–4 | R&D & production | Higher (~$12,000–$50,000+) |
Conclusion
VNAs provide deep insight into how antennas behave across frequency and how well they are matched to their systems. Whether you're building IoT devices, installing wireless infrastructure, or troubleshooting range issues, mastering VNA antenna testing is a crucial skill for RF engineers and technicians alike.
FAQs
What is a Vector Network Analyzer (VNA) and why is it important for antenna testing?
A Vector Network Analyzer (VNA) is an electronic instrument used to measure network parameters of RF, microwave, and millimeter-wave systems. It evaluates how signals are transmitted and reflected by a device under test (DUT), usually expressed as S-parameters. In antenna testing, VNAs are indispensable because they reveal how well an antenna is matched to its system, its bandwidth performance, and its overall efficiency.
What are the key parameters a VNA measures for antennas?
The most common VNA measurements include:
- S11 (Return Loss / Reflection Coefficient): Shows how much signal is reflected back from the antenna.
- S21 (Insertion Loss / Forward Gain): Indicates how much signal passes from one port to another.
- Impedance: Verifies how closely the antenna matches the feed line (usually 50 ohms).
- VSWR (Voltage Standing Wave Ratio): Assesses reflection efficiency, ideally ≤ 2:1.
- Smith Chart Analysis: Visualizes impedance and matching conditions in real time.
Why is impedance matching important in antenna testing?
Impedance matching ensures that the maximum amount of signal is transferred between the antenna and the transmission line. Poor matching causes reflections (high return loss), which reduce range, degrade signal quality, waste power as heat, and can even damage transmitters or shorten battery life in mobile devices.
What are the most common VNA tests performed on antennas?
Key tests include:
- Return Loss (S11): Indicates how efficiently the antenna radiates.
- VSWR: Measures reflection efficiency; a lower ratio means better matching.
- Impedance Plots: Confirms feed-point impedance across frequency.
- Bandwidth Verification: Ensures the antenna maintains performance across its specified operating range.
How do you set up a VNA for antenna testing?
A typical setup includes:
- VNA instrument (e.g., Keysight, Rohde & Schwarz, NanoVNA).
- Calibration kit (Open, Short, Load standards).
- RF cables/adapters for connection.
- Antenna under test (AUT).
- Testing environment (anechoic chamber or open area for far-field tests).
Steps: Calibrate the VNA (SOLT method), connect the antenna to Port 1, and measure S11, VSWR, and impedance across the frequency range.
What are some advantages of using a VNA over simpler tools?
VNAs provide:
- Higher precision compared to SWR meters or spectrum analyzers.
- Wide frequency coverage (from MHz to multi-GHz).
- Real-time diagnostic visuals such as Smith Charts.
- Immediate feedback for tuning antennas or matching networks.
What are common mistakes to avoid when testing antennas with a VNA?
- Not calibrating close to the DUT: Cable effects can skew results.
- Using poor-quality cables: High-loss or stiff cables reduce accuracy.
- Testing near conductive objects: Surrounding metal can distort readings.
- Skipping environment control: Antennas may behave differently indoors vs. in anechoic or open-field setups.
Which VNAs are commonly used for antenna testing, and what do they cost?
Examples of popular models:
- NanoVNA V2 Plus4: 50 kHz–4.4 GHz, portable, ~$170–$300.
- RigExpert AA-230 ZOOM: 100 kHz–230 MHz, great for HF/VHF, ~$300–$400.
- Anritsu ShockLine MS46122B: 1 MHz–6 GHz, production testing, ~$7,000–$10,000.
- Keysight FieldFox N9912A: Rugged field VNA, ~$10,000+.
- Keysight E5071C ENA: Lab-grade, up to 20 GHz, ~$12,000–$50,000+.
The choice depends on whether you’re a hobbyist, field engineer, or working in advanced R&D.