DIY: Optimizing 4G/5G Reception with a Vivaldi Antipodal Antenna
Table of Contents
Antenna Design Projects - This article is part of a series.
Introduction: Why Choose a Vivaldi Antipodal Antenna Over a Classic Vivaldi? #
With the advent of 4G and 5G technologies, the need for high-performance, wide-bandwidth antennas has become crucial. Vivaldi antennas are well-known for their ability to provide broad frequency coverage and good gain, making them ideal candidates for these modern applications. However, among the different variants of this technology, Vivaldi antipodal antennas offer distinct advantages over classic models.
Unlike traditional Vivaldi antennas, which use a simpler design with classical exponential expansions, antipodal Vivaldi antennas are distinguished by their more complex structure and “butterfly” configuration. This particular configuration not only allows better adaptation for lower frequencies but also improves directivity and gain. In other words, the antipodal antenna can offer superior performance in terms of signal coverage and concentration, especially in higher frequency bands.
By opting to design a Vivaldi antipodal antenna, my goal is to leverage these advantages to meet the growing demands of 4G/5G networks. This choice will also allow me to compare the performance between the two types of antennas and gain a clearer understanding of their effectiveness in real-world applications.
This project is thus an opportunity to explore the capabilities of this advanced design while deepening my understanding of Vivaldi antennas in the context of modern telecommunications.
Step 1: Initial Design of the Vivaldi Antipodal Antenna #
The initial goal of this project is to design and fabricate a Vivaldi antipodal antenna with a maximum size based on my PCB milling capabilities, specifically an antenna measuring 180 mm by 200 mm. A larger antenna generally provides better coverage of lower frequencies, which is essential for capturing various bands used by 4G and 5G technologies.
For simulation in CST Studio, I used an elliptical cylinder which I cut to simulate the exponential expansions characteristic of Vivaldi antenna designs. The antenna’s arms are defined by exponential formulas based on the chosen frequency. This allows me to directly adjust these parameters in the software and observe the simulation results. I conducted a total of five simulations to optimize the design.
By designing a large antenna, I aim to create a reference prototype to assess frequency coverage and overall performance. This ensures that even the lower frequencies, which are often more challenging to capture, are well covered. The 4G/5G frequency bands are spread over a wide spectrum, necessitating an antenna capable of handling them effectively.
Step 2: Simulation and Optimization of the Antenna #
Designing a Vivaldi antipodal antenna involves focusing on the length and width of the antenna, which determine the frequencies it can capture, as well as the shape of the arms, which influences signal adaptation. By using an elliptical arc for these arms, the design is simplified while ensuring a smooth transition that helps cover a wide frequency range.
Based on various references, the antenna was expected to be directional and effective around 1.5 GHz, aiming for -10 dB on the S11 (a return loss indicator), ideally below 2 on the SWR (Standing Wave Ratio), and a defined directivity in the far-field.
Technical Concepts Explained: #
S11 (Reflection Coefficient or Scattering Parameter): Indicates how much energy is reflected by the antenna. A value of -10 dB or lower is generally desirable, meaning 90% or more of the energy is transmitted.
SWR (Standing Wave Ratio): This measures the efficiency of power transfer between the antenna and the transmission line. A value close to 1 is ideal, but typically, an SWR of less than 2 is targeted.
Far-Field: The region where the antenna’s radiation pattern is well-formed and where directivity and gain measurements are relevant. It’s in this region that the antenna’s performance is primarily evaluated.
Step 3: Fabrication and 3D Printed Antenna Support #
The antenna was mounted on a PETG 3D-printed support. This material was chosen for its durability and weather resistance. The support is designed to position the antenna vertically, which is essential for signal polarization and maximizing reception efficiency for 4G/5G signals.
The support design includes feet to keep the antenna in place. It is also possible to create a wall or mast-mounted version for more permanent or outdoor installations. These different configurations allow the antenna to be adapted to various environments and reception conditions.
Step 4: Comparison of Simulation Results and Real-World Testing #
After fabricating the antenna and performing real-world measurements with a vector network analyzer (VNA), I compared the results with those from the simulation. The actual S11 curves closely matched the simulations, confirming that the design is robust. Minor differences observed are likely due to manufacturing imperfections or material characteristics. Nevertheless, the antenna functions well across the 4G/5G bands as anticipated, validating the importance of simulations in guiding the design process.
To demonstrate the antenna’s directivity, I conducted a degraded aerial directivity test. This involved using a signal generator set to 0 dBm and 1.5 GHz connected to the Vivaldi antenna, while a vector network analyzer (VNA) with a receiving antenna covering the 200 MHz-2 GHz range captured the signal. By rotating the antenna in various directions, it is evident that the reception varies significantly, clearly demonstrating the antenna’s directivity. As shown in the photo, the received signal level changes depending on the orientation, confirming the antenna’s effectiveness in focusing the signal towards a specific direction.
Step 5: Performance Testing on the 4G/5G Box #
To evaluate the effectiveness of the Vivaldi antipodal antenna, I conducted signal quality tests on my 4G/5G box, comparing results with and without the antenna. The analysis focused on RSRP (Reference Signal Received Power), a key parameter that measures the received signal power.
Analysis of Results #
- RSRP (Reference Signal Received Power): This parameter measures the strength of the received signal and is crucial for assessing connection quality. Before installing the Vivaldi antipodal antenna, the average RSRP was -117 dBm. After adding the antenna, this level improved to -93 dBm. This 24 dBm improvement indicates a significant increase in signal strength, resulting in a more stable and potentially faster connection. Better signal strength typically leads to improved connection quality and faster data transfer speeds.
To maximize this improvement, the Vivaldi antipodal antenna, being directional, was carefully oriented towards the nearest base station. This orientation was achieved using the Opensignal app, which allows precise localization of cell towers and adjustment of antenna orientation to maximize signal transmission.
Here are screenshots showing the difference in signal strength between using no antenna and using the Vivaldi antipodal antenna:
Conclusion and Future Improvements #
The addition of the Vivaldi antipodal antenna has clearly demonstrated its effectiveness in enhancing the 4G/5G signal reception of my box. This project provided insight into antenna design and confirmed the importance of simulations in optimizing performance for modern telecom applications. The real-world results validated the design approach and show that even as an amateur, significant improvements in signal reception can be achieved.
References #
- CST Studio Suite for antenna design simulations.
- Opensignal for antenna orientation optimization.
- Vector Network Analyzer (VNA) for measurements.
- SolidWorks for 3D antenna support design.
Sources #
Optimization of Compact Antennas for Ultra-Wideband Communication Systems: ResearchGate
Vivaldi Antennas:
New Structures of Antipodal Vivaldi Antenna Arrays with Longitudinal Radiation in SIW Technology: University of Tlemcen
Antipodal Vivaldi Antenna Calculator: Changpuak