Enhancing the ESP32-C3 SuperMini: A WiFi Antenna Upgrade

The ESP32-C3 SuperMini is a remarkably budget-friendly module, often available for around €2. While its size is an advantage, it comes equipped with a tiny SMD antenna that severely restricts the effective WiFi range.

To overcome these limitations, a simple hardware modification can be applied to significantly boost signal performance.

🛠️ The Antenna Modification

The goal is to replace the limited radiation of the SMD antenna with a quarter-wavelength ($\lambda/4$) radiator.

Technical Specifications

• Material: 1.0 mm silver-plated wire.
• Total Length: $31\text{ mm}$.
• Geometry:
  • A horizontal loop approximately $16\text{ mm}$ long (forming a circle with a $\approx 8\text{ mm}$ diameter).
  • A vertical section $15\text{ mm}$ long extending upwards.

Installation Process

To achieve the correct shape, the wire was wrapped around a $5\text{ mm}$ drill bit. The ends of the loop were then widened to align with the existing SMD antenna terminals.

• Step 1: Form the loop using a $5\text{ mm}$ drill.
• Step 2: Identify the $50\text{ Ohm}$ antenna pin (left side of the SMD antenna).
• Step 3: Solder one end of the wire to the $50\text{ Ohm}$ pin.
• Step 4: Solder the other end to the "hot" end of the original SMD antenna.
• Step 5: Ensure both solder joints are secure and the vertical wire is positioned correctly.

Note: The original SMD antenna remains on the board. In this configuration, it becomes electrically insignificant, but it helps complete the loop. Electrically, the setup acts as a $\lambda/4$ element in parallel with a $\lambda/8$ wire.

⚠️ Design Warning

Some online guides and YouTube videos suggest elongating the vertical section to create a 5/8 lambda radiator.

This is not recommended if your goal is to maintain a compact form factor and ensure the antenna radiates omnidirectionally.

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📊 Testing and Validation

To quantify the improvement, a custom WiFi logger written in ANNEX32 BASIC was used. The test involved two modules—one stock and one modified—mounted side-by-side on a power bank to ensure identical environmental variables.

Test Setup Logic

Performance Comparison

Scenario	Stock Antenna (RSSI)	Modified Antenna (RSSI)	Improvement
Near Access Point	Baseline	$+6\text{dB}$ to $+8\text{dB}$	More stable connection
Edge of Range	Unstable/Disconnected	$+10\text{dB}$ or more	Usable connection
With Obstacles	Poor penetration	Significantly better	Stable throughput

Key Finding: On average, the signal strength increased by at least $6\text{dB}$. Since a $6\text{dB}$ gain theoretically doubles the range, the modified module could maintain a reliable link in areas where the stock module failed completely.

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🔍 Technical Observations

The original antenna used is the CrossAir CA-C03. Several factors contribute to its poor performance on the SuperMini board:

1. Material & Size: The high-dielectric ceramic and compact geometry are inherently less efficient than a wire antenna standing in open air.
2. Poor Placement: The manufacturer's datasheet provides specific guidelines for PCB edge positioning. However, on the SuperMini, the antenna is placed too close to other components and the ground plane, which shields the RF energy instead of radiating it.

Experimental Variations

During development, different wire types were tested:

• 0.8 mm standard switching wire (with SMD antenna removed) $\rightarrow$ Lower performance.
• 1.0 mm silver-plated wire (with SMD antenna intact) $\rightarrow$ Best performance (approx. $2\text{dB}$ better).

Summary of the CA-C03 Requirements

The datasheet for the Cross Air CA-C03 explicitly requires:

• PCB edge positioning to avoid signal interference.

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🖼️ Visual Documentation

Below are the images illustrating the modification and the results: