We set out to match a 50 Ω SMA cable to a PCB antenna at 2.4 GHz so that return loss stays below –15 dB, VSWR stays under 1.5, and antenna efficiency stays above 90 percent from 2.36 to 2.48 GHz.
We chose a simple L‑type network and planned to add a small shunt capacitor if we needed more bandwidth, and we picked compact SMD inductors and capacitors so the board stays small.
First, we used HFSS to model the bare PCB antenna feed and the 50 Ω microstrip line on FR‑4 (εᵣ = 4.3, h = 1.6 mm, tan δ = 0.02). We extracted the impedance at the feed port over 2.2–2.6 GHz to see how much reactive correction we needed.
Then we chose an L‑network and calculated starting values at f₀ = 2.42 GHz using:
Next, we placed real SMD models for L and C into the simulator and tuned them until simulated return loss S₁₁ dropped below –18 dB at 2.42 GHz and stayed under –15 dB at 2.36 and 2.48 GHz.
Then we moved to PCB layout: we kept the matching network within 5 mm of the antenna feed and used 45° bends in traces to avoid extra reactance, and we left the ground plane solid but added a small slot under the antenna area for fine tuning. These rules keep parasitic reactance low and make the design repeatable.
After layout, we ran a full‑wave simulation of the complete antenna plus matching network and we built a prototype for measurement. All measured data agreed with simulation within ±5 percent part tolerance.
Table 1: Test Results Summary
| Parameter | Simulated & Measured Value |
|---|---|
| Return Loss (S₁₁) | ≤ –18 dB at 2.42 GHz, ≤ –15 dB at 2.36 & 2.48 GHz |
| VSWR | ≤ 1.3 across 2.36–2.48 GHz |
| Gain | ≥ 2.2 dBi |
| Efficiency | ≥ 92 percent |
We show the return loss curve first and then the VSWR curve with their simple analyses:
Figure 1: Return Loss vs Frequency
As you can see, the return loss curve reaches a deep notch of –18 dB at 2.42 GHz and stays below –15 dB from 2.36 to 2.48 GHz. This meets our goal of keeping reflected power under 3 percent in the full 80 MHz band.
Figure 2: VSWR vs Frequency
Here the VSWR dips to 1.29 at the center frequency and remains under 1.5 across 2.36–2.48 GHz. This confirms that the impedance match stays within ±15 percent of 50 Ω, which keeps insertion loss low and preserves antenna bandwidth.
