--- title: "How much ground does a 2.4 GHz PCB antenna need?" topic: "Antenna ground" answer: "About 40 mm behind the antenna. With 10 mm, 22% of the power gets out, and a perfect matching network only lifts that to 43%." url: "https://nearfieldnotes.com/notes/antenna-ground/" site: "Near Field Notes" author: "Michael Walker" note: 3 family: "RF" published: "2026-11-01" revised: "2026-11-01" revision: 1 video: "https://nearfieldnotes.com/videos/antenna-ground/" --- Note 3 · [RF](https://nearfieldnotes.com/families/rf/) · Rev 1 · [Watch the video · 0:22](https://nearfieldnotes.com/videos/antenna-ground/) Antenna ground # How much ground does a 2.4 GHz PCB antenna need? **Short answer:** About 40 mm behind the antenna. With 10 mm, 22% of the power gets out, and a perfect [matching network](https://nearfieldnotes.com/glossary/#g-matching-network) only lifts that to 43%. **Note 3’s opening figure: The ground, cut.** From 40 mm down to 10 mm ![Note 3’s opening figure: The ground, cut](https://nearfieldnotes.com/notes/antenna-ground/fig-opening.png) *What the figure shows:* One board with TI's AN043 antenna, its ground cut from 40 mm down to 10 mm in steps. With 40 mm, 85% of the power radiates and the range in free space is 1.00 of the range at 40 mm. With 35 mm, 77% of the power radiates and the range in free space is 0.95 of the range at 40 mm. With 30 mm, 67% of the power radiates and the range in free space is 0.89 of the range at 40 mm. With 25 mm, 56% of the power radiates and the range in free space is 0.81 of the range at 40 mm. With 20 mm, 44% of the power radiates and the range in free space is 0.72 of the range at 40 mm. With 15 mm, 33% of the power radiates and the range in free space is 0.62 of the range at 40 mm. With 10 mm, 22% of the power radiates and the range in free space is 0.51 of the range at 40 mm. **Key** - Range - Range at 40 mm Share of the radio’s power radiated at 2.44 GHz. Range in free space. ## The antenna and its ground *TI’s CC2511 USB dongle* TI’s AN043 antenna is a copper meander across the end of a 15.2 mm wide board. Two legs reach down over the edge of the ground on layer 2. One is shorted to it and the other is fed from it. The ground is the other half of the antenna, and current runs along it too. Shrink the board and that half gets cut short. **Fig. 3: The antenna.** ![Fig. 3: The antenna](https://nearfieldnotes.com/notes/antenna-ground/fig-3.png) *What the figure shows:* Figure 3: TI's AN043 antenna up close, from above. A copper meander runs across the top of the board. Two legs reach down over the edge of the ground on layer 2: the shorted leg on the left, tied to the ground, and the feed leg, where a 50 Ω source drives it from the ground. Read from TI’s own Gerber of the CC2511 USB dongle, on 1.0 mm FR4. **Fig. 3b: The board.** ![Fig. 3b: The board](https://nearfieldnotes.com/notes/antenna-ground/fig-3b.png) *What the figure shows:* Figure 3b: the whole board from above, lying down, with the antenna at the left end. The ground on layer 2 runs 40 mm back from the antenna. The board is 15.2 mm wide. A dashed line marks where the ground would be cut to 10 mm. The ground runs back from the antenna on layer 2. Each run cut it to one length, from 5 to 120 mm. **Fig. 3c: Four boards.** ![Fig. 3c: Four boards](https://nearfieldnotes.com/notes/antenna-ground/fig-3c.png) *What the figure shows:* Figure 3c: four boards with 10, 20, 40 and 60 mm of ground behind the same antenna, to scale. 10 mm: 22% radiates. 20 mm: 44% radiates. 40 mm: 85% radiates. 60 mm: 73% radiates. Arrows point at the end of the first board's ground and the third's. The same antenna on 10, 20, 40 and 60 mm of ground, to scale, with the share of power each radiates at 2.44 GHz. Antenna ground ### Specimen 3 radiates about four times what specimen 1 does **Field marks.** Specimen 3 has 40 mm of ground behind the antenna. 85% radiates. **Look-alike.** Specimen 1 has the same antenna on 10 mm. 22% radiates. **Range.** Specimen 1 reaches about half as far in free space: `r_10/r_40 = √(P_10/P_40) = √(22%/85%) = 0.51` **Habitat.** TI AN043 from the CC2511 dongle. 1.0 mm FR4, 15.2 mm wide, 2.44 GHz. ## Where the power goes *Specimens 1 and 3* **Fig. 3d: Radiated, lost or sent back.** ![Fig. 3d: Radiated, lost or sent back](https://nearfieldnotes.com/notes/antenna-ground/fig-3d.png) *What the figure shows:* Figure 3d: where the radio's power goes at 2.44 GHz. 10 mm: 22% radiates, 29% heats the board, 49% reflects. 40 mm: 85% radiates, 7% heats the board, 8% reflects. Share of the power a 50 Ω radio offers at 2.44 GHz. Key to antenna ground ### How much ground does a 2.4 GHz PCB antenna need? 1. 1a Room for 40 mm of ground behind the antenna 85% radiates 2. 1b Room for only 10 mm Go to 2 3. 2a A matching network tuned to it 43% radiates 4. 2b The antenna as built 22% radiates A perfect match stops the reflection. The 10 mm board still turns 57% of what it takes in into heat. ## Cut the ground yourself *5 to 60 mm, every 2.5 mm* **Note 3’s explorer: Antenna ground.** ![Note 3’s explorer: Antenna ground](https://nearfieldnotes.com/notes/antenna-ground/fig-explore.png) *What the figure shows:* The board at the chosen ground length, to scale, and its range in free space against the range at 40 mm. *What the figure shows:* Share of the radio's power radiated against ground length, 5 to 60 mm, as built and perfectly matched. Share of the radio’s power radiated at 2.44 GHz. Range in free space. **Fig. 3e: Longer boards.** ![Fig. 3e: Longer boards](https://nearfieldnotes.com/notes/antenna-ground/fig-3e.png) *What the figure shows:* Figure 3e: the share of power radiated against ground length, 5 to 120 mm, as built and perfectly matched. As built it peaks at 88% near 45 mm, dips to 60% at 75 mm and climbs back to 90% at 105 mm. Share of the radio’s power radiated at 2.44 GHz, every 2.5 mm to 60 mm and every 5 mm after. Longer boards ### More ground stops helping past 46 mm **Field marks.** Past 46 mm, more ground makes it worse. At 75 mm only 60% radiates. **Look-alike.** At 105 mm it climbs back to 90%. **Range.** The peaks sit 59 mm apart, about half a wavelength at 2.44 GHz. The ground is part of the antenna, so its length tunes it too. In TI’s own test, plugging the dongle into a laptop cut its bandwidth from about 250 to 100 MHz. #### Conditions - **Antenna:** TI AN043 meandered inverted-F, from TI’s Gerber of the CC2511 USB dongle reference design, rev 1.3 - **Board:** 4-layer FR4, 1.0 mm, εr 4.5, 15.2 mm wide - **Ground:** Layer 2, 0.25 mm below the antenna, cut to each length from 5 to 120 mm - **Source:** 50 Ω at 2.44 GHz - **Measure:** Radiated power over the power the source can deliver - **Solver:** openEMS, rechecked on a 0.125 mm mesh - **Check:** TI’s dongle resonates at 2.525 GHz in the model and 2.49 GHz in TI’s measurement, 1.4% apart Simulated only. TI’s 2.49 GHz is the one measured number on this page. #### Limits - Range here is free-space range. Walls, hands and cases change it. - The model has no case, hand or laptop. TI’s own measurement shows a laptop can move the result. #### Files - antsim/geom.py The antenna’s copper, read from TI’s Gerber - antsim/run.py One board, reduced to its power balance - post/matched.py The best matching network for each board - runs/Every ground length, 5 to 120 mm #### Sources - [TI AN043, Small Size 2.4 GHz PCB Antenna](https://www.ti.com/lit/an/swra117d/swra117d.pdf) What should the next note be? [Ask for one](https://nearfieldnotes.com/#ask-for-a-note) --- Source: https://nearfieldnotes.com/notes/antenna-ground/ Cite as: Michael Walker, “Antenna ground”, Near Field Notes, Note 3, Rev 1, 1 Nov 2026. https://nearfieldnotes.com/notes/antenna-ground/ Figures: free to reuse under CC BY 4.0 (https://nearfieldnotes.com/license/). Each one's image is linked under its name. Credit Michael Walker, Near Field Notes, and link the figure: this address plus #fig- and its number, like https://nearfieldnotes.com/notes/antenna-ground/#fig-3.