Dipole Antenna

A dipole antenna is the most fundamental practical antenna: a straight conductor, classically a half-wavelength long, fed at its centre so the two arms radiate. It serves as the reference against which other antennas are described, and it forms the driven element inside more complex designs. A half-wave dipole presents a convenient feed impedance — around 73 ohms in free space, a comfortable match to common 50-ohm systems — and a well-understood radiation pattern, which is why it appears everywhere from broadcast towers to the whip on a mesh node.

Radiation pattern

A vertical half-wave dipole radiates in an omnidirectional, doughnut-shaped pattern: roughly equal coverage in every horizontal direction with nulls straight off the ends of the conductor. Point the antenna up and the dead zones point at the sky and the ground — usually exactly where you want them. This makes it the natural choice for a hub node that must hear and be heard by peers scattered in all directions, unlike a directional design that favours a single axis. Its modest gain, near 2.15 dBi, is the baseline that gives rise to the dBi unit itself: gain "over isotropic," with the dipole's own figure as the practical reference point (antenna gain quoted in dBd is gain over a dipole).

Sizing and its compact relatives

The dipole's dimensions come straight from the operating wavelength: each arm is a quarter-wave, the whole antenna a half-wave — roughly 16 cm total at 915 MHz, which is why LoRa antennas are conveniently pocket-sized. The ubiquitous "rubber duck" whip on stock hardware is usually a monopole or a helically shortened relative: a single quarter-wave element working against a ground plane (the radio's circuit board), electrically half of a dipole. That shortcut costs performance, and it is why the stock antenna is the first upgrade on any serious node — a properly tuned, full-size dipole or a quality whip with a real ground plane frequently transforms a marginal link. Tuning matters more than size alone: an antenna cut for the wrong band reflects power back at the transmitter instead of radiating it, and no setting in software can fix wrong physics.

Why it matters for mesh nodes

For sovereign off-grid radio, most stock LoRa and Meshtastic nodes ship with a vertical dipole or monopole precisely because omnidirectional coverage suits an ad-hoc mesh where neighbours can lie in any bearing. Three practical rules extract the most from one: mount it vertically, because a tilted dipole loses signal to every vertically polarized peer; get it high and in the clear, since elevation beats gain for a small antenna; and keep it away from metal — a dipole strapped to a mast or pressed against a battery pack detunes and shadows itself. Confirm results by measurement, watching RSSI and SNR from real neighbours rather than trusting spec sheets, and feed its gain honestly into the link budget.

One construction subtlety separates textbook dipoles from working ones: the feed. A dipole is a balanced antenna, while coaxial cable is unbalanced, and connecting the two directly invites current to flow down the outside of the coax shield — turning the feedline into an unintended part of the antenna, distorting the tidy doughnut pattern and dragging noise from indoors up to the radiating element. The fix is a balun or a simple choke, often nothing more than several turns of the coax coiled at the feedpoint. At LoRa frequencies the compact commercial whips sidestep the issue internally, but anyone building a dipole from wire for a fixed node should budget the extra five minutes. It is a small detail with the classic RF property of being invisible until it ruins a link.

The dipole is the building block of larger antennas — see the Yagi antenna, which uses a dipole as its driven element and surrounds it with passive helpers, and dBm for the power units every link calculation runs on.