Antenna
Antenna
The transducer between guided waves on a cable and radio waves in space. Every wireless project — WiFi, LoRa, GSM, GPS, Bluetooth — lives or dies by its antenna, and it's usually the last thing debugged.
Schematic symbol
Antenna
How antenna appears in a circuit diagram.
Types & variants
Key specs
Frequency band
MHz / GHzMust match the radio: 433/868/915 MHz (LoRa/ISM), 1575 MHz (GPS), 2.4/5 GHz (WiFi/BT). An antenna is a tuned device.
Gain
dBiDirectionality, not amplification: 2 dBi whip radiates all round; a 12 dBi Yagi focuses one way. Higher gain = narrower beam.
Impedance
Ω50 Ω standard for radio systems (75 Ω for TV). Mismatch reflects power back into the transmitter.
VSWR
:1How well-matched it is at your frequency — under 2:1 is good; high VSWR can damage transmitter output stages.
Polarisation
—Vertical, horizontal or circular (GPS). Cross-polarised antennas lose ~20 dB — align both ends the same way.
Markings
Usually only a frequency/band label, if anything. Connector type identifies use: SMA/RP-SMA on modules, U.FL/IPEX inside devices, N-type outdoors, F-type for TV.
Standard values
A quarter-wave monopole is λ/4 ≈ 71.25/f(MHz) metres: 17.3 cm at 433 MHz, 3.1 cm at 2.4 GHz. Stock antennas: 2/3/5 dBi duck antennas, ceramic GPS patches, 433 MHz spring coils.
How to choose
1) Match the exact band. 2) Omnidirectional for mobile/unknown directions; directional (Yagi/patch) for fixed point-to-point range. 3) Check connector — SMA vs RP-SMA trips everyone (WiFi gear mostly RP-SMA). 4) Keep the antenna away from ground planes, metal and batteries; the best antenna badly placed loses to a wire whip in clear space. 5) Never transmit without an antenna connected — reflected power can kill the PA stage.
Pinout & package
Single RF terminal (plus ground reference). Module antennas: SMA/RP-SMA jacks, U.FL pigtails, spring coils soldered to an ANT pad, or PCB trace antennas needing keep-out area per the module datasheet.
Example circuits
- ESP32 with external RP-SMA antenna via U.FL pigtail for long-range WiFi
- LoRa node with 17 cm wire soldered to ANT as a quarter-wave monopole (plus ground plane)
- GPS module with active ceramic patch (LNA powered through the coax bias tee)
- Two Yagis making a point-to-point 2.4 GHz link between buildings
Common failures
Broken solder at the feed point (range collapses), water in outdoor connectors (VSWR climbs), wrong-band antenna fitted (looks fine, works terribly), cracked ceramic patches, and RP-SMA/SMA mismatch leaving the centre pin unconnected.
How to test
Comparative RSSI test: swap antennas and read signal strength (dB) at a fixed link. Continuity: a DC-shorted antenna type (loop/some ducks) vs open (whip) — check against its design, not assumptions. Proper lab: a NanoVNA sweeps VSWR/S11 and shows exactly where the antenna resonates — cheap and revolutionary for hobbyists.
Substitutes
Any same-band, same-connector, same-impedance antenna interchanges; gain trades beamwidth for range. A cut-to-length wire is a workable emergency monopole: 71.25/f(MHz) metres ÷ 4.