A clear tube of tap water works as a cellphone antenna: Mitsubishi Electric and KDDI say it matched a metal antenna in tests

Your phone signal depends on antennas. Malls, restaurants, entertainment venues and historic buildings often have dead zones, so carriers add indoor antennas or signal repeaters. But metal antennas are ugly and conspicuous, and many venues don't want them anywhere visible.

On Nov. 10, Japan's Mitsubishi Electric announced that, with help from Japanese carrier KDDI, it had developed an antenna that uses tap water as the radiating element, the part that actually sends and receives radio waves. It's called Liqutenna, a blend of "liquid" and "antenna," and it is essentially a transparent acrylic tube filled with tap water. Mitsubishi says an 800 MHz prototype (800 MHz is one of the common cellphone bands) successfully connected to mobile devices in an indoor environment KDDI uses to evaluate wireless equipment. Connection performance showed "no difference" from a typical metal antenna, and the link held when the team changed the antenna's orientation and the water level in the tube. Mitsubishi says, based on its own research as of November 2026, that this is the first time anyone in the telecom industry has run a mobile-device connection test with a tap-water antenna.

How can water be an antenna? An antenna is basically a conductor in which electric current sloshes back and forth, turning an electrical signal into radio waves. Seawater is salty and conducts well, and Mitsubishi showed a seawater-column antenna called SeaAerial back in 2016. Tap water conducts far worse, so you wouldn't expect it to work. Mitsubishi's explanation is that if the tube's inner diameter is at least a quarter of the radio wave's wavelength inside water, tap water starts acting like metal at high frequencies. Combined with careful shaping of the tube, that gets radiation efficiency on par with a metal antenna. The company also says that bending the tube into an arch along a wall spreads the signal across a wide area in front of it. Crossing two arched tubes sends out two different polarizations (orientations of the radio wave), which makes transmission and reception more stable.

The pitch isn't just that it works, but that it looks good. The clear tubes can be paired with lighting and become part of a room's decor. A tabletop cylinder version can even hold glitter or model sea creatures, like a small aquarium. Mitsubishi pictures it in restaurants, shopping centers, amusement venues and historic buildings where preserving the look matters.

Keep in mind this is a prototype tested in an indoor test environment, not a commercial product. Mitsubishi says it will next run field evaluations with KDDI in places with poor coverage, and it will show the technology at Microwave Exhibition 2026 (MWE2026) in Yokohama, Nov. 25 to 27. It hasn't announced a launch date or price. Durability, changes in water quality and long-term maintenance still have to be proven in real-world settings.

For ordinary people: if this becomes practical, it could get easier to fix weak signals in mall corners or restaurants inside old buildings. The gear doing the work might look like a glowing glass tube instead of a gray plastic box on the wall. It's also a reminder that antennas don't have to be metal. Clever choices in materials and design can solve everyday connectivity problems too.

Original sources published: Mitsubishi Electric press release (via Nikkei press release service), Nov 10, 2026, 11:21 Beijing time / Nov 9, 2026, 10:21 PM EST; CNET Japan, Nov 12, 2026, 05:52 Beijing time / Nov 11, 2026, 4:52 PM EST; IT Home, Nov 12, 2026, 09:55 Beijing time / Nov 11, 2026, 8:55 PM EST