Radio waves are electromagnetic waves below 3THz frequency, used for mobile phones, Wi-Fi, TV, and radio. Mobile phones primarily use 700MHz-3.5GHz bands, with 5G also utilizing the 28GHz millimeter wave band.
Characteristics vary significantly by frequency. Low frequencies (700-900MHz, "platinum band") penetrate buildings well and cover wide areas but offer relatively slow speeds. High frequencies (3.5GHz-28GHz) enable high-capacity, high-speed communication but are weak against obstacles with shorter range. Carriers combine these bands for service delivery.
Japan's Radio Act strictly manages spectrum, with the Ministry of Internal Affairs allocating frequencies. Base stations must meet technical standards, and human exposure limits follow international ICNIRP guidelines.
Radio wave issues include out-of-range problems, interference from other devices, and illegal jamming. Airplane mode stops all radio transmission/reception for use in aircraft and hospitals where radio waves are restricted.