根据IEEE 521-2002标准，X波段是指频率在8-12 GHz的无线电波波段，在电磁波谱中属于微波。而在某些场合中，X波段的频率范围则为7-11.2 GHz。通俗而言，X波段中的X即英语中的“extended”，表示“扩展的”调幅广播。

X波段通常的下行频率为7.25-7.75 GHz，上行频率为7.9-8.4 GHz，也常被称为7/8 GHz波段（英语：8/7 GHz X-band）。而NASA和欧洲空间局的深空站通用的X波段通信频率范围则为上行7145-7235 MHz，下行8400-8500 MHz。

The X band is a segment of the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is rather indefinitely set at approximately 7.0 to 11.2 gigahertz (GHz). In radar engineering, the frequency range is specified by the IEEE at 8.0 to 12.0 GHz.