P-band

P-band refers to radio frequencies approximately in the range 0.2–1.0 GHz. In satellite communications, practical operation is limited to frequencies above roughly 100 MHz, as lower frequencies are reflected or absorbed by the ionosphere and do not propagate reliably through it.

Frequencies in and near P-band are attractive for mobile satellite communications because satellite and user terminal hardware can be relatively simple and robust. User terminals may employ uncomplicated antennas such as Yagi or helical antennas, and the longer wavelengths permit higher transmit powers to be generated onboard satellites with comparatively simple RF hardware. Propagation at these wavelengths is favourable for mobile use, as signals diffract more readily around obstacles and can penetrate foliage and some building materials.

The principal limitation of P-band operation is severe spectrum congestion, as these frequencies are heavily used by terrestrial radio services. As a result, only narrow allocations are available for satellite use, greatly constraining capacity. The combination of limited bandwidth and modest antenna gain means that P-band satellite systems typically support only a small number of channels, with data rates of the order of a few kilobits per second. The broad beamwidths associated with low-frequency antennas also require greater satellite spacing to limit mutual interference.