Waveguide Description The present invention relates to a waveguide. More particularly, the present 5 invention relates to a waveguide having an elongate dielectric inner region, and an electrically conducting outer region spaced apart from the dielectric inner region. Waveguides are commonly used in a wide range of applications, for guiding a wave along a desired path. For example, in a communications satellite, it may be 10 necessary to pass a received microwave signal through a number of components (e.g. amplifiers, filters, multiplexers) before retransmitting the processed signal. In this case, an electromagnetic waveguide may be used to carry the signal from one component to the next. 15 Figure 1 illustrates a conventional rectangular waveguide 100 for guiding an electromagnetic wave. The waveguide 100 comprises a length of hollow metal pipe 101 with end flanges 102, 103 for attaching the waveguide 100 to the appropriate input/output ports. An electromagnetic wave propagates from one end of the waveguide 100 to the other by total internal reflection off the walls of the 20 waveguide pipe 101. However, energy loss occurs due to current flowing in the walls of the waveguide pipe (the 'skin effect'), with typical losses being 0.13 dB/m in the I