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For a considerable time, the efficiency of planar antennas at high frequency has failed to reach its full potential. Since the planar antenna is an important element in an MMIC transceiver system, this poses a major problem. Due to the nature of the electromagnetic environment the antenna operates in, a large amount of the propagating radiation is coupled into the substrate meaning that only around forty percent efficiency is achieved, especially at millimetre wave frequencies. To improve this situation, methods to control the propagation of electromagnetic radiation from planar antennas is being sought. One method is to use a periodic dielectric structure positioned beneath the radiating antenna to act as a reflector. In this work, the periodic dielectric is a woodpile three-dimensional photonic crystal, fabricated using high resistivity silicon. The photonic crystal has a stop-band in which the resonant frequency of the antenna is contained, thus allowing no signal to pass and thereby reflecting the radiation to enhance the radiation pattern. This paper gives a detailed explanation of the problem, through to the practical results obtained to date from fabrication and measurement.