Design of a high efficiency class-F power amplifier integrated with a microstrip patch antenna

Ooi, Shirt Fun (2007) Design of a high efficiency class-F power amplifier integrated with a microstrip patch antenna. Doctoral thesis, Northumbria University.

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Abstract

ABSTRACT This thesis presents the research carried out into the effects of load and source harmonic terminations on the efficiency of a class-F power amplifier (PA). A demonstration on the direct integration of the class-F PA and an H-shaped patch antenna using an active integrated antenna (AIA) approach is also presented. To obtain a high efficiency PA, it is necessary to ensure that the power dissipated in the active device is minimised and this is achieved by ensuring that the overlapping area between the drain voltage and current waveforms in the time domain is minimised. To minimise this overlapping area, optimum source and load harmonic impedances for the fundamental frequency, and second and third harmonics, are obtained using a novel application of the simulated load/source-pull method. New forms of harmonic matching networks were designed to ensure that the active device is terminated by the optimum impedances at the gate and drain for maximum efficiency. Three PAs were designed, one operating at 0.9 GHz and the other two at 2.45 GHz. For the 0.9 GHz PA the load matching network was designed to obtain the required optimum impedances at the fundamental frequency, and second and third harmonics. As the effect of gate capacitance is small at this frequency, the source matching network was designed to obtain a conjugate match at the fundamental frequency only. At the higher frequency of 2.45 GHz, the gate capacitance has a larger effect on the efficiency of the PA and hence two designs were investigated and compared. In the first PA design the load and source matching networks were designed to obtain optimum impedances at the fundamental frequency and second harmonic. For the second PA design, these networks were designed to obtain optimum impedances at the fundamental frequency, and second and third harmonics. For these three PAs the simulated drain voltage/current waveforms, return loss, stability factor, power gain, output power and power added efficiency (PAE) are presented. The practical results are compared with those obtained by simulation. Each PA produced a PAE of greater than 70% and good agreement was obtained between the simulated and measured results. The PAE obtained in these works is comparable to that reported in published papers. Based on this research five papers have been published in journals and conferences. An H-shaped microstrip patch antenna is used in the active integrated antenna (AIA) design. The antenna must not only act as a radiator and a harmonic suppresser but also as an optimum load for the PA so that it can be connected directly to the active device in order to obtain maximum efficiency. An extensive study on this antenna was carried out. The formulas for the first four mode frequencies were derived using odd and even mode analysis while a new and simpler formula for the fourth mode frequency was obtained. A systematic design approach to obtain the dimensions of the antenna is presented for an antenna operating at a given fundamental mode frequency. For matching, a new explicit matrix input impedance formula for the H-shaped antenna has been obtained using segmentation method. Using this formula, the location of the probe feed could be adjusted to obtain the required impedance at the pre-assigned frequency. MathCAD programming is used to implement the calculations in the design of two antennas. Good agreement between the predicted, simulated and measured results is obtained for the resonant mode frequencies, input impedance and return loss. Based on this research two papers have been published in journals. Two AIA designs operating at 2.45 GHz are presented in this thesis. In the first design the load and source matching networks used in the PA were employed with the H- shaped antenna replacing the 50 9 load. In order to further minimise the size, cost, and losses, a new second AIA design was proposed. A probe feed location was found to obtain the required optimum impedance at th...

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