Chapter 2. Horn; Theoretical Calculations and Measurements, IEEE Silver, S. (Ed.) (1984) Microwave Antenna Theory and Design, Trans., AP- 31, 973. Peter Peregrinus (IEE), London. Cha, A.G. (1983) An Offset Dual Shaped Reflector with 84.5 Stutzman, W.L. and Thiele, G.A. (1981) Antenna Theory and De- Percent Efficiency, IEEE Trans., AP-31, 896. sign, Wiley, New York. Clarricoats, P.J.B. and Olver, A.D. (1984a) Corrugated Horns for Williams, W.F. (1965) High Efficiency Antenna Reflector, Micro- Microwave Antennas, Peter Peregrinus (IEE), London. wave J., 8. 79. This page intentionally left blank Analogue modulation Professor J E Flood OBE DSc FInstP CEng FIEE Aston University Contents 18.1 Introduction 18/3 18.2 Amplitude modulation 18/3 18.3 Frequency and phase modulation 18/7 18.4 Pulse modulation 18/12 18.5 Acknowledgement 18/16 18.6 References 18/16 This page intentionally left blank Introduction 18/3 18.1 Introduction 18.2 Amplitude modulation The processing of a signal to make it suitable for sending over a 18.2.1 Simple amplitude modulation transmission medium is called modulation. Reasons for using modulation are: The simplest form of modulation is amplitude modulation. The modulator causes the envelope of the carrier wave to follow the 1. Frequency translating (e.g. when an audio frequency baseband waveform of the modulating signal and the demodulator recovers it signal modulates a radio frequency carrier). from this envelope. 2. Improving signal/noise ratio by increasing the bandwidth (e.g. If a carrier, given by Equation 18.2, is modulated to a depth m by using frequency modulation). a sinusoidal modulating signal given by Equation 18.3, the resulting 3. Multiplexing i.e. enabling many baseband channels to share the AM signal is as in Equation 18.4. same wideband transmission path. Modulation is performed by causing the baseband modulating (18.2) signal to vary a parameter of a carrier wave. A sinusoidal carrier, as given by Equation 18.1, is defined by three parameters: amplitude (18.3) A, frequency w/2 