Amplitude-Modulated Leaky-Wave Antennas

Borrowing the idea of amplitude modulation from classical communications theory, this article proposes and demonstrates a new concept of amplitude-modulated (AM) leaky-wave antennas. In the proposed concept, the traveling wave in a wave-guiding structure serves as the carrier wave whose amplitude is spatially modulated by a predefined modulating waveform to generate the desired modulated waves. Two analysis methods are subsequently developed to analyze the amplitude modulation effects. It is demonstrated that spatial amplitude modulation corresponds to shifting the spatial spectrum of the modulating wave up to the carrier spatial frequency. Therefore, one can judiciously design the modulating waveform to control the spatial frequency spectrum of the modulated waves. The spatial frequencies fallen within the radiation region are fast waves, which can radiate into free space. In this manner, the AM structure works as a leaky-wave antenna. To justify the proposed concept, two AM leaky-wave antennas based on corrugated transmission line are designed. The first one is a sinusoidally modulated AM leaky-wave antenna for high-gain application. The second is a beam-forming AM leaky-wave antenna, whose modulating waveform is synthesized to generate flat-top radiation pattern. Both simulated and measured results are given to demonstrate the concept, theory, and design of the AM leaky-wave antennas.