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An electrically small rectenna was designed and tested at the global positioning system (GPS) L1 frequency (1.5754 GHz). The metamaterial-inspired near-field resonant parasitic antenna size (ka $ 0.467) and its direct match to the input impedance of the rectifying circuit decreased the whole size of the rectenna (ka $ 0.611). The simulated and measured rectifying efficiencies were, respectively, 75.7% and 79.6% when the input power to the rectifying circuit was 0.0 dBm (1 mW). The highest rectifying efficiency, 84.7%, was achieved at the GPS L1 frequency for a 3.0 dBm input power. The simulated and measured results are in good agreement. Rectennas, which is short for rectifying antennas, have received much attention for their use in wireless power transmission (WPT) systems. 1,2 They are promising elements for power harvesting and scavenging, especially for microsystem applications in wireless sensor networks and on unmanned aerial vehicles (UAVs). To evaluate the rectenna designs, their rectifying efficiencies and compact sizes are two significant figures of merit. The antenna, which is typically bigger than the rectifying circuit, is one of the critical components of the rectenna system. On the one hand, the impedance matching between it and the rectifying circuit always affects the overall rectifying efficiency. Furthermore, its size typically dominates the overall size of the rectenna.The basic structure of a rectenna is shown in Fig. 1(a). The antenna is the interface between the external electromagnetic (EM) environment and the rectifying circuit. It plays the significant role of receiving the EM signals and converting them into voltages and currents. Consequently, it also has important consequences in the requisite impedance matching to the rectifying circuit. The rectifying circuit consists of a band-pass filter, a Schottky diode, and a low pass filter. To increase the rectifying efficiency when the input power is low, a Schottky diode with a low built-in voltage and high breakdown voltage is always selected. 3 However, harmonic signals will be generated because the diode has nonlinear characteristics, and hence, could be radiated by the antenna back into the ambient space and absorbed by the board material. These harmonic generation and absorption processes can dramatically decrease the rectifying efficiency. Consequently, a band pass filter and a low pass filter are usually incorporated between the antenna and the diode, and between the diode and the load, respectively, to prevent any harmonics from flowing back into the antenna and forward into the load.The emergence of metamaterials (MTMs) has provided a promising methodology to design electrically small antennas (ESAs). 4 The ESAs in Refs. 4 and 5 are constructed as a combination of electrically small driven and metamaterialinspired near-field resonant parasitic (NFRP) elements. The NFRP elements are generally single epsilon-negative (ENG) or mu-negative (MNG) based unit cells of a metamaterial, not a complete bulk medium. In Refs. 6-8, an extended ...

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We present a reconfigurable microwave frequency measurement technique with adjustable measurement range and resolution. The key novelty of the technique is the employment of stimulated Brillouin scattering, which results in a tunable amplitude comparison function, leading to an adjustable measurement range and resolution. The proposed technique is switchable between a wideband tunable narrow measurement range (~2 GHz) with high resolution (±0.05 GHz) and a fixed wide measurement range (12 GHz) with moderate resolution (±0.25 GHz).