A photonic-assisted multiple radio frequency (RF) measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and high frequency resolution is reported. A two-tone signal is a single-sideband (SSB) modulated on an optical carrier via a dual-parallel Mach–Zehnder modulator to construct one SBS gain and two SBS losses for SBS gain bandwidth reduction. The unknown RF signal is also SSB modulated on a carrier that has been modulated by a sweep signal, thus the unknown RF signal is converted to a sweep optical signal along with the sweep optical carrier. The bandwidth-reduced SBS gain spectrum is detected by the sweep optical signals at different specific time, mapping the RF frequencies to the time domain. An experiment is performed. RF frequencies from 0.3 GHz to 7.6 GHz are simultaneously measured with a root mean square error of less than 1 MHz. In addition, the frequency resolution of the measurement can be much lower than 10 MHz, which is now the best result in the RF frequency measurement methods employing the SBS effect.
This paper presents a broadband bow-tie antenna based on the metamaterial-inspired periodic structure of coupled complementary split-ring resonators substrate-integrated waveguide for the first time. The CSRRs and two branches of the bow-tie patch are etched on the top and bottom metal surfaces of the substrate. The CSRRs produce a resonant frequency, which can be combined with the two resonant frequencies produced by the bow-tie patch and the feedline of the bow-tie patch. The bandwidth can then be broadened. In order to enhance the gain in the low-frequency bandwidth, the gap width g of the CSRR is decreased without destroying its broadband characteristic. By decreasing g from 1 to 0.5 mm, the minimum gain in the low-frequency bandwidth is increased from 3.4 to 5.2 dBi, and the flat gain characteristic is obtained in the whole operating frequency range. The experiment results show that the realized antenna can operate from 7.3 to 10.3 GHz with the gain of 5.1 to 6 dBi. The absolute bandwidth is about 3 GHz, and the relative bandwidth is about 34.1%. Compared with the results for dipole antennas based on traditional SIW which with a series of metalized via holes embedded in a thin metal-backed dielectric substrate as the side walls, the relative bandwidth is improved about at least 17.7%.INDEX TERMS Broadband, complementary split-ring resonators enhanced substrate-integrated waveguide (CSRR-SIW), metamaterial-inspired, gain enhancement.
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