Abstract
In this paper, a single-arm Archimedean spiral (SAAS) antenna with broadband circular polarization is investigated. Unlike traditional single-arm Archimedean spiral antenna, the antenna arm consists of a hybrid meandered strip line and a smooth arc strip line. Especially at low frequencies, the meandered strip line significantly improves the circular polarization performance by extending the antenna surface current path. The effects of the meandered strip line on the radiation pattern and axial ratio (AR) are studied in detail. To obtain unidirectional radiation, a metallic cavity is added below the SAAS antenna. The measurement results show that the voltage standing wave ratio (VSWR) is less than 2 from 0.88 GHz to 8.82 GHz, which indicates a wide impedance bandwidth of 1 : 10 is realized. A wide AR bandwidth of 1 : 5 is available, that the measured AR is less than 3 dB from 1.6 GHz to 8 GHz.
Highlights
Pantograph arcing, caused by the separation of the pantograph and the contact wire, is very common in high-speed railways
Because the electrical current flowing along the antenna arm is extended on the meandered strip line
The lowest working frequency of a traditional Archimedean antenna with two arms can be estimated by 2πr ≈ λL (r is the radius of the Archimedean antenna and λL is the wavelength of the lowest working frequency). is approach is applicable for a single-arm Archimedean antenna [12]
Summary
Pantograph arcing, caused by the separation of the pantograph and the contact wire, is very common in high-speed railways. Polarized (CP) antennas [1,2,3], which are extensively applied in satellite communication systems, can be applied to pantograph arcing detection. Archimedean spiral antennas have attracted extensive attention because of their broad bandwidth, stable half power beam width (HPBW), and good circular polarization (CP) properties [4,5,6,7]. A traditional Archimedean spiral antenna has two symmetrical arms and requires balanced excitations, which limits its applications in engineering applications. A singlearm Archimedean spiral antenna, which takes one-half the space of a traditional Archimedean spiral antenna and does not need balanced excitations, is preferred in UWB communication applications because of its compact size [8,9,10]
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