A frequency-scanning antenna based on hybridization of the quasi-TEM mode and spoof surface plasmon polaritons mode

Abstract

In this letter, we propose the design of a frequency scanning antenna (FSA) based on a hybrid mode of a quasi-TEM mode and a spoof surface plasmon polaritons (SSPPs) mode. The two modes are hybridized using a partially grounded comb-shape microstrip (CSM) structure, a combination of conventional microstrip line and the comb-like structure, the former of which supports propagation of quasi-TEM mode while the latter SSPPs mode. The CSM modulated by periodical radiating elements can achieve wide-angle frequency scanning antennas. Since the dispersion curve of the hybrid mode on CSM lies below that of pure microstrip lines, a larger phase shift can be achieved within the same propagation length than for pure microstrip lines. This is favorable for wide-angle scanning in a narrower bandwidth, so as to take up less spectrum resource. Moreover, dispersion of the hybrid mode can be engineered so that linear frequency scanning can be realized approximately. As an example, an X-band FSA was designed, fabricated and measured. The simulated and measured results agree well, and show that the prototype can achieve ±60° scanning in 8.5–12.5 GHz. In particular, the scanning angles within [−40°, +40°] are linearly proportional to frequency in 9.0–12.0 GHz, with an average gain of about 14 dB and a half-power beam-width of 6°. Moreover, due to the usage of radiating elements with smoothly-varying strip-widths, the open stopband is suppressed and there is no degradation for radiation at the broadside. This work provides an alternative method of designing wide-angle FSAs that may find applications in spectral analysis, direction of arrival estimation, etc.