No abstract

This paper presents a novel Ku wideband circularly polarized (CP) antenna array composed of crossed-dipole element (CDE) and fed through sequential rotation (SR) feeding technique. Unlike the traditional CP-CDE fed by coaxial cable that usually works at low frequencies, the proposed CDE consists of two orthogonal heart-shaped patch dipoles that can work at frequencies as high as Ku-band, at the same time achieving a larger bandwidth. A feeding structure is proposed without welding, so potential errors in the antenna assembly process can be mitigated. A 2 × 2 CP antenna array with wideband SR feeding network is designed based on the CDE to further expand the axial ratio (AR) bandwidth. The designed antenna array is fabricated using the multilayer printed circuit board (PCB) technology and measured in anechoic chamber using the planar near-field measurement facility. The measured results show that −10 dB impedance bandwidth of 44% (11.6–18.15 GHz) along with 3 dB AR bandwidth of 38.7% (12–17.65 GHz) and 3 dB gain bandwidth of 34.6% (12.2–17.3 GHz) as well as 11.02 dBic peak gain have been achieved while maintaining a lower profile.

We investigate the superimposed pilot (SP) based channel estimation (CE) for long-haul coherent optical OFDM (CO-OFDM) systems. With specifically designed SP, we demonstrate the impacts that both SP and phase noise have on the performance of CE, from which we obtain the optimal signal-to-pilot power ratio (SPR). To enhance the estimation quality of the SP-aided scheme, we exploit an iterative decision feedback algorithm, and in turn, improve the system performance. Experimental results show that the SP-aided CE behaves robust to the phase noise when lasers with moderate linewidth (<100 KHz), and can offer similar performance as the conventional preamble based methods without scarifying bandwidth efficiency. A CO-OFDM transmission over 5000 km of standard single mode fiber (SSMF) is successfully demonstrated using the SP-aided CE scheme, which shows a spectral efficiency (SE) gain of about 10%.Index Terms-Channel estimation, coherent optical OFDM (CO-OFDM), superimposed pilot.