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measured ARs versus the elevation angle at the center frequencies of 1542 MHz (space-to-earth) and 1643.5 MHz (earth-to-space) (helixes are oriented along y-axis) and it can be seen that they have a low value for large angular envelope. It is perceived that the simulated angular envelope of AR below 3 dB for both frequencies are nearly 82 and 85 , which is about half of the upper half-space and can generate CP radiation. The simulated and measured far-field radiation patterns of array at the frequency of 1542 MHz are shown in Figure 5. We can see that the pattern has only one main lobe with almost 221 dB side lobe level. Its halfpower beamwidth is 38.3 . The photograph of the antenna array is demonstrated in Figure 6. CONCLUSIONDesign, simulation, and fabrication of an L-band axial mode 2 3 2 tapered dielectric-loaded helical antenna array are presented for INMARSAT-M mobile vehicles. This antenna array is low profile in structure. It is found that a high gain, an improved AR, and excellent matched input impedance can be reached at the same time. These results are obtained by including a DR rod. By using this innovation the half power beam width reduces and the gain will increase. Also, it is found that by adding DR with suitable permittivity the miniaturization has been achieved. Additionally, using incorrect turn at the end of the helix (0.7 turn), the angular envelope of AR below 3 dB and 3-dB AR bandwidths are 85 and15%, respectively. It is observed that AR has a low value for large angular scan. The antenna array can give a stable gain of nearly 15.1 dB with a 221 dB side lobe level. ABSTRACT: We experimentally compare four commonly used interpolation algorithms including linear interpolation, spline interpolation, low-pass interpolation and time domain interpolation for channel estimation based on pilot in baseband direct-detected optical orthogonal frequency division multiplexing system. The results show that the time domain DFT interpolation method exhibits the best BER performance and the most compact constellation.

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