tailieunhanh - Micowave and Millimeter Wave Technologies Modern UWB antennas and equipment Part 10

Tham khảo tài liệu 'micowave and millimeter wave technologies modern uwb antennas and equipment part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 262 Microwave and Millimeter Wave Technologies Modern UWB antennas and equipment Because the modulation scheme discussed in section is adopted pure 40-GHz reference can be yielded together with the modulated signal in BS. Unlike the BS design in section both 40-GHz carrier and modulated signals are transmitted from BS to MT in this system. Therefore the 40-GHz carrier can be used as mm-wave reference for both BS and MT. In the uplink each BS transmits the down-converted signal back to CS with a different wavelength. 4. Millimeter-wave fading induced by fiber chromatic dispersion in RoF system The fiber chromatic dispersion is always one of critical problems in optical communications. Optical components at different frequencies travel through the fiber at different velocities. A pulse of light broadens and becomes distorted after passing through a single-mode fiber Meslener 1984 . To mm-wave RoF system the fiber chromatic dispersion causes the remarkable mm-wave fading Schmuck 1995 . Analysis of chromatic dispersion in intensity modulated RoF system The intersity modulation schemes of yielding mm-wave signal have been introduced in Section . Those schemes may be sensitive to fiber chromatic dispersion. For example an external optical modulator MZM is used to modulate CW optical signal with a RF signal. The electric field at the output of optical modulator is express as Schmuck 1995 n n E t Ec cos d -y m 2 cos mt cosaip 16 where E is the amplitude of electric field ữc is the central angular frequency of optical source ữ is the angular frequency of RF signal m V V is normalized amplitude of the driving RF signal d Vb Vn is the normalized bias voltage of the modulator Vn is the n shift voltage of the modulator. The electric field for V V 2 after the transmission over a fiber link can be expressed by Bessel functions E E E t rzJ0 p cos ct 4 J1 p cos c - m t 4 cos c m t o V2 V2 where p mn 2 40 41 and 42 represent the different .