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Transmitting MMDS Antennas Part 1

Keywords:

V. V. Demidov, A. D. Egorov, M. W. Indenbom, V. A. Hrisanov


MMDS is a wireless-cable television system in the frequency range from 2.5 to 2.7 GHz, and also often includes data transmission channels both in consumer and the opposite directions. This article covers MMDS transmitting antennas with horizontal polarization, implemented as a printed stripline linear antenna arrays located within cylindrical fiberglass radoms. Printed stripline construction ensures the minimum number and a high degree of integration of antenna components, low losses, forming of the desired radiation pattern shape. Slotted printed radiators fed by stripline transmission lines have been designed for omnidirectional, cardioid and for directional azimuth pattern. The impedance matching is ensured in the working frequency band with VSWR ≤ 1.11 ... 1.27 for each type of radiators. Antennas are developed in three standard sizes: with a length of radiating aperture L = 1.22 m, 2.08 m and 4.1 m, and containing, respectively, N = 14, 24 and 48 radiators along the axis of the antenna. Antenna power divider has a variable wave impedance of the transmission lines: 50 ohms at the divider input, 107 ohms at the divider outputs (inputs of the radiators). The divider is built on reactive division elements. To ensure the high stability of the pattern in the frequency band, a parallel scheme of power division is used with approximately equal lengths of transmission lines from the entrance to each of the divider outputs. The divider entrance and the first level of the power division (except for the antenna with length 1.22 m) use a flat transmission line, which is a cylindrical conductor, located between the plane screens. The use of a flat line reduces losses and increases the antenna power throughput. The upper levels of power division are realized using the three-plane stripline, close in design to a symmetrical stripline. The difference between the lines’ design is in the presence of a thin dielectric substrate (thickness t = 0.12 mm, with ε = 3.4...4.2), carrying printed stripline conductors. Symmetrical arrangement of the substrate with stripline conductors between shields is provided by sheets of filler with a low value of permittivity ε = 1.045. The designing of stripline divider was carried out basing on Oliner’s models of stripline heterogeneities. Some elements of a divider have been computed using the full electromagnetic model. Input VSWR of dividers of all antenna types does not exceed 1.13 in the operational frequency range. The measured gain, direction of the maximum and a beamwidth, the calculated value of the directivity of antennas at a frequency 2.6 GHz, as well as the value of the power average throughput by the different types of antennas are shown in Table 1. VSWR of all antenna types in the MMDS frequency range does not exceed 1.3
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