Electromagnetics and Antenna Technology, Chapters 4 and 5
MASSACHUSETTS INST OF TECH LEXINGTON LEXINGTON United States
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This chapter describes simulations and measurements of antennas that are omnidirectional in azimuth. Omnidirectional coverage is desired in applications where the desired signal direction is arbitrary. Omnidirectional coverage can be provided for vertical polarization with vertical monopole or dipole antennas which can typically have a cylindrical or conical shape. A monopole antenna with a cone shape is referred to as a monocone or conical monopole. Similarly, a dipole antenna with cone-shaped arms is referred to as a bicone or biconical antenna. Omnidirectional horizontally polarized coverage can be achieved with horizontal loops or slotted cylinder antennas. Section 4.2 describes vertically polarized cylindrical and conical monopole antennas. Section 4.3 describes a vertically polarized disconeantenna. The turnstile crossed dipole was described as an omnidirectional antenna in Chapter 1 Section 1.12.2, where the arms were aligned in a plane. Section 4.4 describes an omnidirectional monopole array designed for simultaneous transmit and receive application. Section 4.5 describes omnidirectional horizontally polarized loop and slotted cylinder antennas. Section 4.6 investigates the turnstile crossed-dipole antenna where the dipole arms are swept back to provide omnidirectional pattern coverage for horizontal and vertical polarization. Each of the antennas described in this chapter can be considered wideband depending on how the bandwidth is defined, either in terms of the radiation pattern or impedance match or both. For transmit applications both the radiation pattern and impedance match will be important. For some receive applications involving communications, only the radiation pattern gain will be of primary importance as long as the communications link closes.
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