ANTENNA’S MURRAY AMATEUR RADIO CLUB – KJ7HRI PRESENTS ANTENNA’S, TYPES AND PURPOSES

WHAT IS AN ANTENNA? Basic component of any electrical circuit. Interconnecting link between Transmitter and free space Interconnects free space and a Receiver. Converts electrical signals into electromagnetic energy waves. Converts electromagnetic energy waves into electrical signals.

ANTENNA PROPERTIES Antenna GAIN Aperture Directivity & Bandwidth Polarization Effective Length Polar diagram

ANTENNA GAIN The parameter that measures the degree of directivity of the antenna’s radial pattern. An antenna with a higher gain is more effective in its radiation pattern. Antennas are designed in such a way that power raises in wanted direction and decreases in unwanted direction. G=(Pwr radiated by antenna) / (Pwr radiated by reference antenna)

APERTURE Aperture is also known as the Effective Aperture of the Antenna that actively participates in the transmission and reception of electromagnetic waves. The power received by the antenna gets associated with this collective area. The collective area of an antenna is known as Effective Aperture Pr=Pd*A watts A=pr / pd*m2

DIRECTIVITY & BANDWIDTH The directivity is the measure of concentrated power radiation in a particular direction. The capability of an antenna to direct radiated power in a given direction. It’s the ratio of the radiation intensity in a given direction to the average radiation intensity. Bandwidth is a range of frequencies over which an antenna can properly radiate energy and receives energy.

POLARIZATION An electromagnetic wave launched from an antenna may be polarized Vertically and Horizontally. If the wave gets polarized vertically, then the E vector is Vertical and requires a Vertical Antenna to launch it. If the wave gets polarized horizontally, then the E vector is Horizontal and requires a Horizontal Antenna to launch it. Sometimes, Circular polarization is used. It is a combination of Vertical and Horizontal polarization.

EFFECTIVE LENGTH The parameter of antennas that characterizes the efficiency of the antenna in transmitting and receiving electromagnetic waves. Effective Length can be defined for both Transmitting and Receiving antennas. The ratio of EMF at the receiver input to the intensity of the electric field occurred on the antenna is known as the receivers’ Effective Length. The Effective Length of the transmitter can be defined as the length of the free space in conductor, and current distribution across its length generates same field intensity in any direction of radiation. EL=(Area under non-uniform current distribution) / (Area under uniform current distribution)

POLAR DIAGRAM The most significant property of an antenna is its Radiation Pattern, or Polar Diagram. In the case of a Transmitting antenna, this is a plot of the strength of the power field radiated by the antenna in various angular directions. A plot can be obtained for both Vertical and Horizontal planes.

DIPOLE RADIATION PATTERN

YAGI RADIATION PATTERN

TYPES OF ANTENNAS

ANTENNA TYPES MICROWAVE Reflector Just to name a few LOG PERIODIC WIRE Bow Tie Dipole Array WIRE Short Dipole Monopole Loop TRAVELING WAVE Helical Yagi-Uda MICROWAVE Rectangular Micro Strip Planar Inverted-F Reflector Corner Parabolic Just to name a few

LOG PERIODIC ANTENNAS A LOG PERIODIC antenna is a multi-element narrow beam antenna that works on a wide range of frequencies. Made of up a series of DIPOLES placed along the antenna axis at different space intervals of time followed by a logarithmic function of frequency. Used where variable bandwidth is required along with antenna gain and directivity. $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

LOG PERIODIC ANTENNAS

LOG PERIODIC ANTENNAS Bow-Tie antenna is also known as a Biconical antenna, or Butterfly antenna. Omnidirectional and Wide-banded. The Discone antenna is a type of a Half-Biconical antenna. The Bow-Tie antenna is Planar, and therefore, directional.

LOG PERIODIC ANTENNAS LOG-PERIODIC DIPOLE ARRAY antenna is comprised of multiple dipole elements. These dipole-array antennas reduce in size from the back-end to the front-end. The leading beam of the antenna comes from the smaller front-end.

WIRE ANTENNAS Wire antennas are also known as linear or curved antennas. Very simple, cheap, and used in a wide variety of applications. DIPOLE ANTENNA SHORT DIPOLE ANTENNA MONO-POLE ANTENNA LOOP ANTENNA

DIPOLE ANTENNA One of the most straight-forward antenna alignments and design. Consists of two thin metal rods (wire) with a sinusoidal voltage flow that makes an electromagnetic wave and the RF signals get radiated. Current is fed from a Feeder (SO239 or 450 Ohm) Multiple types of dipoles: Half-wave, Multiple, Folded, Non-resonant, etc.

SHORT-DIPOLE ANTENNA Simplest of all types of antennas. A open-circuited wire in which “short” denotes ‘relative to a wavelength’. A dipole is considered “short” if the length of the radiating element is less than a 10th of the wavelength.

MONOPOLE ANTENNA Half of a simple dipole antenna located over a grounded plane. The radiation pattern above the grounded plane will be the same as the half wave dipole antenna, however, the total power radiated is half that of a dipole. Used as vehicle mounted antennas as they (the vehicles) provide the required ground-plane for the antenna mounted above the earth.

LOOP ANTENNA Come in different shapes: Circular, Elliptical, Rectangular, etc. The circumference of the loop antenna determines the efficiency of the antenna, similar to that of dipole and monopole antennas. Small loop antennas are not efficient, therefore are used for Rx. Resonant loop antennas are relatively large, and are directed by the operation of wavelength.

TRAVELING WAVE ANTENNAS Helical Antennas are AKA Helix Antennas. Simple structures with one, two, or more wires each wound to form a Helix, usually backed by a ground-plane or shaped reflector. This antenna acts like a Short Dipole and is very Directional.

TRAVELING WAVE ANTENNAS Yagi-Uda Antennas AKA Yagi, constructed with one or more reflector elements and one or more director elements. Very directional, depending on # of elements.

REFLECTOR ANTENNAS Corner Reflector antennas are comprised of one or more dipole elements placed in front of a corner reflector. Parabolic-Reflector antennas diverges a spherical wave front into parallel waves that produce a narrow beam.