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TYPES OF ANTENNAS USED IN MOBILES

INTRODUCTION

Anantenna(oraerial) is an electrical device which convertselectric currentsintoradio waves, and vice versa.

An antenna consists of two parts; Transmitter and Receiver. The antenna at the time of transmitting electromagnetic waves is called transmitting antenna and the same antenna in the time of receiving electromagnetic waves is called receiving antenna.

MOBILE BASESTATION ANTENNA

PARAMETERS OF ANTENNA

BANDWIDTH

Itspecifies the range of frequencies over which its performance does not suffer due to a poor impedance match.

GAIN

Gainis a parameter whichmeasures the degree of directivity of the antenna's radiation pattern.

EFFECTIVE AREA OR APERTURE

Theeffective areaor effective aperture of a receiving antenna expresses the portion of the power of a passing electromagnetic wave .

RADIATION PATTERN

It is typically represented by a three dimensional graph, or polar plots of the horizontal and vertical cross sections.

IMPEDANCE

As an electro-magnetic wave travels through the different parts of the antenna system it may encounter differencesinimpedance. EFFICIENCY

Efficiencyof a transmitting antenna is the ratio of power actually radiated (inall directions) to the power absorbed by the antenna terminals.

POLARIZATION

Thepolarization of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation.

EFFICIENCY

Efficiencyof a transmitting antenna is the ratio of power actually radiated (inall directions) to the power absorbed by the antenna terminals.

BASIC TYPES

ISOTROPIC ANTENNA

An isotropic antenna is a hypothetical lossless antenna having equal radiation in all directions.

DIRECTIONAL ANTENNA

Directional antenna receives or radiates electromagnetic waves more effectively in one particular direction than in other directions.

OMNI DIRECTIONAL ANTENNA

This type of antenna radiates or receives electromagnetic waves in all direction except in azimuth plane.

ANTENNAS USED IN MOBILES

MOBILE ANTENNA

A. ROOF MOUNTED ANTENNA

The antenna pattern of a roof mounted antenna is more or less uniformly distributed around the mobile unit when measured at an antenna range in the 3 dB high gain antenna shows a 3 dB gain over the quarter wave antenna.

A. ROOF MOUNTED ANTENNA

The antenna pattern of a roof mounted antenna is more or less uniformly distributed around the mobile unit when measured at an antenna range in the 3 dB high gain antenna shows a 3 dB gain over the quarter wave antenna.

B. GLASS MOUNTED ANTENNA

There are many kinds of glass-mounted antennas. Energy is coupled through the glass: therefore there is no need to drill a hole. However, some energy is dissipated on passage through the glass. The antenna gain range is 1 to 3 dB depending on the operating frequency.

C. MOBILE HIGH GAIN ANTENNAS

This type of high gain antenna should be distinguished from the directional antenna. In the directional antenna, the antenna beam pattern is suppressed horizontally; in the high gain antenna, the pattern is suppressed vertically.

D. HORIZONTALLY ORIENTED SPACE DIVERSITY ANTENNA

A two-branch space diversity receiver mounted on a motor vehicle has the advantage following factor. The two antennas can be mounted either in line with or perpendicular to the motion of the vehicle.

E. VERTICALLY ORIENTED SPACE DIVERSITY ANTENNA

The vertical separation between the two space diversity antennas can be determined from the correlation between their received signals. A set of measured data was obtained by using two antennas vertically separated by 1.5 wavelengths.

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