Design of Antennas for Handheld DVB-H ... - Lunds tekniska högskola

3.3 Loop
Figure 3.1. Yagi-Uda antenna.
A simple, inexpensive and very versatile antenna type is the loop antenna, that
takes many different forms such as a rectangle, square, triangle, ellipse, circle and
many other configurations and they are usually classified in two categories,
electrically small and electrically large. Electrically small antennas are those
whose overall length (number of turns times circumference) much shorter than a
wavelength and the electrically large loops are those with a circumference about
one free-space wavelength. Most of the applications of the loop antennas are in
the HF (3-30 MHz), VHF (30-300 MHz) and the UHF (300-3000 MHz) bands.
Loop antennas with electrically small circumference are very poor radiators and
are very seldom employed for transmission in radio communication. When they
are used in such application, it is usually in receiving mode where antenna
efficiency is not as important as the signal-to-noise ratio. Electrically large loop
antennas are used primarily to achieve directional characteristic [28].
3.4 Microstrip antenna
Microstrip antennas provide interesting features for spacecraft, aircraft, mobile,
radio and wireless communication, in particular their low weight, cost,
performance, ease installation and thin profile. They are easily mounted on flat or
gently curved surfaces. Printed antennas (patches, microstrip) can use square,
rectangular, circular, triangular, elliptical or even more complex shapes as
radiating elements. It is parameters like bandwidth, side lobes, polarization that
decide which shapes that are most suitable. Since patches are narrow band
radiators, their main dimension is about a half-wavelength. The directivity for a
microstrip is therefore comparable to that of a half-wave dipole. This drawback
may be overcome by grouping a number of patches to form an array.
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