Communications: radio wave antennas – Antennas – High frequency type loops
Patent
1998-02-18
1999-11-02
Wong, Don
Communications: radio wave antennas
Antennas
High frequency type loops
343866, 343868, H01Q 2129, H01Q 124
Patent
active
059779217
DESCRIPTION:
BRIEF SUMMARY
This patent application concerns a circular-polarization two-way (i.e. receiving and transmitting) antenna, for left-hand or right-hand circular polarization.
Circular polarization is typical of satellite systems.
This field is in rapid expansion due to the vast range of possible applications and the relative low cost of implementing these systems.
Parallel to the development of satellite communication systems, the fixed and mobile land devices require increasingly more specialised antennas designed to perform specific functions effectively.
Two types of antennas have to date been used install circular polarization communication and navigation systems on mobile means: the first is the antenna known as the "HELIX" or helicoidal antenna, while the second is known by the experts in the field as the "PATCH" or "MICROSTRIP" antenna.
In helicoidal antennas, circular polarization is obtained by exciting a progressive wave on a helicoidal wire; the direction of the circular polarization (left or right) is determined by the sense of helicoidal wire winding.
The helicoidal antennas have the advantage of being very simple to design and produce and have a considerable band width which ensures low sensitivity; this characteristic of the helicoidal antenna makes the tolerance range wider, making it possible to use inexpensive materials which are easy to obtain on the market. This type of antenna has the added advantage of having a good gain value in an axial direction with an equally good axial ratio that, as the experts in the field know, is the most important reference parameter for the quality of circular polarization.
The disadvantage of helicoidal antennas is their by no means negligible height which makes them inconvenient for certain applications, such as installation on vehicles where low profile antennas are required, obviously because they must be streamlined.
The low profile is the main characteristic of the second type of antenna mentioned above, known as the patch antenna, where circular polarization is obtained by exciting a resonant current distribution on a planar conducting surface. The direction of circular polarization is determined by a precise calculation of the position of the "point of excitation" of the surface.
This type of antenna, however, requires the use of relatively expensive materials, and, above all great precision during setting up and production due to the small tolerances to respect.
The main disadvantage of the patch antenna is that its surface area can hardly be used for mounting other devices, so that it is not possible to use the radiant surface together with components for different applications.
Considering the above state of the art, another type of circular polarization two-way antenna was designed with the aim of offering all the advantages of both of the above antennas, without the disadvantages or application limitations of either.
In the case of the new antenna according to the invention, circular polarization is obtained by exciting a wave along a loop wire, in the sense that its profile has a closed path, which need not necessarily be circular.
Said loop is characterised by a perimeter equal, or approximately equal to a wavelength at the operating frequency.
Said loop wire is mounted above a ground plane, which is parallel to the plane on which the loop lies.
The system consisting of the ground plane and the loop wire gives rise to a resonant structure.
Different ways may be used to determine the polarization (left-hand or right-hand) of the wave; the first consists in exciting the loop wire at two separate points staggered at an angle of 90.degree. with respect to the centre of the loop wire and providing a source in phase quadrature.
Alternatively, the loop wire may be excited at only one point by discriminating one of the two polarizations by means of a passive probe, a directional probe or other suitable means.
By measuring the performance of this type of antenna it is observed that: in the region of 30-50 dB, giving a significant simplification of the phasing circui
REFERENCES:
patent: 1702039 (1929-02-01), Chireix
patent: 4924237 (1990-05-01), Honda et al.
patent: 5847683 (1996-10-01), Wolfe et al.
Djordjevic Antonije
Niccolai Luca
ALFA Accessori-S.R.L.
Bloom Leonard
Clinger James
Wong Don
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