US 3725940 A
A horizontal rooftop antenna is adapted to be mounted on rolling stock or a highway truck. It is in the form of an end fed shunt-type closed loop radiator tuned to frequencies between 2 and 30 MHz.
Description (OCR text may contain errors)
Umtd States Patent 1 91 1 11 3,725,940 Siple 1451 Apr. 3, 1973  HORIZONTAL VEHICLE MOUNTED OMNIDIRECTIONAL LOOP ANTENNA  References Cited HAVING A SHORTING STUB UNITED STATES PATENTS  Inventor: Ralph J. Siple, Idaho Falls, Idaho 2,22l,939 11/1940 Bennett ..343/744  Assignee: The United States of America 88 3,299,428 1/1967 Tessari ..343/743 represented by the United States Atomic Energy Commission Primary Examiner-Eli Lieberman  Filed; 8, 1972 Attorney-Roland A. Anderson 1 pp NW 224,490 57 ABSTRACT 1 A horizontal rooftop antenna is adapted to be  0.8. CI. 343/713, 343/743, 343/748, mounted on rolling stock or a highway truck. It is in 343/882 the form of an end fed shunt-type closed loop radiator  Int. Cl. ..H0lq 1/32 tuned to frequencies between 2 and 30 MHZ  Field of Search ..343/71l,-7l3, 741, 743, 744,
1 343/748; 882 5 Claims, 4 Drawing Figures 26 28 LINE TUNER 2 ANTENNA 1.001
VEHICLE ROOF GROUND PLANE/ HORIZONTAL VEHICLE MOUNTED OMNIDIRECTIONAL LOOP ANTENNA HAVING A SHORTING STUB BACKGROUND OF THE INVENTION There exists a need for a radiating antenna designed for installation on the top of a semi-trailer truck having a transmitter. In portions of the radio spectrum, difficulties are encountered in mounting antennae on vehicles because of the vertical height necessary to achieve efficiency. To overcome the difficulties, varioushorizontally polarized antennae have been tried. It has been determined that inches above the trailer roof is the maximum height allowable to permit the vehicle to pass under bridges, underpasses, etc. An antenna mounted by means of suction cups has been tried and discarded as impractical. In order to have the antenna sturdily mounted yet avoid the possibility of collisions with overpasses or the like, a construction using a hinged support has proved to be the most satisfactory. The entire antenna can then be raised or lowered as the road conditions require. For rolling stock, the horizontal antenna need not be mounted to be raised and lowered.
SUMMARY OF THE INVENTION The present invention comprises a mobile horizontal rooftop antenna which may be used on highway vehicles or rolling stock. It has been found that an antenna .in the form of a horizontally mounted stainless steel a line tuning network for a necessary impedance match to a transmitter. The antenna structure can be either rigidly mounted or made to be retractile.
It is an object of this invention to provide an improved mobile antenna for horizontal mounting on a vehicle roof. It is a further object of this invention to provide an improved retractile roof-mounted antenna controlled remotely by air pressure. It is also an object of the present invention to provide an improved radiating antenna for a mobile transmitter.
BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown in FIG.
1 an embodiment of the present invention to be mounted on a mobile vehicle. A horizontal metal section of the vehicle roof indicated at 10, serves as an electrical ground plane. The antenna, 12, is shaped in the fonn of a rectangle and is supported above the ground plane, 10. A coaxial cable, 14, has the inner conductor, 16, connected to the antenna, 12. The outer shield, 18, is fastened to the metal surface, 10, with a terminal conductor. The coaxial cable, 14, will vary from 20 to 30 feet in length depending on the installation.
A line tuning network, 20, having a variable capacitor, 22, and variable inductor, 24, is connected to the coaxial cable, 14, and to a transmitter, 26, by means of a lead-in line in the form of coaxial cable, 28. An RF signal is fed from the transmitter, 26, into the variable inductor, 24, which varies from 0-10 microhenries, through the variable capacitor, 22, which varies between 12 and 202 micro micro farads and through the coaxial cable, 14, to the antenna feedpoint, 30. The gain of the antenna is approximately 8 db.
The antenna structure itself may be made from three-eighths inch stainless steel or copper tubing. As
shown in FIG. 2, the antenna loop can be made up'of two long sides, designated A, and two shorter sides, B and C. A stainless steel stub, D, is attached at a distance, E, from the first side of the loop and parallel to it. A shorting stub, F, connected at a distance, G,
from the feedpoint, 30, joins the stub to the first side. An antenna loop design which performs very well has distance E 5 in.
distance G 10 in.
In the embodiment of FIG. 3, a polyvinyl chloride plastic pipe supporting structure, 32, for the antenna, 12, is depicted. The plastic supporting structure, 32, has a series of legs, 34, with a crossbar, 36, joining the legs in pairs as shown. The legs, 34, are hinged, 38, at the bottom to the vehicle roof so that the entire antenna may be retracted. A chain, 40, may be used to connect adjacent vcrossbar-s, 36. The hinged supporting structure, 32, may be raised and lowered by means of a hydraulic cylinder, 42, as shown in FIG. 4. The cylinder, 42, may be mounted on top of the vehicle along with the antenna and supporting structure. Air can be supplied from the vehicle air supply that is used for the vehicles air brakes. The antenna then mayv be raised or lowered by remote control at the drivers discretion.
It has been found that an antenna positioned a distance of 15 inches above the vehicle reflector surface provides the best performance. It has also been' found that the position of the shorting stub at about 10 inches from the feedpoint provides the best radiation of the transmitter signal.
The same configuration described above has been used on rolling stock with excellent results. On a railroad car, however, the supporting structure need not a first end of said loop being the feedpoint and connected to receive a transmitter signal through an inner conductor of a coaxial cable,
an outer conductor of the coaxial cable being connected to the vehicle roof which constitutes a reflecting ground plane,
a second end of said loop having a conductive stub connected thereto spaced parallel to and at a short distance from the first loop side,
a conductive shorting stub positioned at substantially right angles to and joiningthe first side and the conductive stub at a distance from the feedpoint serving to close the loop,
and an insulating supporting structure attached to the vehicle roof and to the antenna loop in the vicinity of the four corners of the loop,
the supporting structure holding the antenna loop in a horizontal position at a distance above the vehicle roof.
2. The radiating antenna structure of claim 1 wherein the loop is made of stainless steel tubing and the supporting structure is made of polyvinyl chloride tubing.
3. The radiating antenna structure of claim 2 wherein the supporting structure is hinged to the top of the vehicle so that the antenna structure may be raised and lowered.
4. The radiating antenna structure of claim 3 wherein a hydraulic cylinder having a remote control operates to raise and lower the supporting structure.
5. The radiating antenna structure of claim 1 wherein the loop is supported at a distance of about 15 inches above the vehicle roof. I