Support assembly for portable microwave antenna

A portable foldable support assembly for a microwave dish antenna in which three or more legs are hinged to a vertical center post near its upper end to engage the ground plane beyond the center of gravity of the antenna, and a torsional stabilizer secured to the lower end of the post having three or more moment arms respectively disposed circumferentially between adjacent pairs of legs and in which a pair of tension members couple the lower end of each leg to two adjacent moment arms on opposite sides of the central axis to resist rotation of the post in either direction.

This invention relates to antennas and more particularly to portable 
support structures for holding microwave dish antennas in their operative 
modes at randomly selected sites. 
BACKGROUND OF THE INVENTION 
Microwave communication is dependant on precision antenna mounting 
including stabilization of aim in altitude and azimuth with respect to the 
remote counterpart source or target antenna. In the case of portable 
antennas there is an obvious trade-off between the mass or complexity of 
the support structure and antenna stability. U.S. Pat. Nos. 2,827,629, 
4,799,642 and 5,061,945 are examples of the present state of the art in 
portable and semi-portable dish antenna support structures. They are 
massive; clumsy and time consuming in assembly and disassembly; present 
complicated, multiple packaging for transport; and share with all designs 
a vulnerability to torsional load displacement deriving from wind on the 
dish. 
The present invention, therefore, has for its objects and features an 
antenna support design in which weight is minimized; foldability quickly 
presents a compact, manageable package for transport; and the ability of 
the support to resist torsional loading on the surmounted dish is achieved 
with minimized weight and at low cost. 
BRIEF SUMMARY OF THE INVENTION 
A central torsion-resistant post, which supports the tiltable and rotatable 
antenna dish assembly, is stabilized against movement by an articulated 
leg assembly, preferably a tripod. The three legs are pinned at 
equi-angularly spaced points in a collar firmly attached near the upper 
end of the post and splayed outward and downward to the ground plane 
through vertically-adjustable foot pads. 
The lower end of the post is coupled to a radially enlarged base adjacent 
the ground plane and which affords 3 radially extending moment arms which 
are respectively angularly centered between the legs. Thus the arms form 
an angle of 60.degree. with each of the pair of proximate legs. Two 
tension members, preferably in the form of flexible wire cable, connect 
each leg at its lower end to the two proximate moment arms. Each leg is, 
therefore, effectively tied to the center post on opposite sides of the 
vertical centerline of the post and thereby opposes both clockwise and 
counterclockwise movement of the post under wind loads on the antenna. In 
all, therefore, 3 cables at all times resist one hand of antenna 
displacement and 3 the other. The legs are compression members which 
resist bending and therefore resist tilting of the post when it is coupled 
by the cables to the legs. The weight of the antenna assembly is picked up 
by the legs, freeing the post of compression forces below the junction 
with the legs. The post can, therefore, be designed for the primary 
function of torsion resistance, thereby conserving mass. 
The structure is articulated so that it is foldable for portability. 
Bracing by means of compression links running from the base to the legs 
prevents twisting forces on the post under high wind loads from inching 
the legs inward to cause slack in the tension wires and to prevent angular 
movement of any leg which might be momentarily lifted from the ground. If 
desired, the size of the folded assembly can be further reduced by hinging 
the three moment arms on horizontal axes close to the post.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the invention is illustrated as embodied in a portable 
support structure 10 for a conventional portable antenna unit 11 including 
a mounting collar 11a, a frame 11b carrying a reflector dish 11c (adapted 
to be broken down into 3 pieces for transport) and a horn 11d tripod 
mounted at the focal point of the dish. The antenna is adjustable in 
azimuth by means of the collar 11a and in attitude by the lead screw 11e, 
all as known in the art. 
The portable support structure 10, illustrated separately in FIG. 2, is an 
articulated unitary structure shown in its open or working mode in FIGS. 1 
and 2 and in a partially folded mode in FIG. 3. The central support member 
is a tubular post or column 12 configured to sustain torsional loads. The 
upper end 12a of the column fits within the mounting collar 11a of the 
antenna which bears on vertical pad-pairs 13a arranged at 120 degree 
angles around the circumference. Permanently pivotally mounted in the 
respective pad-pairs are legs 14 to form a tripod configuration in which 
the weight of the antenna unit is transferred to the legs at their 
junctions with the collar 11a. The legs carry substantial compression and 
bending loads and can be formed, for example, of box beam stock. The legs 
splay outward at a relatively shallow angle, 20 to 30 degrees being 
typical, and have attached at their outer ends ground pads 15 which pivot 
on vertical adjustment posts 15a in a conventional manner. A wide range of 
ground pad configurations can be used to suit a variety of terrains. 
Secured to the lower end of the column 12 adjacent the ground plane is a 
torsion control assembly 16 comprising an inner pad 17 secured to the 
column 12 having pinned thereto by means of relatively long horizontal 
hinge pins 17, three equi-angularly spaced, i.e. 120 degrees apart, moment 
arm legs 18 which preferable lock against upward pivotal moment beyond the 
ground plane. The length of the moment arm legs is a function of material 
strength, antenna geometry and anticipated wind loads. In general the 
length should substantially exceed the diameter of the central column 12 
on the order, for example, of 2 to 4 times. The angular positioning of the 
torsion control assembly on the column 12 is such that the moment arms 18 
are substantially centered between the legs 14 or in the illustrated 
embodiment at 60 degree angles to both proximate legs. 
Tension members 19, all co-planar as illustrated, join the lower ends of 
the legs 14 to the moment arms 18, with each leg having two such members 
connected to the outer ends of the two proximate moment arms. Thus, as 
viewed from the outer end of each leg, one tension member connects to the 
left hand moment arm to resist clockwise turning of the central column and 
the other connects to the right hand moment arm to resist counterclockwise 
rotation. The length of the moment arms is less than the distance to the 
cord line between the lower ends of adjacent legs so that an angle is 
formed between the respective right and left hand tension members of 
adjacent legs where they join their common moment arm. The tension members 
should not be disposed beyond the cord line between the adjacent legs. 
As described above, the system is fully functional to control unwanted 
axial turning movement of the central column 12. The column 12 is relieved 
of the weight of the antenna by the legs 14 at their junctions with the 
column, enabling weight reduction in the design of the column below the 
junction. The lower end of the column is able, therefore, to ride above 
the ground, secured against both lateral and torsional displacement by the 
torsion control assembly 16. 
Control of downward angular motion of the pivoted legs is imparted by 
compression beams 20 coupling the torsion control assembly 16 to the 
respective legs. In the illustrated arrangement the compression beams 20 
are permanently pinned in a hinge coupling near the lower ends of the 
legs. The inner ends are detachably pinned to the lower end of the central 
column by means of brackets 21 disposed between the hinges 17. The beams 
are in the form of channels to receive the box beam of which the legs are 
formed when the support assembly is detached from the antenna assembly and 
folded as seen in FIG. 3. 
It will be understood that the legs 14, while bearing the weight of the 
antenna unit above, are relieved of the torsional forces which the antenna 
imposes on the central column 12 under wind loads. Thus the legs, like the 
central column, can be configured in cross section to meet the design 
specifications at minimum weight. 
Referring to FIG. 3, the assembly is shown partially folded. This is 
accomplished by unpinning the compression beams from the lower end of the 
column 12, and swinging the beams toward the legs on the pivot joint 
therebetween. The beams and legs then together fold into the brackets 21 
and all three are pinned through appropriate holes to lock the system 
closed. Meantime, the moment arms are swung toward the axis of the column 
12, while the tension members or cables 19 fold upon themselves, and are 
confined by the folded legs. 
While the invention has been illustrated and described in one preferred 
embodiment, it will be understood that it can take other forms all in 
accordance with the invention. For example, a quadrapod configuration is a 
natural and obvious extension of the design. Also, the tension members 19 
shown as cable can be bar-or tubular-form to impart compression strength 
and thereby duplicate more or less the function of the compression bars 
20, which can be omitted. While the moment arm for each tension member is 
approximately but not quite at its optimum length, i.e. the tangent line 
from the leg to the horizontal circle circumscribing the movement arm 
assembly, such can be achieved by laterally enlarging the outer ends of 
the arms 18 and cross-attaching the two cables at the end of each arm in a 
circumferentially overlapping fashion. Also, the compression bars 20 can 
be coupled to the legs 14 at other points along the leg, thereby reducing 
length and weight. The invention also lends itself to all conventional 
supplementary stabilizing techniques such as staking the rig down by 
stakes and cables or providing a ground-secured second central post of 
smaller o.d. than the i.d. of the central post 12 to fit concentrally 
therein for imparting supplementary lateral support and, with a key-way, 
supplementary torsional support. The invention should not, therefore, be 
regarded as limited except as set forth in the following claims.