A method for the precision forming of thin walled, slotted waveguide arrays was devised. Models were constructed with temporary tools and evaluated. The application of the method to the solar power satellite requirements was investigated

Brown, W. C.

English

NASA Technical Reports Server

METHOD FOR PRECISION FORMING OF LOW-COST, THIN-WALLED SLOTTED WAVEGUIDE 
ARRAYS FOR THE SPS 
William C. Brown 
Raytheon Company 
Presented at the RADIATING ELEMENTS SESSION OF THE SPS MICROWAVE SYSTEMS WORKSHOP 
January 15-18, 1980, Lyndon B. Johnson Space Center, Houston, Texas 
ABSTRACT 
A method for the precision-forming of thin-walled, slotted-waveguide arrays has been devised. Models have 
been constructed with temporary tools and evaluated. The application of the method to the SPS requirements is 
discussed. 
Introduction 
The method for forming thin-walled slotted 
waveguide arrays that will be described grew out of a 
necessity to narrow down the broad range of estimated 
cost for slotted waveguide arrays in ground based 
arrays. In most items that are designed for automated 
production the cost of the material is the dominant 
element of cost. Therefore the use of thin material is 
attractive because of the large reduction in material 
cost. Then, if a rapid, inexpensive method of 
fabrication can be devised, the cost of the slotted 
waveguide arrays will be low and can be accurately 
estimated. 
Such a fabrication method had been devised in 
principle by the author. An opportunity then arose 
to build working models of the design as part of a 
contract with JPL for the improvement of microwave 
beamed power technology, using a slight modification 
of their electrical design for such an array. 
The working models that were made from 
0.020 inch material were mechanically so strong and 
the fabrication technique so well adapted to even 
thinner material that the potential for a slotted wave- 
guide array made from 0.005 inch or even thinner 
material for the SPS applications is very good. 
Early estimatks of the mass of a slotted waveguide 
array for the 1 kilometer diameter transmitting antenna 
for the SPS were based on the use of 0.020 inch thick 
aluminum material and these estimates may still persist 
and show up in current estimates of mass for the SPS. 
An array based on the use of 0.005 inch material in 
place of the 0.020 inch would save nearly 2.5 x ' 1 0 6  
kilograms of material. Savings in transportation costs 
alone would be 250 million dollars if transportation 
costs were only $100 per kilogram. 
The fabrication of thin-walled guides can also be 
accomplished with great precision. Tolerances of 
+2-3 mils should be possible. 
Finally it appears, as shown in Figure 1, that the 
arrays can be relatively easily fabricated in space 
from rolls of aluminum foil which represents an ideal 
packing factor for transportation purposes. 
8 
Figure 1. Proposed Method for Precision Forming and Assembly of Low-Cost, Thin-Walled, Slotted Waveguide 
Arrays for the SPS. 
25 3 
https://ntrs.nasa.gov/search.jsp?R=19810008039 2020-03-21T15:12:28+00:00Z
Description of Fabrication Method 
The slotted waveguide array as shown in Figure 1 
consists basically of a folded top plate whose 
corrugations contribute the three sides of the wave- 
guide and a bottom plate into which the radiating slots 
are punched. The two sections then flow together and 
are joined to each other either by resistance spot 
welding or by laser beam welding to form the finished 
assembly shown in Figure 2.  
 POINTW WELDS 
Figure 2.  Finished Assembly. 
The holes which are punched into the material 
are spaced accurately from each other and serve to 
accurately locate the material in the bending fixture 
which is also accurately machined and ground. The 
holes also serve to jig the top and bottom halves to 
each other for accurate assembly. 
The method as originally proposed by the author 
utilized a third piece in the assembly that joined the 
top and bottom at their ends. An improvement to 
simply eliminate the end plate by the upward fold of 
the end of the top and bottom pieces as shown in 
Figure 1 is the suggestion of R.M . Dickinson. 
It is possible that the broad faces of the wave- 
guide members, both top and bottom, may need some 
stiffening to avoid bending and "oil canning". The 
thin flat channels that are proposed to house the phase 
and amplitude references and auxiliary power lines 
perform this function on the slotted surface. The 
unslotted surfaces could be embossed to stiffen them. 
The individual slotted waveguides in the array 
are fed from a feed waveguide shown in Figure 3 as 
the transverse waveguide. Transfer of energy is 
made through diagonal slots between the feed wave- 
guide and radiating waveguides. The feed 
waveguide is attached to the array by means of pop 
rivets. 
Construction and Evaluation 
Two 8 x 8 ( 8  slots in 8 waveguides) arrays were 
constructed from 0.020 inch aluminum with the use of 
temporary tooling of a simple nature. The 4 inch 
separation between waveguides that is necessary in 
the forming process and which have become attractive 
as a region in which to mount solid state devices and 
through which to run cables made it necessary to 
adjust the dimensional specifications of the JPL design 
which was designed for a different fabrication method. 
The slotted face plate, folded waveguide section, 
and the end channels were assembled to each other 
by spot welding. Back and front view of the 
finished assembly are shown in Figures 3 and 4. 
In the absence of any antenna testing range a 
method was evolved to test the array by electrically 
probing each slot for amplitude and phase, as  shown 
in Figure 5. This arrangement gave the phase and 
amplitude information tabulated in Table I. When 
readings around the outside are disregarded because 
of edge effects, the rms phase and amplitude per- 
centage deviation of the remaining sections are 6.22O 
and 10% respectively. With the outer elements included 
the phase deviation is 8. 8g0. 
Figure 3.  Back View of the 8 x 8 Slotted Waveguide 
Array as Constructed from 0.020 Inch Aluminum Sheet 
Throughout and Assembled bv Means of S ~ o t  Welding. 
Figure 4 .  Front View of the 8 x 8 Slotted Waveguide 
Array as Constructed from 0.020 Inch Aluminum ' 
Sheet Throughout and Assembled by Means of Spot 
Welding. 
Finally, 'the antenna range data taken by JPL on 
the array that was Gade for them as a portion of the 
contractual work effort for them is presented in 
Figures 6 and 7. 
Figure 5. Probe Arrangement for Measuring Phase 
and Amplitude of Microwave Power Radiated at 
Individual Slots. The Phase and Amplitude Sensed by 
the Pmbe were Compared by Means of a Hewlett- 
Packard Network Analyzer with the Amplitude and 
Phase of the Power Input to the Single Waveguide Feed 
to the Slotted Waveguide Array. 
TABLE I 
Matrix Array of Amplitude and Phase Information 
on Thin Metal Slotted Array #1 
10 
m 
u g 
2 20 
W 
1. 
3 [r 
30 
40 9 
ANGLE, deg 
Figure 6. Antenna Pattern for 8-Slot x 8-Stick Slotted 
Waveguide Antenna. 
H-PLANE PATIERN 
;2;;;42dBi 1 
ANGLE, deg 
Figure 7. Antenna Pattern for 8-Slot x 8-Stick Slotted 
Waveguide Antenna. 
Overall array is  an 8 x 8 matrix 
"Internal" array is  a 6 x 6 matrix 
Test data obtained by dipole probe placed in front of each 
radiating slot. 
RMS of phase deviation of internal array is  6 . 2 Z 0 .  
RMS of phase deviation of overall array is 8 .8g0 .  
RMS of amplitude variation of internal array is 0.0628 from a 
mean value of 0 .627 .  


Method for precision forming of low-cost, thin-walled slotted waveguide arrays for the SPS

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server