US2691760A

US2691760A - Variable attenuator calibrator

Info

Publication number: US2691760A
Application number: US652195A
Authority: US
Inventors: Theodore S Saad
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-03-05
Filing date: 1946-03-05
Publication date: 1954-10-12
Anticipated expiration: 1971-10-12

Description

Oct. 12, 1954 s, B 2,691,760

VARIABLE ATTENUATOR CALIBRATOR Filed March 5, 1946 CRYSTAL CURRENT INDICATOR 3 SOURCE INVENTOR. THEODORE S. SAAD ATTORNEY Patented Oct. 12, 1954 A UNITED STATES PATENT OFFICE VARIABLE ATTENUATOR CALIBRATOR Theodore S. Saad, West Roxhury, Mass, assig'nor,

by mesn'e assignments, to the United States of America as represented by the Secretary of the Navy Application March 5, 1946, Serial No. 652,195

4 Claims. ,1

This invention pertains to calibrators for wave guide variable attenuators, and more particula'rly to such calibrators designed and constructed so as to retain their own calibration essentially constant with time, and so as to render them stable and efiective over wide ranges of operation.

Attenuator calibrators hitherto known in the art were undesirable in that either they were fragile and so did not retain constant their own calibration, or were unstable for a complete calibration over wide range. I

An object of this invention is to provide a c'alibrator for calibrating variable atteunators at microwave frequencies.

Another object of this invention is to provide a calibrator for calibrating variable attenuators at microwave frequencies which will accurately retain'its calibration.

Still another object of this invention is to provide a calibrator of the class described which is of rugged construction and which is simple to use.

Further objects and advantages of this invention will be apparent from the claims and description, taken in connection with the drawings in which:

Fig. 1 is a diagram showing (a) relative position of all the component parts of a system for operating the invention herein described, and (b) detailed arrangement of the several parts of the calibrator alone; and

Fig. 2 is a plan view of the critical component of the calibrator, showing position of the openings in a broad face of the wave guide section, upon which openings the operation of this invention is dependent.

Referring to Fig. 1 there is shown a short wave guide section It having openings I I and I2 in one broad face, said openings leading into other short wave guide sections I3 and I4, fixedly secured to section It. Both ends of wave guide section It and the open ends of sections I3 and I 4 have flanges I5, It, I! and I8 respectively to form conventional choke joints for electrical continuity when opposed by appropriate faces. Openings I I and I2 are separated from each other by an odd multiple of quarter wave lengths in order to cancel reflections which they would otherwise introduce. Openings II and 20 are both down from the line by an appreciable amount, at least 20 db being recommended. In other words, the power passing out through either opening is defined approximately by the following relation: 20:10 logm of ratio amounts that diifer slightly, oneor two db being suitable in many cases. The absolute value of 2 this difference may be any fixed value within suitable limits, but that value must be known accurately. Fig. 1 also shows a short wave guide section 59 with choke joint flanges 20 and El and a fixed attenuator 22 fixedly secured, and a crystal 23 with a crystal holder 2 8 fixedly secured to its own choke joint flange 25. Fixed pad attenuator 22 is to prevent resonance effects, and is on the order of 5 to 10 db. A crystal current indicator 2% is shown schematically in Fig. 1. Wave guide section I9 is readily movable with respeot to wave guide section It, and in operation alternately opposes choke joint flanges I? and I8. The assembly comprising short wave guide section I9, crystal 23, crystal holder 24 and crystal current indicator 2t will hereinafter be referred to as a padded crystal holder.

In operation energy from a source passes down a wave guide, reaching the attenuatorunder calibration, the calibrator herein described, and a matched load, in that order. Fig. 1 illustrates this arrangement. The attenuator is first set on zero. Assume that opening I2 is down 20 db from the line, and that opening I I is down 21 from the line. The padded crystal holder is placed first over opening Ii and the crystal current is observed. The padded crystal holder is then placed over opening l2 and the attenuator is stopped down until the new crystal current drops to the value previously observed. The reading on the attenuator scale should now be observed and recorded, and it will be noted that the advance in attenuator setting resulted in an attenuation increase of 1 db.

The next step is to place the padded crystal holder again over opening II and observe the crystal current now present. As before, the padded crystal holder then is placed over opening I2, and the attenuator is advanced further to make the current indication equal the one immediately preceding. The new reading on the attenuator scale is observed and recorded, it being noted that the advance in attenuator setting has resulted in an attenuator increase of 1 db from 1 dbto 2 db.

It is apparent that continuation of this stepby-step process will result in data which may be tabulated as suggested in the following hypothetical example:

Total Atten- This calibration information may be presented appropriately and conveniently in the form of a calibration curve.

What is claimed is:

1. Apparatus for calibrating variable microwave attenuators comprising, a source of microwave electromagnetic energy, a matching load, a wave guide section for coupling said load to said source through the attenuator to be calibrated, said wave guide section having a pair of openings differing in size therein and spaced by an odd multiple of a quarter wave length of the energy from said source and adapted to couple energy from said wave guide section with a constant, predetermined, known difference of attenuation, and means to provide an indication proportional to the amount of energy coupled from said wave guide section through each of said openings.

2. Apparatus for calibrating variable microwave attenuators, comprising a source of microwave electromagnetic energy, a matching load, a rectangular wave guide section for coupling said load to said source through the attenuator to be calibrated, said wave guide section having a pair of openings in the broad side thereof spaced by an odd multiple of a quarter wave length of the energy from said source and difiering in size to couple energy from said wave guide section with a constant predetermined, known difference of attenuation, and an indicator for measuring the amount of energy coupled from said wave guide section through each of said openings.

3. Apparatus for calibrating variable microwave attenuators comprising, a source of microwave energy, a matched load, a rectangular wave guide section for coupling said lead to said source through the attenuator to be calibrated, said wave guide section having in the broad side thereof a pair of openings differing in size to couple energy from said wave guide section at two constant, differing, known values of attenuation, said openings being spaced axially in said wall by an odd multiple of a quarter wave length of the energy of said source to prevent reflection of energy from said opening, and an indicator for measuring the amount of energy drawn from said wave guide section through each of said openings.

4. Apparatus for calibrating a variable microwave attenuator, comprising a source of microwave energy, a matching load, a rectangular wave guide section for coupling said load to said source through the attenuator to be calibrated, said wave guide section having two branches coupled to the broad side thereof through a pair of openings differing in size to couple energy from said wave guide section at two constant differing known values of attenuation, said openings being spaced axially along said Wall by an odd multiple of a quarter wave length of the energy of said source to prevent reflection of energy from said branches, and an indicator for measuring the amount of energy drawn from said wave guide section through each of said branches.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,419,208 Frantz et a1 Apr. 22, 1947 2,422,601 Tashjian June 1'7, 1947 2,444,060 Ohl June 29, 1948 2,522,563 Blitz Sept. 19, 1950