MICROWAVE VARIABLE ATTENUATOR

Abstract: A microwave variable attenuator (10) comprises a conductive substrate (30), a microstrip line (55), and a movable attenuator means (40) sandwiched between the microstrip line (55) and the substrate (30). The attenuator means is shaped so that the amount of its area between the microstrip line (55) and the substrate (30) can be changed by moving the attenuator means (40). In a preferred embodiment, a segment (45) of a disc embodies the attenuating material, and the disc is rotated to the desired orientation in an alumina guide (35). The attenuating material and the alumina guide (35) have the same dielectric constant.

Description: MICROWAVE VARIABLE ATTENUATOR TECHNICAL FIELD This invention relates to the field of microwave frequency attenuators and, more particularly, to variable attenuators. BACKGROUND OF THE INVENTION 1. Field of the Invention In microwave systems, microwave attenuators are invariably necessary for proper operation of the systems. To facilitate the adaptability of the attenuators to various applications, variable attenuators are used. 2. Description of the Prior Art Microwave power variable attenuators are known in the prior art. In the past such attenuators could only be realized in two forms: coaxial and waveguide. Attenuators having these forms are physically large and heavy, which is a severe disadvantage in size and weight limited environments such as satellites and spacecraft. Coaxial attenuators were made by inserting a microwave absorbing material between the inner and outer conductors at some point in the coaxial line. The attenuator was necessarily fixed and invariable. Since a discrete section of the coaxial line had to be connected into the microwave circuit along with the attendant connectors, the attenuator was bulky and somewhat heavy. OM WIP S " ? A To obtain variable attenuation , waveguide sections have been used as attenuators . Attenuation was achieved by inserting a resistance card partially into the interior of the waveguide through a slot in a wall of the waveguide . The amount of attenuation was varied by moving the re si stance card in or out . This type of attenuator also was bulky and heavy. SUMMARY OF THE INVENTION In view of the deficiencies in the prior art , it i s a primary purpose of the pre sent invention to provide a variable microwave attenuator that is minimal in we ight and si ze . A variable attenuator that substantially solves the above-de scribed problems of the prior art comprises an electrically conductive substrate , an electrically conductive transmission line disposed near the substrate and a movable attenuator disposed between the transmission line and the substrate can be changed by moving the attenuator . BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a plan view of a microwave variable attenuator in accordance with the preferred embodiment of the present invention . DETAILED DESCRIPTION OF THE INVENTION The FIGURE shows a variable attenuator 10 having an electrically conductive frame 15 , a coaxial microwave power input port 20 , and a coaxial microwave power output port 25. Each of the input port 20 and the output port 25 has an outer conductor (not shown ) which is bolted to frame 10 , and an inner conductor (also not shown ) which extends through frame 10 while being electrically isolated from it . OMP An electrically conductive substrate 30 is bolted to the interior of frame 10, thereby bringing it into electrical contact with outer ports 20 and 25. An insulating guide 35 is disposed on the top surface of substrate 30. Guide 35 has a circular hole in its center that is filled with a segmented chip 40. The segmented chip 40 has an attenuator segment 45 that comprises a microwave absorbing material, such as Emerson Cumming MF 116 or 117 with a dielectric constant of 9 to 10. Segmented chip 40 also has an alumina segment 50 that comprises alumina (AIO3, 99.6%). Alumina segment 50 of segmented chip 40 makes up approximately 220° of the circular arc of the chip, and attenuator segment 45 makes up approximately the other 140°. The inner conductors of coaxial input port 20 and coaxial output 25 extend through wall of frame 15 while being electrically isolated from it . The two inner conductors are connected with one another by a microstrip line 55 that extends across segmented chip 40. Segmented chip 40 is closely sandwiched between microstrip line 55 and substrate 30 , but can be freely rotated in the hole of guide 35. Several impedance-matching dots 60 are disposed on guide 35 at e ither side of microstrip line 55 for obtaining a good impedance match between the portion of the microstrip line 55 extending across segmented chip 40 and the portion of microstrip line 55 on either side of segmented chip 40. The use of impedance-matching dots is well known . Variable attenuator 10 can be placed in a microwave power transmi ssion line and can attenuate the power transmitted therethrough , depending on the setting of segmented chip 40. If no portion of attenuator segment 45 of segmented chip 40 lies between microstrip line 55 and substrate 30 , then power will flow unattenuated through variable attenuator 10. But , as segmented chip 40 i s rotated to bring more of attenuator segment 45 between microstrip line 55 and substrate 30 , variable attenuator 10 attenuates more of the power flowing into it . Segmented chip 40 may be mechanically rotated by conventional techniques .

Claims: CLAIMS What is Claimed is; 1. A microwave variable attenuator (10) for use in a microwave system having microwave frequency electro¬ magnetic energy propagating therethrough, said attenuator comprising: an electrically conductive substrate (30) ; an electrically conductive transmission line (55) disposed near said substrate (30), the improvement comprising: a rotatable attenuator chip (45) comprising a material that substantially attenuates said microwave frequency electromagnetic energy, said chip being sandwiched between said transmission line (55) and said substrate (30), said chip being shaped so that rotating said chip changes the amount of area of said chip which lies between said transmission line and said substrate. 2. The microwave variable attenuator as claimed in Claim 1, wherein said chip (45) is generally planar shaped. 3. The microwave variable attenuator as claimed in Claim 2, wherein said transmission line is a microstrip line (55). 4. The microwave variable attenuator as claimed in Claim 3, wherein said chip is disposed within a guide (35). 5. A microwave variable attenuator (10) for use in a microwave system having microwave frequency electro¬ magnetic energy propagating therethrough, said attenuator comprising: an electrically conductive substrate (30), the improvement comprising: an electrically insulating guide piece (35) disposed on one surface of said substrate (30), said guide piece having a round hole therein; an electrically conductive microstrip line (55) disposed across said round hole of said guide piece on the side of said guide piece opposite said substrate, said microstrip line being positioned away from the center of said guide piece hole; and a rotatable disc (40) comprising at least two segments (45, 50), one of the segments comprising a material (45) that substantially attenuates said microwave frequency electromagnetic energy. 6. The microwave variable attenuator as claimed in Claim 5, further including a coaxial microwave power input port (20) which has an inner conductor which is electrically connected to one end of said microstrip line (55) and an outer conductor is electrically connected to said substrate (30); and having a coaxial microwave power output port (25) which has an inner conductor which is electrically connected to the other end of said microstrip line (55) and an outer conductor which is electrically connected to said substrate (30). 7. The microwave variable attenuator as claimed in Claim 6, wherein said disc material (45) that substantially attenuates said microwave frequency electromagnetic energy has a dielectric constant that is substantially equal to the dielectric constant of said guide piece (35) D : 1 :

Inventors: CRAMM HERMAN W JR, SHISHIDO TSUNEO, SHOLLEY MICHAEL D, CRAMM, HERMAN, W., JR., SHISHIDO, TSUNEO, SHOLLEY, MICHAEL, D.
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1983
Main classification: H01P1
IPC codes: H01P1