Pre-matched coaxial transistor test fixture
View Patent ↗Coaxial microwave transistor test fixtures provide lowest insertion loss possible and include, as part of the input and output sections, transformer networks either in form of single stage λ/4 segments, or, for larger bandwidth, multiple step segments or ramped transitions from 50Ω to the impedance closer to the internal impedance of the power transistor. The transforming networks are flat or cylindrical and can be made exchangeable in order to accommodate various transforming ratios using the same fixture body and coaxial adapters. The fixtures can be calibrated using standard TRL method.
1. A coaxial pre-matched RF transistor (DUT) test fixture comprising an input section attached to an input port,
an output section attached to an output port,
a metallic block (INSERT), which is inserted between the sections and carries the DUT, and
a metallic cover extending from the input port to the output port,
wherein the input and the output sections are slabline segments, each comprising a bottom metallic block,
an associated section of the metallic cover,
a coaxial connector attached to the corresponding port, and
a center conductor attached to the connector and reaching from the connector to the INSERT, and wherein the center conductors of the slabline segments comprise a 50Ω section and at least one non-50Ω section,
whereby the 50Ω sections are attached to the connectors and the non-50Ω sections are inserted between the 50Ω sections and the DUT.
2. The test fixture of claim 1 , wherein a length of the at least one non-50Ω section is one quarter wavelength long at an operation frequency.
3. The test fixture of claim 1 , wherein at least one non-50Ω section comprises a number N≥1 of cascaded segments 1, 2, . . . N with characteristic impedances Z1, Z2, . . . ZN, wherein segment 1 is attached to the 50Ω section and segment N is attached to the DUT, and wherein 50Ω>Z1>Z2 . . . >ZN,
and wherein a length of the segments is optimized for DUT impedance matching and frequency bandwidth.
4. The test fixture of claim 1 , wherein the center conductor of at least one slabline segment has a contour form of a lateral ramp, the ramp having a narrow end and a wide end, wherein the narrow end approximately matches a cross section of and is attached to the center conductor of a 50Ω section, which said 50Ω section is attached to the coaxial connector,
and wherein the wide end has a width approaching a width of and is attached to a DUT terminal lead,
and wherein a contour form and a length of the ramp are optimized to cover a frequency bandwidth.
5. The test fixture of claim 1 or 3 , wherein the non-50Ω section has a form of a parallelepiped block.
6. The test fixture of claim 1 or 3 , wherein the non-50Ω section is a co-axial cylinder.
7. The test fixture of claim 1 wherein the non-50Ω segment is a co-axial ellipsoid.
8. The test fixture of claim 1 , wherein at least one non-50Ω segment is exchangeable.
9. The test fixture of claim 1 , wherein at least one non-50Ω segment is co-axial ellipsoidal ramp.