Adjustable pre-matching 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 transforming segments from 50Ω to the impedance closer to the internal impedance of the power transistor. The transforming networks are flat or elliptical and can be rotated around the axis of the center conductor and allow adjusting the characteristic impedance of the pre-matching section by a typical ratio of up to 2.3:1, resulting in a DUT presented Max to Min impedance transforming ratio of over 5:1.
1. A coaxial pre-matching RF transistor (DUT) test fixture having an adjustable impedance transforming ratio comprising:
an input section attached to an input port,
an output section attached to an output port,
a metallic block disposed between the input and output sections for carrying the DUT, and
a metallic cover extending from the input port to the output port, wherein the input section and the output section each comprise:
a bottom metallic block,
a coaxial connector associated with the corresponding port, and
a center conductor attached to the connector and extending from the connector to the metallic block within a space defined by the metallic cover and the bottom metallic block, the center conductor forming a lateral slabline; wherein the center conductor of the slabline in each of the input and output sections comprises a 50Ω segment and at least one non-50Ω segment, wherein the at least one non-50Ω segment is disposed between the at least one 50Ω segment and the DUT and is axially rotatable around the center conductor of the slabline, and wherein each of the at least one non-50Ω segments, the DUT and the metallic block are secured as a single assembly that is rotatable as a single unit around the center conductor of the slabline.
2. The test fixture of claim 1 , wherein a length of the at least one non-50Ω segment is one quarter wavelength at an operation frequency.
3. The test fixture of claim 1 , wherein at least one non-50Ω segment comprises a number N>1 of cascaded segments 1, 2 . . . N with characteristic impedances Z1, Z2, . . . ZN, whereby segment 1 is attached to the 50Ω segment and segment N is attached to the DUT, and wherein 50Ω>Z1>Z2 . . . >ZN,
and wherein a length of the segments is optimized for maximum frequency bandwidth.
4. The test fixture of claim 1 or 3 , wherein at least one non-50Ω segment is a parallelepiped block.
5. The test fixture of claim 1 or 3 , wherein at least one non-50Ω segment is a co-axial ellipsoid.
6. The test fixture of claim 1 , wherein at least one non-50Ω segment is exchangeable.