Microwave test fixtures for determining the dielectric properties of a material

A fixture for determining the dielectric properties of a material over a wide range of microwave frequencies comprising:

• a housing;
• an electrically shielded cavity defined in said housing, said cavity for confining therein test material surrounding an electrical conductor;
• input circuit means for coupling energy into said cavity, said input circuit means including:
• a transmission line having a center conductor spaced from said cavity and extending into said housing;
• port means for coupling energy into said center conductor;
• tap means having a distal end spaced a distance from said cavity for coupling energy out of said center conductor and into a first location in said cavity, said first location being coincident with a portion of the electrical conductor in said cavity, said tap means including adjustment means for adjusting the distance said distal end of said tap means is spaced from said cavity whereby to vary the amount of microwave energy coupled from said center conductor into said cavity;
• and
• output circuit means for coupling microwave energy out of said cavity from a second location, said second location being coincident with another portion of the electrical conductor in said cavity.

A method for determining the dielectric properties of a material comprising:

• confining test material surrounding an electrical conductor within an electrically shielded cavity;
• coupling microwave energy into a center conductor at one end of a transmission line spaced from the cavity and extending transversely the electrical conductor in the cavity such that said center conductor is spaced from said cavity;
• measuring microwave energy with power measuring equipment coupled to the center conductor at another end of the transmission line;
• coupling microwave energy from a tap of the center conductor between the ends of the transmission line and into the cavity at a first location, said first location being coincident a first portion of the electrical conductor in the cavity, the power measuring equipment having a characteristic impedance to render the transmission line flat between the tap of the center conductor and the other end of the transmission line;
• measuring microwave energy from a second location in the cavity, said second location being oppositely disposed from said first location and being coincident a second, oppositely disposed portion of the electrical conductor in the cavity.

A method for determining the dielectric properties of a material comprising:

• confining test material surrounding an electrical conductor within an electrically shielded cavity;
• coupling microwave energy into a center conductor at one end of a transmission line spaced from the cavity;
• coupling microwave energy from a tap member electrically connected to the center conductor and into the cavity at a first location, the first location being coincident a first portion of the electrical conductor in the cavity;
• moving the tap member relative the cavity to vary the spacing therebetween without removing the test material and surrounded electrical conductor from the cavity;
• measuring microwave energy at the tap member;
• and
• measuring microwave energy from a second location in the cavity, the second location being oppositely disposed from the first location and being coincident with a second, oppositely disposed portion of the electrical conductor in the cavity.

A method for determining the dielectric properties of a material comprising:

• confining test material surrounding an electrical conductor within an electrically shielded cavity;
• coupling microwave energy into a center conductor at one end of a first transmission line spaced from the cavity and extending transversely the electrical conductor confined in the cavity;
• coupling microwave energy from a first tap member electrically connected to the center conductor of the first transmission line into the cavity at a first location, the first location being coincident a first portion of the electrical conductor in the cavity;
• measuring the power of the microwave energy coupled from the first tap member with first power measuring equipment having a characteristic impedance to render the first transmission line flat between the first tap member and the first power measuring equipment;
• coupling microwave energy from the cavity at a second location to a second tap member electrically connected to a center conductor in a second transmission line spaced from the cavity and extending transversely the electrical conductor confined in the cavity, the second location being oppositely disposed from the first location and being coincident with a second, oppositely disposed portion of the electrical conductor;
• measuring the power of the microwave energy coupled into the second tap member with second power measuring equipment having a characteristic impedance to render the second transmission line flat between the second tap member and the second power measuring equipment;
• and
• moving the first and second tap members relative the cavity to vary the spacing between the member and the cavity until at least a predetermined difference is obtained between the measured power of the microwave energy coupled from the first tap member and the measured power of the microwave energy coupled into the second tap member.