Printed circuit board impedance matching step for microwave (millimeter wave) devices
An impedance matching ground plane step, in conjunction with a quarter wave transformer section, in a printed circuit board provides a broadband microwave matching transition from board connectors or other elements that require thin substrates to thick substrate (>quarter wavelength) broadband microwave (millimeter wave) devices. A method of constructing microwave and other high frequency electrical circuits on a substrate of uniform thickness, where the circuit is formed of a plurality of interconnected elements of different impedances that individually require substrates of different thicknesses, by providing a substrate of uniform thickness that is a composite or multilayered substrate; and forming a pattern of intermediate ground planes or impedance matching steps interconnected by vias located under various parts of the circuit where components of different impedances are located so that each part of the circuit has a ground plane substrate thickness that is optimum while the entire circuit is formed on a substrate of uniform thickness.
1. A microwave or millimeter wave circuit, comprising:
a multi-layered dielectric substrate;
a conductive trace formed on one surface of the substrate, the trace being patterned to define circuit elements and transmission lines;
a base ground plane formed on the opposed surface of the substrate;
an intermediate ground plane formed on a layer of the substrate below a circuit element or transmission line; and
vias connecting the intermediate ground plane to the base ground plane to from a stepped ground plane structure, wherein the intermediate ground plane is positioned to control the impedance of the overlying circuit element or transmission line;
wherein the trace comprises a microwave patch antenna, a transmission line for connecting the patch antenna to an energizing coaxial cable, and a quarter wave transformer between the transmission line and the patch antenna.
2. The circuit of claim 1 , wherein the trace is a microstrip.
3. The circuit of claim 1 , wherein the trace is a stripline or coplanar line.
4. The circuit of claim 1 , further comprising additional intermediate ground planes on substrate layers under circuit elements or transmission lines, and vias connecting the additional intermediate ground planes to the base ground plane.
5. The circuit of claim 1 , wherein the via number, diameter and pitch are functions of the circuit operating frequency.
6. A method of constructing microwave and other high frequency electrical circuits on a substrate of uniform thickness, where the circuit is formed of a plurality of interconnected elements of different impedances that individually require substrates of different thicknesses, the method comprising:
providing a substrate of uniform thickness that is a composite or multilayered substrate; and
forming a pattern of intermediate ground planes or impedance matching steps interconnected by vias located under various parts of the circuit where components of different impedances are located so that each part of the circuit has a ground plane substrate thickness that is optimum while the entire circuit is formed on a substrate of uniform thickness;
wherein the circuit comprises a microwave patch antenna, a transmission line for connecting the patch antenna to an energizing coaxial cable, and a quarter wave transformer between the transmission line and the patch antenna.
7. The method of claim 6 , wherein the intermediate ground planes are formed on layers of the multilayered substrate and connected to a base ground plane on the substrate.
8. The method of claim 6 , wherein the circuit elements are formed by patterning a conductive trace on the substrate.
9. The method of claim 8 , wherein the circuit elements are formed by patterning a microstrip.
10. The method of claim 8 , wherein the circuit elements are formed by patterning a stripline or coplanar line.
11. The method of claim 8 , wherein the conductive trace is patterned to form the patch antenna, the quarter wave transformer, and the transmission line, and a ground plane step is formed under the transmission line.