Radio frequency interconnect circuits and techniques

Abstract

A multilayer circuit board assembly includes one or more radio frequency (RF) interconnects between different circuit layers on different circuit boards which make up the circuit board assembly. The RF interconnects can include one or more RF matching pads which provide a mechanism for matching impedance characteristics of RF stubs to provide the RF interconnects having desired insertion loss and impedance characteristics over a desired RF operating frequency band. The RF matching pads allow the manufacture of circuit boards having RF interconnects without the need to perform any back drill and back fill operation to remove stub portions of the RF interconnects in the multilayer circuit board assembly.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a Divisional of co-pending application Ser. No. 11 / 533,848 filed on Sep. 21, 2006.FIELD OF THE INVENTION[0002]This invention relates generally to phased array antennas adapted for volume production at a relatively low cost and having a relatively low profile and more particularly to radio frequency (RF) circuits and techniques utilized in phased array antennas.BACKGROUND OF THE INVENTION[0003]As is known in the art, a phased array antenna includes a plurality of antenna elements spaced apart from each other by known distances coupled through a plurality of phase shifter circuits to either or both of a transmitter or receiver. In some cases, the phase shifter circuits are considered to be part of the transmitter and / or receiver.[0004]As is also known, phased array antenna systems are adapted to produce a beam of radio frequency energy (RF) and direct such beam along a selected direction by controlling the phase (via the...

AI Technical Summary

Benefits of technology

[0012]As mentioned above, the relatively high cost of phased arrays has precluded the use of phased arrays in all but the most specialized applications. Assembly and component costs, particularly for active transmit / receive channels, are major cost drivers. Phased array costs can be reduced by utilizing batch processing and minimizing touch labor of components and assemblies. It would be advantageous to provide a tile sub-array for an Active, Electronically Scanned Array (AESA) that is compact, which can be manufactured in a cost-effective manner, that can be assembled using an automated process, and that can be individually tested prior to assembly into the AESA. There is also a need to lower acquisition and life cycle costs of phased arrays, while at the same time improving bandwidth, polarization diversity and robust RF performance characteristics to meet increasingly more challenging antenna performance requirements.

[0013]At least some embodiments of a tile sub-array architecture described herein enable a cost effective phased array solution for a wide variety of phased array radar missions or communication missions for ground, sea and airborne platforms. In addition, in at least one embodiment, the tile sub-array provides a thin, lightweight construction that can also be applied to conformal arrays on an aircraft wing or fuselage or on a Unmanned Aerial Vehicle (UAV).

[0014]In one so-called “packageless T / R channel” embodiment, a tile sub-array simultaneously addresses cost and performance for next generation radar and communication systems. Many phased array designs are optimized for a single mission or platform. In contrast, the flexibility of the tile sub-array architecture described herein enables a solution for a larger set of missions. For example, in one embodiment, a so-called upper multi-layer assembly (UMLA) and a lower multi-layer assembly (LMLA), each described further herein, serve as common building blocks. The UMLA is a layered RF transmission line assembly which performs RF signal distribution, impedance matching and generation of polarization diverse signals. Fabrication is based on multi-layer printed wiring board (PWB) materials and processes. The LMLA integrates a package-less Transmit / Receive (T / R) channel and an embedded circulator layer sub-assembly. In a preferred embodiment, the LMLA is bonded to the UMLA using a ball grid array (BGA) interconnect approach. The package-less T / R channel eliminates expensive T / R module package components and associated assembly costs. The key building block of the package-less LMLA is a lower multi-layer board (LMLB). The LMLB integrates RF, DC and Logic signal distribution and an embedded circulator layer. All T / R channel monolithic microwave integrated circuits (MMIC's) and components, RF, DC / Logic connectors and thermal spreader interface plate can be assembled onto the LMLA using pick and place equipment.

[0016]With this particular arrangement, a tile sub-array can be manufactured without the need to perform any back-drill and back-fill operations typically required to eliminate RF via stubs. The RF matching pad technique refers to a technique in which a conductor is provided on blank layers (i.e., layers with no copper) of a circuit board or in ground plane layers (with etched relief area) of a circuit board. The conductor and associated relief area provided the mechanism to adjust impedance characteristics of RF vias (also referred to as RF interconnect circuits) provided in a circuit board. Since the need to utilize back-drill and back-fill operations is eliminated, the RF matching pad approach enables a standard, low aspect ratio drill and plate manufacturing operation to produce an RF via that connects inner circuit layers and which also has a low insertion loss characteristic across a desired frequency band such as X-Band (8 GHz-12 GHz).

[0017]As is known, mode suppression vias help electrically isolate the RF interconnects from surrounding circuitry, thereby preventing signals from “leaking” between signal paths. In conventional systems, the mode suppression vias are also drilled and plated at the same time the interconnecting RF via is drilled and plated.

[0018]With the RF matching pad approach of the present invention, however, all RF and mode suppression vias can be drilled and plated through the entire assembly and there is no need to utilize and back drill and fill operations on the RF interconnects. Thus, manufacturing costs associated with back drill and back fill operations can be completely eliminated while simultaneously improving RF performance because channel to channel variations due to drill tolerances and backfill material tolerances are eliminated.

Problems solved by technology

As mentioned above, the relatively high cost of phased arrays has precluded the use of phased arrays in all but the most specialized applications.

Assembly and component costs, particularly for active transmit / receive channels, are major cost drivers.

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