W-band active phased array antennas have a very small inter-element pitch (≈2 mm). In this innovation, instead of trying to integrate isolators into the unit cell to separate transmit and receive signals, an interlaced triangular grid of metal patch elements has been developed. The isolation between transmit elements and receive elements has been demonstrated to be on the order of 25 dB or more, precluding the need for discrete isolator circuits. Using metal patch technology, the element and associated interconnect loss has been demonstrated to be 0.5 dB at 94 GHz, which represents an efficiency of 89%.
Metal patch elements and interconnects are constructed using PolyStrata®, a wafer-level, multi-layer, micro-fabrication process. Structures up to a millimeter in thickness, with dimensional control on the order of microns across multiple centimeters, are readily fabricated using this technique. Antenna arrays comprising hundreds of elements at W-band can be fabricated using this process. The antenna elements are probe-fed, half-wavelength patches supported on a relatively large cylindrical column at the patch center. This concept is an adaptation of an antenna element originally designed for the Juno microwave radiometer for dual-polarized operation at W-band. There is one probe for each orthogonal polarization, connected to a 50-ohm recta-coax interconnect. The patch elements are recessed in a shallow cavity, which helps to improve isolation. Impedance matching is accomplished by adjusting probe position and by removing material from the corners of the patch. The elimination of dielectric in the construction of the antenna eliminates hysteresis losses and improves tuning accuracy (due to the uncertainty in the dielectric constant). This makes for a highly precise, low-loss antenna element.
A metal patch unit cell prototype was recently developed at JPL for application to a cloud and precipitation scanning radar instrument. The unit cell was designed to interface with a WR10 test-fixture for testing purposes. The unit cell prototype produced measurements that agree very closely to HFSS predictions. The interlacing of elements in a triangular grid for this prototype limits scan angles to less than 16 degrees, which is sufficient for the intended application.
This work was done by Neil F. Chamberlain, Mauricio Sanchez Barbetty, and Gregory A. Sadowy of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
Refer to NPO-49396