The upper part of Figure 1 illustrates an antenna derived by widening the middle strip conductor of a finite-width coplanar waveguide (FCPW) to form a rectangular patch. An FCPW offers all the advantages of a conventional coplanar waveguide, along with the additional advantage that its finite-width ground planes suppress the propagation of spurious substrate electromagnetic modes that would otherwise degrade the electrical performance of an array of patch antenna elements.

The lowest order of resonance of an FCPW patch antenna occurs at a frequency for which the guide wavelength, lg(slot), equals the sum of mean lengths of slots from point a to point i. At resonance, the electric-field lines are oriented as shown by the curved arrows, and the antenna radiates with a polarization parallel to sides c-d and f-g.

Figure 1. An FCPW Patch Antenna is derived by widening the middle strip conductor of a finite-width coplanar waveguide to form a rectangular patch.

An experimental FCPW antenna element like that of Figure 1 was fabricated by use of gold paste and screen printing on ceramic substrates. The substrate material had a relative permittivity of 5.9, making it possible to reduce patch dimensions significantly to make an array of such elements more compact. Dimensions includedD = 0.01125 in. (0.286 mm), S = 0.012 in. (0.305 mm), W= 0.004 in. (0.102 mm), and G = 0.024 in. (0.700 mm). The input impedance of the antenna was measured by use of through-reflect-line on-wafer calibration standards, a pair of microwave probes, an automatic network analyzer, and de-embedding software from the National Institute of Standards and Technology; these measurements revealed that the antenna resonated at frequency of 19.95 GHz with a de-embedded input impedance of 534 Ω at plane P-Q.

The upper part of Figure 2 illustrates two back-to-back FCPWs on the top side of a dielectric substrate, a connecting FCPW on the bottom side of the substrate, and FCPW-to-FCPW vertical interconnections (vias). An experimental unit having this configuration was made of substrate material and conductor strips with dimensions D, S, W, and G as described above, and with vias of ≈0.01 in. (≈0.25 mm) diameter.

Figure 2. FCPWs and FCPW Patch Antennas are elements of developmental modules that will eventually be used to make compact phased-array antennas.

The lower part of Figure 2 shows a system-level integrated circuit (SLIC) module that was undergoing development at the time of reporting the information for this article. The completed module would contain all the circuitry of an eight-element phased-array antenna. The module would contain four dual-channel monolithic microwave integrated circuits (MMICs) and supporting circuitry. Each of the dual channels would contain a three-bit phase shifter, an analog attenuator, and amplitude-calibration and -control elements. A photonic link would bring the radio-frequency signals and digital control signals into the module. Another photonic link would return information on the status of the module to an external controller.

This work was done by Richard Q. Lee and Kurt A. Shalkauser of Glenn Research Center; Jonathan Owens, James Demarco, Joan Leen, and Dana Sturzebecher of PSD, Army Research Laboratory, AMSRL-PS-E; and Rainee N. Simons of NYMA, Inc.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Commercial Technology Office
Attn: Tech Brief Patent Status
Mail Stop 7-3
21000 Brookpark Road
Ohio 44135

Refer to LEW-16666

NASA Tech Briefs Magazine

This article first appeared in the May, 1999 issue of NASA Tech Briefs Magazine.

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