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The design and fabrication of a 76.5 GHz, planar, three beam antenna is presented. This antenna has greater than 31 dB of gain and sidelobes that are less than -29 dB below the main beam. This antenna demonstrates the ability to achieve very low sidelobes in a simple, compact, and planar structure. This is accomplished uniquely by feeding waveguide slots that are coupled to microstrip radiating elements. This illumination technique allows for a very low loss and highly efficient structure. Also, a novel beamscanning concept is introduced. To orient a beam from bore sight it requires phase differences between the excitations of the successive elements. This is achieved by varying the width of the W-band waveguide. This simple, beam steering two-dimensional structure offers the advantage of easy manufacturing compared to present lens and alternative technologies.

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A dual-band shorted annular ring patch antenna with interference rejection at the horizon is presented for GPS timing applications. It is shown that the dimensions of the annular ring can be optimized to make a null in the RHCP pattern at low elevation near the horizon for all azimuth angles. This null attenuates interfering signals originating from ground based sources. The antenna achieves circular polarization utilizing radial shunted stubs. The effect of the stubs on the resonance is analytically derived and verified through simulations. A novel feed configuration that incorporates a coplanar waveguide transition improves the impedance match for both L1 and L2 GPS frequency bands compared to previous designs that present compromises between the feed impedance of the two bands. Additionally, since the shunted stubs reduce the number of required electronic components compared to other antennas with similar horizon nulling capability, the cost is reduced. A prototype antenna operating at GPS L1 and L2 bands has been fabricated and validated through measurements.