Past and present technological developments in microstrip antenna arrays are summarized. Emphasis is on exploring the potential of such arrays for satisfying the requirements of advanced military and commercial applications.

Microstrip array technology

A grid array antenna is presented in this paper with sub grid arrays and multiple feed points, showing enhanced radiation characteristics and sufficient design flexibility. For instance, the grid array antenna can be easily designed as a linearly- or circularly-polarized, unbalanced or balanced antenna. A design example is given for a linearly-polarized unbalanced grid array antenna in Ferro A6M low temperature co-fired ceramic technology for 60-GHz radios to operate from 57 to 66 GHz (≈ 14.6% at 61.5 GHz ). It consists of 4 sub grid arrays and 4 feed points that are connected to a single-ended 50-Ω source by a quarter-wave matched T-junction network. The simulated results indicate that the grid array antenna has the maximum gain of 17.7 dBi at 59 GHz , an impedance bandwidth (|S11| ≤ -10ndB) nearly from 56 to 67.5 GHz (or 18.7%), a 3-dB gain bandwidth from 55.4 to 66 GHz (or 17.2%), and a vertical beam bandwidth in the broadside direction from 57 to 66 GHz (14.6%). The measured results are compared with the simulated ones. Discrepancies and their causes are identified with a tolerance analysis on the fabrication process.

Grid Array Antennas With Subarrays and Multiple Feeds for 60-GHz Radios

An integrated retroreflective data communication display (2) for visual and electromagnetic communication is described. The display (2) may be configured as an integrated retroreflective electronic license plate, with printed visual information (4), similar to the information printed on traditional license plates, on retroreflective sheeting (6). An antenna network (8) is integrated within the license plate for electromagnetic communication and may be connected to external electronic modules. The display may also be configured as an integrated retroreflective electronic road sign (140), also providing visual and electromagnetic information in a unitary structure.

Integrated retroreflective electronic display

In this communication, we present a new circularly-polarized array antenna using 2×2 linearly-polarized sub grid arrays in a low temperature co-fired ceramic technology for highly-integrated 60-GHz radio. The sub grid arrays are sequentially rotated and excited with a 90°-phase increment to radiate circularly-polarized waves. The feeding network of the array antenna is based on stripline quarter-wave matched T-junctions. The array antenna has a size of 15×15×0.9 mm3. Simulated and measured results confirm wide impedance, axial ratio, pattern, and gain bandwidths.

A Circularly-Polarized Array Antenna Using Linearly-Polarized Sub Grid Arrays for Highly-Integrated 60-GHz Radio

The design of a high-gain microstrip grid array antenna (MGAA) for 24-GHz automotive radar sensor applications is first presented. An amplitude tapering technique utilizing variable line width on the individual radiating element is then applied to lower sidelobe level. Next, the MGAA is simplified to a microstrip comb array antenna (MCAA). The MCAA shows broader impedance bandwidth and lower cross-polarization radiation as compared with those of the MGAA. The MCAA is designed not as a travelling-wave but a standing-wave antenna. As a result, the match load and the reflection-cancelling structure can be avoided, which is important, especially in the millimeter-wave frequencies. Finally, an emphasis is given to 45° linearly-polarized MCAA because the radiation with the orthogonal polarization from cars coming from the opposite direction does not affect the radar operation.

Microstrip Grid and Comb Array Antennas

A description is given of an antenna consisting of an interconnected wire grid formed by etching metallic lines on a dielectric sheet backed by a metallic ground plane. The theory of operation, analytical model, and experimental findings for this approach to a printed array are described. The device is low cost, light weight, and has sufficient bandwidth to be of use in a variety of applications. An analytical model is developed which establishes transmission line equivalent circuits for the wire grid elements. Current distributions determined from the model are shown to predict accurately the measured pattern performance of a typical implementation. The bandwidth as established by various pattern parameters is quantitatively assessed. Particular emphasis is given to methods of amplitude control through control of line impedances. A particular design implementation is presented for a five-wavelength circular array with independent quadrant control. Measured results from this configuration are compared to theory.

T. Dowling

Papers

The wire grid microstrip antenna