Waveguide Slot Array Antenna Snares 120 GHz

June 29, 2015
This compact array antenna achieves a broad bandwidth of 118 to 140 GHz.

As lower-frequency bandwidths are consumed by communications and other applications, researchers attempt to find cost-effective methods to make use of millimeter-wave frequencies. Using the 60- and 120-GHz bands for short-range, high-data-rate communications is one such example. Dongjun Kim, Jiro Hirokawa, and Makato Ando from the Department of Electrical and Electronics Engineering of the Tokyo Institute of Technology (Tokyo, Japan), along with Jun Takeuchi and Ahihiko Hirata from the NTT Microsystem Integration Laboratory (Kanagawa, Japan), have proposed the design of a 4 × 4 element corporate-feed waveguide slot array antenna for the 120-GHz band.

This antenna achieves impressive performance levels, with gain of 21.1 dBi and efficiency of 80%. The antenna features a 1-dB-down bandwidth of 22 GHz from 118 to 140 GHz. The array antenna features two types of cavities to adjust mutual coupling effects. The outer cavities of the design provide sufficient mutual coupling to achieve effects similar to that of an infinite array. The outer cavities also work as a choke and suppress contributions from neighboring radiating elements, enabling the characteristics of each radiating element with an outer cavity to be maintained in the array.

Elements are arranged at 0.86-wavelength intervals, and the aperture size of the array is defined as 8.4 mm square (2.1 mm × four elements) for the 120-GHz band. The structure has four sets of 2 × 2 element subarrays with outer cavities and an H-junction feed network. The peak gain of the 4 × 4 element array with the outer cavities is 21.2 dBi with 80% antenna efficiency; the peak gain is only 20.2 dBi with 71% efficiency without the outer cavities. Simulations were performed using the High-Frequency Structure Simulator (HFSS) electromagnetic (EM) simulation software from Keysight Technologies. Based on the standard value of copper conductivity, the conductivity loss of the antenna array is only 0.1 dB at 125 GHz.

With and without the outer cavities, the array antenna achieved uniform aperture distribution. Measured gain appeared to be stable in spite of some instability in the measurement system—e.g.,  less-than-adequate electromagnetic-interference (EMI) shielding. Radiation patterns were measured only for the center frequency at 125 GHz, although the simulations indicate a wide operating bandwidth with high gain. See “4 × 4 Element Corporate-Feed Waveguide Slot Array Antenna with Cavities for the 120 GHz Band,” IEEE Transactions on Antennas and Propagation, December 2013, p. 5,968.

About the Author

Jack Browne | Technical Contributor

Jack Browne, Technical Contributor, has worked in technical publishing for over 30 years. He managed the content and production of three technical journals while at the American Institute of Physics, including Medical Physics and the Journal of Vacuum Science & Technology. He has been a Publisher and Editor for Penton Media, started the firm’s Wireless Symposium & Exhibition trade show in 1993, and currently serves as Technical Contributor for that company's Microwaves & RF magazine. Browne, who holds a BS in Mathematics from City College of New York and BA degrees in English and Philosophy from Fordham University, is a member of the IEEE.

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