4$\,\times\,$ 4-Element Corporate-Feed Waveguide Slot Array Antenna With Cavities for the 120 GHz-Band

We propose a 4 × 4-element corporate-feed waveguide slot array antenna with outer cavities for the 120 GHz band. To adjust the mutual coupling effects in a small sized array antenna, an outer cavity structure is employed for each radiating slot. The outer cavity in this antenna structure provides adequate mutual coupling effects for each radiating element. As a result, high antenna efficiency is achieved over a broad bandwidth. A 4 × 4-element array with the outer cavities was fabricated by diffusion bonding of laminated thin copper plates, which has the advantages of high precision and low loss characteristics even in a high frequency region such as the 120 GHz band. The antenna gain of 21.1 dBi and the antenna efficiency of 80.0% are measured at the center frequency. The measured 1 dB-down gain bandwidth is 22 GHz (from 118 to 140 GHz) which is corresponding to 17.6%.