Abstract—This paper presents the de

Abstract—This paper presents the design and realization ofa high data rate radio front-end module for point-to-pointbackhaul links at E-band. The design module consists of fourvertically stacked unconnected metal layers without any galvanicand electrical contact requirements among the building blocks,by using gap waveguide technology. The module componentsare a high-gain array antenna, diplexer, and circuitry con-sisting of a transmitter (Tx) and a receiver (Rx) monolithicmicrowave integrated circuits (MMICs) on a carrier board,which is successfully integrated into one package with a novelarchitecture and a compact form. The diplexer consists of twodirect-coupled cavity bandpass filters with channels at 71–76 GHzand 81–86 GHz with a measured return loss of 15 dB and anisolation greater than 50 dB. A wideband 16 × 16 slot arrayantenna with a measured gain of more than 31 dBi is usedto provide high directivity. The measured results show that thepackaged transmitter provides a conversion gain of 22 and 20 dBat 76 and 86 GHz, respectively, with an output power of 14 and16 dBm at 1-dB gain compression point, at the same frequencies.The packaged receiver shows an average conversion gain of 20 dBat 71–76-GHz and 24 dB at 81–86-GHz bands. A real-timewireless data transmission is successfully demonstrated with adata rate of 8 Gbit/s using 32-quadrature amplitude modulatedsignal over 1.8-GHz channel bandwidth with spectral efficiencyof 4.44 bit/s/Hz. The proposed radio front end provides theadvantages of low loss, high efficiency, compact integration, anda simple mechanical assembly, which makes it a suitable solutionfor small-cell backhaul links.Index Terms—Frequency-division duplex (FDD), gapwaveguide, integration, millimeter-wave, slot array antenna,wireless communication.