Dual-Linearly Polarized Pillbox Beamformer in Hybrid CNC-PCB Technologies at W-Band

This work introduces a novel low-profile dual-linearly polarized pillbox beamformer operating at W-band in hybrid CNC-PCB technologies. The dual-linear polarization is achieved by exciting two orthogonal modes in an overmoded parallel plate waveguide (OPPW) namely: the quasi-TEM mode (qTEM) and the $\mathbf{quasi - TE}_{\mathbf{1}}$ mode $(\mathbf{qTE}_{1})$ . The pillbox transition is made of two distinct couplers that transfer efficiently the energy of the two operation modes that propagate from the feeding source in the lower PPW to the uppermost PPW layer via separate coupling regions. The qTEM-mode coupler is built in Aluminum, whereas a multilayer PCB stack-up is used for the $\mathbf{qTE}_{1}-\mathbf{mode}$ coupler. To the best of our knowledge, this is the first time that this topology has been proposed to achieve dual-linear polarization in a single pillbox beamformer at mm-wave frequency. The structure provides a -10dB bandwidth of 22.2% and 13% with a maximum gain of 21dB and 19.7 dBi for the qTEM and $\mathbf{TE}_{1}$ mode, respectively. The proposed pillbox beamformer is an attractive solution for the dual-polarized quasi-optical beamformers at mm-wave frequencies.