Reconfigurable broadband transceivers for spatial and polarization diversified wireless communication systems
Authors:   , Zhou Liming , Daryoush Afshin S. 
Published: July 2021

Polarization reconfigurable receivers are used to track the deviation of polarization orientations and axial ratios of radio waves for satellite communication systems. This type of receiver may be used for the reception of dual elliptically polarized (EP) waves with variable axial ratios, or dual linearly polarized (LP) waves with variable tilt angle in a dual polarized frequency reuse (DPFR) radio link. The tuning of the receiver polarization factor is typically realized by combining amplitude-adjusted and phase-delayed signals of a polarized antenna with its cross-polar counterpart. A significant source of imperfection is the phase shifter accuracy and bandwidth, whereas the phase and gain flatness of analog phase shifters may limit the usable bandwidth of such polarization tunable receivers in integrated circuits (IC). A novel broadband polarization reconfigurable direct conversion receiver structure is proposed in this thesis to address the bandwidth and feasibility of integration of existing implantations. In the design of such a receiver the required phase shifts are transferred to the information signal through the phase delayed local oscillator (LO) carrier signals of the downconverter units. Amplitude and phase vector combination of the two cross-polarized signals produces a new receiver polarization factor. The relocation of the phase shifters to the LO path of the mixers allows for a broader phase shifter bandwidth. A 2.45GHz band hybrid transceiver based on commercial off-the-shelf components was designed to operate with a custom built 1x4 single feed circularly polarized (CP) patch antenna array. The multi-element antenna arrays are important building blocks of the next generation cellular frequency reuse system. The components of transmission and reception modes were reused in this transceiver to achieve a 30% space-saving over the full-duplex transceiver structure. The transmission mode of the transceiver board shows a 15.9dB conversion gain, and an 8.9dBm output 1dB compression point (P1dB); the receiver mode exhibits a 45.5dB gain, a 6.3dB noise figure (NF), and a -28.5dBm input 1dB compression point (IP1dB). An integrated digital direct conversion receiver is also reported in this thesis for the evaluation of broadband polarization agile radios. This brute force single conversion receiver contains a low noise amplifier (LNA) and a double balanced Gilbert-cell mixer. Both components were fabricated on K*on 65GHz fT InGaP/GaAs heterojunction bipolar transistor (HBT) technology. The combined receiver front-end has a gain of 25.7dB, NF of 5.8dB, and IP1dB of -23.3dB. The variation on the gain of three LNA and mixer units under test is better than 0.6dB. Performance of this proposed polarization reconfigurable receiver structure is compared against analytical predictions. The hardware was implemented based on hybrid-based test setup using two down-converters along with the required additional signal distribution circuits on discrete FR-4 substrate. Measurements were performed, where a cross-polar rejection (CPR) of 14dB is maintained for an observing bandwidth of 500MHz using 2.45GHz LO signal. The obtained CPR is 6dB below the achievable limit set by the hybrid coupler of the transmitting polarization transformer. This CPR performance is on par with a fixed FR-4 90° hybrid couplers based dual polarization receiver.