Candidate: Soroush Rasti Boroujeni
Title: Active-Antenna Front-Ends for Large Phased-Array Transmitters
Date: October 7, 2020
Time: 12:00 PM
Place: REMOTE ATTENDANCE
Supervisor(s): Safavi-Naeini, Safieddin
The ever-increasing demand for wireless broadband connectivity requires infrastructures that can support multi-Gbps of data transfer. To facilitate such a heavy traffic demand, the channel capacity for the given spectrum should be utilized more efficiently. Wideband millimeter-wave phased-array systems can enhance the capacity of the channel by providing multiple steerable directional beams. The cost, complexity and high power consumption of phased-array systems are the key barriers to commercializing this technology. Silicon-based beam-former chips along with scalable phased-array technology offer promising solutions for lowering the cost of phased-array systems. However, the implementation of low-power phased-array architectures is still a challenge. The millimeter wave power generation in silicon beam-formers suffers from low efficiency, and the stringent linearity requirements for multi-beam wide-band arrays further limit the efficiency. In scalable phased-arrays, each module consists of an antenna sub-array and a beam-former chip that feeds the antenna elements. Improving overall efficiency requires a design methodology that considers the beam-former chip and the antenna array as one entity. This thesis presents power efficient solutions for mm-wave phased-array transmitter and proposes different high efficiency power amplifier structures for broadband applications.
A 27-30 GHz RF front-end consisting of a variable gain amplifier, a 360 degree phase shifter, and a two-stage linear power amplifier with the output power of 12 dBm is fabricated using 0.13 µm SiGe technology. The measurement results show 26.7% total efficiency for this chip. This chip is the RF-core of a beam-former chip with eight outputs for feeding 2×2 dual feed sub-arrays for large phased-arrays used in SATCOM. This chip achieved the highest efficiency among the reported Ka-band phased-array transmitters.
Furthermore, novel transformer based output matching structures are proposed for harmonic-tuned power amplifiers. Harmonic tuned power amplifiers have high peak-efficiency but their complicated output matching structure was limiting their use in beam-former RF front-ends. The proposed output matching structures have a layout footprint of a transformer and make their application in beam-former chips possible. A 26-38 GHz power amplifier based on non-inverting 1:1 transformer is fabricated. The measured efficiency of higher than 27% across the band and output power of 12 dBm is achieved. Furthermore, two continuous class F-1 power amplifiers using a 1:1 inverting transformer are implemented. Simulation results show the peak-efficiency of 35% and output power of 12 dBm from 24 to 30 GHz. A common-base power amplifier with inverting transformer output matching is also demonstrated. This amplifier has a peak-efficiency of 42% and peak output power of 16 dBm.
Lastly, a low loss Ka-band re-configurable output matching structure based on tunable lines is proposed and implemented. A double stub matching structure with three tunable segments is introduced to maximize the impedance matching coverage. This structure can potentially compensate for the antenna impedance variation in phased-array antennas.