Current research projects:

RF Power Amplifiers

Our research is focused on the design and implementation of high efficiency RF power amplifiers for wireless applications. The specific areas which our research group is concentrating on are related to the implementation of switch-mode and digital power amplifier technology. In order to resolve the challenges of implementing high efficiency amplifiers a system approach is required which includes both the signal design and the RF hardware design. A key theme in our work is to create constant envelope or reduced envelope signals which can be amplified efficiently and then reconstructed after amplification. Our work includes pulse encoding methods for switch-mode amplifiers, RF PA design, filters and energy recycling in RF amplifiers.


  1. S. Abbasian and T. Johnson, "Effect of second and third harmonic input impedances in a class-F amplifier," Progress in Electromagnetics Research (PIER) C, Vol. 56, 2015, pp. 39-53.
  2. L. Xiao, S. Abbasian and T. E. Johnson, "All Digital Encoders for RF Switch-mode Power Amplifier Applications," IEEE Wireless and Microwave Tech. Conf. (WAMICON), Cocoa Beach FL, USA, Jun. 6, 2014.
  3. S. Abbasian and T. Johnson, "Analysis of Current Mode Class D Amplifiers Under Periodic and Non-periodic Switching Conditions," IEEE International Symposium on Circuits and Systems, Beijing, China, May 19-23, 2013, pp. 610-613.
  4. S. N. Ali, MASc Thesis, Aug. 2012.
  5. S. N. Ali and T. E. Johnson, "RF switch-mode power amplifier with an integrated diplexer for signal reconstruction and energy recovery," IEEE International Microwave Symposium Digest, Montreal, Canada, Jun. 17-22, 2012, pp. 1-3.
  6. S. N. Ali and T. E. Johnson, "A new high efficiency RF switch-mode power amplifier architecture for pulse encoded signals," IEEE Wireless and Microwave Tech. Conf. (WAMICON), Cocoa Beach FL, USA, Apr. 15-17, 2012, pp. 1-6.
  7. T. Johnson, K. Mekechuk, and D. Kelly, "Noise Shaped Pulse Position Modulation for RF Switch-mode Power Amplifiers," European Microwave Week (EuMW), Manchester, UK, Oct. 9-14, 2011, pp. 340-343.
  8. T. Johnson, K. Mekechuk, D. Kelly, and J. Lu, "Asynchronous Modulator for Linearization and Switch-mode RF Power Amplifier Applications," IEEE RFIC Symposium, Boston, MA, June 7-9, 2009, pp. 185-188.

RF Rectifiers

Our research is focused on the design and implementation of high efficiency RF synchronous rectifiers. The principle concept used in these designs is derived from time reversal duality where high efficiency amplifier circuit topologies can be converted into high efficiency rectifier circuits. Our specific research projects relate to the implementation of low power CMOS synchronous rectifiers, high power GaN synchronous rectifiers, and optimal load circuits to maximize rectification efficiency.


  1. S. Abbasian and T. Johnson, "High Efficiency and High Power GaN HEMT Inverse Class-F Synchronous Rectifier for Wireless Power Applications," European Microwave Conference (EuMW), Paris, France, Sep. 6-11, 2015, pp. 1-3 (accepted).
  2. S. Dehghani and T. Johnson, "2.4 GHz CMOS Class D Synchronous Rectifier," IEEE International Microwave Symposium Digest, Phoenix, USA, May 17-22, 2015, pp. 1-3.
  3. S. Dehghani and T. Johnson, "Tracking load to optimize power efficiency in RF to DC rectifier circuits," IEEE Wireless Power Technology Conference, Boulder, Colorado, May 13-15, 2015, pp. 1-3.
  4. S. Abbasian and T. Johnson, "High efficiency GaN HEMT class-F synchronous rectifier for wireless applications," IEICE Electronics Express, Vol. 12, No. 1, 2015, pp. 20140952 (11 pages).

Industrial Applications of RF and Microwave Power

Given our background in RF and microwave power amplifiers we have been expanding our interest in multi-disciplinary research projects which use RF power for industrial heating applications. Our most recent research project involved the design of a 1 kW RF heating system for pre-treating wastewater sludge (bio-solids) which are byproducts of sewage treatment plants. The research has been focused on employing RF heating as a way to increase the throughput of anaerobic digesters which generate bio-gas from the sludge. This multi-disciplinary project is part of an ongoing collaboration with the Bio-reactor research group at UBC led by Dr. Cigdem Eskicioglu.

There are many other applications of RF power in industrial heating processes. Research challenges of employing this technology are include achieving uniform heating, implementing high efficiency amplifiers, applicator designs, and adaptive matching to maintain high power transfer to the load as material properties change during the heating process.


Our antenna work is focused on the design of an ultra-wideband nested coaxial waveguide feed antenna. The feed has applications in radio astronomy such as the Square Kilometre Array.


We have two sensor related design projects which we are currently working on. The first project is a contactless or single point contact voltage measurement method for high voltage distribution line voltage monitoring applications.The second sensor project relates to the design of a portable blood pressure sensor that can be integrated into wearable technology.


  1. T. Worthing, W. Wenngren, R. Nakamatsu and T. Johnson, "Portable blood pressure monitoring using pulse transit time," Canadian Medical and Biological Engineering Conference (CMBEC37), Vancouver, BC, May 21-23, 2014.