Analytical formulations for systematic design of dual-/tri-frequency impedance transformation networks required in software-defined radios (SDRs) and energy harvesting applications

Abstract

The proliferation of multi-band and multi-standard wireless systems are well known but very little is known about the challenges associated in the design and development of such systems. For example, the RF front-ends in such systems require operation of all of the system components optimally functioning at more than one carrier frequency at a time. Traditional solution to address the above problem is to use multiple RF front-ends for each different standard. However, this essentially leads to large board size, higher power consumption along with other technical issues. This scenario has led to an extensive research in the devices and systems which are capable of operating at multiple frequencies concurrently. Such multi-frequency RF components have numerous advantages over the traditional narrow band components. For example, a dual-band power amplifier (PA) not only simplifies the hardware complexity but also provides higher re-configurability and hence makes it a front runner for deployment in multi-band wireless transceiver architectures.

In addition, the concept of multi-frequency components is also crucial for simultaneous energy harvesting from more than one RF radiation sources. Distance of the harvester from RF energy source has profound impact on the amount of available power. Since, RF to DC conversion efficiency is not uniform over the entire input power levels; concurrent RF energy harvesting from multiple RF sources is envisaged as a means to enhance the conversion efficiency over a wider range of the available input power.

Impedance transformation circuit is a sine qua non to the many RF front-end blocks and energy harvesting systems. Design of RF/Microwave components such as amplifiers, mixers, oscillators, antennas, and power dividers/combiners require impedance matching as a key component. Conventionally, quarter-wavelength/single/double-stub impedance transformers have been used for this purpose. But, the ever growing interest in multi-frequency RF/Microwave devices necessitates that the age-old theory of impedance transformation circuits must be now investigated to come up with new multi-frequency transformation circuits, in general, and dual- and tri-frequency impedance transformation circuits, in particular.

In this thesis, novel and advanced techniques for dual- and tri-frequency impedance matching networks have been explored. Specifically, since the limited frequency- and transformation-ratio ails state-of-the-art of dual-frequency matching networks, therefore, the first part of this thesis presents design techniques to mitigate these limitations. Moreover, applications of the proposed techniques have been demonstrated for advanced dual-frequency components such as power dividers and couplers with significantly enhanced performance.

The current state-of-the-art of tri-frequency impedance matching network is still in its infancy. Therefore, a novel systematic and analytical design technique to implement them has been introduced.

The concept of DC-feed as applied in RF/microwave amplifiers is a special kind of impedance matching network where the idea is to establish infinite input impedance at the frequency of interest. In this thesis, a streamlined synthesis procedure for DC-feeds has been proposed to cater to the multi-frequency amplifier requirements.