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Electronically reconfigurable wideband high-power amplifier architecture for modern RF systems (LMBA)

Shepphard, Daniel 2018. Electronically reconfigurable wideband high-power amplifier architecture for modern RF systems (LMBA). PhD Thesis, Cardiff University.
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As mobile communications and other microwave systems continue to evolve designers and system architects are pushing for ever increasing bandwidth as multiple RF systems are increasingly sharing a common front-end amplifier to save space and reduce routing complexity and losses associated with having separate amplifier systems. The power amplifier in many RF systems typically accounts for the majority of the power consumption of the device or transmitter platform, it is therefore paramount that to improve the efficiency of these systems RFPA designs must be tailored to achieve the highest possible efficiency. RFPA modes of operation and architectures to achieve higher efficiency have been developed, but often come with compromises to other system aspects such as linearity, control complexity and most commonly bandwidth. With the next generation 5G communications specification including frequency bands of up to the Ka frequency spectrum and the high capacity multi-octave spectrum bands allocated at L-C band, traditional RFPA efficiency enhancement techniques struggle to be implementable due to either the high frequency requirements of the control systems needed or due to the bandwidth restrictions of such techniques. II Conventionally narrow bandwidth X-band radar systems that used to be operated at saturated output power conditions are starting to explore multimode operation that require more power back-off (PBO) and control of the RFPA, so are searching for techniques that are applicable at X-band and can achieve the same level of PBO requirements demanded by modern communication modulation standards while working to the power and cooling restraints that come from a limited application platform such as fighter aircraft. Similarly, such fighter platforms are demanding increased electronic warfare (EW) capability which are restrained to the same platform limitations but often need to cover multi-octave bandwidths where traditional efficiency enhancement techniques cannot be applied. This research will focus on wideband efficiency enhancement for both saturated and PBO scenarios that present a frequency agnostic technique of overcoming conventional limitations. The novel work presented is based around the quintessential, but relatively old, bandwidth extension architecture known as the balanced amplifier. The addition of a secondary control signal has been proposed whereby the operating impedance of the amplifier can be dramatically modulated while maintaining the fundamental advantage the balanced amplifier allow, that is multi-octave bandwidth. III The power of this architecture can draw similarities in impedance control afforded by load pull systems, in particular active load-pull. With the correct control signal, any impedance is able to be presented to the transistors to keep them operating at maximum efficiency, where passive matching alone is not able to achieve such efficiency due to fundamental matching theory. Due to the active element of this novel architecture, named the Load Modulated Balanced Amplifier (LMBA), frequency restrictive and thus band limiting elements present in other efficiency enhancement techniques; such as the quarter wave inverter present in the Doherty Amplifier or the difficulty of realizing the modulator in Envelope Tracking (ET) are not present. This thesis will present the fundamental theory driving the operation of an LMBA along with multiple implementations, each targeted at differing applications and different frequency bands to demonstrate the versatility and frequency independence of the technique.

Item Type: Thesis (PhD)
Date Type: Publication
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: Reconfigurable; Wideband; LMBA; GaN; Power Amplifier; Balanced Amplifier.
Date of First Compliant Deposit: 4 April 2019
Last Modified: 04 Aug 2022 02:10

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