Switch-Based Variable Length Stubs Network for PA Load Sensitivity Reduction

Abstract

In Fifth Generation (5G) Multiple-Input Multiple-Output (MIMO) transceivers, Power Amplifiers (PAs) driving antenna arrays experience varying loading conditions. In fact, the input impedance of each antenna element changes within a Smith chart region, a phenomenon attributed to mutual coupling, which will affect PA behavior. Although PA performance is load dependent, its output power and drain efficiency contours are nearly constant along specific straight lines in the Smith chart, a characteristic that can be exploited to improve PA performance in variable load scenarios. This work presents a compression network, featuring switch-based variable length stubs, capable of transforming any load within a 2.1 Voltage Standing Wave Ratio (VSWR) circle into a purely resistive load. This network was designed, implemented, measured and used in the Output Matching Network (OMN) of two Class E PAs being able to compensate the output power variation of the first PA and the efficiency degradation of the second PA under the defined load variation. The innovation of this network is the capability to reduce output power or efficiency load sensibility, which is very much desired in many applications, by using an easily implementable and low loss (0.3dB-0.5dB) network. By properly adjusting the distance between stubs and switches it is also able to transform slightly different load patterns into other optimal lines or curves.INDEX TERMS Compression network, load insensitiveness, load modulation, MIMO, mutual coupling, power amplifiers.

3D Smith Chart Constant Quality Factor Semi-Circles Contours for Positive and Negative Resistance Circuits

“…If ≠ 0 is constant, we observe that the expression (5) represents radial lines in the normalized impedance (z plane). Fig.…”

“…Imposing now Q constant and positive in (3) one gets the contours obtained in [8][9][10][11][12][13][14][15][16][17] irrespective of the presence of the absolute value in (1). However, by using inversive geometry [18], it can be proven that imposing (5) in (3), the set of radial constant Q lines is proven to generate a family of coaxal circles as r and x are swept from -∞ to +∞.…”

“…The Smith chart [1][2], which, was invented by Philip Hagar Smith in 1939, has survived the passing of years, becoming an icon of microwave engineering [3]. It is still being used in the design and measurement stage of various radio frequency or microwave range devices [4][5][6][7], for plotting a variety of frequency dependent parameters. Constant quality factor (Q) representations on the Smith chart are a visual way to determine the quality factor of various passive microwave circuits, being mostly known in the microwave frequency range community [8][9][10][11][12][13][14][15][16][17].…”

Investigation of power amplifier performance under load mismatch conditions

“…From the PA perspective, there are different mechanisms to compensate the degrading effect due to load variations [2]. These can be arranged in three main categories: 1) circulators/isolators which eliminate PA-antenna interactions and impose a one-directional signal flow; 2) tunable matching networks (TMNs) and resistance compression networks; 3) load insensitivity PA topologies.…”

Dynamic Supply Voltage Control for PA Output Power Correction Under Variable Loading Scenarios

“…Transmission line resistance compression networks (TLRCNs) are very promising, but they require at least two loads varying synchronously [11]. Various tunable matching networks (TMNs), using varactors [12], [13], switched capacitor banks [14], or switched variable-length stubs [15] to perform a dynamic load matching, have also been implemented. This approach is very versatile and has a good tunability range but suffers from the extra losses added by the additional tunable components.…”