High efficiency Doherty power amplifiers for modern wireless communication systems: A brief review

Dueto the high peak to average power ratio (PAPR) of modern modulated signals, power amplifiers (PAs) have been forced to operate at the back-off (BO) region of their saturation power in order to avoid signal clipping and distortion. However, classical PAs suffer from low efficiency in the BO region operation. Therefore, efficiency has to be enhanced in that region. Many techniques have been proposed. Among them, the Doherty power amplifier (DPA) is considered as the most suitable technique due to its simple structure and high performance. However, its conventional design is limited to a 6 dB BO level, which does not satisfy the requirements of modern communication systems. In this paper, a brief review of the most significant techniques of high-efficiency DPA is presented. First, DPA topology and its operation principles are briefly discussed. Second, efficiency enhancement techniques such as an asymmetrical DPA, output combiner modification, gate bias adaption, offset line optimization, and multi-way DPA were discussed. The study shows that the most suitable, simple, and effective solution is an asymmetrical approach. However, it needs to be investigated in terms of bandwidth in order to meet the efficiency-bandwidth requirements of modern wireless communication systems such as 5G

Dual-Band Bandpass Filter Based On Two U-Shaped Defected Microstrip Structure

This paper presents design of dual-band bandpass filter by integrating conventional quarter-wavelength short circuit stubs bandpass filter with Ushaped defected microstrip structure notch filter. Based on the parametric analysis, it is found that high attenuation level can be achieved by using two U-shaped defected microstrip structure separated by specific distance. The designed circuit simulated using advanced design system and fabricated based on Roger 4350B. The simulation results are in good agreement with measured results. The designed filter covered two pass bands centered at 2.51 GHz and 3.59 GHz with 3-dB fractional bandwidth of 15.94% and 15.86%, respectively, return losses better than 15 dB, and insertion losses better than 1 dB. The designed device can be used for wireless communication applications such as WLAN and WiMAX

New CPW-Fed Broadband Circularly Polarized Planar Monopole Antenna Based On A Couple Of Linked Symmetric Square Patches

A new broadband circularly polarized planar monopole antenna with coplanar waveguide feeding (CPW-fed) is proposed. This antenna consists of a couple of linked symmetric square patches (CLSSP), an asymmetric ground plane and two strips connected to the left ground plane by the CLSSP radiator and a straight strip. A broad impedance bandwidth (IBW) is achieved. Moreover, a broad axial ratio bandwidth (ARBW) is obtained by using an asymmetric ground plane and an inverted L-shaped strip. Simulation results demonstrate that IBW reaches 119% (1.56-6.18 GHz) and ARBW is 88.9% (2-5.2 GHz). The latter is completely overlapped by the simulated IBW. In addition, antenna performance is investigated by studying different parameters

Compact CPW-Fed Broadband Circularly Polarized Monopole Antenna With Inverted L-Shaped Strip And Asymmetric Ground Plane

The design of a coplanar waveguide-fed (CPW-fed) broadband circularly polarized printed monopole antenna is proposed. The antenna consists of a simple rectangular radiator monopole, an inverted L-shaped strip, a horizontal stub, and a modified asymmetric ground plane. Simulation results indicate that the impedance bandwidth (IBW) is 121% (1.575-6.4 GHz), and the axial ratio bandwidth (ARBW) is 64.3% (2.85-5.55 GHz). A parametric study is performed for verification. Results: indicate that the proposed antenna is suitable for different wireless communications systems

Review Of Recent Trends On Power Amplifier Design For Modern Communication Systems

Next-generation wireless communication standard 5G requires power amplifiers capable of maintaining high efficiency in the presence of modulated signals with high Peak-toAverage Power Ratio (PAPR) in order to avoid signal clipping and distortion. Meanwhile, a wideband or multi-band capability is necessary for multi-standard applications. In this paper, a brief review of the most recent wideband and high-efficiency power amplifier designs was presented, with a particular focus on Doherty Power Amplifier (DPA) as the most suitable technique. A comparison between different efficiency enhancement techniques was discussed in detail, while the basic concept and principle of operation for the DPA were presented accordingly. Moreover, many innovative designs to enhance the power amplifier's performance in terms of the back-off efficiency and bandwidth extension were discussed. The first topic considered was efficiency enhancement, whereby different solutions such as multi-stage DPA, asymmetrical devices, and output combiner optimization were presented. Meanwhile, another significant topic discussed was bandwidth extension in which a large number of papers was discussed accordingly. Besides, the most important factors of DPA designs limiting the efficiency enhancement and bandwidth extension were highlighted. Most of the presented designs focused on a single approach, either efficiency enhancement or bandwidth extension. Therefore, symmetrical DPA based on the asymmetrical matching network in combination with multi-section impedance matching can be suggested to solve the problem of efficiency degradation at a Back-Off (BO) region. This will extend the bandwidth simultaneously in order to meet the requirements of modern wireless communication systems