Shiwei Zhao

Linearity Improved Doherty Power Amplifier Using Coupled-Lines and a Capacitive Load

A Doherty power amplifier, using a pair of coupled lines loaded by a capacitor, is proposed for linearity improvement. The conventional λ/4 transmission line is substituted by capacitor-loaded coupled lines to perform impedance inversion, and to compensate phase delay. At the same time, the proposed structure is also utilized to suppress the second and higher order harmonic of the output of the main amplifier. Furthermore, the phase distortion of the peak amplifier at a high power level can be corrected by tuning capacitor-loaded coupled lines. Compared to a conventional Doherty PA, the third-order intermodulation distortion of the proposed Doherty PA is reduced by 23 dB.

An unequal broadband power divider using Composite Right/Left-Handed Transmission Lines

A unequal power divider using anti-coupled and Microstrip Metamaterial Lines over a large bandwidth is proposed. The structure comprises anti-coupled power divider, followed by a +90° negative-refractive index (NRI) metamaterial (MM) phase-shifting line along the top branch, and traditional microstrip line along the bottom branch. The structure is used to deliver flexible variation of power division ratio and phase using Composite Right/Left-Handed Transmission Lines (CRLH-TL), besides, anti-coupled power divider to suppress the second harmonic. The proposed power divider exhibits a measured differential output phase 90° ± 5°bandwidth from 1.62 to 2.75GHz, while the output quantities S21 and S31 remain above-4dB from 0.7 to 2.5GHz.

The design of waveguide Slot Taylor circular arrays

Two dimensional arrays formed by arranging a number of linear slotted waveguides side-by-side are presented. Theory, synthesis procedure, and implementation of the two dimensional Taylor Slot Array are demonstrated. The performances of the two dimensional Taylor Slot circular array with 972 slots in the ka-band at the center frequency of 30 GHz are demonstrated. A less than 1.51dB input voltage standing-wave ratio (VSWR) with the band width of 600MHz is achieved. At the center frequency 30 GHz, main beam is 35.48dB with a 25dB sidelobe level of the H-plane and 21.3dB sidelobe level of the E-plane are also achieved.