The coupled states of a pair of Tamm plasmon polaritons and a microcavity mode are studied through the transfer matrix method in a metal–Bragg reflectors–cavity–Bragg reflectors–metal configuration. The properties of coupled states can be adjusted through the cavity thickness, but there is one coupled state for which the frequency remains the same as for the uncoupled Tamm plasmon polariton and independent of the cavity thickness. When the frequency of the uncoupled cavity mode is equal to that of the bare Tamm plasmon polariton, an anticrossing behavior with the most intense coupling occurs. There are three coupled modes with antisymmetry coupling and symmetry coupling in the anticrossing region. As cavity thickness increases, two coupled modes are degenerated into one state with frequency equal to that of the bare Tamm plasmon polariton. The third lower coupled mode and the uncoupled cavity mode are merged into one frequency by steps, but a huge amplification of field occurs in the cavity with the coupled mode. An analytical description is in good agreement with the numerical results.
A novel optimization design method using boundary-based weighted sum filtering operator is proposed for microstrip filter design. The proposed operator is combined with multiobjective evolutionary algorithm based on decomposition combined with enhanced genetic operators and two-dimensional median filtering operator (MOEA/D-GO-II), which can maintain the population diversity and obtain wider rejection bandwidth. For verification, it is used to design fragment-type microstrip band-stop filter for rejecting one of the fifth generation (5G) bands, 3.3 GHz-3.6 GHz. Both simulated and measured results verified the expected responses of the design. Comparison result shows that more alternative designs could be obtained using the proposed method.
A symmetric Doherty power amplifier (DPA) based on integrated enhancing reactance (IER) was proposed for large back-off applications. The IER was generated using the peaking amplifier with the help of a desired impedance transformation in the low-power region to enhance the back-off efficiency of the carrier amplifier. To convert the impedances properly, both in the low-power region and at saturation, a two-impedance matching method was employed to design the output matching networks. For verification, a symmetric DPA with large back-off power range over 2.2–2.5 GHz was designed and fabricated. Measurement results show that the designed DPA has the 9 dB back-off efficiency of higher than 45%, while the saturated output power is higher than 44 dBm over the whole operation bandwidth. When driven by a 20 MHz LTE signal, the DPA can achieve good average efficiency of around 50% with adjacent channel leakage ratio of about –50 dBc after linearization over the frequency band of interest. The linearity improvement of the DPA for multistandard wireless communication system was also verified with a dual-band modulated signal.
This paper presents a method to extend the back-off range of an asymmetric Doherty power amplifier (DPA) to 12 dB using a reactive output impedance of the peaking amplifier. An analytical method is employed to determine the desired reactive output impedance for specific output power back-off (OPBO) range. Then, a peaking output matching network is designed to achieve the desired impedance to enlarge the efficiency of the carrier amplifier. When compared with conventional design, the OPBO range can be improved by about 2 dB using the proposed method. For verification, a 3.4-3.6 GHz asymmetric DPA with enhanced OPBO range was designed using 10 and 30 W GaN HEMT transistors. The measured efficiencies of 47%-49% at 12 dB back-off and 63%-66% at saturation are obtained over the whole frequency range. For a 40 MHz LTE signal at 3.5 GHz, the adjacent channel leakage ratio is −50 dBc after linearization with an average efficiency of higher than 50%.
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