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The effect of the output impedance of peaking power amplifier (PA) on Doherty PAs (DPAs) is analyzed in this paper. In the design procedure of DPAs, the ideal case is that the output impedance of auxiliary PA is infinite at output power back-off (OPBO) level. However, it is almost impossible to realize this perfect condition in broadband DPAs. Therefore, when the output impedance of peaking path deviates from infinity, some potential effects on DPAs must be produced. In this paper, these effects are explained at the internal plane of transistors. The conclusion is that, at different normalized frequencies, there are different optimal impedance regions for the output impedance of peaking stage. This means that the noninfinite output impedances of peaking stage can enhance the performances of broadband DPAs so long as they are elaborately processed. A 1.65–2.7-GHz (48% bandwidth) broadband DPA is designed considering the effects of peaking PA. The experimental results show that this DPA obtains a drain efficiency of 41%–59.6% at 6-dB OPBO levels and a drain efficiency of 55.8%–72.2% at saturation power levels. The maximum output power across the entire operating band is 43.1–45.2 dBm with a gain of 9.0–10.2 dB. Furthermore, the designed DPA achieves an adjacent channel leakage ratio of −45.8 dBc with an output power of 36.1 dBm at 2.0 GHz after digital predistortion when it is excited by 5-MHz WCDMA signal with a peaking-to-average power ratio of 8.6 dB.

In this letter, a series of inverse continuous modes for implementing highly efficient broadband power amplifiers (PAs) are proposed. These series of inverse continuous modes are extended from continuous Class-F−1 mode. A broadband PA, which operates across 2.4–3.9 GHz, is designed based on the series of inverse continuous modes (SICMs). The experimental results show that this power amplifier achieve drain efficiency of 62.2%–74.7% in the whole interesting band. The average output power of this designed PA is 11.9 W with average drain efficiency of 68.1%.

An extended Class-B to Class-J continuum mode is presented and a power amplifier(PA) based on this theory is realized in this paper. The enhanced voltage waveform formulation, which gives multiple impedances solutions of the fundamental and harmonics for the target performance by adding the harmonic elements, has been described mathematically. Unlike conventional continuous Class-J mode, the optimal impedance solutions of the new mode can contain real and imaginary parts of arbitrary even harmonics. To verify this theory, a high-efficiency PA from 2.85–4.25 GHz is designed at the package plane. The measurement results illustrate that the fabricated PA outputs 11.7–15.8 W saturation power with drain efficiency(DE) of 58% to 78% and PAE of 54.5%–74% across the entire band. For a 5 MHz WCDMA signal with a peak-to-average ratio (PAR) of 8.6 dB, an adjacent channel leakage ratio (ACLR) of −31.5 to −38 dBc is measured at an average DE of 38%–48% when the output power $(P_{\mathrm{out}})$ is 36 dBm from 2.85–4.25 GHz.

In this letter, the bandwidth of the series of continuous modes (SCMs) power amplifiers (PAs) is extended. The SCMs are composed of a series of continuous working modes between Class-B/J and Class-F continuums. The second harmonic load of the series of continuums is purely reactive. By introducing resistive part to the purely reactive second harmonic load of the series of continuous modes, the operation bandwidth of power amplifiers is expanded. A broadband PA working across 0.8–3.05 GHz (117% bandwidth) is simulated and fabricated. Experimental results show that the drain efficiencies in interesting band are 57.4%–79%. The fabricated PA can deliver output power of 10.1–20.7 W.

This paper presents the modeling and optimization of a manifold-coupled superconducting quadruplexer at VHF-band. The quadruplexer consists of four individually designed channel filters with a bandwidth of 400 kHz centered at 216, 224, 232, and 240 MHz, respectively, connected to a common manifold. The complex interactions between the channel filters make the design and optimization of the quadruplexer difficult and even impossible. An equivalent circuit for the manifold and the capacitive external couplings of the four channel filters in the quadruplexer is presented. The parameters of the equivalent circuit are accurately extracted from electromagnetic simulations. Afterward, the equivalent circuit is optimized to compensate for the interactions between the channel filters and obtain a good common-port return loss and channel transfer characteristics. Thereafter, the design of the individual channel filters is improved according to the optimized parameters of the equivalent circuit. The superconducting quadruplexer is successfully designed and fabricated. The measurements show high performance and match well with the simulations. The experimental insertion losses of the four channels are less than 0.45 dB, the center frequency discrepancies of the four channels are less than 40 kHz, the common-port return loss is greater than 16.3 dB, and the out-of-band rejection is higher than 90 dB. Moreover, a high isolation greater than 75 dB between the channels is achieved.

A superconducting resonator, consisting of a microstrip spiral and a 2 b interdigital capacitor array, is proposed. The resonator has a measured unloaded Q over 51 000 in all four states. A two-pole reconfigurable superconducting filter at P-band with a fractional bandwidth of 1% is designed with this resonator and fabricated. The measurements show that the tuning range of the center frequency is from 499.4 to 484.9 MHz with insertion losses of less than 0.1 dB in all four states, and are in good agreement with the simulations.

This paper proposes a modified spiral resonator with a tight three-turn spiral and inner/outer tails. The resonator has good spurious response because the mutual inductances between the three turns at the fundamental mode are positive and thus reduce the fundamental resonant frequency f0, whereas those at the first spurious mode are negative and increase the first spurious resonant frequency fS. By further optimizing the lengths of the spiral and inner/outer tails of the proposed resonator, a spurious resonant frequency fS up to 3.4 f0 is obtained. Moreover, the couplings between such resonators at spurious modes are much weaker than that at the fundamental mode, which is helpful to suppress the spurious response of bandpass filters consisting of such resonators. Furthermore, three dissimilar types of resonators with the same fundamental frequency but with different spurious resonant frequencies are used to compose a bandpass filter and further suppress the spurious response in the stopband. With these methods, a ten-pole superconducting filter at 360 MHz with a 15-MHz bandwidth is successfully designed and fabricated on a LaAlO3 substrate. The overall measurements show a high performance and agree very well with the simulations. The maximum insertion loss is 0.15 dB, the return loss is greater than 19 dB, and the rectangle coefficient (the ratio between the 40-dB bandwidth and the 3-dB bandwidth) is 1.35. Moreover, the out-of-band rejection is higher than 76 dB up to 2030 MHz, which is 5.64 f0. The ten-pole filter occupies a compact area of 33 mm × 15 mm, which amounts to only 0.15 λg0 × 0.07 λg0, where λg0 is the guided wavelength of the 50-Ω line on the substrate at f0.