Key Takeaways & Executive Findings
- •• The proposed dual-band filtering push-pull PA achieves a frequency ratio of approximately 5:1 by combining MSL and SIW filtering baluns in a hybrid-mode configuration. • It operates at S-band (2.6–2.86 GHz) and Ku-band (13–13.65 GHz), delivering peak output powers of 36.8 dBm and 36 dBm, respectively, with a small-signal gain of 7 dB. • The hybrid-mode filtering balun inherently suppresses even-order harmonics and provides out-of-band spurious rejection, eliminating the need for external harmonic filtering stages. • The design demonstrates the integration and miniaturization advantages of hybrid-mode transmission lines, making it highly suitable for advanced 5G and radar communication systems.
Abstract
A dual-band filtering push‒pull power amplifier (PA) with a large frequency ratio is presented in this paper. The proposed filtering power dividing/combining network is based on a hybrid-mode filtering balun using microstrip line (MSL) and substrate integrated waveguide (SIW). The MSL filtering balun operates in the S-band, with a frequency range of 2.6‒2.86 GHz. Meanwhile, the SIW filtering balun is designed for Ku-band operation, covering a frequency range of 13‒13.65 GHz. Under these conditions, the prototype is capable of attaining a frequency ratio as high as five times the original value. Due to the inherent differential characteristic of the hybrid-mode filtering balun with a large frequency ratio, the proposed push‒pull PA not only realizes filtering functionality but also achieves second-harmonic suppression. To validate the designed concept, the proposed prototype has been designed, fabricated, and measured. Measurement results demonstrate that the proposed PA achieves a 7 dB small-signal gain while maintaining out-of-band spurious rejection during active testing. The developed dual-band filtering push‒pull PA delivers excellent performance, with a peak output power of 36.8 dBm at low frequencies and 36 dBm at high frequencies. Moreover, by employing dual-band filtering baluns, the PA inherently suppresses even-order harmonics while simultaneously providing filtering characteristics in both operational bands, which effectively suppresses near-band spurious signals.
1. Introduction
With the rapid advancement of the 5th generation (5G) communication and radar technologies, the demand for high-power microwave components has grown substantially, spurring extensive research in this field. However, constrained by the limitations of semiconductor technology, the output power of individual devices remains inherently constrained. To address this challenge, push‒pull power amplifiers (PAs) have attracted extensive research attention (Jobs et al., 2018; Chen WJ et al., 2020; Tiwari et al., 2020; Dong et al., 2022; Chen JX et al., 2024; Fahmi et al., 2025; Koh et al., 2025; Liu and Zhang, 2025; Zhou et al., 2025). These systems manipulate the superposition of electromagnetic waves to combine multiple low-power signals into a single high-power output.
For instance, a broadband power combiner based on a ridge waveguide was introduced by Dang et al. (2020), operating from 18 to 40 GHz and ultimately achieving a peak output power of 3.9 W by combining outputs from 16 gallium arsenide (GaAs) monolithic microwave integrated circuit (MMIC) PAs. Similarly, a push‒pull PA presented by Feng WJ et al. (2019) uses two back-to-back filtering baluns to perform power combining while achieving a power-added efficiency (PAE) of 48.7% and effectively suppressing second-harmonic signals. As a device capable of providing differential signals, a balun is particularly suitable for push‒pull power combining applications where harmonic suppression is required (Chiu et al., 2006; Stameroff et al., 2013; Geng et al., 2016; Wang et al., 2016; Feng LP and Zhu, 2017; Huang et al., 2019; Naeini et al., 2020; Shi et al., 2024; Steele and Psychogiou, 2024; Guo X et al., 2025).
Push‒pull PAs have been designed and implemented across various transmission line technologies. Alternatively, hybrid-mode transmission lines have been widely adopted in multiple microwave devices owing to their high integration, compact size, and multifunctionality (Guo JP and Wu, 2018; Tang et al., 2019; Zhang et al., 2021; Ning et al., 2025). By using two microwave devices with distinct transmission line structures but similar functionalities, the hybrid-mode transmission line enables multiple functions while maintaining a compact form factor. For instance, the design presented by Tang et al. (2019) integrates two filters based on microstrip line (MSL) and waveguide technologies, separately, allowing operations in two distinct frequency bands without increasing the overall footprint and with the minimal mutual interference.
This paper presents a dual-band filtering push‒pull PA with a large frequency ratio, designed using a hybrid configuration that combines an MSL-based filtering balun and a substrate integrated waveguide (SIW)-based filtering balun. The low-frequency MSL filtering balun features a symmetric output topology.
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Jiyang CHU, Xiang WANG, Tianxiang CHEN, Jindong ZHANG, Jun HU, Huangyan LI, Boyu SIMA, Wen WU (2025). A dual-band filtering push‒pull power amplifier with a large frequency ratio employing a hybrid-mode bandpass response balun. Engineering Information Technology and Electronic Engineering. https://doi.org/10.1631/ENG_ITEE_2025_0149
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Frequently Asked Questions
What is the frequency ratio achieved by the proposed dual-band power amplifier?
The proposed design achieves a frequency ratio of approximately 5:1, with the low band operating at 2.6–2.86 GHz and the high band at 13–13.65 GHz.
How does the hybrid-mode filtering balun enable dual-band operation?
The hybrid-mode filtering balun combines a microstrip line (MSL) balun for S-band operation and a substrate integrated waveguide (SIW) balun for Ku-band operation, allowing two distinct frequency bands to be processed with minimal mutual interference and a compact footprint.
What are the key performance metrics of the fabricated prototype?
The measured prototype exhibits a small-signal gain of 7 dB, a peak output power of 36.8 dBm at low frequencies and 36 dBm at high frequencies, along with effective out-of-band spurious rejection.
What are the main advantages of using filtering baluns in a push-pull PA?
The filtering baluns inherently provide differential signals, enabling even-order harmonic suppression and filtering characteristics in both operational bands, which removes the need for additional harmonic filtering components and reduces spurious signals.
Where was the research for this paper conducted?
The research was conducted at the School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, China.
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