95～105 GHz SiGe BiCMOS Wideband Digitally Controlled Attenuator for Metasurface Antenna Design

LUO Jiang; ZHANG Wenzhu; CHENG Qiang

doi:10.11999/JEIT240059

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LUO Jiang, ZHANG Wenzhu, CHENG Qiang. 95～105 GHz SiGe BiCMOS Wideband Digitally Controlled Attenuator for Metasurface Antenna Design[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240059

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LUO Jiang, ZHANG Wenzhu, CHENG Qiang. 95～105 GHz SiGe BiCMOS Wideband Digitally Controlled Attenuator for Metasurface Antenna Design[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT240059

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95～105 GHz SiGe BiCMOS Wideband Digitally Controlled Attenuator for Metasurface Antenna Design

doi: 10.11999/JEIT240059

1.
School of Electronics and Information Engineering, Hangzhou Dianzi University, Hangzhou 310018, China
2.
State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China

Funds: The National Key Research and Development Program of China (2023YFB3811503), The Zhejiang Provincial Natural Science Foundation of China (LQ23F040009), The State Key Laboratory of Millimeter Waves (K202316)

Received Date: 2024-01-26
Rev Recd Date: 2024-09-05

Available Online: 2024-09-10

Abstract

Abstract

Objective The W-band spectrum, spanning from 75 to 110 GHz, offers valuable spectrum resources, making it well-suited for high-speed wireless communication, radar detection, and biomedical imaging. Its lower atmospheric attenuation, compared to the commonly used 60 GHz band, further enhances its suitability for these applications. As modern wireless devices and electronic systems operate in increasingly complex electromagnetic environments, the demands on antenna systems are growing. These systems must independently control both radiated and scattered electromagnetic waves. Active phased array antennas, which integrate numerous transmit/receive (T/R) modules, provide precise control over the amplitude and phase of radiation elements, enabling superior manipulation of the radiated electromagnetic field. Meanwhile, rapidly advancing intelligent metasurface technology allows programmable, real-time modulation of scattered electromagnetic wave characteristics such as amplitude, phase, frequency, and polarization. This technology has attracted significant interest in the fields of communications, radar, and antenna systems. Consequently, metasurface antennas with active T/R modules offers a novel technological approach for efficient beam control of both radiated and scattered electromagnetic fields, providing new insights into solving complex electromagnetic environment problems. Digitally controlled attenuators (DSAs) are essential in metasurface antenna array systems, serving as millimeter-wave signal amplitude control modules. They primarily compensate for amplitude errors introduced by phase shifters or other components while also suppressing sidelobe levels in array antennas to enhance beam directivity. Additionally, these attenuators must exhibit minimal phase variation to reduce tracking errors, thus simplifying the calibration process. However, existing commercial millimeter-wave amplitude control chips are expensive and may face export restrictions, emphasizing the urgent need for high-performance, low-cost solutions to support the hardware implementation of metasurface antennas. Methods A 95 to 105 GHz DSA with 5-bit resolution is proposed. To address the issues of high insertion loss (IL), poor accuracy, and limited bandwidth in the large attenuation unit at W-band, a reflective structure based on a cross-coupled broadband coupler is proposed. The proposed coupler features a 180° inverter core and quasi-parallel stripline connections on both sides. At millimeter-wave frequencies (e.g., W-band), coupling capacitance introduced by the gaps creates a series resonance condition, achieving lower transmission loss and ensuring wide operational bandwidth. The 4 dB and 8 dB attenuation units, built using this structure, achieve high accuracy and low IL within a compact area. To minimize impedance mismatch during state switching, the attenuation units are cascaded in an order that reduces variations in amplitude and phase. Specifically, the 4 dB and 8 dB units are placed at the two ends of the attenuator to limit mutual interference. Smaller attenuation units (0.5 dB, 1 dB, and 2 dB) adopt a simplified T-type structure. The 0.5 dB unit, being more sensitive to impedance changes, is strategically positioned between the 1 dB and 2 dB units. Furthermore, phase changes during state switching are mitigated through a combination of positive- and negative-slope phase compensation networks. A positive-slope network is applied to the 4 dB unit, while negative-slope networks are used for the 0.5 dB, 1 dB, and 8 dB units. This dual compensation approach effectively avoids overcompensation, ensuring consistent amplitude and phase performance across all states, significantly improving the attenuator’s root means square (RMS) phase errors. Results and Discussions The layout of the proposed wideband DSA is shown in Fig. 10; the whole chip occupies a silicon area of 840 μm × 430 μm including all testing pads with a small core size of only 610 μm × 200 μm. It has five attenuation cells providing independent control of binary-coded attenuation levels of 0.5, 1, 2, 4, and 8 dB with a total of 32 states. Fig. 11 shows the simulated attenuation levels relative to the reference state for all 31 attenuation states within the desired frequency range of 95～105 GHz. The DSA achieves a dynamic attenuation range of 15.5 dB with a step resolution of 0.5 dB. The frequency response curves of adjacent states are evenly spaced with no overlap, indicating that the attenuator delivers precise amplitude control characteristics. The maximum phase variation relative to the reference state across all 31 attenuation states is less than 4.8°, as plotted in Fig. 12. As shown in Fig. 13, the IL in the reference state is less than 2.5 dB across the entire frequency band of interest. Fig. 14 illustrates the simulated RMS amplitude error and phase error versus frequency. The RMS amplitude errors remain below 0.31 dB over 95～105 GHz, while the RMS phase error is better than 2.2°. Table 3 summarizes the performance of the designed W-band attenuator and compares it with recently reported millimeter-wave DSAs. Compared to other attenuators, the proposed DSA demonstrates superior overall competitiveness, achieving low IL, high attenuation accuracy, and low RMS phase error within a compact chip size. While [6] achieves the lowest RMS phase error, it suffers from a high IL of 11.2 dB. In contrast, [22] offers excellent IL performance but is limited to a small attenuation range of only 4.7 dB. Conclusions In conclusion, the 5-bit W-band DSA presented in this paper, implemented in a 0.13 ${\text{µm}} $ SiGe BiCMOS process, offers an efficient and compact solution for wideband attenuation with low IL and minimal phase shift. The design integrates reflective and simplified T-type topologies, along with RC-based positive and negative slope correction networks applied to different attenuation units, enabling precise attenuation steps and optimized phase errors. The attenuator achieves an attenuation range of 0–15.5 dB with 0.5 dB steps over the 95–105 GHz frequency range, occupying a compact area of 0.12 mm². Simulated results show an IL of less than 2.5 dB, RMS amplitude error below 0.25 dB, and RMS phase error under 2.2°. The proposed DSA can serve as a key component empowering the hardware implementation of an integrated T/R metasurface antenna system with simultaneous radiation and scattering control.
- SiGe BiCMOS,
- W-band,
- Attenuator,
- Wideband coupler with cross-coupling,
- Metasurface

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References(22)

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