Abstract
In this paper, a novel multi-layered microstrip line with built-in parallel-plate capacitors is proposed for DC-blocking applications, with its transmission characteristics measured up to 50 GHz. The microstrip lines are fabricated via screen printing directly onto polyurethane films laminated on standard textile substrates which would otherwise be unsuitable for printing. Compared to a standard microstrip line on the same substrate, the proposed 10 cm-long line on felt (with an embedded 44 pF capacitance) suffers from less than 0.1 dB higher insertion loss up to 4 GHz. Furthermore, varying the overlapping length of the lines and hence the capacitance enables the realization of DC blocking and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 3 dB high-pass filtering with pass-bands starting between 88 MHz and 1.2 GHz. This is achieved without altering the cut-off frequency of the microstrip line’s mode-free propagation, measured up to 50 GHz, exhibiting a low attenuation of 0.32 dB/mm at 50 GHz on a felt fabric substrate. Compared to a lumped capacitor, the proposed microstrip-embedded printed capacitor demonstrates a significant improvement in mechanical reliability, withstanding over 10,000 bending cycles, and RF power handling with under 6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C temperature rise at 1 W. The lines are fabricated on two textile substrates and their transmission characteristics were measured up to 50 GHz, which represents the highest frequency characterization of textile-based lines to date, demonstrating a stable group delay and insertion losses. Based on the proposed multi-layered integration method, low-cost screen-printed microstrip-embedded capacitors on textiles can be used for microwave applications up to mmWave bands.
Highlights
Flexible, printable, and conformable microwave and millimeter-wave components have attracted significant research interest for a variety of Internet of Things (IoT) and 5G+/6G applications [1], [2]
In this paper, a novel microstrip-embedded parallel-plate capacitor was proposed based on screen-printing for flexible microwave and mmWave components
By integrating the capacitor’s plates within an impedance-controlled microstrip line, low-cost low-resolution printed capacitors can operate as DC-blocks up to 50 GHz, without altering the mode-free propagation response of the line
Summary
Printable, and conformable microwave and millimeter-wave (mmWave) components have attracted significant research interest for a variety of Internet of Things (IoT) and 5G+/6G applications [1], [2]. Despite the growing popularity of additively-manufactured microwave components including multi-layered microstrip lines operating up to 10 GHz [17], there are no reported broadband DC-blocking lines implemented using additive manufacturing on low-cost flexible substrates. The demonstration of microwave inkjet printed capacitor, up to 3 GHz, has been limited to smooth and homogeneous substrates such as LCP and silicon, using a layer of costly SU-8 polymer as the bonding interface. A range on inkjet printed microwave and mmWave transmission lines have been demonstrated and characterized up to 30 GHz, on smooth low-loss LCP substrates [3]. Namely capacitors, have been realized using inkjet printing but only for low frequency applications [29], where all the sub GHz RF passives have only been demonstrated on smooth polymers and up to 5GHz [19].
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