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This paper deals with the research and development of printed flexible capacitors and inductors predominantly designed for the construction of RFID labels. These printed RF passive components are required for the construction of fully printed low cost passive RFID labels. The passive components are directly printed on PET substrate by the screen printing technique. The printing process was optimized in order to achieve a high yield and good electrical parameters at the frequency of 13,56 MHz.Electrical parameters of printed capacitors, such as impedance to frequency characteristic, capacity to temperature characteristic, capacity to bias voltage characteristic were measured in detail. The bending tests were also performed for verifying of printed capacitors flexibility. The performance of capacitors was verified in the real sample of resonant circuit at 13,56 MHz.

Keywords interdigital capacitor (IDC), planar inductor, screen printing technology, polymer films, resonant circuits, resonant frequency IntroductionThe fast growing of the wireless market has created an urgent demand for smaller and cheaper handsets with increased functionality and performance while still meeting the tight constraints for mass production within a short product life cycle. Due to economic aspects, there is a necessity of cheap production of highfrequency components with the specified parameters. In particular, it is also actually for the wireless identification devices.Many transmission lines and waveguides have been used for microwave and millimeter-wave frequencies. Among them, the rectangular waveguide, coaxial line, and microstrip line are the most commonly used [1]. This article investigates the passive planar components that may be used in particular in passive RFID tags. The authors had a task to make a resonant circuit with an operating frequency of 100 MHz. Moreover, its maximum dimensions should not be more than ID1 (85.6×53.98 mm) format according to ISO / IEC 7810 and technology should provide the minimum cost of the finished product.Previous research has demonstrated various technologies applicable to the planar components manufacture. This article describes the passive elements manufactured by the photolithography technology as the most wide-spread and screen printing technology [2] which allows maximum reduce the cost of the finished product [3]. Also, screen printing provides a wide range of substrate materials (including paper, fabric) [4].The basic structure of a capacitor with two electrodes is shown in (a) Fig. 1. Interdigital capacitors (IDC) as lumped circuit elements in RF circuits can be used. IDC represent a multifinger periodic structure as shown in (b) Fig. 1. IDC use the capacitance that occurs across a narrow gap between thin-film conductors. These gaps are essentially very long and folded to use a small amount of area. IDC has a larger size compared with the overlay capacitor (see (a) Fig. 1) with the same capacitance value. The quality factor for such type capacitor is higher than that for overlay capacitors [3 pp. 229-230].The total capacitance C 0 of an interdigital structure (see (b) Fig. 1) depends on finger length l, finger width w and finger spacing s. When s=w, capacitance C 0 can be calculated according to [4 p. 60] by the Eq. (1):

The article describes various options of receiving printing inductors for passive RFID tags which work at frequency 13.56 MHz. Different variants of producing inductors using the technology of screen printing with different materials of the conductive paste and the number of layers deposited by a variety of substrate materials were investigated. Assessments of the impact of the factors stated above on electrical parameters of the researched samples were made. After the analysis of measurement data of inductance, quality factor, resonant frequency and impedance the authors offered the option of manufacturing printed inductors for RFID tags.

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