High Frequency Properties of RF Planar Passive Components

Abstract

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):

A compact omnidirectional to directional frequency reconfigurable antenna for wireless sensor network applications

“…A dielectric resonator antenna uses a PIN diode for switching and a varactor diode for fine-tuning the reconfigurable frequency bands [21]. The variation in high-frequency planar inductance and capacitance in patch antennas based on its shape and construction is presented [22]. A flexible, reconfigurable, and multiband antenna for wearable sensor applications was introduced [23][24][25].…”