UHF band switchable superconducting filter with pin diode switches

Abstract

A low-loss switchable superconducting filter is presented. High Q resonators loaded with switchable superconducting interdigital capacitors are introduced. A two-pole 2-bit switchable high-temperature superconducting (HTS) filter at 516 MHz with a bandwidth of 29 MHz is designed and fabricated. The measured centre frequency tuning range is 33 MHz (6.4%). In all states, the HTS filter with pin diode switches exhibits an insertion loss <0.81 dB and a good return loss better than 16.8 dB.Introduction: Switchable filters have been widely researched and used in engineering applications owing to their flexibility, compact size and frequency switching property [1][2][3][4][5][6]. Many switches and components, including MEMS filters [1], varactors [2], bonding wire [3], tuning screws [4] and pin diodes [5,6], are adopted to realise the frequency switching of filters in different bands. The MEMS filter is used to adjust the centre frequency of the filter and to ensure a large tuning range [1]. The varactor is utilised to switch frequencies continuously [2]. Pin diodes have the advantages of small size and fast switching speed. However, traditional switchable filters have the disadvantages of a low Q-value resonator and high insertion loss [5,6]. A 14.7% fractional bandwidth filter with pin diodes for 9-11 GHz has a 1.76 dB insertion loss [5], whereas the switchable bandpass filter with pin diodes for 0.3-0.6 GHz has a 1.32-1.95 dB insertion loss and an 11-19 equivalent Q-value [6].High-temperature superconducting (HTS) thin films, which have very low surface resistance, are used to fabricate high-performance filters with low insertion loss and extraordinarily steep skirts [1,3,4,7]. An HTS filter switching frequency by bonding wire has a high Q-value resonator in all four states [3], but it cannot be used for practical applications because of its long switching time. The high-speed mechanical tuning system with screws and step motors for HTS filters is complex and requires the installation of numerous peripheral components [4].In this Letter, a new type of switchable HTS filter with pin diodes is proposed. The proposed filter combines the advantages of a high Q-value resonator and fast switching speed. The high Q-value resonator has a novel structure with interdigital capacitors (IDCs) at the two ends to connect switches, giving it the advantages of constant bandwidth and compact size. The frequency switching principle is discussed and analysed in detail in this Letter. The two-pole switchable HTS filter is fabricated on an MgO substrate with double-sided coated YBCO films. The measured results of the filter match well with the simulations.

Recent Progress in the Design of 4G/5G Reconfigurable Filters

“…The design delivers the exact expected performance with the aid of the equivalent transmission line circuit of the microstrip filter. Compared with the PIN diode tuneable filters in Reference [65][66][67][68], the MEMS tuneable filter has a high quality factor and a good rejection in the stopband. Figure 15 shows the design with the installed layout.…”

Novel microfluidically tunable bandpass filter with precisely‐controlled passband frequency

“…Thus, multiplication of devices can be avoided while maintaining a small footprint. In the developed tunable/reconfigurable filters, several techniques have been explored, such as microelectromechanical systems (MEMS) [1], and semiconductor diodes including pin diode [2] and varactor [3,4]. These reconfiguration mechanisms are highly robust in terms of operation and technological maturity.…”