Research On Tunable Switch Filter Circuit Based On PIN Diodes

The increasing number of frequency bands that need to be integrated into radar and wireless communication systems and the gradual development of systems towards miniaturization have also placed demands on the design of RF front-end circuits in systems that are miniaturized and highly integrated.RF switches and filters are two important devices in RF front-end circuits,which are usually connected in a cascade manner in systems that can result in large circuit sizes and certain connection losses.The integrated design of the switch and filter circuit can integrate the functions of the two devices and has a good practical value.The main work and research in this paper is as follows.(1)A study of RF switching circuits based on PIN diodes was carried out and the design of two single-blade double-throw switches was completed.A single knife double-throw(SPDT)switch for L-band was designed using a series-parallel structure,and its minimum insertion loss could reach0.38 d B,verifying that the series-parallel structure has better switching performance and providing a design basis for filtering integrated switches.A tunable matching network is used to improve the traditional parallel structure switch,and a tunable SPDT switch is proposed to achieve a switch with an operating frequency tunable from 1.5GHz to 3.7GHz.(2)A study of PIN diode-based reconfigurable filters was carried out and two reconfigurable filters were designed.A bandwidth switchable reconfigurable filter was designed using parallel coupled lines and short cut-off lines loaded with PIN tubes.By controlling the on/off of PIN tubes,three filter modes,ultra-broadband(2.06-3.72GHz),broadband(2.62-3.28GHz)and dual-band(2.31-2.55 GHz and 3.26-3.48GHz),can be achieved,and the fabricated of the real object was verified by real tests.The structure of the step impedance resonator loaded with short-circuit branches is improved,and a single-and dual-band switchable reconfigurable filter is designed.Variable capacitance diodes are integrated into the resonator to achieve tunable filter frequency,and PIN diodes are introduced to enable single band filtering and dual band filtering modes to be switched.(3)Based on the research of RF switch and filter,the microstrip filter circuit and PIN diode switch are integrated into the design,and the filter switch is equipped with frequency tunable function by embedding varactor diode to realize a PIN diode-based tunable filter integrated switch.The results show that the center frequency of the integrated filter switch can be continuously tuned in the range of 1.55 to 1.99 GHz,with a minimum in-band insertion loss of 1.5 d B and a port isolation of more than 22 d B,offering the advantages of high integration.