Compact Second-Order Highly Linear Varactor-Tuned Dual-Mode Filters With Constant Bandwidth

• Published in: IEEE transactions on microwave theory and techniques Vol. 59; no. 9; pp. 2214 - 2220
• Main Authors: Athukorala, Lakshman, Budimir, Djuradj
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-09-2011; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Bandwidth; Capacitance; Circuit properties; Constant bandwidth; Distortion; dual mode; Electric potential; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; Frequency filters; Impedance; Linearity; microstrip filter; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Microwaves; Noise levels; Oscillators, resonators, synthetizers; Resonant frequency; Simulation; tunable filter; Tuning; varactor; Varactors; Voltage; Tunable circuit; Microstrip filters; Second order; Non linear filter; Low voltage; Elliptic filter; Bias voltage; microstrip filter; Resonator; Constant bandwidth; dual mode; Third order; Compact design; Coverage; Tuning; Mode filter; Varactor diode; Intercept point; Simulation; Tunable filter; Linearity; Insertion loss; Equivalent circuit; varactor; Signal distortion; distortion
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2011.2160279

This paper presents a compact highly linear tunable second-order quasi-elliptic filter with constant 3-dB bandwidth. The proposed filter is thoroughly analyzed to clearly describe the filter equivalent circuit and the tuning mechanism involved. In addition, the tunable resonator configuration employed is shown to improve filter linearity, especially for low bias voltages where distortion is normally stronger. A quasi-elliptic tunable filter was designed, built, and tested for illustration and verification. With a 3-dB bandwidth variation of only 4.6%, the filter had a frequency coverage from 1.45 to 1.96 GHz, an insertion loss better than 2.5 dB, and measured IIP3 >; 43 dBm throughout. The experimental results are in excellent agreement to theory and simulations.