Inline Interdigital Pseudo-Elliptic Helical Resonator Filters

• Published in: IEEE microwave and wireless components letters 2011-08, Vol.21 (8), p.400-402
• Main Authors: Doumanis, E., Goussetis, G., Kosmopoulos, S. A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Cavity resonators; Circuit properties; Couplings; Dispersive-coupling; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; Filtering theory; filters; Frequency filters; Handling; Helical; helical resonator; Insertion loss; interdigital filters; Materials handling; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Microwaves; Narrowband; Noise levels; Oscillators, resonators, synthetizers; Passband; Prototypes; quasi-elliptic; Resonant frequency; Resonators; Topology; UHF
• ISSN: 1531-1309; 2771-957X; 1558-1764; 2771-9588
• DOI: 10.1109/LMWC.2011.2160162

A new inline coupling topology for narrowband helical resonator filters is proposed that allows to introduce selectively located transmission zeros (TZs) in the stopband. We show that a pair of helical resonators arranged in an interdigital configuration can realize a large range of in-band coupling coefficient values and also selectively position a TZ in the stopband. The proposed technique dispenses the need for auxiliary elements, so that the size, complexity, power handling and insertion loss of the filter are not compromised. A second order prototype filter with dimensions of the order of 0.05λ, power handling capability up to 90 W, measured insertion loss of 0.18 dB and improved selectivity is presented.