Magnetically coupled series-tuned air coil resonators having very low C/L ratios to achieve higher QL, lower insertion loss and improved out-of band rejection

• US 20020011906A1
• Filed: 04/10/2001
• Published: 01/31/2002
• Est. Priority Date: 03/16/1998
• Status: Active Grant

• Current Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Original Assignee: Broadband Innovations, Inc.
• Inventors: Petrovic, Branislav
• Granted Patent: US 6,538,532 B2
• Time in Patent Office: Days
• US Class Current: 333/177
• CPC Class Codes: H03H 7/09 Filters comprising mutual inductance
• CPC Class Codes: H03H 7/1775 Parallel LC in shunt or branch path H03H7/1791 takes precedence

Abstract

A series tuned resonator circuit topology permits implementation of narrow band-pass filters having higher loaded quality factors (Q_L) and lower insertion loss than was previously achievable in the prior art employing such a topology. The topology employs an additional parallel capacitor for the series-tuned topology, with very low C/L ratios to achieve the combination of higher values of Q_L, low insertion loss and a steeper roll-off between the pass-band and the stop-band (at both lower and higher frequencies). Air coils are used to achieve the large inductor values desirable for the series-tuned topology.

Claims

1. A resonator circuit comprising:

a first resonator having a resonance frequency, said first resonator further comprising;

a circuit combination comprising a first capacitance connected in series with a single inductance, said single inductance comprising an air coil;

a second capacitance connected in parallel with said circuit combination; and

wherein said second capacitance has a value that is substantially greater than the value of said first capacitance.

2. The resonator circuit of claim 1 further comprising;

a second resonator having resonance frequency substantially equal to the resonance frequency of said first resonator, said second resonator comprising;

a circuit combination comprising a first capacitance connected in series with a single inductance, said single inductance comprising an air coil; and

a second capacitance connected in parallel with said second combination; and

wherein said first and said second resonators are magnetically coupled to one another.

3. The resonator circuit of claim 2 having a transfer function that is 6th order in nature.

4. The resonator circuit of claim 2 wherein said magnetic coupling between said first and second resonators is characterized by a coupling coefficient k having a value substantially less than 1.

5. The resonator circuit of claim 4 wherein said coupling coefficient k is on the order of 0.02 or less.