Electrically tunable filters with dielectric varactors

Abstract

This invention provides a voltage tunable filter comprising an input connection point, an output connection point, and at least one circuit branch electrically coupled to the input connection point and the output connection point and including a voltage tunable dielectric varactor electrically connected to an inductor. The voltage tunable filter can be one of a low-pass, high-pass, band-pass, or band-stop filter. The varactor can include built-in DC blocking capacitors.

What is claimed is:  
     
         1 . A tunable filter comprising: 
 an input connection point;    an output connection point; and    a first circuit branch electrically coupled to said input connection point and said output connection point and including voltage tunable dielectric varactor electrically connected to an inductor.    
     
     
         2 . A tunable filter in accordance with  claim 1 , wherein the filter comprises one of a low-pass, high-pass, band-pass, or band-stop filter.  
     
     
         3 . A tunable filter in accordance with  claim 1 , wherein said varactor includes built-in DC blocking capacitors.  
     
     
         4 . A tunable filter in accordance with  claim 1 , wherein the filter comprises one of a Bessel, Butterworth, Chebyshev or elliptical filter.  
     
     
         5 . A tunable filter in accordance with  claim 1 , wherein said voltage tunable dielectric varactor comprises: 
 a substrate having a first dielectric constant and having generally a planar surface; a tunable dielectric layer positioned on the generally planar surface of the substrate, the tunable dielectric layer having a second dielectric constant greater than said first dielectric constant; and first and second electrodes positioned on a surface of the tunable dielectric layer opposite the generally planar surface of the substrate, said first and second electrodes being separated to form a gap therebetween.    
     
     
         6 . A tunable filter in accordance with  claim 5 , wherein said voltage tunable dielectric varactor further comprises: 
 an insulating material in said gap.    
     
     
         7 . A tunable filter in accordance with  claim 5 , wherein the tunable dielectric layer has a permittivity greater than about 100.  
     
     
         8 . A tunable filter in accordance with  claim 5 , wherein the substrate has a permittivity of less than about 30.  
     
     
         9 . A tunable filter in accordance with  claim 5 , wherein the tunable dielectric layer has a permittivity in a range from about 20 to about 2000, and a tunability in a range from about 10% to about 80% at a bias voltage of about 10 V/μm.  
     
     
         10 . A tunable filter in accordance with  claim 5 , wherein the substrate comprises one of the group of: MgO, Alumina, LaAlO 3 , sapphire, and a ceramic.  
     
     
         11 . A tunable filter in accordance with  claim 5 , wherein the tunable dielectric layer comprises one of: 
 a tunable dielectric thick film;    a tunable dielectric bulk ceramic; and    a tunable dielectric thin film.    
     
     
         12 . A tunable filter in accordance with  claim 5 , wherein the tunable dielectric includes an RF input and an RF output for passing an RF signal through the tunable dielectric layer in a first direction, and wherein the gap extends in a second direction substantially perpendicular to the first direction.