Filter, communication module, and communication apparatus

Abstract

A filter includes a substrate; a signal line formed on the substrate and including an input terminal and an output terminal at either end of the signal line; and a first pair of resonant lines connected between the signal line and a ground portion, wherein the first pair of resonant lines are connected to the signal line at the same point.

1 . A filter comprising:
 a substrate;   a signal line formed on the substrate and including an input terminal and an output terminal at either end of the signal line; and   a first pair of resonant lines connected between the signal line and a ground portion, wherein   the first pair of resonant lines are connected to the signal line at a same point.   
   
   
       2 . The filter according to  claim 1 , further comprising:
 a second pair of resonant lines connected between the signal line and the ground portion; and   a coupling section provided between the first pair of resonant lines and the second pair of resonant lines.   
   
   
       3 . The filter according to  claim 2 , wherein
 the coupling section includes:   a first circuit block connected to the signal line and including a first terminal and a second terminal;   a second circuit block connected between the first terminal of the first circuit block and the ground portion; and   a third circuit block connected between the second terminal of the first circuit block and the ground portion.   
   
   
       4 . The filter according to  claim 2 , wherein
 the coupling section includes:   a first circuit block and a second circuit block connected in series to the signal line; and   a third circuit block connected between a point between the first circuit block and the second circuit block, and the ground portion.   
   
   
       5 . The filter according to  claim 1 , wherein
 the resonant lines are connected on opposite sides across the signal line.   
   
   
       6 . The filter according to  claim 1 , wherein
 a length of the resonant line is (λ/8)×n (λ is a resonant wavelength, and n is a positive integer).   
   
   
       7 . The filter according to  claim 2 , wherein
 a characteristic impedance of the resonant line is lower than a characteristic impedance of the signal line.   
   
   
       8 . The filter according to  claim 1 , wherein
 the plurality of resonant lines are connected to the same ground portion.   
   
   
       9 . The filter according to  claim 7 , wherein
 the resonant lines are formed into an arc shape.   
   
   
       10 . The filter according to  claim 1 , further comprising:
 a variable capacitor including a variable capacitor electrode provided above the resonant line via an air gap and a drive electrode for changing distance between the variable capacitor electrode and the resonant line.   
   
   
       11 . The filter according to  claim 1 , wherein
 the substrate is a ceramic substrate including a plurality of laminated internal wirings.   
   
   
       12 . The filter according to  claim 2 , wherein
 the coupling section includes a variable capacitor or variable inductor.   
   
   
       13 . The filter according to  claim 2 , wherein
 an impedance of the resonant line is lower than an impedance of the signal line.   
   
   
       14 . The filter according to  claim 1 , wherein
 an input-output impedance of the filter is about 50Ω.   
   
   
       15 . A communication module including a filter, wherein
 the filter includes:   a substrate;   a signal line formed on the substrate and including an input terminal and an output terminal at either end of the signal line; and   a pair of resonant lines connected between the signal line and a ground portion, wherein   the resonant lines are connected to the signal line at a same point.   
   
   
       16 . A communication apparatus including a filter, wherein
 the filter includes:   a substrate;   a signal line formed on the substrate and including an input terminal and an output terminal at either end of the signal line; and   a pair of resonant lines connected between the signal line and a ground portion, wherein   the resonant lines are connected to the signal line at a same point.