Bandpass filter for UHF band

• US 4,423,396 A
• Filed: 09/29/1981
• Issued: 12/27/1983
• Est. Priority Date: 09/30/1980
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Makimoto, Mitsuo, Yamashita, Sadahiko
• Primary Examiner(s): Nussbaum, Marvin L.
• Application Number:
  US06/306,855
• Time in Patent Office: 819 Days
• Field of Search: 333/167, 333/168, 333/202-208, 333/219-235, 333/246
• US Class Current: 333/204
• CPC Class Codes: H01P 1/20363 Linear resonators
• CPC Class Codes: H03H 7/0123 comprising distributed impedance elements together with lumped impedance elements
• CPC Class Codes: H03H 7/1708 Comprising bridging elements, i.e. elements in a series path without own reference to ground and spanning branching nodes of another series path H03H7/07 takes precedence
• CPC Class Codes: H03H 7/1775 Parallel LC in shunt or branch path H03H7/1791 takes precedence

Abstract

In a bandpass filter having five or more resonator stages, a sub transmission line is coupled to the main transmission line at the first and fourth resonators. The first to fourth resonators provide peak attenuation points at both sides of the center frequency in the attenuation curve, while the remaining resonators following the fourth resonator further sharpen the attenuation characteristics of the bandpass filter. The main and sub transmission lines may be formed by striplines on a printed circuit board, while the sub transmission line can be capacity coupled to the main transmission line. Coupling capacitances are freely set by setting the length of each gap between adjacent striplines to a desired value. Thus, the peak attenuation points can be accurately controlled to provide a bandpass filter having superior characteristics.

Claims

1. A bandpass filter for UHF band, comprising:

(a) a dielectric substrate;

(b) a main transmission line having input and output electrodes, said main transmission line being formed of a plurality of striplines formed in line on said dielectric substrate;

(c) five or more resonators respectively coupled to said striplines between said input and output electrodes;

(d) first and second coupling striplines formed on said dielectric substrate, said first coupling stripline being located adjacent to the first stripline which is immdediately next to said input electrode, said second coupling stripline being located adjacent to the fourth stripline; and

(e) a sub transmission line stripline formed on said dielectric substrate and interposed between said first and second coupling striplines.

2. A UHF bandpass filter comprising:

(a) a main transmission line formed on a dielectric substrate and having input and output ports and capacitive coupling circuits connected between said ports, each of said circuits including a capacitor formed on the dielectric substrate;

(b) five or more stages of resonators respectively coupled to said main transmission line; and

(c) a sub transmission line interposed between the first and fourth resonators.

3. A bandpass filter for UHF band as claimed in claim 2, wherein said sub transmission line comprises a stripline formed on a dielectric substrate, the length of said stripline being equal to three fourth of the wavelength.

4. A UHF bandpass filter comprising:

a dielectric substrate;

a main transmission line having an input port and an output port;

five or more stages of resonators respectively coupled to said main transmission line; and

a sub transmission line interposed between the first and fourth resonators;

means for capacitively coupling said sub transmission line to said main transmission line, said capacitive coupling means including at least one coupling capacitor, each of the coupling capacitors being formed on the dielectric substrate.

5. A bandpass filter for UHF band as claimed in claim 4 wherein said sub transmission line comprises a stripline formed on the dielectric substrate, the length of said stripline being equal to three fourths of a wavelength of a signal passed by the bandpass filter.

6. The filter of claim 5 wherein the main transmission line comprises a strip line formed on the dielectric substrate.

7. The filter of claim 6 wherein the main transmisson line includes capacitive coupling circuits connected between said ports, each of said circuits including a capacitor formed on the dielectric substrate.

8. The filter of claim 4 wherein the main transmission line comprises a strip line formed on the dielectric substrate.

9. The filter of claim 8 wherein the main transmission line includes capacitive coupling circuits connected between said ports, each of said circuits including a capacitor formed on the dielectric substrate.