US 4,186,359 A · Notch filter network

Abstract

An electrical filter network with improved characteristics is disclosed for selectively attenuating and passing two different, closely spaced frequencies. The notch filter network includes a low Q reactive circuit tuned to be parallel resonant at the frequency to be attenuated. A cavity resonator with a high Q is inductively coupled to the reactive circuit and is tuned to be resonant at the frequency to be passed. Utilizing these concepts, a multicoupler may be constructed to consist of two or more such filter networks in combination with a transmission line. In such a multicoupler, the network adjacent to the antenna terminal is separated therefrom by a multiple of a half wavelength. Additional filter networks are separated from one another by an odd number of a quarter wavelength. With this arrangement, each network passes a band around the frequency to which the high Q cavity is tuned and rejects a band of frequencies around the reactive circuit resonant frequency.

Claims31

Dependent claims

An electrical filter network for selectively attenuating and passing first and second predetermined closely spaced frequencies respectively when inserted in series in a transmission line, said filter network comprising in combination:

(a) a reactive circuit adapted to be series connected in said transmission line and tuned to be parallel resonant at said first predetermined frequency;
and p1 (b) a cavity resonator whose internal field is inductively coupled with said reactive circuit, said cavity resonator being resonant at said second predetermined frequency.

A multicoupler comprising:

(a) a first piece of electrical apparatus for transmitting or receiving a signal having a first carrier frequency;
(b) a second piece of electrical apparatus for transmitting or receiving a signal having a second carrier frequency closely spaced from said first carrier frequency;
(c) an antenna shared in common by said first and second pieces of electrical apparatus;
(d) first and second transmission lines coupling said first and second pieces of apparatus respectively to said antenna at a common terminal;
and
(e) first and second notch filter networks each connected in series in said first and second transmission lines respectively and each being spaced from said common terminal by a distance which is approximately equal to a multiple of a half wavelength of a frequency at the middle of the band of frequencies passed by the opposite line, each of said notch filter networks including:
(1) a reactive circuit tuned to be parallel resonant at a rejection notch frequency substantially equal to one of said first and second frequencies, said reactive circuit including a capacitance and an inductor in parallel;
and
(2) a cavity resonator inductively coupled to said inductor and tuned to resonate at the other of said first and second frequencies.

6 more elements

Dependencies are inferred from the claim text.

Notch filter network

Life of this patent

Notch filter network

Life of this patent

Abstract

Claims31