Asymmetrical trap comprising coaxial resonators, reactance elements, and transmission line elements

#The present invention generally relates to an electrical trap and more particularly, to a so-called "asymmetrical trap" to be used, for example, in an ultra-high frequency (UHF) section of an electronic circuit to reject undesired frequencies.

#Conventionally, there has been available an electrical trap adapted to attenuate a signal in a region of a specific frequency as shown by a solid line curve T in FIG. 1(aa) by producing a series resonance at such a specific frequency through the connection of a resonant line between a hot line (e.g. a line through which a signal is transmitted) and a cold line (e.g. a line which is grounded) of a signal transmission line. An electrical trap in which modes of attenuation at opposite side regions of a trap frequency f.sub.t are similar to each other as shown by the solid line curve T in FIG. 1(a), is generally called a symmetrical trap. Meanwhile, as shown by a solid line curve T' in FIG. 2(a), an electrical trap in which modes of attenuation at opposite side regions of the trap frequency f.sub.t are different from each other due to presence of an anti-resonant frequency f.sub.p at a frequency region higher or lower than the trap frequency f.sub.t, is sometimes referred to as an asymmetrical trap.

#The anti-resonant frequency f.sub.p as described above may be utilized in the case where there is a frequency region which is not desired to be subjected to attenuation in the vicinity of the trap frequency f.sub.t.

#These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which:

#FIGS. 1(a) and 1(b) are frequency-attenuation diagrams explanatory of characteristic curves for a conventional trap (already referred to);

#FIGS. 2(a) and 2(b) are also frequency-attenuation diagrams explanatory of characteristics curves for an asymmetrical trap to which the present invention may be applied (already referred to);

#Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings.

#In the first place, referring to FIGS. 3(a) and 3(b), one example of a conventional electrical trap employing a dielectrical material coaxial resonator will be explained hereinbelow.

#The prior art trap shown in FIGS. 3(a) and 3(b) generally includes a dielectric material coaxial resonator 1 having a dielectric member 1d provided between an inner conductor 1a and an outer conductor 1b, a reactance element or capacitor 2 having a pair of electrodes provided on opposite faces of a dielectric member, and a signal transmission line 3 formed, for example, by a coaxial cable having a central conductor 4 and an outer conductor 5, with an insulator therebetween. According to a preferred embodiment, a semi-rigid cable is used for the coaxial cable 3. One electrode of the capacitor 2 is fixedly connected to the inner conductor 1a of the coaxial resonator 1, while the other electrode thereof is connected to the central conductor 4 of the signal transmission line 3, with the outer conductor 1b of the coaxial resonator 1 being connected to the outer covering conductor 5 of said signal transmission line 3. The signal transmission line 3 described as formed by the semi-rigid cable in the above example may be replaced by a strip line as will be understood from the embodiments according to the present invention given hereinbelow, in which like parts in FIGS. 3(a) and 3(b) are designated by like reference numeral for brevity of description.