Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
1998-09-04
2001-05-22
Gensler, Paul (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S167000
Reexamination Certificate
active
06236285
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a lumped element circulator used as a high frequency circuit element in for example a portable or mobile communication equipment. Particularly, the present invention relates to a lumped element circulator operable in a plurality of frequency bands.
DESCRIPTION OF THE RELATED ART
A circulator is an element for giving non-reciprocal characteristics to a high frequency circuit so as to suppress reflecting waves in the circuit. Thus, standing waves can be prevented from generation resulting that stable operations of the high frequency circuit can be expected. Therefore, in recent portable telephones, such non-reciprocal elements are usually provided for suppress standing waves from generation.
Recently, demand for a portable telephone capable of operating in a plurality of different frequency bands (multi-bands telephone) has been increased in order to enable effective use of the portable telephone. However, the conventional circulator can be operated in only one frequency band. Thus, in order to operate in a plurality of frequency bands, it is necessary (A) to broaden the frequency bandwidth of the single band circulator by using an impedance matching circuit, or (B) to combine a plurality of single band circulators with a band-pass filter for individually operating the circulators.
According to the above-mentioned solution (A) where the frequency bandwidth of the single band circulator is broadened, a sufficiently wide bandwidth cannot be expected but only about 30% of the center frequency can be broadened. Thus, as for a recent dual band portable telephone operable at dual frequencies which differ twice with each other, the solution (A) cannot be adopted.
According to the solution (B) where a plurality of single band circulators operating at different frequency bands are connected in parallel and are selected by filters and switching means, the dimension of the combined circuit becomes large. In addition, the impedance characteristics out of the bandwidths of the circulators interfere with each other causing the operating characteristics to become unstable.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a lumped element circulator which alone can suppress standing waves from generation in a plurality of frequency bands.
According to the present invention, a lumped element circulator having a plurality of operation bands, has a circulator element with a plurality of signal ports and a grounded terminal, and resonance circuits connected between the signal ports and the grounded terminal, respectively, each of the resonance circuits having a plurality of resonance points. The number of the operation bands is equal to the number of the resonance points of each of the resonance circuits.
The invention focuses attention on that, in a lumped element circulator, difference between eigenvalues of the circulator element excited by positive and negative rotational eigenvectors is 120 degrees (in case of three port circulator) without reference to frequency. Thus, according to the invention, a network exhibiting a frequency performance for satisfying circulator conditions in a plurality of necessary frequency bands is connected to each port so that the circulator can operate in the plurality of frequency bands. This is realized by inserting a resonance circuit having a plurality of resonance points between each of the signal ports and the grounded terminal of the circulator element of the lumped element circulator.
As a result, according to the invention, a lumped element circulator alone can suppress any standing wave from generation in a plurality of frequency bands. Thus, in a high frequency circuit in a telephone which operates in a plurality of frequency bands such as a dual band telephone, the circulator according to the present invention can be alone used to suppress standing wave from generation in a plurality of frequency bands.
It is preferred that each of the resonance circuits is a series-parallel resonance circuit having at least one pair of a series resonance point and a parallel resonance point.
It is also preferred that the number of the operation bands is equal to the number of the pair of the series resonance point and the parallel resonance point plus one.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
REFERENCES:
patent: 3818381 (1974-06-01), Konishi et al.
patent: 2671912 (1992-07-01), None
patent: 56-24815 (1981-03-01), None
patent: 10-107509 (1998-04-01), None
patent: 1334224 (1987-08-01), None
“Lumped Element Y Circulator”, Konishi,IEEE Transactions on Microwave Theory and Techniques,vol. MTT-13, No. 6, Nov. 1965, pp. 852-864.
“Proposed Dual Band Lumped Element Y Circulator”, Konishi,Microwave and Optical Technology Letters,vol. 17, No. 1, 1998, pp. 13-16.
Konishi Yoshihiro
Misu Yoshifumi
Miura Taro
Usami Akira
Arent Fox Kintner & Plotkin & Kahn, PLLC
Gensler Paul
K Laboratory Co.
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