Wave transmission lines and networks – Coupling networks – Delay lines including elastic bulk wave propagation means
Reexamination Certificate
2001-05-31
2003-10-07
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Delay lines including elastic bulk wave propagation means
C333S202000, C333S219200
Reexamination Certificate
active
06630873
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to a magnetostatic wave filter. More particularly, the invention relates to a magnetostatic wave filter capable of controlling the property of flatness and the width of the band-pass that are characteristics within a transfer band of a filter, by adjusting the pattern shape of a transformation section in input and output section.
BACKGROUND OF THE INVENTION
In a conventional magnetostatic wave filter, the distance between a line and its neighboring line is constant in the longitudinal direction of the line even when a line having the constant size or multiple lines are used with various shapes of input/output electrodes. Also, a A structure having a magnetic thin film at one side is used. Therefore, there are problems that the band-pass width of the filter is narrow and a band-pass ripple occurs severely.
In addition, in order to expand the band-pass width and reduce the ripple, the thickness of a ferromagnetic thin film must be increased, thus resulting high manufacturing cost.
Also, as there is not used a metal shield film for electrically isolating an input and an output in a flat structure, the coupling of the input and the output occurs outside the pass frequency band. Thus, there is a problem that the attenuation rate of the magnetostatic wave filter is poor.
Prior references relating to conventional magnetostatic wave filters for overcoming these problems are now explained.
First, there is U.S. Pat. No. 5,663,698, issued to ‘Japan Murata’, invented by ‘Takekazu Okada, Satoru Kanaya and Shinichiro Ichiguchi’ and entitled ‘Magnetostatic Wave Device having Slanted End Portions’.
In order to implement a miniature and low-cost magnetostatic wave filter, the prior patent implements the filter by cutting the ends of a YIG (yttrium, iron, garnet) thin film (the YIG thin film grown on a GGG substrate, see “120” shown in
FIG. 1
) formed on transducers at a constant angle or by putting absorbers on the surface of which is rugged and having a large loss at an end portion of the YIG thin film in order to terminate magnetostatic waves. Therefore, it can reduce the usage of magnetic thin films and accomplish miniaturization, thus resulting a low cost magnetostatic wave filter.
Examining particularly the structure of this prior patent, transducers are formed on a dielectric substrate, having the electrode patterns having the same widths and are constituted by a single line. The end portion of the YIG thin film is slanted (see “
128
a
” and “
128
b
” shown in
FIG. 1
) or has absorbers on it. Also, the YIG thin film is located at one side of the GGG (gadolinium, gallium, garnet) substrate, and the end portion of the YIG thin film is slanted or has absorbers on it, thus reducing the amount reflected from the end portion of the YIG thin film.
There is another U.S. Pat. No. 4,983,937, issued to ‘Japan Hitach’, invented by ‘Yasnaki Kinoshita, Sadami Kubota and Shigern Takeda’ and entitled ‘Magnetostatic Wave Band-Pass Filer’.
The prior patent relates to the field of a magnetostatic wave filter in which a signal processing filter for processing a high frequency signal such as a high frequency device is implemented using magnetostatic waves. The magnetostatic wave filter has a magnetostatic filter formed by using a plurality of resonators and a photolithography technology, so that a good frequency response characteristic and a good reappearance can be provided and it is suited for mass production.
In order to accomplish this object, after a YIG film is grown on a GGG substrate, an input/output electrode pattern is formed on the surface of the YIG film or the rear surface of the GGG substrate, using an etching technology. If a high frequency signal is incident to the magnetized YIG film, magnetostatic waves are excited. The excited magnetostatic waves are reflected from the end portion of the YIG film and the reflected waves produce standing waves between both ends of the YIG film, so that the YIG film is resonated by the standing waves. Therefore, if the output electrode is formed in the film parallel to the end portion of the YIG film, high frequency components excited by means of the magnetostatic waves are outputted. At this time, the input/output electrodes may be formed not of a single line but a plurality of electrodes.
In other words, the prior patent has transducers formed on the YIG film or the GGG substrate, transducer electrode patterns having the same widths, the transducer longitudinal direction parallel to the YIG longitudinal direction, and the input/output electrodes made of a plurality of lines, not a single line.
If a filter is manufactured using the technology, proposed in the prior patent, it could obtain a good frequency response characteristic and a good reappearance and is also suited for a mass production.
Further, there is U.S. Pat. No. 4,199,737, issued to ‘US Westing house’, invented by ‘Ralph W. Patterson, Terence W. O'keeffe and John D. Adam’ and entitled ‘Magnetostatic Wave Device’.
In order to provide a magnetostatic wave filter capable of processing a signal in a high frequency region (in the region of about 20 GHz) and having a low loss and that can be manufactured by a photolithography method, structure is proposed for designing transducers having various shapes and for exciting magnetostatic waves. Thus, it can reduce reflection of a magnetostatic wave at a desired frequency and can design a filter having a relatively narrow bandwidth.
In other words, the transducer has transducer electrode patterns with the same width. The transducer is weighed so that the length of the transducer can be varied and two transducers are paired to reduce reflection in ½ wavelength. Also, the YIG thin film is located at one side of the GGG substrate.
Also, there is an article published in ‘Ultrasonics Symposium’ (written by ‘Takuro Koike and Hiroaki Nakazawa’, 1994) entitled ‘A new method for controlling Resonant frequencies of Straightedge MSW resonators’.
In the article, when the bandwidth required in a microwave frequency is narrow, it proposes a method of controlling the frequency in a line-shape magnetostatic wave resonator. In order to accomplish this object, the transducer has transducer electrode patterns with the same widths. It further includes a PIN diode serially connected to an end of the transducer and has a line-shape transducer. Also, the YIG thin film is located at one side of the GGG substrate.
In addition, there is an article published in ‘IEICE Trans ELECTRON.’(Vol. E77-C, No.2) (‘Yatsuya Omori, K. Yashiro and Sumio Ohkawa’) entitled ‘A study on magnetostatic surface wave excitation by Microstrip’.
The above article proposes a method by which the current density and the radiating resistance in the transducer are calculated, thus implementing a magnetostatic wave filter capable of processing signals in a microwave frequency.
In order to accomplish these objects, it calculates the radiating resistance of the transducer by predicting the current distribution by interpreting the distribution of the electric field in the transducer in a single line using a TE mode and by then predicting the flow of current. When a filter is constituted using a magnetostatic wave, the results are used to design the transducer so that the impedance match can be made well.
In the above mentioned conventional magnetostatic wave filters, an input/output is formed on a magnetically active ferromagnetic thin film that is formed on a magnetically inactive dielectric substrate, or after forming an input/output electrode on a magnetically inactive dielectric substrate, a ferromagnetic thin film is located on it. Therefore, an external magnetic field is applied to the central frequency to implement the function of the filter through transformation and propagation of energy. Also, the shape of the conventional input/output electrode has the shape connected by a line in which the size of the exciting line is uniform. In addition, even when multiple lines are used, the distance between the line and its neighboring line is constant i
Kim Dong-Young
Kim Meyng-Soo
Lee Sang-Seok
Electronics and Telecommunications Research Institute
Pascal Robert
Seed IP Law Group PLLC
Takaoka Dean
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