Signal-to-noise enhancer

Abstract: A signal-to-noise enhancer 10 includes a first 90 degree hybrid set 20. A first output end of the first 90 degree hybrid set 20 is connected to an input end of a limiter used a magnetostatic wave element 62a utilized the magnetostatic surface wave mode. Also, a second output end of the first 90 degree hybrid set 20 is connected to an input end of a filter used a magnetostatic wave element 62b similar to the magnetostatic wave element 62a in structure, via a resistor 32 as a first attenuator. Furthermore, an output end of the limiter is connected to a first input end of a second 90 degree hybrid set 40 via a resistor 52 as a second attenuator. Also, an output end of the filter is connected to a second input end of the second 90 degree hybrid set 40.

Description: The present invention relates to a signal-to-noise enhancer, more particularly, to a signal-to-noise enhancer which has a limiter for limiting an amplitude of a main signal in an input signal, which improves a ratio of the main signal to noise (S/N) in the input signal, and which is used for receiving, for example, a satellite broadcasting signal. An example of the conventional signal-to-noise enhancers is disclosed in Japanese Patent Provisional Publication No. 123502/1992. Fig. 11 is a circuit diagram showing an example of the conventional signal-to-noise enhancers. The signal-to-noise enhancer 1 shown in Fig. 11 includes an input terminal 2. The input terminal 2 is connected to an input end of a directional coupler 3 as a divider. The directional coupler 3 is for dividing an input signal applied to the input terminal 2 into a high-level signal which is almost the same in level as the input signal and a low-level signal which is less in level than the input signal by, for example, 30 dB. Two output ends of the directional coupler 3 are connected to input ends of two magnetostatic wave filters 4 and 5 utilizing the magnetostatic surface wave mode, respectively. These magnetostatic wave filters 4 and 5 have the same frequency-selective nonlinear limiting characteristics. The frequency-selective nonlinear limiting characteristic means a characteristic wherein even if a signal of a frequency f1 is limited in excess of a saturation level, when a signal of a frequency f2 different from the frequency f1 has the saturation level or less, the signal of the frequency f2 is not limited. That is, the frequency-selective nonlinear limiting characteristic means a characteristic wherein when a signal is over a saturation level, a saturation operation is generated, each limiting by the saturation operation is individually generated in each frequency. One magnetostatic wave filter 4 is used as a limiter for limiting an amplitude of a high-level main signal in the high-level signal obtained from the directional coupler 3. Also, the other magnetostatic wave filter 5 is used for passing the low-level signal obtained from the directional coupler 3. An output end of the magnetostatic wave filter 4 is connected to an input end of an attenuator 6. The attenuator 6 is for attenuating a level of a signal obtained from the magnetostatic wave filter 4. Also, an output end of the other magnetostatic wave filter 5 is connected to an input end of a delay line 7. The delay line 7 is for delaying a phase of a signal obtained from the magnetostatic wave filter 5. Furthermore, an output end of the the attenuator 6 and an output end of the delay line 7 are connected to two input ends of a directional coupler 8 as an combiner, respectively. The directional coupler 8 is for attenuating a level of a signal obtained from the attenuator 6, and is for combining the signal having the attenuated level and a signal obtained from the delay line 7. Also, an output end of the directional coupler 8 is connected to an output terminal 9. Thus, in the signal-to-noise enhancer 1, between the input terminal 2 and the output terminal 9, a first path is composed of the directional coupler 3, the magnetostatic wave filter 4, the attenuator 6 and the directional coupler 8, a second signal path is composed of the directional coupler 3, the magnetostatic wave filter 5, the delay line 7 and the directional coupler 8. In the signal-to-noise enhancer 1, when an input signal including a high-level main signal and a low-level noise different from the main signal in frequency is applied to the input terminal 2, the input signal is divided by the directional coupler 3 into a high-level signal which is almost the same in level as the input signal and a low-level signal which is less in level than the input signal by, for example, 30 dB. In this case, the high-level signal includes a high-level main signal and a low-level noise different from each other in frequency, the low-level signal includes a low-level main signal and a lower-level noise different from each other in frequency. In the magnetostatic wave filter 4, though the main signal in the high-level signal is limited because the main signal has a high-level, the noise in the high-level signal is not limited because the noise is different from the main signal in frequency and has a low-level. On the other hand, in the other magnetostatic wave filter 5, the main signal and the noise in the low-level signal are not limited as low-levels. Meanwhile, by insertion loss in the magnetostatic wave filters 4 and 5, the high-level signal and the low-level signal are slightly attenuated in level, respectively. Also, a level of a signal obtained from the magnetostatic wave filter 4 is attenuated by the attenuator 6, a phase of a signal obtained from the other the magnetostatic wave filter 5 is delayed by the delay line 7. Then, by the directional coupler 8, a level of a signal obtained from the attenuator 6 is attenuated, the signal having the attenuated level and a signal obtained from the delay line 7 are combined. In this case, the level of the signal obtained from the magnetostatic wave filter 4 is attenuated by the attenuator 6 and the phase of the signal obtained from the magnetostatic wave filter 5 is delayed by the delay line 7 so that noises in two signals combined by the directional coupler 8 become the same levels and the opposite phases. Thus, the noise passed the first signal path including the magnetostatic wave filter 4 and the noise passed the second signal path including the magnetostatic wave filter 5 are offset in the directional coupler 8. Also, though the main signal passed the first signal path is limited by the magnetostatic wave filter 4, the main signal passed the second signal path in not limited by the magnetostatic wave filter 5. Thus, from the output end of the directional coupler 8 and the output terminal 9, a main signal having a level corresponding to the limited level is obtained. Accordingly, in the signal-to-noise enhancer 1, the signal-to-noise ratio in the input signal is improved. Also, in the signal-to-noise enhancer 1, the minimum level of the input signal wherein the signal-to-noise ratio can be improved is -12 dBm, the level of the input signal wherein it begins to improve the signal-to-noise ratio is -19 dBm, the difference between these levels is small as 7 dB, therefore a great effect on improving of the signal-to-noise ratio of noisy signals can be obtained on receiving, for example, a satellite broadcasting signal. However, in the signal-to-noise enhancer 1, since the phase difference between the first signal path and the second signal path is set to 180 degree by using the delay line 7, an operating frequency bandwidth having a desired enhancement, for example, 20 dB or more is narrow as about 100 MHz (Toshihiro Nomoto, Yoshihiro Matsushita, "A Signal-to-Noise Enhancer Using Two MSSW Filters and its Application to Noise Reduction in DBS Reception", IEEE Trans. MTT-41, 8, PP. 1316-1321 (1993)). Thus, the signal-to-noise enhancer 1 can not cover the bandwidth of about 300 MHz which is the bandwidth of all the satellite broadcasting signals received in Japan. Accordingly, the signal-to-noise enhancer 1 can not collectively improve the signal-to-noise ratio in the signals of all the channels for receiving the satellite broadcasting in Japan. Furthermore, in the signal-to-noise enhancer 1, since the operating frequency bandwidth is narrow as above-mentioned, when the temperature changes, the operating frequency bandwidth changes and easily becomes out of the frequency desired for using in fact, besides it is difficult to adjust the operating frequency bandwidth so that the used frequency becomes in the operating frequency bandwidth, it requires many hours, for example, 2-3 hours to adjust the operating frequency bandwidth. EP 04754008A1 concerns a magnetostatic wave s/n enhancer including a divider for dividing an input signal into a first and second path signal, first and second MSW transducers for transducing the first and second path signals into a first and second path transduced signals, and a combiner for combining the first and second path transduced signals in opposite phase to each other. The output combiner comprises in its second path a phase shifter providing for a phase shift of 180 degrees of the second signal on the second path. Therefore, it is primary object of the present invention to provide a signal-to-noise enhancer having a wide operating frequency bandwidth. This object is achieved by a signal-to-noise enhancer according to claim 1. In the signal-to-noise enhancer according to the present invention, as the first hybrid set and the second hybrid set, for example, a first 90 degree hybrid set and a second 90 degree hybrid set. Meanwhile, for the reason described in the latter part, it is preferable to use 90 degree hybrid sets as the first hybrid set and the second hybrid set. Also, in the signal-to-noise enhancer according to the present invention, a filter such as a low-pass filter, a high-pass filter, a band-pass filter and a band-stop filter, consisting of a magnetostatic wave element, can be used as the limiter. Meanwhile, it is preferable to use a magnetostatic wave element in the limiter for the reason described in the latter part. In this case, as the magnetostatic wave element, it is more preferable to use a magnetostatic wave element utilizing the magnetostatic surface wave mode for the reason described in the latter part. Furthermore, for the reason described in the latter part, it is preferable that the signal-to-noise enhancer according to the present invention comprises a level adjusting means, provided between the first hybrid set and the second hybrid set, for equalizing levels of noises in two signals combined by the second hybrid set each other. Meanwhile, the level adjusting means comprises, for example, a first attenuator, provided between the first hybrid set and the second hybrid set, for attenuating a level of the second signal obtained from the first hybrid set, a filter, provided between the first attenuator and the second hybrid set, having the same input-to-output characteristic as the limiter, for passing a signal obtained from the first attenuator, and a second attenuator, provided between the limiter and the second hybrid set, for attenuating a level of a signal obtained from the limiter. That is, as the signal-to-noise enhancer according to the present invention, it is preferable to use, for example, a signal-to-noise enhancer comprising a first 90 degree hybrid set for dividing an input signal including a main signal and noise into a first signal and a second signal, the first signal and the second signal having a phase difference of 90 degree in a wide bandwidth, a limiter, provided to the post-stage of the first 90 degree hybrid set, using a magnetostatic wave element utilizing the magnetostatic surface wave mode, for limiting an amplitude of a main signal in the first signal, a first attenuator, provided to the post-stage of the first 90 degree hybrid set, for attenuating a level of the second signal, a filter, provided to the post-stage of the first attenuator, using a magnetostatic wave element utilized the magnetostatic surface wave mode, having the same input-to-output characteristic as the limiter, for passing a signal obtained from the first attenuator, a second attenuator, provided to the post-stage of the limiter, for attenuating a level of a signal obtained from the limiter, and a second 90 degree hybrid set, provided to the post-stage of the second attenuator and the filter, for combining a signal obtained from the second attenuator and a signal obtained from the filter with a phase difference of 90 degree in a wide bandwidth, wherein levels of noises in two signals combined by the second 90 degree hybrid set are equalized by the first attenuator, the filter and the second attenuator, and a phase difference between the two signals combined by the second 90 degree hybrid set is set by the first 90 degree hybrid set and the second 90 degree hybrid set to (2n+1)·180 degree where n is 0 or an integer. The input signal including the main signal and the noise is divided by the first hybrid set into the first signal and the second signal having the first phase difference in the wide bandwidth. In this case, each the first signal and the second signal includes the main signal and the noise. Also, the main signal in the first signal is limited by the limiter. Furthermore, the signal obtained from the limiter and the second signal obtained from the first hybrid set are combined by the second hybrid set with the second phase difference in the wide bandwidth. In this case, the sum of the first phase difference and the second phase difference is (2n+1)·180 degree where n is 0 or an integer. Thus, the two signals combined by the second hybrid set become opposite phase to each other in the wide bandwidth. Accordingly, the noises in the two signals combined by the second hybrid set are offset in the wide bandwidth. Furthermore, from the output end of the the second hybrid set, the main signal corresponding to the level limited by the limiter is obtained. According to the present invention, since the two signals combined by the second hybrid set become the opposite phase to each other in the wide bandwidth, it can obtain a signal-to-noise enhancer wherein an operating frequency bandwidth having a desired enhancement, for example, 20 dB or more is a wide bandwidth, for example, about 350 MHz. Thus, in the signal-to-noise enhancer according to the present invention, when it used for receiving a satellite broadcasting signal, it can completely cover the bandwidth of about 300 MHz which is the bandwidth of all the satellite broadcasting signals received in Japan. Also, in the signal-to-noise enhancer according to the present invention, since the operating frequency bandwidth is wide, when the temperature changes, even if the operating frequency bandwidth changes, the operating frequency bandwidth hardly becomes out of the used frequency desired for using in fact, besides it is easy to adjust the operating frequency bandwidth so that the used frequency becomes in the operating frequency bandwidth, it requires only a short time to adjust the operating frequency bandwidth. In the present invention, when the 90 degree hybrid sets are used as the first hybrid set and the second hybrid set, since the same hybrid sets can be manufactured for the first hybrid set and the second hybrid set, the efficiency for manufacturing the first hybrid set and the second hybrid set is increased. Also, in the present invention, when the magnetostatic wave element is used in the limiter, since a signal in a more wide bandwidth is limited by the limiter, a signal in a more wide bandwidth can be applied. Meanwhile, in the present invention, when the magnetostatic wave element utilizing the magnetostatic surface wave mode is used in the limiter, since the minimum level of the main signal is limited by the limiter, that is, the saturation level of the limiter becomes low, even if the level of the main signal is low, the signal-to-noise ratio in the input signal can be improved. Furthermore, in the present invention, when comprising the level adjusting means, since the levels of the noises in the two signals combined by the second hybrid set are equalized by the level adjusting means, these noises are further offset. Thus, the signal-to-noise ratio can be further improved. The above and other objectives, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the embodiment with reference to the accompanying drawings. Fig. 1 is a plan view showing an embodiment of the present invention. Fig. 2 is a front view of the embodiment shown in Fig. 1. Fig. 3 is a plan view showing an essential part of a first 90 degree hybrid set (a second 90 degree hybrid set) used in the embodiment shown in Fig. 1. Fig. 4 is a circuit diagram showing an essential part of the first 90 degree hybrid set (a second 90 degree hybrid set) used in the embodiment shown in Fig. 1. Fig. 5 is a circuit diagram of the embodiment shown in Fig. 1. Fig. 6 is a graph showing transmission characteristics of the embodiment shown in Fig. 1 where a level of an input signal is decreased at an interval of 10 dB from 10 dBm as a reference. Fig. 7 is a graph showing an input-to-output characteristic at 1.9 GHz in the embodiment shown in Fig. 1. Fig. 8 is a graph showing one example of an input signal applied to the embodiment shown in Fig. 1. Fig. 9 is a graph showing an output signal obtained from the embodiment shown in Fig. 1 where the input signal shown in Fig. 8 is applied to the embodiment. Fig. 10 is a graph showing relations between carrier-to-noise ratio and signal-to-noise ratio where the embodiment shown in Fig. 1 is used for receiving a satellite broadcasting signal and is not used. Fig. 11 is a circuit diagram showing an example of the conventional signal-to-noise enhancers. Fig. 1 is a plan view showing an embodiment of the present invention, Fig. 2 is a front view thereof. The signal-to-noise enhancer 10 includes, for example, a rectangular substrate 12 consisting of a dielectric material such as synthetic resin and ceramic. Four through-holes 14a, 14b, 14c and 14d are formed to the substrate 12. In this case, the two through-holes 14a and 14c are formed a little off to one side from the central line perpendicular to the long side of the substrate 12, the other two through-holes 14b and 14d are formed a little off to the other side from the central line perpendicular to the long side of the substrate 12. Also, the through-hole 14a is formed near one long side of the substrate 12, the through-hole 14b is formed a little off to one side from the central line perpendicular to the short side of the substrate 12, the through-hole 14c is formed a little off to the other side from the central line perpendicular to the short side of the substrate 12, the through-hole 14d is formed near the other long side of the substrate 12. A first 90 degree hybrid set 20 as a first hybrid set is formed from one short side to the center on one main surface of the substrate 12. The first 90 degree hybrid set 20 includes, for example, two cranked line electrodes 22 and 24. The line electrode 22 consists of a wide end portion 22a extending along the long side from the short side of the substrate 12, an intermediate portion 22b extending along the short side of the substrate 12, and another wide end portion 22c extending along the other long side of the substrate 12. As shown in Fig. 3 and Fig. 4, the intermediate portion 22b of the line electrode 22 includes two thin line portions 22b1 and 22b2 disposed in parallel each other at an interval. The line portion 22b1 is formed so as to extend from the end portion 22a, the other line portion 22b2 is formed so as to extend from the other end portion 22c. Also, both ends of the line portion 22b1 are electrically connected to both ends of the other line portion 22b2, for example, with two U-shaped lead wires 23a and 23b such as gold wires and aluminum wires, for example, by wire bonding. As shown in Fig. 1, the other line electrode 24 consists of a wide end portion 24a extending along the other long side from the short side of the substrate 12, an intermediate portion 24b extending along the short side of the substrate 12, and another wide end portion 24c extending near the through-hole 14a along the long side of the substrate 12. As shown in Fig. 3 and Fig. 4, the intermediate portion 24b of the line electrode 24 includes three thin line portions 24b1, 24b2 and 24b3 formed in parallel one another at an interval. The line portion 24b1 is formed so as to extend from the end portion 24a to the other end portion 24c between the two line portions 22b1 and 22b2 of the line electrode 22. Also, the other two line portions 24b2 and 24b3 are formed out sides of the line portions 22b1 and 22b2 in half length of the line portion 24b1 so as to extend from the end portion 24a and the other end portion 24c. Also, the ends of the line portions 24b2 and 24b3 are electrically connected to the center of the line portion 24b1, for example, with two U-shaped lead wires 25a and 25b such as gold wires and aluminum wires, for example, by wire bonding. As shown in Fig. 1, one end of a resistor 26 of 50 ohms as a terminator is connected to the end portion 24a of the line electrode 24. The other end of the resistor 26 is grounded. The above first 90 degree hybrid set 20 is for dividing an input signal including a main signal and noise into a first signal and a second signal having a phase difference of 90 degree in a wide bandwidth, for example, 1.4-2.4 GHz. In this case, in the first 90 degree hybrid set 20, the end portion 22a of the line electrode 22 is used as an input end, the other end portion 24c of the line electrode 24 is used as a first output end, the other end portion 22c of the line electrode 22 is used as a second output end. Then, the input signal applied to the input end is divided into the first signal and the second signal having a half level of the input signal at the first output end and the second output end. Meanwhile, the phase of the second signal is later than the phase of the first signal by 90 degree. Furthermore, on the main surface of the substrate 12, an L-shaped drawing electrode 30 is formed from the neighborhood of the end portion 22c of the line electrode 22 of the first 90 degree hybrid set 20 to the neighborhood of the through-hole 14c. Then, both ends of a resistor 32 of 50 ohms as a first attenuator are connected to the end portion 22c and the drawing electrode 30. The resistor 32 is for attenuating a level of a signal obtained from the second output end of the first 90 degree hybrid set 20, for example, by 30 dB. Also, a second 90 degree hybrid set 40 as a second hybrid set is formed from the center to the other short side on the main surface of the substrate 12. The second 90 degree hybrid set 40 has the same structure as the first 90 degree hybrid set 20. That is, the second 90 degree hybrid set 40 includes, for example, two cranked line electrodes 42 and 44. The line electrode 42 consists of a wide end portion 42a extending along the long side of the substrate 12, an intermediate portion 42b extending along the short side of the substrate 12, and another wide end portion 42c extending along the other long side of the substrate 12. As shown in Fig. 3 and Fig. 4, the intermediate portion 42b of the line electrode 42 includes two thin line portions 42b1 and 42b2 disposed in parallel each other at an interval. The line portion 42b1 is formed so as to extend from the end portion 42a, the other line portion 42b2 is formed so as to extend from the other end portion 42c. Also, both ends of the line portion 42b1 are connected to both ends of the other line portion 42b2, for example, with two U-shaped lead wires 43a and 43b such as gold wires and aluminum wires, for example, by wire bonding. As shown in Fig. 1, the other line electrode 44 consists of a wide end portion 44a extending along the other long side of the substrate 12 from the neighborhood of the through-hole 14d, an intermediate portion 44b extending along the short side of the substrate 12, and another wide end portion 44c extending along the long side of the substrate 12. As shown in Fig. 3 and Fig. 4, the intermediate portion 44b of the line electrode 44 includes three thin line portions 44b1, 44b2 and 44b3 formed in parallel one another at an interval. The line portion 44b1 is formed so as to extend from the end portion 44a to the other end portion 44c between the two line portions 42b1 and 42b2 of the line electrode 42. Also, the other two line portions 44b2 and 44b3 are formed out sides of the line portions 42b1 and 42b2 in half length of the line portion 44b1 so as to extend from the end portion 44a and the other end portion 44c. Also, the ends of the line portions 44b2 and 44b3 are electrically connected to the center of the line portion 44b1, for example, with two U-shaped lead wires 45a and 45b such as gold wires and aluminum wires, for example, by wire bonding. As shown in Fig. 1, one end of a resistor 46 of 50 ohms as a terminator is connected to the end portion 42c of the line electrode 42. The other end of the resistor 46 is grounded. The above second 90 degree hybrid set 40 is for combining two signals applied thereto with a phase difference of 90 degree in a wide bandwidth, for example, 1.4-2.4 GHz. In this case, in the second 90 degree hybrid set 40, the end portion 42a of the line electrode 42 is used as a first input end, the end portion 44a of the line electrode 44 is used as a second input end, the other end portion 44c of the line electrode 44 is used as an output end. Then, the two signals applied to the first input end and the second input end of the second 90 degree hybrid set 40 are combined at the output end. Meanwhile, when combining the two signals, the phase of the signal applied to the second input end is later than the phase of the signal applied to the first input end by 90 degree. Furthermore, on the main surface of the substrate 12, an L-shaped drawing electrode 50 is formed from the neighborhood of the end portion 42a of the line electrode 42 of the second 90 degree hybrid set 40 to the neighborhood of the through-hole 14b. Then, both ends of a resistor 52 of 50 ohms as a second attenuator are connected to the end portion 42a and the drawing electrode 50. The resistor 52 is for attenuating a level of a signal applied to the first input end of the second 90 degree hybrid set 40, for example, by 30 dB. On the center of the other main surface of the substrate 12, four transducers 60a, 60b, 60c and 60d consisting of four line electrodes are formed along the long side of the substrate 12 from the neighborhood of the through-holes 14a, 14b, 14c and 14d. In this case, ends of the transducers 60a, 60b, 60c and 60d are electrically connected to the end portion 24c of the line electrode 24, the drawing electrode 50, the drawing electrode 30 and the end portion 44a of the line electrode 44 via the through-holes 14a, 14b, 14c and 14d, respectively. Furthermore, the other ends of the transducers 60a-60d are grounded. Also, on the other main surface of the substrate 12, a magnetostatic wave element 62a is installed on the two transducers 60a and 60b, another magnetostatic wave element 62b is installed on the other two transducers 60c and 60d. The magnetostatic wave elements 62a and 62b include, for example, two rectangular GGG substrates, two YIG thin films as two ferrimagnetic substrates are formed on main surfaces of the GGG substrates, respectively. Then, the magnetostatic wave elements 62a and 62b are installed so as to oppose the surfaces of the YIG thin films to the other main surface of the substrate 12. Meanwhile, on both end parts of the surfaces of the YIG thin films, magnetostatic wave absorbers 64 for absorbing an unnecessary magnetostatic wave reflected in the YIG thin films are formed, respectively. Furthermore, on the other main surface of the substrate 12, permanent magnets 66a and 66b consisting of, for example, ferrite are installed both sides of the magnetostatic wave elements 62a and 62b, respectively. In this case, the permanent magnets 66a and 66b are disposed so as to generate a magnetic field therebetween in the extending direction of the transducers 60a-60d. Thus, a magnetic field is applied to the magnetostatic wave elements 62a and 62b in the extending direction of the transducers 60a-60d. Accordingly, the magnetostatic wave elements 62a and 62b become magnetostatic wave elements utilizing the magnetostatic surface wave mode, respectively. Then, the two transducers 60a and 60b, the magnetostatic wave element 62a and so on are used as a limiter. The limiter has a frequency-selective nonlinear limiting characteristic. The limiter is for limiting an amplitude of the main signal in the first signal obtained from the first output end of the first 90 degree hybrid set 20. In this case, in the limiter, one end of the transducer 60a is used as an input end, one end of the transducer 60b is used as an output end. Also, the other two transducers 60c and 60d, the magnetostatic wave element 62b and so on are used as a filter. Since the filter has the same structure as the above limiter, the filter has the same input-to-output characteristic as the above limiter. The filter is for passing a signal applied thereto. In this case, in the filter, one end of the transducer 60c is used as an input end, one end of the transducer 60d is used as an output end. Meanwhile, on the other main surface of the substrate 12, a C-shaped yoke 68 made of magnetic material is installed so as to fix the permanent magnets 66a and 66b applying a magnetic field to the magnetostatic wave elements 62a and 62b. The yoke 68 is for decreasing a magnetic reluctance between the permanent magnets 66a and 66b, and is for protecting the magnetostatic wave elements 62a and 62b, the permanent magnets 66a and 66b and so on. Thus, the signal-to-noise enhancer 10 has a circuit shown in Fig. 5. That is, in the signal-to-noise enhancer 10, the first output end of the first 90 degree hybrid set 20 is connected to the input end of the limiter using the magnetostatic wave element 62a. Also, the second output end of the first 90 degree hybrid set 20 is connected to the input end of the filter using the magnetostatic wave element 62b via the resistor 32 as the first attenuator. Furthermore, the output end of the limiter is connected to the first input end of the second 90 degree hybrid set 40 via the resistor 52 as the second attenuator. Also, the output end of the filter is connected to the second input end of the second 90 degree hybrid set 40. Thus, in the signal-to-noise enhancer 10, between the input -end and the output end, a first signal path is composed of the first 90 degree hybrid set 20, the limiter including the magnetostatic wave element 62a, the second attenuator consisting of the resistor 52 and the second 90 degree hybrid set 40, a second signal path is composed of the first 90 degree hybrid set 20, the first attenuator consisting of the resistor 32, the filter including the magnetostatic wave element 62b and the second 90 degree hybrid set 40. Next, the operation of the signal-to-noise enhancer 10 is described. In the signal-to-noise enhancer 10, when an input signal including a main signal and a low-level noise different from the main signal in frequency is applied to the input end of the first 90 degree hybrid set 20, that is, the end portion 22a of the line electrode 22, the input signal is divided by the first 90 degree hybrid set 20 into a first signal and a second signal having a phase difference of 90 degree in a wide bandwidth of 1.4-2.4 GHz. In this case, the input signal is divided into the first signal and the second signal having a half level of the half level of the input signal at the first output end and the second output end of the first 90 degree hybrid set 20. Also, the first signal and the second signal respectively include the main signal and the low-level noise. Furthermore, the phase of the second signal is later than the phase of the first signal by 90 degree. The main signal in the first signal is limited by the limiter consisting of the magnetostatic wave element 62a and so on. On the other hand, the noise in the first signal is not limited by the limiter because the noise is different from the main signal in the first signal in frequency and has a low-level. Meanwhile, by insertion loss in the limiter, the first signal is slightly attenuated in level. Also, the second signal is attenuated by 30 dB in level by the first attenuator consisting of the resistor 32. Furthermore, the attenuated second signal is passed the filter consisting the magnetostatic wave element 62b and so on because the level thereof is low. Meanwhile, the attenuated second signal is slightly attenuated in level by insertion loss in the filter. Also, a signal obtained from the limiter is attenuated by 30 dB in level by the second attenuator consisting of the resistor 52. Then, a signal obtained from the second attenuator and a signal obtained from the filter are combined by the second 90 degree hybrid set 40 with a phase difference of 90 degree in a wide bandwidth of 1.4-2.4 GHz. In this case, levels of noises in the two signals combined by the second 90 degree hybrid set 40 in the first signal path and the second signal path are equalized by the first attenuator, the filter and the second attenuator as the level adjusting means. Furthermore, a phase difference between the two signals combined by the second 90 degree hybrid set 40 in the first signal path and the second signal path becomes 180 degree, that is, an opposite phase in a wide bandwidth by the first 90 degree hybrid set 20 and the second 90 degree hybrid set 40. Thus, the noises in the two signals combined by the second 90 degree hybrid set 40 in the first signal path and the second signal path are offset in a wide bandwidth. Furthermore, from the output end of the second 90 degree hybrid set 40, the main signal having a level corresponding to the level limited by the limiter is obtained. In the signal-to-noise enhancer 10, since the two signals combined by the second 90 degree hybrid set 40 in the first signal path and the second signal path become the opposite phase to each other in a wide bandwidth, it can obtain an operating frequency bandwidth having a desired enhancement, for example, 20 dB or more in a wide bandwidth, for example, about 350 MHz. Thus, when the signal-to-noise enhancer 10 is used for receiving a satellite broadcasting signal, it can completely cover the bandwidth of about 300 MHz which is the bandwidth of all the satellite broadcasting signals received in Japan. Also, in the signal-to-noise enhancer 10, since the operating frequency bandwidth is wide, when the temperature changes, even if the operating frequency bandwidth changes, the operating frequency bandwidth hardly becomes out of the used frequency desired for using in fact, besides it is easy to adjust the operating frequency bandwidth so that the used frequency becomes in the operating frequency bandwidth, it requires only a short time to adjust the operating frequency bandwidth. Furthermore, in the signal-to-noise enhancer 10, since the 90 degree hybrid sets are used as the first hybrid set and the second hybrid set, the same hybrid sets can be manufactured for the the first hybrid set and the second hybrid set, the efficiency for manufacturing the first hybrid set and the second hybrid set is increased. Also, in the signal-to-noise enhancer 10, since the magnetostatic wave element is used in the limiter, a signal in a wide bandwidth is limited by the limiter, a signal in a wide bandwidth can be applied. Meanwhile, in the signal-to-noise enhancer 10, since the magnetostatic wave element utilizing the magnetostatic surface wave mode is used in the limiter, the minimum level of the main signal limited by the limiter, that is, the saturation level of the limiter becomes low, even if the level of the main signal is low, the signal-to-noise ratio in the input signal can be improved. Furthermore, in the signal-to-noise enhancer 10, since the levels of the noises in the two signal combined by the second hybrid set are equalized by the level adjusting means consisting of the first attenuator, the filter and the second attenuator, these noises can be certainly offset. Thus, the signal-to-noise ratio can be certainly improved. That is, Fig. 6 shows transmission characteristics of the signal-to-noise enhancer 10 where a level of an input signal is decreased at an interval of 10 dB from 10 dBm as a reference. As it is apparent from the graph shown in Fig. 6, in the signal-to-noise enhancer 10, an enhancement of 10 dB is obtained in a wide bandwidth of about 600 MHz which is about 2 times of the conventional example, an enhancement of 20 dB is obtained in a wide bandwidth of about 350 MHz which is about 3.5 times of the conventional example. Also, Fig. 7 shows an input-to-output characteristic at 1.9 GHz in the signal-to-noise enhancer 10. As it is apparent from the graph shown in Fig. 7, in the signal-to-noise enhancer 10, the minimum level PH of the input signal wherein the signal-to-noise ratio can be improved is -8 dBm, the level PL of the input signal wherein it begins to improve the signal-to-noise ratio is -17 dBm, the difference between these levels is small as 9 dBm, therefore a great effect on improving of the signal-to-noise ratio can be obtained on receiving, for example, a satellite broadcasting signal. Furthermore, in the signal-to-noise enhancer 10, when the input signals including the three signals of 1.8 GHz, 1.95 GHz and 2.1 GHz with input level of 0 dBm shown in Fig. 8 are applied at the same time, the output signals shown in Fig. 9 are obtained. As it is apparent from the graphs shown in Fig. 8 and Fig. 9, in the signal-to-noise enhancer 10, the noise is attenuated by 10 dB or more at 10 MHz separation from each signal, the signal-to-noise enhancer operates separately to each signal. Also, Fig. 10 shows relations between carrier-to-noise ratio and signal-to-noise ratio where the signal-to-noise enhancer 10 is used for receiving a satellite broadcasting signal and is not used. In this case, the relations between the carrier-to-noise ratio and the signal-to-noise ratio are measured by using a video signal having an average picture level (APL) of 50%, that is, a video signal including a signal for white of 50% and a signal for black of 50%. As it is apparent from the graph shown in Fig. 10, when the signal-to-noise enhancer 10 is used for receiving the satellite broadcasting signal, compared with the case wherein the signal-to-noise enhancer is not used for receiving the satellite broadcasting signal, the signal-to-noise ratio can be increased by 2-8 dB when the carrier-to-noise ratio is 9 dB or less, the signal-to-noise ratio can be increased by 0.5 dB when the carrier-to-noise ratio is 9 dB or more. Also, though the magnetostatic wave element utilizing the magnetostatic surface wave mode having a bandpass filter characteristic is used as the limiter in the above-mentioned embodiment, a magnetostatic wave element utilized the magnetostatic forward volume wave mode or the magnetostatic backward volume wave mode may be used, or a filter such as a low-pass filter utilized a magnetostatic wave, a high-pass filter utilized a magnetostatic wave and a bandstop filter utilized a magnetostatic wave may be used. Furthermore, though the first attenuator, the filter and the second attenuator are used as the level adjusting means in the above-mentioned embodiment, in place of providing the first attenuator and the second attenuator, an attenuator may be provided to the pre-stage of the first hybrid set, an amplifier may be provided to the pre-stage of the limiter, and an amplifier may be provided to the post-stage of the filter. Or, each amplifier or each attenuator may be provided to the pre-stage of the the first hybrid set, the pre-stage and the post-stage of the limiter, and the pre-stage and the post-stage of the filter. Meanwhile, "90 degree" and "180 degree" in the present invention include not only the literal degrees but also the approximate degrees in view of the objective, the action and the effect of the present invention.

Claims: A signal-to-noise enhancer (10) comprising: an input terminal and an output terminal; a first signal path extending from the input terminal to the output terminal; a second signal path extending from the input terminal to the output terminal; and a limiter (62a), provided in the first signal path, for limiting an amplitude of a main signal in said first signal path; characterized by a first hybrid set (20) receiving an input signal from the input terminal and for dividing the input signal including the main signal and noise into a first signal on the first signal path and a second signal on the second signal path, said first signal and said second signal having a first phase difference in a wide bandwidth, said first phase difference being not zero; and a second hybrid set (40) for combining a signal obtained from said first signal path and a signal obtained from said second signal path, for introducing a second phase difference in a wide bandwidth between the signals to be combined, and for outputting the combined signal to the output terminal, said second phase difference being not zero; wherein the sum of said first phase difference and said second phase difference is (2n+1)·180 degree where n is 0 or an integer. A signal-to-noise enhancer (10) according to claim 1, wherein 90 degree hybrid sets are used as said first hybrid set (20) and said second hybrid set (40). A signal-to-noise enhancer according to claim 1 or 2 wherein a magnetostatic wave element is used in said limiter (62a). A signal-to-noise enhancer according to claim 3, wherein said magnetostatic wave element is a magnetostatic wave element utilizing the magnetostatic surface wave mode. A signal-to-noise enhancer according to one of claims 1 to 4, which further comprises a level adjusting means, provided between said first hybrid set (20) and said second hybrid set (40) in the second signal path for equalizing levels of noises in two signals combined by said second hybrid set each other. A signal-to-noise enhancer according to claim 5, wherein said level adjusting means comprises: a first attenuator (32), provided in the second signal path between said first hybrid set (20) and said second hybrid set (40), for attenuating a level of said second signal obtained from said first hybrid set (20); a filter (62b), provided in the second signal path between said first attenuator (32) and said second hybrid set (40), having the same input-to-output characteristic as said limiter (62a), for passing a signal obtained from said first attenuator (32); and a second attenuator (52), provided in the first signal path between said limiter (62a) and said second hybrid set (40), for attenuating a level of a signal obtained from said limiter (62a). A signal-to-noise enhancer according to claim 6, wherein said first hybrid set (20) is a first 90 degree hybrid set, said first phase difference is a phase difference of 90 degree, a magnetostatic wave element utilizing the magnetostatic surface wave mode is used in said limiter (62a), a magnetostatic wave element utilizing the magnetostatic surface wave mode is used in said filter (62b), said second hybrid set (40) is a second 90 degree hybrid set, said second phase difference is a phase difference of 90 degree, said levels of said noises in said two signals are equalized by said first attenuator (32), said filter (62b) and said second attenuator (52), and a phase difference between said two signals is set by said first 90 degree hybrid set (20) and said second 90 degree hybrid set (40) to (2n+1)·180 degree where n is 0 or an integer.

Inventors: ICHIGUCHI SHINICHIRO, ISHIKAWA YOUHEI, KANAYA FUMIO, NOMOTO TOSHIHIRO, OKADA TAKEKAZU, SHINMURA SATORU, UMEGAKI TOSHIHITO, ICHIGUCHI, SHINICHIRO, ISHIKAWA, YOUHEI, KANAYA, FUMIO, NOMOTO, TOSHIHIRO, OKADA, TAKEKAZU, SHINMURA, SATORU, UMEGAKI, TOSHIHITO, ICHIGUCHI, SHINICHIRO, C/O MURATA MANUF. CO.,LTD., ISHIKAWA, YOUHEI, C/O MURATA MANUF. CO., LTD., KANAYA, FUMIO, C/O MURATA MANUF. CO.,LTD., NOMOTO, TOSHIHIRO, C/O NIPPON HOSO KYOKAI, OKADA, TAKEKAZU, C/O MURATA MANUF. CO.,LTD., SHINMURA, SATORU, C/O MURATA MANUF. CO.,LTD., UMEGAKI, TOSHIHITO, C/O MURATA MANUF. CO.,LTD.
Applicants: JAPAN BROADCASTING CORP, MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD., NIPPON HOSO KYOKAI
Application year: 1995
Main classification: H03H2
IPC codes: H03H2, H01P1