阅读说明：本技术 一种高概率宽带信号精确测量系统和方法 (High-probability broadband signal accurate measurement system and method ) 是由 陈吉欣 鄢勃 师勇 陈少勇 于 2020-03-30 设计创作，主要内容包括：本发明公开了一种高概率宽带信号精确测量系统和方法,所述系统包括：具有两路输出端的射频功分器、宽带接收机、具有n路输出端的时间缓存模块、n个射频变换单元和n个窄带接收机；射频功分器的2路输出端分别连接宽带接收机和时间缓存模块的输入端；宽带接收机的输出端连接每个射频变换单元和窄带接收机；时间缓存模块的n路输出端经n个射频变换单元与n个窄带接收机一一对应连接。本发明采用宽带引导窄带信号接收处理,结合宽带信号时间缓存技术,有效解决了窄带接收机与宽带接收机准确时间匹配接收的难题,在保证信号不丢失的基础上,实现对多种类型的宽带信号高灵敏度、高精度、实时参数测量能力。(The invention discloses a high-probability broadband signal accurate measurement system and a method, wherein the system comprises: the system comprises a radio frequency power divider with two paths of output ends, a broadband receiver, a time cache module with n paths of output ends, n radio frequency conversion units and n narrow-band receivers; the 2-path output end of the radio frequency power divider is respectively connected with the input ends of the broadband receiver and the time cache module; the output end of the broadband receiver is connected with each radio frequency conversion unit and the narrow-band receiver; and n paths of output ends of the time cache module are correspondingly connected with n narrow-band receivers one by one through n radio frequency conversion units. The invention adopts the broadband to guide the narrow-band signal receiving processing, combines the broadband signal time caching technology, effectively solves the problem of accurate time matching receiving of the narrow-band receiver and the broadband receiver, and realizes the high sensitivity, high precision and real-time parameter measurement capability of various broadband signals on the basis of ensuring that the signals are not lost.)

1. A high probability broadband signal precision measurement system, comprising: the system comprises a radio frequency power divider with two paths of output ends, a broadband receiver, a time buffer module with n paths of output ends, a multi-channel radio frequency conversion module with n radio frequency conversion units and a multi-channel narrow-band receiving module with n narrow-band receivers; the 2-path output end of the radio frequency power divider is respectively connected with the input ends of the broadband receiver and the time cache module; the output end of the broadband receiver is connected with each radio frequency conversion unit and the narrow-band receiver; and n paths of output ends of the time cache module are correspondingly connected with n narrow-band receivers one by one through n radio frequency conversion units.

2. The system according to claim 1, wherein the time buffer module comprises an electro-optical conversion unit, an optical power splitter with n output ports, n optical fiber delay lines, and n photoelectric conversion units; the input end of the electro-optical conversion unit is used as the input end of the time cache module and is connected with the output end of the 1 path of the radio frequency power divider, and the output end of the electro-optical conversion unit is connected with the input end of the radio frequency power divider; the n output ends of the optical power splitter are correspondingly connected with the n photoelectric conversion units one by one through n optical fiber delay lines; the output ends of the n photoelectric conversion units are n paths of output ends of the time cache module.

3. The system according to claim 1, wherein each rf conversion unit in the multi-channel rf conversion module comprises a mixer, a narrow band filter, and a low noise amplifier, which are connected in sequence, and an adjustable local oscillator connected to the mixer.

4. The system of claim 1, wherein each of the narrowband receivers in the multi-channel narrowband receiving module comprises an analog-to-digital converter and a high-speed signal processor connected in sequence.

5. A method for accurate measurement of high probability broadband signals, the method comprising:

the broadband radio frequency signal is input into a measuring system and is divided into two paths by a radio frequency power divider, one path is input into a broadband receiver, and the other path is input into a time cache module;

the broadband receiver carries out rapid measurement on broadband radio-frequency signals input into the broadband receiver, obtains rough parameters of n radio-frequency signals when the input signals contain n simultaneously arriving signals, generates guide information and sends the guide information to each radio-frequency conversion unit and the narrow-band receiver; the coarse parameters comprise the type, frequency and arrival time of the broadband radio frequency signal; the guiding information comprises an address code, a signal type code, a frequency code, a time code and a data length code;

the time buffer module is used for carrying out time buffer on the broadband radio frequency signal input into the time buffer module;

according to the corresponding guide information, n radio frequency conversion units in the multi-channel radio frequency conversion module convert n paths of broadband radio frequency signals after time buffering into n intermediate frequency signals;

n narrow-band receivers in the multi-channel narrow-band receiving module perform accurate measurement on n intermediate frequency signals to obtain accurate measurement results of the input n radio frequency signals.

6. The method for accurately measuring high-probability broadband signals according to claim 5, wherein the time buffering module performs time buffering on the broadband radio-frequency signals input into the time buffering module by:

the electro-optical conversion unit converts the broadband radio frequency signal input into the electro-optical conversion unit into an amplitude-modulated optical signal;

the optical power divider divides an optical signal into n paths;

the n optical fiber delay lines respectively carry out time delay on the n optical signals;

the n photoelectric conversion units restore the n paths of optical signals after the time delay into n paths of broadband radio frequency signals.

7. The method as claimed in claim 6, wherein the delay time of the optical fiber delay line for time-delaying the optical signal is determined by the length of the optical fiber delay line, and the calculation formula is as follows:

τ＝n_oL/c

where τ is the delay time, n_oIs the refractive index of the optical fiber delay line, L is the length of the optical fiber delay line, and c is the speed of light in vacuum。

8. The method according to claim 6 or 7, wherein when the n optical fiber delay lines delay the n optical signals, the delay time of each optical fiber delay line may be set to be the same or different.

9. The method for accurately measuring high-probability broadband signals according to claim 5, wherein each radio frequency conversion unit in the multi-channel radio frequency conversion module converts broadband radio frequency signals after time buffering into intermediate frequency signals by the following method:

after tuning the internal adjustable local oscillation frequency according to the guide information, the frequency mixer moves the broadband radio frequency signal after time buffering to a fixed intermediate frequency band;

the narrow-band filter selects a signal with a determined frequency range from the intermediate frequency band signals output by the mixer;

and the low-noise amplifier performs gain compensation on the signal selected by the narrow-band filter and outputs an intermediate-frequency signal.

10. The system of claim 5, wherein each narrowband receiver in the multi-channel narrowband receiving module performs accurate measurement on the if signal by:

the analog-digital converter samples the intermediate frequency signal to obtain a high-precision digital signal;

the high-speed signal processor performs fast Fourier transform, filtering and time-frequency analysis on the digital signal, and then completes parameter calculation and detection to obtain all parameters of the input broadband radio-frequency signal, including frequency, amplitude, phase, pulse width and repetition period; on the basis that the broadband receiver conducts time buffering on the signals through the guide information guide and the time buffering module, the high-speed signal processor can change the signal processing data length according to the actual requirement on the signal parameter precision.

Technical Field

The invention relates to the field of broadband radio frequency signal detection, in particular to a high-probability broadband signal accurate measurement system and method, which can be used for high-precision and rapid extraction and measurement of radio frequency signal parameters in electronic equipment such as radio frequency spectrum monitoring and target reconnaissance.

Background

Electronic equipment such as radio frequency spectrum monitoring, target reconnaissance and the like must realize the analysis and the identification of the characteristics of a radiation source by receiving and processing radio frequency signals from the outside so as to obtain accurate electromagnetic spectrum situations. Since the radiation source is a non-cooperative object, there is an uncertain distribution of target number, signal type and parameters within a wide instantaneous frequency range. Particularly, on the basis of the development of digital signal processing, parameters such as frequency, pulse width, pulse period and amplitude of a radiation signal have more flexible changing capability, which brings great challenges to traditional signal receiving.

At present, in electronic devices such as spectrum monitoring and target reconnaissance, in order to receive and process broadband radio frequency signals in a complex electromagnetic environment, corresponding receivers are basically adopted to realize the functions, such as an instantaneous frequency measurement receiver and a digital receiver. The instantaneous frequency measurement receiver is an analog signal processing system, has the advantages of large instantaneous bandwidth, quick response time, simple realization framework and the like, but has the problems of low sensitivity, low signal parameter measurement accuracy, poor multi-signal adaptability and the like. The digital receiver adopts an analog-digital converter to convert an input radio frequency signal into a digital signal, and then calculates signal parameters through a signal processor through complex mathematical operations. The digital receiver has the advantages of high sensitivity, flexible processing mode, strong multi-signal adaptability and the like, but is limited by the performance of a high-speed analog-digital converter and a signal processor, and the maximum instantaneous processing bandwidth of a single receiving channel does not exceed 1 GHz. In order to realize the working capability of a wider instantaneous frequency range (such as 6-18 GHz), the working bandwidth can only be expanded by splicing a plurality of receiving channels in parallel, and at the moment, the size, the power consumption, the complexity, the cost and the like of a receiving system are quite high. When electronic equipment for spectrum monitoring, target reconnaissance and the like needs to simultaneously receive signals from a plurality of antenna units in a wide instantaneous frequency range in real time, such as multi-signal simultaneous measurement and target signal direction measurement. The splicing type broadband receiving system is difficult to realize in engineering and cannot be applied at all. In addition, because the digital receiver needs to adopt a large amount of complex mathematical transformation and operation to obtain signal parameters, the real-time processing capability and the parameter measurement precision are mutually limited, and the requirements on high precision and real-time receiving and processing of signals cannot be simultaneously met. In order to ensure the real-time receiving processing capability, the traditional digital receiver can only adopt a signal processing method with fixed data length, and the method has poor measurement flexibility and accuracy on different types of signals. In order to improve the measurement accuracy of the signal parameters, the receiver must increase the signal processing data length and time, which may cause a high probability of losing the arriving signal in a dense electromagnetic environment, and seriously affect the identification of the complete characteristics of the target.

In order to meet the requirements of broadband, high probability, high precision, and real-time signal reception and measurement, the receiving system needs to have high capability in terms of instantaneous frequency range, processing time, high precision parameter measurement, and the like. The existing single receiver can not simultaneously meet all performances, and only realizes partial performances under certain conditions. For example, when the digital receiver operates at the instantaneous bandwidth of 1GHz, in order to improve the receiving sensitivity and the frequency measurement accuracy, the length of signal processing data must be increased, which greatly increases the computational processing resources and prevents signals queued behind the response time from entering the processing flow, resulting in signal loss and crash of the receiving system.

Disclosure of Invention

The purpose of the invention is as follows: the method has the advantages of large bandwidth, high interception probability, high parameter measurement precision and simple and convenient engineering realization, and has practical application value for receiving and processing the broadband radio frequency signals in electronic equipment such as radio frequency spectrum monitoring, target reconnaissance and the like.

The invention discloses a high-probability broadband signal accurate measurement system, which comprises: the system comprises a radio frequency power divider with two paths of output ends, a broadband receiver, a time buffer module with n paths of output ends, a multi-channel radio frequency conversion module with n radio frequency conversion units and a multi-channel narrow-band receiving module with n narrow-band receivers; the 2-path output end of the radio frequency power divider is respectively connected with the input ends of the broadband receiver and the time cache module; the output end of the broadband receiver is connected with each radio frequency conversion unit and the narrow-band receiver; and n paths of output ends of the time cache module are correspondingly connected with n narrow-band receivers one by one through n radio frequency conversion units.

Furthermore, the time buffer module comprises an electro-optical conversion unit, an optical power splitter with n output ends, n optical fiber delay lines and n photoelectric conversion units; the input end of the electro-optical conversion unit is used as the input end of the time cache module and is connected with the output end of the 1 path of the radio frequency power divider, and the output end of the electro-optical conversion unit is connected with the input end of the radio frequency power divider; the n output ends of the optical power splitter are correspondingly connected with the n photoelectric conversion units one by one through n optical fiber delay lines; the output ends of the n photoelectric conversion units are n paths of output ends of the time cache module.

Furthermore, each radio frequency conversion unit in the multi-channel radio frequency conversion module comprises a mixer, a narrow band filter and a low noise amplifier which are connected in sequence, and an adjustable local oscillator connected with the mixer.

Further, each narrow-band receiver in the multi-channel narrow-band receiving module comprises an analog-digital converter and a high-speed signal processor which are connected in sequence.

The invention also provides a high-probability broadband signal accurate measurement method, which comprises the following steps:

the broadband radio frequency signal is input into a measuring system and is divided into two paths by a radio frequency power divider, one path is input into a broadband receiver, and the other path is input into a time cache module;

the broadband receiver carries out rapid measurement on broadband radio-frequency signals input into the broadband receiver, obtains rough parameters of n radio-frequency signals when the input signals contain n simultaneously arriving signals, generates guide information and sends the guide information to each radio-frequency conversion unit and the narrow-band receiver; the coarse parameters comprise the type, frequency and arrival time of the broadband radio frequency signal; the guiding information comprises an address code, a signal type code, a frequency code, a time code and a data length code;

the time buffer module is used for carrying out time buffer on the broadband radio frequency signal input into the time buffer module;

according to the corresponding guide information, n radio frequency conversion units in the multi-channel radio frequency conversion module convert n paths of broadband radio frequency signals after time buffering into n intermediate frequency signals;

n narrow-band receivers in the multi-channel narrow-band receiving module perform accurate measurement on n intermediate frequency signals to obtain accurate measurement results of the input n radio frequency signals.

Further, the implementation method for the time caching module to time cache the broadband radio frequency signal input into the time caching module is as follows:

the electro-optical conversion unit converts the broadband radio frequency signal input into the electro-optical conversion unit into an amplitude-modulated optical signal;

the optical power divider divides an optical signal into n paths;

the n optical fiber delay lines respectively carry out time delay on the n optical signals;

the n photoelectric conversion units restore the n paths of optical signals after the time delay into n broadband radio frequency signals.

Further, the delay time of the optical fiber delay line for time-delaying the optical signal is determined by the length of the optical fiber delay line, and the calculation formula is as follows:

τ＝n_oL/c

where τ is the delay time, n_oThe index of refraction of the fiber delay line is L the length of the fiber delay line and c the speed of light in vacuum.

Further, when n optical signals are time-delayed by n optical fiber delay lines, the delay time of each optical signal may be set to be the same or different.

Furthermore, the implementation method for converting the broadband radio frequency signal after time buffering into the intermediate frequency signal by each radio frequency conversion unit in the multi-channel radio frequency conversion module is as follows:

after tuning the internal adjustable local oscillation frequency according to the guide information, the frequency mixer moves the broadband radio frequency signal after time buffering to a fixed intermediate frequency band;

the narrow-band filter selects a signal with a determined frequency range from the intermediate frequency band signals output by the mixer;

and the low-noise amplifier performs gain compensation on the signal selected by the narrow-band filter and outputs an intermediate-frequency signal.

Further, the method for each narrowband receiver in the multi-channel narrowband receiving module to accurately measure the intermediate frequency signal includes:

the analog-digital converter samples the intermediate frequency signal to obtain a high-precision digital signal;

the high-speed signal processor performs fast Fourier transform, filtering and time-frequency analysis on the digital signal, and then completes parameter calculation and detection to obtain all parameters of the input broadband radio-frequency signal, including frequency, amplitude, phase, pulse width and repetition period; on the basis that the broadband receiver conducts time buffering on the signals through the guide information guide and the time buffering module, the high-speed signal processor can change the signal processing data length according to the actual requirement on the signal parameter precision.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

the invention provides a high-probability broadband signal accurate measurement system and method, which adopt broadband to guide narrowband signal receiving processing and combine broadband signal time cache technology, effectively solve the problem of accurate time matching receiving of a narrowband receiver and a broadband receiver, and realize high sensitivity, high precision and real-time parameter measurement capability on various types of broadband signals on the basis of ensuring no signal loss. The method provided by the invention can effectively solve the defects of low interception probability, poor adaptability, low precision, insufficient processing resources and the like in the existing broadband signal measurement, and has remarkable advantages in the aspects of performance level, realizability, engineering application and the like.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

Fig. 1 is a schematic diagram of an implementation of the high-probability broadband signal accurate measurement of the present invention.

FIG. 2 is a schematic diagram of a time buffer module implementation of the present invention.

Fig. 3 is a schematic diagram of an implementation of the rf conversion unit of the present invention.

Fig. 4 is a schematic diagram of a narrowband receiver implementation of the present invention.

Fig. 5 is a schematic diagram of the guiding message composition of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, a high probability broadband signal precision measurement system includes: the system comprises a radio frequency power divider with two paths of output ends, a broadband receiver, a time buffer module with n paths of output ends, a multi-channel radio frequency conversion module with n radio frequency conversion units and a multi-channel narrow-band receiving module with n narrow-band receivers; the 2-path output end of the radio frequency power divider is respectively connected with the input ends of the broadband receiver and the time cache module; the output end of the broadband receiver is connected with each radio frequency conversion unit and the narrow-band receiver; and n paths of output ends of the time cache module are correspondingly connected with n narrow-band receivers one by one through n radio frequency conversion units.

As shown in fig. 2, the time buffer module includes an electrical-to-optical conversion unit, an optical power splitter with n output ports, n optical fiber delay lines, and n photoelectric conversion units; the input end of the electro-optical conversion unit is used as the input end of the time cache module and is connected with the output end of the 1 path of the radio frequency power divider, and the output end of the electro-optical conversion unit is connected with the input end of the radio frequency power divider; the n output ends of the optical power splitter are correspondingly connected with the n photoelectric conversion units one by one through n optical fiber delay lines; the output ends of the n photoelectric conversion units are n paths of output ends of the time cache module.

As shown in fig. 3, each rf conversion unit in the multi-channel rf conversion module includes a mixer, a narrow band filter, a low noise amplifier, and an adjustable local oscillator connected to the mixer.

As shown in fig. 4, each of the narrowband receivers in the multi-channel narrowband receiving module includes an analog-to-digital converter and a high-speed signal processor connected in sequence.

Based on the above-mentioned high-probability broadband signal accurate measurement, the present invention further provides a high-probability broadband signal accurate measurement method, as shown in fig. 1, the method includes:

(1) the broadband radio frequency signal is input into a measuring system and is divided into two paths by a radio frequency power divider, one path is input into a broadband receiver, and the other path is input into a time cache module;

(2) the broadband receiver carries out rapid measurement on broadband radio-frequency signals input into the broadband receiver, obtains rough parameters of n radio-frequency signals when the input signals contain n simultaneously arriving signals, generates guide information and sends the guide information to each radio-frequency conversion unit and the narrow-band receiver; the coarse parameters comprise the type, frequency and arrival time of the broadband radio frequency signal; the guiding message includes an address code, a signal type code, a frequency code, a time code and a data length code, as shown in fig. 5; each rf translation unit and the narrowband receiver corresponds to a unique address. The address code indicates the corresponding radio frequency conversion unit and the narrow-band receiver; the signal type code indicates the type of the received signal at the address; the time code indicates the arrival time of the received signal at the address; the data length code indicates the length of data that the narrowband receiver can process at that address.

The broadband receiver can be realized by adopting a digital instantaneous frequency measurement and multi-channel channelization technology, and can work in a wide instantaneous frequency range according to requirements, such as 2-6 GHz, 8-12 GHz, 6-18 GHz and the like; the wideband receiver has multiple signal processing capabilities and is able to resolve coarse parameters of simultaneously arriving signals. Under the condition of guiding information and signal time buffering, according to a receiving strategy, the broadband receiver can simultaneously guide a plurality of narrow-band receivers to accurately measure the input broadband radio-frequency signals.

(3) The time buffer module is used for carrying out time buffer on the broadband radio frequency signal input into the time buffer module;

as shown in fig. 2, specifically:

the electro-optical conversion unit converts the broadband radio frequency signal input into the electro-optical conversion unit into an amplitude-modulated optical signal;

the optical power divider divides an optical signal into n paths;

the n optical fiber delay lines respectively carry out time delay on the n optical signals;

the n photoelectric conversion units restore the n paths of optical signals after the time delay into n paths of broadband radio frequency signals.

The delay time of the optical fiber delay line for time delay of the optical signal is determined by the length of the optical fiber delay line, and the calculation formula is as follows:

τ＝n_oL/c

where τ is the delay time, n_oIn addition, the delay time is generally from a few mu s to dozens of mu s for effective guiding and accurate processing, the working bandwidth of the time buffer module is determined by the electro-optical conversion unit and the photoelectric conversion unit, and corresponding broadband optoelectronic devices are needed to construct the functional unit for achieving large-bandwidth operation (such as more than 20 GHz)Under normal circumstances, a laser and a broadband electro-optical modulator can be used to realize the electro-optical conversion function of the electro-optical conversion unit, and a broadband photoelectric detector is used to realize the photoelectric conversion function of the photoelectric conversion unit. In the embodiment, the time cache module is used for storing the broadband radio-frequency signal input into the time cache module in a high fidelity manner for a period of time so as to compensate the time required by the broadband receiver for carrying out rapid measurement and generating guide information and the radio-frequency conversion unit for carrying out frequency conversion, thereby effectively ensuring accurate time matching reception of the narrowband receiver and the broadband receiver, realizing no loss of real-time measurement signals and ensuring high interception probability and accurate measurement capability.

(4) According to the corresponding guide information, n radio frequency conversion units in the multi-channel radio frequency conversion module convert n paths of broadband radio frequency signals after time buffering into n intermediate frequency signals;

as shown in fig. 3, the implementation method for converting the wideband radio frequency signal after time buffering into the intermediate frequency signal by each radio frequency conversion unit in the multi-channel radio frequency conversion module is as follows:

after tuning the internal adjustable local oscillation frequency according to the guide information, the frequency mixer moves the broadband radio frequency signal after time buffering to a fixed intermediate frequency band;

the narrow-band filter selects a signal with a determined frequency range from the intermediate frequency band signals output by the mixer;

the low-noise amplifier performs gain compensation on the signal selected by the narrow-band filter and outputs an intermediate-frequency signal:

wherein the bandwidth of the intermediate frequency signal matches the instantaneous operating bandwidth of the narrowband receiver, typically set to 200MHz or 20 MHz.

(5) N narrow-band receivers in the multi-channel narrow-band receiving module perform accurate measurement on n intermediate frequency signals to obtain accurate measurement results of the input n wide-band radio-frequency signals;

as shown in fig. 4, the method for each narrowband receiver in the multi-channel narrowband receiving module to accurately measure the intermediate frequency signal includes:

the analog-digital converter samples the intermediate frequency signal to obtain a high-precision digital signal;

the high-speed signal processor performs fast Fourier transform, filtering and time-frequency analysis on the digital signal, and then completes parameter calculation and detection to obtain all parameters of the input broadband radio-frequency signal, including frequency, amplitude, phase, pulse width and repetition period; on the basis that the broadband receiver conducts time buffering on the signals through the guide information guide and the time buffering module, the high-speed signal processor can change the signal processing data length according to the actual requirement on the signal parameter precision.

The processing method with variable data length overcomes the problems of low precision, low interception probability and insufficient operation resources in high-speed and real-time digital signal processing. That is, according to the type of the radio frequency signal in the bandwidth to be measured and the actual requirement of the signal parameter precision, in the signal processing of the digital signal by the high-speed signal processor, the data length of the digital signal processing can be changed under the guidance information, and is specifically determined by the data processing code in the guidance information. In general, the processing data length can be set to 128 dots, 256 dots, 512 dots, 1024 dots, 2048 dots, and the like. The length of the processed data is increased, the sensitivity and parameter precision of signal measurement are improved, and the signal processing time is also increased. The digital processing method with variable data length can better adapt to the requirements of high sensitivity, high precision and real-time measurement of various signals such as conventional pulse, frequency hopping, frequency diversity, linear frequency modulation, spectrum spreading, phase coding and the like.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.