GB2237649A

GB2237649A - Separating and measuring frequency signals

Info

Publication number: GB2237649A
Application number: GB9019290A
Authority: GB
Inventors: P Michael Gale
Original assignee: GALE PETER MICHAEL
Current assignee: GALE PETER MICHAEL
Priority date: 1989-09-08
Filing date: 1990-09-04
Publication date: 1991-05-08
Anticipated expiration: 2010-09-04
Also published as: GB9019290D0; DE4028681C2; GB2237649B; DE4028681A1

Abstract

A method of separating and measuring simultaneously received separate frequency signals (3) in an input signal (1) comprises subjecting power divided representations (2) of the input signal separately to various time or amplitude weighting (4A to 4N) to exaggerate differences between various ones and others of the separate frequency signals, passing the exaggerated signals through separate limiters (5A to 5N) to exaggerate one separate frequency signal relative to the others in each of the various separate frequency signals, and measuring (8) the frequency of each exaggerated one frequency signal. <IMAGE>

Description

v 1 1 i WEIGHTED CHANNELIZED RECEIVER This invention relates to a receiver

for separating or sorting simultaneously received signals.

Instantaneous frequency measurement (IFM) receivers have been developed for use in electronic warfare, to effect electronic support measures, electronic counter measures, or electronic intelligence applications. Instantaneous frequency measurement receivers are variously known in the art as Digital Instanteous Frequency Measurement (DIFM) receivers or Digital Frequency Discriminators (DFD). DIFF, receivers are typically required to operate in dense and complex electromagnetic signal environments. It is therefore desirable that the receivers should be capable of separating individual ones of plural simultaneously received signals from single or multiple emitters.

U.S. Patent 4,791,360 issued December 13th, 1988 and assigned to Telemus Electronic Systems Inc. describes prior art DIFY, systems which use a discriminator to separate a signal from an input signal and a delayed representation of the input signal. However such prior art systems could only provide the strongest one of simultaneous signals# and in some circumstances, in the event a second signal arrives prior to completion of the frequency measurement of a first signal and the second signal is stronger than the first, there is a significant likelihood of an erroneous output signal.

To overcome that problem in the invention described in that patent the received signals ate successively applied to respective signal modifying circuits, each for isolating a piedetermined one of the received signals from the other one of the signals, and an output signal is generated corresponding to the isolated one of the simultaneous sionals separated in time and frequency from the other ones of the sionals. Either similar amplitude ones of 1( 1 the separated signals are filtered and amplifiedt while the others are attenuatedt or time coincident ones of the simultaneous signals are dispersively delayed by predetermined lengths of time proportionate to their respective frequencies. In such a system, the successive application of the received signals to respective ones of the plurality of signal modifying means requires the use of a switching circuit.

For input signals which use pulse lengths longer than n times the switching circuit switching time, and where the switch dwell period is long enough for the frequency measurements to be made to the desired accuracy, the patented system has been found to be satisfactoryl especially where there is a single received signal with multiple pulsed frequencies. However it has been found that if the duration of the input signal is short relative to the switching time, or if there is a need to handle more than one received signal at a time? the patented system can be improved. The present invention is an improved system which can handle more than one received signal at a time? and can operate successfully if the duration of the received signal is short compared to the required switching time of the patented system.

in accordance with the present invention, the received signal is power divided into a plurality of separate signals, each containing the simultaneous signals. Each separate signal is passed through a weighting means, each weighting means for receiving one of the separate signals and for translating it so as to exaggerate differences between various ones and others of the simultaneous signals. The weighting means can be dispersive delay linest filters, amplifiers, channelizers, etc. Each of the weighting-biased translated signals is passed through a limiter, which further exaggerates the maximum amplitude one of the simultaneous signals relative to ------------------ v i the others. Each of the resulting signals is passed through a frequency measurement circuit, such as a discriminator, pulse counter or halver which selects the maximum amplitude signal corresponding to its channel. in the case of the frequency disciminatort it is followed by an AID converter or digitizer. In the case of the pulse counter that output is in digital format. The halver can be used prior to the discriminator or pulse counter to prescale the signal frequency# but its operation as a threshold device also helps to separate the strongest signal. The outputs of the counters or AID converter are applied to a latch# or latches. The output signalr representing the frequencies of the simultaneously received signalsq are n bit words representing the frequencies of the simultaneous signals, and are preferably compared to data stored in a software library to match the n bit latched wordsi and thereby sort and identify the received signal and thus its emitter.

More particularly# an embodiment of the invention is a method of detecting simultaneously received separate frequency signals in an input signal comprising subjecting representations of the input signa separately to various time or amplitude weighting to exaggerate differences between various ones and others of the separate frequency siqnalsi passing individual exaggerated difference various ones of the separate frequency signals through separate limiters to exaggerate one separate frequency signal relative to the others in each of the various separate frequency signals, and measuring the frequency of each exaggerated one frequency signal.

Another embodiment of the invention is a signal detection apparatus comprising apparatus for receiving an input signal comprised of a plurality of simultaneous signals of different frequenciest a power 1 1 C - 4 divider for dividing the input signal into a plurality of separate signals each containing the simultaneous signalsi a plurality of weighting means each for receiving one of the separated signals and for translating it so as to exaggerate differences between various ones of the simultaneous signalso a plurality of limiting apparatus each for receiving one of the translated signals and for further exaggerating the amplitude of a maximum amiplitude one of the 10. simultaneous signals relative to the others, and frequency measurement means for receiving the further exaggerated signals for distinguishing each of the maximum amplitude signal signals.

A better understanding of the invention will be obtained by reference to the detailed description below. with reference to the following drawings# in which:

Figure 1 is a block schematic of a system in accordance with an embodiment of the present invention, Figure 2 is a block schematic of a portion of the circuit of Figure 1 modified in accordance with another embodiment. and Figure 3 is a block schematic of a portion of the circuit of Figure 1 modified in accordance with another embodiment of the invention.

Turning to Pigure l# an input signal is received at input 1 where it is applied to an n-way power divider 2. The outputs of the power divider define various channels. The input signal is comprised of several simultaneous signals of different frequencies, as shown on the graph 3f which illustrates the signals as vertical bars on a set of axes having an abscissa f representing frequency and an ordinate a representing amplitude.

The separate signals resulting from power division of the input signal are each applied in a 1 ------------------------------ X f corresponding channel to a weighting means 4As 4Be... EN-2), EN-1) and 4N. The weighting ineans perforin different weighting functions to the separate signals. Each of the weighting means can be an &mplituc3e vs frequency weighting filter. or a time vs frequency weighting filter. such as a dispersive delay line.

Representative translation characteristics of the weighting means are shown within the blocks 4A-4N. Representatives of the resulting weighted signals are shown at the outputs of the blocks 4A-4N, and It can be seen that there has been exaggeration Of the amplitudes of different frequency signals in accordance with the weighting functions. It is the purpose of the weighting means to exaggerate differences between various ones and others of the simultaneous signals in each of the channels defined by the outputs of the power divider 2.

The weighted signals in each channel are applied to a corresponding limiteri or limiting amplifier SA-SN. As is known in the arti the limiting amplifier further exaggerates the amplitude of the highest amplitude one of the simultaneous signals applied to it relative to the others. The result is shown in the amplitude vs frequency graphs at the output of limiting amplifiers SA-5N. One signal at one frequency in each channel is of significantly higher amplitude than the remaining ones.

The further exaggerated signals in each channel are applied to a corresponding discriminator or pulse counter 6A-6N, where thb highest amplitude one of the further exaggerated signals is selected. providing an output in each channel to a corresponding AID converter U-7N if discriminators are used. The discriminators and pulse counters constitute a frequency measurement unit 8, which can be in the form of a digital frequency discriminator and counter as - 6 r 1 described above, or other apparatus to measure the frequency of the highest amplitude separate frequency component of the output signal of the limiting amplifier in each channel.

The outputs of the frequency measurement unit 8, each constituting an nbit word designating the frequency of the highest amplitude signal# are applied to a latch 9. The total latched data word is Preferably applied to a memory 10 for access by a processor 11 which can control the comparison of the latched or stored word With another word stored in memory, thus to identify the input signal, It should be noted that each of the channels can be gated into the latch all at once# or sequentiallyr depending on the preference of the designer for its application (sequentially, in the time vs frequency weighted case), and either the word representing the channel data, or the complete data word representing all the channelst compared with data stored in the memory.

Since the above-described system does not use a switch, as is required in the system described in the aforenoted patent# the problem of the time differences between the leading edge of individual pulses of different signals being smaller than the switching time of the switch has been substantially eliminated. In addition, plural signals, rather than only a single one as in earlier types of systems, can be distinguished by frequency.

In addition, the problem in prior art systems being unable to distinguish signals due to the shadow time (the time between the presence of the signal and the time of determining the presence of that signal# at which time the signal to be determined 35 may already be absent) is substantially reduced.

In case there is a problem with standing waves between the power divider and the weighting 4.4 X, means 4A-4N# for example for signals between 2 and 4 GHz, a variation of the system shown in Figure 1 can be used, as illustrated in Figure 2. In this instance, between the power divider 2 and each weighting means 4A-4N an isolator 12A-12N is connected. Preferably in the case of a pulse form of input signal a bandpass filter or isolation filter 13A-13N is connected between each isolator and each output of the power divider 2. The filter and isolator substantially decrease the V5WR# thus substantially decreasing or eliminating reflected signals. The remainder of the system is as described with respect to Figure 1.

Pigure-3 illustrates another embodiment of the system shown in Figure 1, in which the signals applied to the weighting means are at Intermediate frequenciesy and therefore may he referred to as the superheterodyne version of the present invention. An input signal at input 14 is applied to a mixer 15 with an output signal from a first local oscillator 16. The resulting up or down-converted intermediate frequency band signal is applied to an intermediate frequency amplifier 17, the output of which is applied as the input signal at input 1 to the power divider 2. The divided separate output signals, which are within the first intermediate frequency band are applied to corresponding second mixers ISA-18N to which individual second local oscillator signals Lc) are applied. The resulting up or down- converted output signals from local oscillators 1BA-18N are applied to the corresponding weighting means 4A-4N in the individual channels. If desired# narrow bandwidth bandpass filters can be connected between the outputs of the mixers 1BA-18N and the weighting means 4A-4N.

The local oscillator 16, which can be a switched local oscillator, can be varied for coarse frequency adjustment. Either separately or in unison r 0 4 is - 8 each of the second local oscillator signals can be varied for fine frequency adjustment. This can allow adjustment of the input signals to the weighting means so that the maximum output of a particular frequency signal can be obtainedy and in particular the input signals can be positioned relative to the weighting means for maximum efficiency. Indeedi the local oscillator signals could be fast switched relative to the weighting filters' transfer functions so as to improve the probability of distinguishing pdrticular signals.

In this embodiment the intermediate frequency bandwidth can be narrower than in the previously described embodiments. This allows the use of narrow bandpass filters between the mixers 18A-18N and the weighting means# thus inproving the performance against simultaneous signals which are close together in frequency and phaset as well as reducing the noise floor by modifying kTB, where V is Boltsman constant, T is temperature in degrees Kelvin, and a is the bandwith. With the use of narrow bandpass filters, the weighting means can have high transfer function slopes, and narrow bandwidth, which decreases the effective noise bandwidtho and increases the signal to noise ratio. An additional advantage of this embodiment is a relatively low cost of lower frequency components which would be used to process the lower down converted second intermediate frequency signal.

It should be noted that the frequency band to be sorted can be expanded, e.g. from 2-4 GHZ to 2-18 GHZ by connecting a mixer 15 in series with a linear amplifier 17 in series with the input 1, as shown to the left of the vertical dashed line in Figure 2. A local oscillator 16 provides a local oscillator signal to mixer 1, which receives the input signal. The converted signal is applied to the input 0 ('4 ------------------------of power divider 2. A switch 20 bypasses the mixer and linear amplifier to allow the input signal to pass straight into the power divider 2. With the switch open, various bands (e.g. 4-6 GHZ etc.) can be down-converted into the frequency ranges of the filters 13A-13Ns or weighting means 4A- 4N.

while the frequency band of the intermediate frequency signal in one embodiment should span the same frequency band as the weighting means# in another embodiTnentg it can overlap the frequency band of the weighting means# and be subject to variation or rapid change, in order to fit the received signals best to the weighting means, or to facilitate identification or sorting thereof. The filters and isolators can be dispensed with# If VSWR is not a problem or If pulse signals are not to be received. as in the embodiment of Pigure 1.

The present invention can provide intrapulse frequency measurement so that discrete and integrated frequency measurement can be made. The combination of these two parameters, especially on complex input signals, is believed to be a powerful signal sorting and identification tool. It should also be noted that since various weighting means are used having differing slopes or delays# multiple simultaneous signals from one or more sources can be measured.

Numerous other applications and other embodiments may now occur to a person skilled in the art understanding this invention. All such modifications and embodiments falling within the scope of the claims are considered to be part of the present invention.

1 f

Claims

1. Signal detection means comprising:

(a) means for receiving an input signal comprised of a plurality of simultaneous signals of different frequenciest (b) a power divider for dividing the input signal into a plurality of separate signals each containing said simultaneous signals.

(c) a plurality of weighting means each for receiving one of the separate signals and for translating It so as to exaggerate differences between various ones of said simultaneous signals.

(d) a plurality of limiting means each for receiving one of the translated signals and for further exaggerating the amplitude of a maximum amplitude one of said simultaneous signals relative to the others, and (c) frequency measurement means for receiving the further exaggerated signals for distinguishing each of the maximum amplitude signal signals.

2. Signal detection means as defined in claim 1 in which the weighting means is an amplitude vs frequency weighting filter.

3. Signal detection means as defined in claim 1 in which the weighting means is a time vs frequency weighting filter.

4. signal detection means as defined in claim 1 in which the weighting means is a dispersive delay line.

-------------- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ( -11 5. Signal detection means as defined in claim 1, 21 3 or 4 in which the frequency measurement means is comprised of a plurality of discriminators each for receiving a corresponding signal from a limiting amplifier and for providing a signal corresponding to the maximum exaggerated maximum amplitude one of the simultaneous signals applied thereto.

6. Signal detection means as defined in claim Ii in which the frequency measurement means is comprised of a plurality of discriminators each for receiving a corresponding signal from a limiting amplifier and for providing a signal corresponding to the maximum exaggerated maximum amplitude one of the simultaneous signals applied thereto. and a plurality of analog to digital converters connected to outputs nf nnrrpsiponding discriminators each for orovidinc a digital word indicating the frequency of a corresponding discriminated signal.

7. Signal detection means as defined in clain 61 further including a latch connected to the outputs of the analog to digital converters for temporarily storing digital words representing each of the frequencies of the discriminated signals.

8. Signal detection means as defined in claim 1, 2, 3, 4, 6 or 7 further comprising an isolator interposed between each output of the power divider and an input of a corresponding weighting means.

9. Signal detection means as defined in claim 1, 2, 3, 4# 6 or 7 further comprising a filter in series with an isolator interposed between each ------------------------------------------------ output of the power divider and an input of a corresponding weighting means.

lo. signal detection means as defined in claim 1, 2# 3, 4r 6 or 7 further comprising a first mixer for converting a first signal to a first intermediate frequency signal and for applying the first intermediate frequency signal as the input signal to the receiving means, and a plurality of second mixers interposed between the power divider and corresponding weighting means for converting the first signal to a plurality of second intermediate frequency signals for application to corresponding weighting means as said separate signals.

11. Signal detection means as defined in claim l# 2$ 3# 4r 6 or 7 further comprising a first mixer for converting a first signal to a first intetmediate frequency signal and for applying the first intermediate frequency signal as the input W signal to the receiving meanst and a plurality of second mixers interposed between the power divider and corresponding weighting means for converting the first signal to a plurality of second intermediate frequency signals for application to corresponding weighting means as said separate signals, separate local oscillator signals which are separately variable being, applied to each of the second mixers.

12. Signal detection means as defined in claim 1, 2r 3, 4r 6 or 7 further comprising a first mixer for converting a first signal to a first intermediate frequency signal and for applying the first intermediate frequency signal as the input siqnal to the receiving means# and a plurality of second mixers interposed between the power divider and r C -! 1 1 corresponding weighting means for converting the first signal to a plurality of second intermediate frequency signals for appiication to cortesputidlity welgl&Ling means, and means for applying separate local oscillator signals to each of the second mixers and rapidly varying the frequencies thereof.

13. Signal detection means as defined in claim ly 2, 3o 4r 6 or 7 further comprising a first mixer for converting a first signal to a first intermediate frequency signal and for applying the first intermediate frequency signal as the input signal to the receiving ineanst and a plurality of second mixers interposed between the power divider and corresponding weighting means for converting the first signal to a plurality of second intermediate frequency signals for application to corresponding weighting means. local oscillator signals having similar frequencies being applied to each of the second mixers.

14. Signal detection means as defined in claim 1, 2, 3# 4, 6 or 7# further comprising a first mixer for receiving a local oscillator signal and converting a first signal to a first intermediate frequency signal and applying the first intermediate frequency signal as the input signal to the receiving means, the Intermediate frequency signal spanning the same frequency band as the weighting means.

IS. A method of detecting simultaneously received separate frequency signals in an input signal comprising subjecting representations of the input signal separately to various time or amplitude weighting to exaggerate differences between various ones and others of said separate frequency signals, 1 f 1,; passing individual exaggerated difference various ones of said separate frequency signals through separate limiters to exaggerate one separate frequency signal relative to the others in each of the various separate frequency signals, and measuring the frequency of each exaggerated one frequency signal.

16. A method as defined in claim 151 including the step of translating the input signal to intermediate frequency narrow band signals prior to subjection to said weighting.

17. A method as defined in claim 16, including the step of varying the intermediate frequency of the narrowband signals relative to a weighted frequency transfer function.

18. A method as defined in claim 15, including the step of translating the input signal to an intermediate frequency signal spanning the same frequency band as the weighting means.

19. A method as defined in claim 15 including the step of.translating the input signal to an intermediate frequency signal overlapping the same frequency band as the weighting means.

20. Signal detection means, substantially as hereinbefore described with reference to or as illustrated in any of the accompanying drawings.

21. A method of detecting simultaneously received separate frequency signals in an input signal, substantially as hereinbefore described.

Putfthed 1991 at7hePatentOffice. State House. 66/71 High Holborn. LA)rbdonWCIR47P.FurthercoplesTriay be obtained frorn Saks Branch. Unit 6. Nine Mile Point. Cwrnfelinfacb. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd, St Mary Cray. KenL