EP3114531A2

EP3114531A2 - Photonic-assisted rf spectrum scanner for ultra-wide band receivers

Info

Publication number: EP3114531A2
Application number: EP15736315.1A
Authority: EP
Inventors: Alessandro ALBERTONI; Antonio Tafuto; Marco Bartocci; Maurizio Gemma; Raffaella MAZZOLI; Daniel ONORI; Francesco LAGHEZZA; Paolo Ghelfi; Sergio PINNA; Filippo SCOTTI; Giovanni SERAFINO; Antonella Bogoni
Original assignee: Elettronica SpA
Current assignee: Elettronica SpA
Priority date: 2014-03-07
Filing date: 2015-03-06
Publication date: 2017-01-11
Also published as: WO2015132772A2; WO2015132772A3

Abstract

Disclosed herein is a photonic-assisted radio frequency spectrum scanning device for use in a receiver (100), including: a first optical waveguide arm (110) comprising, in cascade, an input end, a first electro-optical modulator (111), a tunable optical filter (112) and an output end, wherein said first electro-optical modulator (111) is designed to be connected to an antenna to receive therefrom an incoming radio frequency signal; a second optical waveguide arm (120) comprising, in cascade, an input end, a second electro-optical modulator (121), an optical delay line (122) and an output end; a mode-locked laser (101) connected, through an optical splitter (102), to the input ends of the first and second optical waveguide arms (110,120) to supply the latter with optical pulses; an optical hybrid coupler (105) connected to the output ends of the first and second optical waveguide arms (110,120) and operable to combine optical signals received from the latter to produce corresponding output optical signals; and photodetection means (131,132) connected to the optical hybrid coupler (105) to receive the output optical signals and configured to convert the latter into corresponding baseband electrical analog signals. The first electro- optical modulator (111) is configured to modulate the optical pulses supplied by the mode-locked laser (101) by means of the incoming radio frequency signal so as to carry out an optical sampling of the latter, whereby a modulated optical signal is produced, which is indicative of said optical sampling. The tunable optical filter (112) is operable to filter the modulated optical signal so as to select a portion of spectrum of the latter. The second electro-optical modulator (121) is operable to decimate the optical pulses supplied by the mode-locked laser (101). The optical delay line (122) is operable to delay the decimated optical pulses.

Description

PHOTONIC-ASSISTED RF SPECTRUM SCANNER FOR ULTRA-WIDE BAND

RECEIVERS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a photonic-assisted Radio Frequency (RF) spectrum scanner and a receiver including the same for use in Ultra-Wide Band (UWB) reception. In particular, the present invention finds advantageous, but non-exclusive, application in Electronic Warfare (EW) systems, such as Electronic Support Measure (ESM) systems and Electronic Counter-Measure (ECM) systems.

BACKGROUND ART

As is known, for ESM applications UWB receivers are employed that can be designed to cover microwave bands from 0.5 GHz up to 20 GHz, or even 40 GHz.

Nowadays, two types of receivers are mainly used for ESM applications, namely Wide-Open (WO) and superheterodyne receivers .

In particular, a WO receiver is designed so as to operate, at each time instant, in an instantaneous frequency band corresponding to its own overall operating frequency band, while a superheterodyne receiver is designed so as to operate, at each time instant, in an instantaneous frequency band that is narrower than its own overall operating frequency band.

In detail, a WO receiver typically includes:

four or more goniometric channels, each of which is

- coupled to a respective directional antenna to receive incoming RF signals, and

- configured to apply a pre-processing to the incoming RF signals so as to obtain corresponding video signals; and

a processing unit, that is

- coupled to the goniometric channels to receive the video signals, and

- configured to process the video signals so as to detect any threat and determine, for each detected threat, a corresponding Direction Of Arrival (DOA) .

More in detail, each of the goniometric channels typically includes:

a respective RF chain comprising

- a respective RF signal amplifier for amplifying the incoming RF signals, and

- respective filtering means for filtering the amplified RF signals;

a respective square-law diode detector, which is

- coupled to the respective RF chain to receive the filtered RF signals, and

- configured to output video signals proportional to the square of the filtered RF signals, i.e., proportional to power levels of the filtered RF signals; and

· a respective video signal amplifier for amplifying the video signals outputted by the respective square-law diode detector, wherein the amplified video signals are then supplied to the processing unit.

As is known, square-law diode detectors perform an incoherent detection thereby losing phase information of the signals .

Moreover, WO receivers are particularly sensitive to the presence, in the surrounding electromagnetic environment, of Continuous Waves (CWs) (i.e., electromagnetic waves of constant amplitude and frequency) and Interrupted, Continuous Waves (ICWs) (i.e., CWs modulated with an on-off keyed carrier) . In fact, WO receivers, when are illuminated by one or more CW/ICW signal (s), could be totally blinded by the latter thereby being unable to detect other pulsed signals of interest, i.e., pulsed-threat-related signals.

In particular, WO receivers typically protect their detection capability by looking beyond CW/ICW level, namely by increasing detection thresholds up to CW/ICW power level, thereby reducing their operative dynamic range so as to detect only pulsed-threat-related signals having a power level higher than the CW/ICW power level.

Instead, superheterodyne receivers are typically designed to:

· shift incoming RF signals to lower frequencies, in particular to predetermined Intermediate Frequencies (IFs), by means of mixers operatively coupled to suitable local oscillators ;

convert the analog IF signals into corresponding digital IF signals by means of Analog-to-Digital (A/D) conversion means with suitable sampling performances; and process the digital IF signals by means of digital processing means, conveniently programmable devices such as Digital Signal Processors (DSPs) and/or Field-Programmable Gate Arrays (FPGAs) .

In particular, super-heterodyne receivers perform a coherent detection by exploiting, as previously explained, mixers and local oscillators, that, as is known, introduce noise and nonlinearities thereby degrading the down- converted signals.

Thence, as previously explained, both types of receivers nowadays mainly used for, in general, UWB reception and, in particular, ESM applications (i.e., WO and superheterodyne receivers) have several drawbacks.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is, thence, that of providing a UWB receiver which can overcome, at least in part, the above cited drawbacks of the receivers nowadays used for, in general, UWB reception and, in particular, ESM applications .

This and other objects are achieved by the present invention in that it relates to a photonic-assisted radio frequency spectrum scanning device and a receiver including the same, as defined in the appended claims.

In particular, the photonic-assisted radio frequency spectrum scanning device according to the present invention includes :

a first optical waveguide arm comprising, in cascade, an input end, a first electro-optical modulator, a tunable optical filter and an output end, wherein said first electro-optical modulator is designed to be connected to an antenna to receive therefrom an incoming radio frequency signal;

· a second optical waveguide arm comprising, in cascade, an input end, a second electro-optical modulator, an optical delay line and an output end;

a mode-locked laser connected, through an optical splitter, to the input ends of the first and second optical waveguide arms to supply the latter with optical pulses;

an optical hybrid coupler connected to the output ends of the first and second optical waveguide arms and operable to combine optical signals received from the latter to produce corresponding output optical signals; and · photodetection means connected to the optical hybrid coupler to receive the output optical signals and configured to convert the latter into corresponding baseband electrical analog signals.

The first electro-optical modulator is configured to modulate the optical pulses supplied by the mode-locked laser by means of the incoming radio frequency signal so as to carry out an optical sampling of the latter, whereby a modulated optical signal is produced, which is indicative of said optical sampling.

The tunable optical filter is operable to filter the modulated optical signal so as to select a portion of spectrum of the latter.

The second electro-optical modulator is operable to decimate the optical pulses supplied by the mode-locked laser.

The optical delay line is operable to delay the decimated optical pulses.

Preferably, the mode-locked laser is operable to generate the optical pulses with a given repetition rate; the first electro-optical modulator is configured to produce the modulated optical signal so that the latter has an optical spectrum that is a periodic repetition of a spectrum of the incoming radio frequency signal with said given repetition rate; and the tunable optical filter is a periodic tunable optical filter, that has a free spectral range related to said given repetition rate and that is operable to filter the modulated optical signal so as to select a portion of the spectrum of the incoming radio frequency signal.

Preferably, the optical delay line is a tunable optical delay line operable to delay the decimated optical pulses so as to synchronize the latter with the filtered modulated optical signal reaching the optical hybrid coupler from the first optical waveguide arm.

Conveniently, the optical hybrid coupler is operable to :

combine the filtered modulated optical signal received from the first optical waveguide arm and the delayed decimated optical pulses received from the second optical waveguide arm into a corresponding combined optical signal; and

output optical in-phase and quadrature components of said combined optical signal.

Moreover, the photodetection means conveniently comprise two balanced photodetectors configured to perform a coherent balanced detection based on said optical in- phase and quadrature components, thereby converting the latter into corresponding baseband electrical analog in- phase and quadrature components.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, preferred embodiments, which are intended purely by way of example and are not to be construed as limiting, will now be described with reference to the attached drawings (not to scale), where:

Figure 1 shows timing jitter associated with a laser source;

Figure 2 shows a transfer function of an electro- optical modulator along with its associated sensitivity time control according to an aspect of the present invention;

Figure 3 schematically illustrates a UWB receiver according to a preferred embodiment of the present invention; and

Figure 4 shows some examples of signal spectra during operation of the UWB receiver shown in Figure 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The following discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the embodiments will be readily apparent to those skilled in the art, without departing from the scope of the present invention as claimed. Thus, the present invention is not intended to be limited to the embodiments shown and described, but is to be accorded the widest scope consistent with the principles and features disclosed herein and defined in the appended claims.

The present invention stems for the following observations made by the Applicant while carrying out an in-depth study on UWB receivers for ESM applications.

First of all, the Applicant has noticed that, for ESM applications, a Software-Defined Radio (SDR), wideband RF receiver should be used, which avoids problems due to noisy and nonlinear RF down-conversions, and performs digital processing directly at RF in order to enhance system's flexibility. However, bandwidth limitations of current digital devices impose fixed channelized implementation to analyze the entire RF spectrum. For this reason, and according to the relentless increasing of the operating frequencies, a significant growth in system's cost, size, weight and power requirements is inevitable.

Moreover, in order to match the requirements of a SDR receiver, a wideband Analog-to-Digital Converter (ADC) with high resolution and high dynamic range should be used, which enables RF signals to be instantly analyzed with arbitrary frequency and bandwidth by means of digital signal processing techniques. Under-sampling techniques can achieve a high precision with a reduced instantaneous bandwidth, though with intrinsic limitations due to ambiguities produced by unwanted aliased signals.

In order to avoid ambiguities related to under- sampling, and to down-convert only frequencies of interest, a tunable microwave filter should be employed. Even though the speed of modern semiconductor devices already supports RF integrated circuits with bandwidths exceeding many tens of gigahertz, a competitive filter technology to facilitate radio operations with a similar bandwidth and tunability does not exist yet.

On the other hand, the Applicant has noticed that current photonic technologies offer extremely large electro-optical bandwidths, wide and fast tunability, very low noise, high linearity, and intrinsic electromagnetic immunity, allowing to manage microwave signals with superior precision, and enabling implementation of SDR paradigm while reducing size, weight, power and costs. In particular, current microwave photonic filters have very high quality factors (up to 200.000) and extremely large tunability (in excess of 100 GHz), which make the use of these devices attractive for microwave operations up to 100 GHz .

Proceeding from the aforesaid observations, the Applicant has succeeded in conceiving and realizing the present invention, that relates to a photonic-assisted RF spectrum scanner and a receiver including the same for use in UWB reception.

In particular, the basic concept of the present invention arises from the consideration that high-sampling rate, low-jitter optical pulses can largely overcome the performance of electronic ADCs in terms of analog bandwidth and precision. In fact, the precision of the digitalization process is affected by time jitter and amplitude noise of the sampling pulses. Specifically, the noise introduced by the sampling pulses must be lower than the quantization noise. So, thanks to the use of a Mode-Locked Laser (MLL) , which has high repetition rate (up to tens of GHz), very low timing jitter (<30 femtoseconds) and low amplitude jitter (<0.03%), these requirements can be easily achieved. In this respect, Figure 1 shows timing jitter associated with a laser source.

Moreover, the 70dB expected received dynamic range required for an ESM receiver can be obtained by means of an electro-optical modulator with huge electro-optical bandwidth (up to a hundred of GHz), which enables optical sampling of wideband RF signals with carrier frequencies in the millimeter-wave band, and which is associated with a sensitivity time control that avoids strong nonlinearities at the modulator. In this respect, Figure 2 shows the transfer function of said electro-optical modulator along with its associated sensitivity time control.

Therefore, according to the present invention high- frequency wideband RF signals are optically sampled by exploiting such an electro-optical modulator along with optical pulses generated by a MLL.

Moreover, since high-precision electrical ADCs (used for the quantization of the optically sampled pulses) can manage low sampling rate, only a portion of the whole expected RF spectrum can be treated. So, according to the present invention a tunable optical filter is used to dynamically select the desired spectrum portion.

Additionally, in order to match the repetition rate of the optically sampled pulses with the electrical ADC s sampling rate, a decimation stage is introduced.

For a better understanding of the present invention,

Figure 3 shows a block diagram schematically representing an architecture of a UWB receiver (denoted as a whole by 100) according to a preferred embodiment of the present invention .

In particular, the UWB receiver 100 includes a photonic-assisted RF spectrum scanner comprising a MLL 101 connected to a first optical waveguide arm 110 and a second optical waveguide arm 120 through an optical splitter 102.

Moreover, the first optical waveguide arm 110 includes: · a first Mach-Zehnder Modulator (MZM) 111 designed to receive

- optical pulses generated by the MLL 101, and

- incoming RF signals from an antenna (not shown in Figure 3), conveniently through an anti- aliasing filter 103; and

a periodic Tunable Optical Filter (TOF) 112 connected to the first MZM 111.

Instead, the second optical waveguide arm 120 includes: a second MZM 121 designed to receive

- the optical pulses generated by the MLL 101, and

- signals generated by a Pattern Generator (PG) 104; and

an Optical Delay Line (ODL) 122 connected to the second MZM 121.

Moreover, the photonic-assisted RF spectrum scanner further comprises:

an optical hybrid coupler 105 connected to the first and second optical waveguide arms 110 and 120 to receive optical signals therefrom (in particular from the TOF 112 and the ODL 122) ; and

photodetection means, preferably two balanced photodetectors 131 and 132, conveniently a first photodiode 131 and a second photodiode 132, connected to the optical hybrid coupler 105.

Additionally, as shown in Figure 3, the UWB receiver 100 further includes:

a first filter 141 and a second filter 142 respectively connected to the first photodiode 131 and the second photodiode 132;

a first ADC 151 and a second ADC 152 respectively connected to the first filter 141 and the second filter 142; and

a Digital Signal Processor (DSP) 160 connected to the first and second ADCs 151 and 152.

During operation of the UWB receiver 100, the MLL 101 generates optical pulses with a predefined repetition rate (inset A in Figure 3 schematically illustrating an example of optical spectrum downstream of the MLL 101), and said optical pulses are supplied, as input, to both the first and second optical waveguide arms 110 and 120 through the optical splitter 102.

As for the first optical waveguide arm 110, in the first MZM 111 an incoming RF signal received from the antenna is optically sampled by the optical pulses received from the MLL 101 through the optical splitter 102. In particular, in the first MZM 111 the incoming RF signal modulates the optical pulses received from the MLL 101 so that the resulting modulated optical signal has an optical spectrum that is a periodic repetition of the spectrum of the modulating incoming RF signal with a repetition rate equal to the repetition rate of the MLL 101 (inset B in Figure 3 schematically illustrating an example of optical spectrum downstream of the first MZM 111) . Conveniently, if double-sideband modulation (DSB) is performed, the repetition rate of the MLL 101 is larger than twice the maximum acceptable RF frequency to avoid aliasing.

The modulated optical signal (i.e., the optically sampled RF signal) is then filtered by the periodic TOF 112 so as to select a spectrum portion of interest (which has, conveniently, a bandwidth such that to allow the ADCs 151 and 152 to perform the A/D conversion) . Conveniently, the periodic TOF 112 has a Free Spectral Range (FSR) related to the repetition rate of the MLL 101 (inset C in Figure 3 schematically illustrating an example of optical spectrum downstream of the periodic TOF 112) . More conveniently, the periodic TOF 112 has an FSR equal to the repetition rate of the MLL 101. Preferably, the periodic TOF 112 is a Fabry- Perot filter.

As for the second optical waveguide arm 120, the optical pulses received from the MLL 101 through the optical splitter 102 are decimated to a lower rate by the second MZM 121 on the basis of a predefined decimation- related signal provided by the PG 104 (inset D in Figure 3 schematically illustrating an example of optical spectrum downstream of the second MZM 121) . Conveniently, the PG 104 is operable to provide different decimation-related signals so as to cause the decimation performed by the second MZM 121 to be reconfigurable .

The ODL 122 delays the decimated optical pulses so as to synchronize the optical signals that reach the optical hybrid coupler 105 from the first and second optical waveguide arms 110 and 120 (i.e., the filtered modulated optical signal from the TOF 112 and said (delayed) decimated optical pulses) . Conveniently, the ODL 122 is operable to match relative phase of the two optical waveguide arms 110 and 120. Preferably, the ODL 122 is a tunable optical delay line.

The optical hybrid coupler 105 combines the filtered modulated optical signal received from the first optical waveguide arm 110 and the delayed decimated optical pulses received from the second optical waveguide arm 120 into a corresponding combined optical signal (inset E in Figure 3 schematically illustrating an example of optical spectrum resulting from combination performed by the optical hybrid coupler 105), and outputs optical in-phase (I) and quadrature (Q) components of said combined optical signal.

The first and second photodiodes 131 and 132 receive, respectively, the optical component I and the optical component Q from the optical hybrid coupler 105, perform a coherent balanced detection in order to reduce even-order inter-modulation distortion, common-mode noise terms and direct detection contributions, and, thence, output corresponding baseband electrical analog components I and Q, which are:

respectively filtered by the first filter 141 and the second filter 142; and then

respectively converted by the first ADC 151 and the second ADC 152 into corresponding baseband digital components I and Q.

Lastly, said baseband digital components I and Q are supplied to the DSP 160 to be processed by the latter.

It is worth noting that the beating of the signal's filtered replicas and the MLL' s decimated pulses provides the under-sampling of the filtered signal. This can be also seen as an optical self-homodyne receiver, where the first optical waveguide arm 110 performs an up-conversion to optical frequencies, and the second optical waveguide arm 120 provides the local oscillator for the successive baseband down-conversions that take place in the balanced photodetectors 131 and 132. In this respect, inset F in Figure 3 schematically illustrates an example of frequency spectrum of a baseband electrical analog component Q downstream of the second photodiode 132.

Preferably, since different path lengths and vibration effects in the two optical waveguide arms 110 and 120 produce fluctuations on the detected signal, optical hybrid coupler 105 is a 90-degree optical hybrid coupler so as to avoid phase noise and fading on the detected signal.

Conveniently, the first and second ADCs 151 and 152 are operatively synchronized with the MLL 101.

For a better understanding of the operation of the UWB receiver 100, Figure 4 shows from top to bottom:

an example of optical spectrum generated by the MLL 101;

an example of incoming RF spectrum;

the corresponding optical spectrum produced by the first MZM 111; and

the corresponding baseband spectrum at input to the ADC 151/152.

The advantages of the present invention are clear from the foregoing.

In particular, it is worth highlighting the fact that the architecture according to the present invention combines the functions of RF filtering, down-conversion, and analog-to-digital conversion, in a single device. This architecture enables direct detection of signals up to hundreds of GHz, with high precision over an instantaneous bandwidth of few GHz, implementing a fast scan of the spectrum, with reduced size, weight, power and costs. Moreover, the present invention allows to improve performances of a classical microwave ultra-wideband down- converter in terms of wider RF bandwidth, lower noise, and lower size, weight and power.

Additionally, the UWB receiver according to the present invention can be advantageously integrated on a single chip .

The above advantages of the present invention can be of benefit to several applications, such as:

· low-weight UWB radar systems with high electromagnetic immunity for Unmanned Aerial Vehicles (UAVs) and avionic systems;

airport and port integrated traffic control (both land-side and air-side) ;

· UWB signal intelligence (SIGINT) and Electronic

Warfare (EW) ;

frequency hopping and phase coded radar systems (such as fully adaptive radar systems for frequency and waveform diversity and Signal Intelligent Detection) ;

· dual-use UWB systems (such as UWB detection and imaging systems for radar with integrated communication functions for huge data exchange and streaming;

distributed multifunctional radar systems (Radio- over-Fiber (RoF) microwave signal distribution in Multi-In- Multi-Out (MIMO) applications or for different site locations) ; and

reconfigurable beam forming (adaptive true time delay beam forming for radar/telecom adaptive systems) .

Finally, it is clear that numerous modifications and variants can be made to the present invention, all falling within the scope of the invention, as defined in the appended claims.

Claims

1. Photonic-assisted radio frequency spectrum scanning device for use in a receiver (100), including:

· a first optical waveguide arm (110) comprising, in cascade, an input end, a first electro-optical modulator (111), a tunable optical filter (112) and an output end, wherein said first electro-optical modulator (111) is designed to be connected to an antenna to receive therefrom an incoming radio frequency signal;

a second optical waveguide arm (120) comprising, in cascade, an input end, a second electro-optical modulator (121), an optical delay line (122) and an output end;

a mode-locked laser (101) connected, through an optical splitter (102), to the input ends of the first and second optical waveguide arms (110,120) to supply the latter with optical pulses;

an optical hybrid coupler (105) connected to the output ends of the first and second optical waveguide arms (110,120) and operable to combine optical signals received from the latter to produce corresponding output optical signals; and

photodetection means (131,132) connected to the optical hybrid coupler (105) to receive the output optical signals and configured to convert the latter into corresponding baseband electrical analog signals;

wherein :

the first electro-optical modulator (111) is configured to modulate the optical pulses supplied by the mode-locked laser (101) by means of the incoming radio frequency signal so as to carry out an optical sampling of the latter, whereby a modulated optical signal is produced, which is indicative of said optical sampling;

the tunable optical filter (112) is operable to filter the modulated optical signal so as to select a portion of spectrum of the latter;

the second electro-optical modulator (121) is operable to decimate the optical pulses supplied by the mode-locked laser (101); and

· the optical delay line (122) is operable to delay the decimated optical pulses.

2. The device of claim 1, wherein:

the mode-locked laser (101) is operable to generate the optical pulses with a given repetition rate;

· the first electro-optical modulator (111) is configured to produce the modulated optical signal so that the latter has an optical spectrum that is a periodic repetition of a spectrum of the incoming radio frequency signal with said given repetition rate; and

· the tunable optical filter (112) is a periodic tunable optical filter, that has a free spectral range related to said given repetition rate and that is operable to filter the modulated optical signal so as to select a portion of the spectrum of the incoming radio frequency signal .

3. The device according to claim 1 or 2, wherein the optical delay line (122) is a tunable optical delay line operable to delay the decimated optical pulses so as to synchronize the latter with the filtered modulated optical signal reaching the optical hybrid coupler (105) from the first optical waveguide arm (110) .

4. The device according to any claim 1-3, wherein: the optical hybrid coupler (105) is operable to

- combine the filtered modulated optical signal received from the first optical waveguide arm

(110) and the delayed decimated optical pulses received from the second optical waveguide arm (120) into a corresponding combined optical signal, and

- output optical in-phase and quadrature components of said combined optical signal; and the photodetection means comprise two balanced photodetectors (131,132) configured to perform a coherent balanced detection based on said optical in-phase and quadrature components, thereby converting the latter into corresponding baseband electrical analog in-phase and quadrature components.

5. The device of claim 4, wherein the optical hybrid coupler (105) is a 90-degree optical hybrid coupler, and wherein the two balanced photodetectors comprise:

a first photodiode (131) configured to convert the optical in-phase component into a corresponding baseband electrical analog in-phase component;

a second photodiode (132) configured to convert the optical quadrature component into a corresponding baseband electrical analog quadrature component.

6. The device according to any preceding claim, further including a pattern generator (104) connected to the second electro-optical modulator (121) and operable to supply the latter with a decimation-related signal; wherein said second electro-optical modulator (121) is configured to decimate the optical pulses supplied by the mode-locked laser (101) on the basis of the decimation-related signal supplied by the pattern generator (104) .

7. The device according to any preceding claim, further including an anti-aliasing filter (103); wherein the first electro-optical modulator (111) is designed to be connected to the antenna through said anti-aliasing filter (103) .

8. The device according to any preceding claim, wherein the first and second electro-optical modulators (111,121) are Mach-Zehnder modulators.

9. The device according to any preceding claim, wherein the tunable optical filter (112) is a Fabry-Perot filter.

10. Receiver (100) comprising the photonic-assisted radio frequency spectrum scanning device claimed in any preceding claim.

11. The receiver of claim 10, further comprising:

analog-to-digital conversion means (151,152) configured to convert the baseband electrical analog signals from the photodetection means (131,132) into corresponding baseband digital signals; and

processing means (160) connected to the analog-to- digital conversion means (151,152) to receive the baseband digital signals, and configured to process the latter.

12. The receiver of claim 11, wherein:

the optical hybrid coupler (105) is operable to

- combine the filtered modulated optical signal received from the first optical waveguide arm (110) and the delayed decimated optical pulses received from the second optical waveguide arm (120) into a corresponding combined optical signal, and

- output optical in-phase and quadrature components of said combined optical signal;

the photodetection means comprise two balanced photodetectors (131,132) configured to perform a coherent balanced detection based on said optical in-phase and quadrature components, thereby converting the latter into corresponding baseband electrical analog in-phase and quadrature components; and

the analog-to-digital conversion means comprise

- a first analog-to-digital converter (151) configured to convert the baseband electrical analog in-phase component into a corresponding baseband digital in-phase component;

- a second analog-to-digital converter (152) configured to convert the baseband electrical analog quadrature component into a corresponding baseband digital quadrature component .

13. The receiver according to claim 11 or 12, further comprising filtering means (141,142) connected to the photodetection means (131,132) and configured to filter the baseband electrical analog signals; wherein the analog-to- digital conversion means (151,152) are connected to said filtering means (141,142) to receive the filtered baseband electrical analog signals and are configured to convert the latter into corresponding baseband digital signals.

14. Electronic warfare system comprising the receiver claimed in any claim 10-13.

15. Radar system comprising the receiver claimed in any claim 10-13.