# JRG 1A-1C-8B -- Radar Out-of-Band Emissions

# Drafting Group JRG-DG1 -- FMCW Modulated Waveforms

# Work Program

## Introduction

At its' May 2005 meeting the JRG 1A-1C-8B resolved that a drafting group
be formed to review the out-of-band emission limits given in ITU-R
SM.1541 for primary radars using FMCW waveforms. This drafting group is
to operate entirely via email correspondence and report back to the next
JRG 1A‑1C‑8B meeting with recommended changes to ITU-R SM.1541 (if any).

## Terms-of-Reference

1.  Review the current necessary bandwidth (-20 dB) and --40 dB
    bandwidth formulas for FMCW modulated waveforms; and, if
    appropriate, recommend more representative formulas. Priority 1.

2.  Clarify the definition of frequency deviation (Bd) for FMCW
    waveforms. Priority 1.

3.  Review the feasibility of the application of a 40 dB/decade roll-off
    from the --40 dB bandwidth for practical combinations of waveform
    parameters. Priority 2.

Priority 1 Milestone: December 15, 2005

Priority 2 Milestone: June 15, 2006

Relevant JRG Contributions: JRG-7, page 158, and JRG-39

## Membership

The following administrations/sector members and people have expressed
interest in participating in the work of Drafting Group JRG-DG1:

+--------------+-------------------+-----------------------------------+
| **Admi       | ### Name          | **Email Address**                 |
| nistration** |                   |                                   |
+==============+===================+===================================+
| Australia    | Leith Mudge\*     | [leith.mudge@defence.gov.au](m    |
|              |                   | ailto:Leith.Mudge@defence.gov.au) |
+--------------+-------------------+-----------------------------------+
| Australia    | Gordon Frazer     | <g                                |
|              |                   | ordon.frazer@dsto.defence.gov.au> |
+--------------+-------------------+-----------------------------------+
| Australia    | Rod Barnes        | <rod.barnes@defence.gov.au>       |
+--------------+-------------------+-----------------------------------+
| UK           | Andy Stove        | <andy.stove@uk.thalesgroup.com>   |
+--------------+-------------------+-----------------------------------+
| USA          | Larry Brunson     | <lbrunson@ntia.doc.gov>           |
+--------------+-------------------+-----------------------------------+
| USA          | Robert Sole       | <rsole@ntia.doc.gov>              |
+--------------+-------------------+-----------------------------------+
| USA          | Joseph Thomason   | <joe.thomason@nrl.navy.mil>       |
+--------------+-------------------+-----------------------------------+
| USA          | Robert Hinkle     | rhinkle@toad.net                  |
+--------------+-------------------+-----------------------------------+
| USA          | Serafin Rodriguez | serf@radar.nrl.navy.mil           |
+--------------+-------------------+-----------------------------------+
| The          | Abraham van Den   | <abrah                            |
| Netherlands  | Berg              | am.vandenberg@nl.thalesgroup.com> |
+--------------+-------------------+-----------------------------------+

\* Lead contact

Please contact the lead contact (Leith Mudge, Australia,
<Leith.Mudge@defence.gov.au>) with names and email addresses of any
others interested in participating in the work of this drafting group.

## Work Program

1.  Resolve definition of necessary bandwidth to be adopted.

> Background:
>
> Within the JRG 1A-1C-8B the common definition of necessary bandwidth
> that appears to have been adopted is the ‑20 dB bandwidth as this is
> referred to in ITU-R SM.1541 for pulsed waveforms. Recommendations
> ITU-R SM.853 and SM.1138 address necessary bandwidth formula. It was
> the view of the JRG, that it may be necessary for the JRG to propose
> revisions to recommendations ITU-R SM.853 and SM.1138 (JRG-25, Report
> of the First meeting). Currently, neither of the ITU-R Recommendations
> contain formula for FMCW waveforms. The NTIA RSEC (from which the
> ITU-R formulas for FMCW have a heritage) also defines the necessary
> bandwidth as the ‑20 dB bandwidth. However the Radio Regulations give
> the following definition of necessary bandwidth:
>
> *For a given class of emission, the width of the frequency band which
> is just sufficient to ensure the transmission of information at the
> rate and with the quality required under specified conditions.* (RR
> No. 1.152)
>
> The Radio Regulation definition appears to be the primary definition
> and the use of the ‑20 dB bandwidth appears to be what is appropriate
> for pulse waveforms. However for FMCW waveforms this is not
> necessarily the case.

2.  Clarify the definition of frequency deviation (*B~d~*) for FMCW
    waveforms.

> Background:
>
> At the May 2005 meeting of the JRG 1A-1C-8B there was some confusion
> as to how to interpret the definition of frequency deviation (*B~d~*)
> given in ITU-R SM.1541. The ITU-R SM.1541 definition is "...the
> maximum frequency deviation." This could be interpreted as either the
> frequency deviation from the centre frequency or the whole range of
> the frequency shift.

3.  Establish a suitable parameterised model for the bounds of the
    emission spectrum of a linear FMCW waveform.

> Background:
>
> Two JRG contributions(JRG-7, page 158; and JRG-39) have established
> that the current formulas for the necessary bandwidth (*B~N~*) and the
> --40 dB bandwidth (*B~-40~*) given in ITU-R SM.1541 result in
> unrealistically narrow values. This was based on both theoretical and
> practical considerations. This effect was particularly pronounced for
> the waveform parameter combinations used in long wavelength radars. In
> order to establish better formulas, a suitable parameterised model
> needs to be established for the bounds of the emission spectrum of a
> linear FMCW waveform. This model could then be used to establish be
> formulas for *B~N~* and *B~-40~*. Preliminary analysis suggests that
> some form of sweep-by-sweep amplitude modulation or finite flyback (or
> equivalent spectrum limiting technique) will need to be maintained in
> order to produce *B~N~* and *B~-40~* values that make efficient use of
> the available radio spectrum. The model should therefore be capable of
> modelling the effects of these commonly used spectrum limiting
> techniques. A number of submissions to the JRG 1A-1C-8B have indicated
> the success of the 'Newhouse method' documented in Report 837 (JRG-10)
> for establishing a parameterised model for the bounds on a pulsed
> linear FM radar spectrum. A single linear FMCW sweep could be
> considered a limiting case of this model and it may therefore be
> possible to adapt the 'Newhouse method' for modelling a linear FMCW
> spectrum.

4.  Through simulations and/or measurements establish the ability of the
    parameterised model established in step above to correctly model the
    emission spectrum of linear FMCW waveforms.

> Background:
>
> Firstly through simulation and later through measurements the
> parameterised model established in step above should be compared with
> the 'real' spectrum of a linear FMCW waveform. These
> simulations/measurements should also include the effects of common
> spectrum limiting techniques (i.e. sweep-by-sweep amplitude modulation
> and finite flyback). The simulation may be performed using analytical
> equations derived by performing a Fourier Transform of an equation
> representing the time domain linear FMCW waveform or by numerical
> simulation using an FFT model (i.e. the periodogram method).
> Measurements should be made using the guidance provided in ITU-R
> M.1177. The output of this step will be a level of confidence that the
> parameterised model adequately represents the 'real' spectrum of a
> linear FMCW waveform.

5.  Use the parameterised model established in steps 3 and above to
    derive more representative formulas for *B~N~* and *B~-40~*.

> Background:
>
> At this stage of the process the decision will have to be made as to
> whether the formula for *B~‑40~* should be set such that the use of a
> linear FMCW waveform is fully legitimised or it should be set such
> that some form of spectrum limiting technique is needed. There is a
> need for an acceptable compromise to be reached that balances the need
> to conserve spectrum and reduce interference with the need to be able
> to utilise that spectrum for radar with acceptable performance. There
> may need to also be some consideration of the cost implications of
> these measures. It may be that the formula for *B~-40~* can be
> fashioned such that with a modest use of a spectrum limiting technique
> (e.g. sweep-by-sweep amplitude modulation) the resultant waveform can
> comply with the proposed 40 dB/decade roll-off.

6.  Review the feasibility of the application of a 40 dB/decade roll-off
    from *B~-40~* (derived from the new formula) for practical
    combinations of waveform parameters.

> Background:
>
> JRG-39 established that the 'natural' roll-off rate for out-of-band
> emissions for linear FMCW waveforms is 20 dB/decade without the use of
> some form of spectrum limiting technique. This would suggest that an
> exemption from any decision to adopt 40 dB/decade in ITU-R SM.1541
> should be given for FMCW waveforms. However if the method outline in
> the background section of step above is judged to be practical and
> adopted then FMCW waveforms would not require such an exemption. This
> step would involve the gathering of representative combinations of
> waveform parameters for real radars (particularly those operating at
> long wavelengths) and using simulations and/or measurements to
> determine the feasibility of compliance with the 40 dB/decade
> roll-off.