**JRG-25**

**August 3, 2004**

**ITU-R JRG 1A-1C-8B**

**Report of the First Meeting**

**July 13-15, 2004**

The first meeting of the Joint Rapporteurs Group (JRG) 1A-1C-8B was held
on 13-15 July 2004 in Geneva Switzerland. There were 24 participants
representing eight administrations at the first meeting of the JRG.

The meetings of the JRG 1A-1C-8B have the aim of presenting proposals to
the ITU-R for the development of unwanted emission limits in the
out-of-band (OOB) domain of primary radar systems at future ITU-R
Administrative Conferences. Specifically, the task before the JRG
concerns the feasibility of adopting more stringent requirements for
radars with regards to the "roll-off" of out-of-band emissions from the
--40 dB bandwidth. This is a significant and important issue for the
world-wide radar community.

The terms-of-reference for the JRG tasked the group to:

1\. review the current ITU-R limits for unwanted emissions in the
out-of-band domain contained in Annex 8 of Recommendation ITU-R SM.1541,
and assess the feasibility of establishing guidance to promote more
effective and efficient use of the spectrum by radar stations in the
radiodetermination service. Propose draft revisions to ITU-R SM.1541 as
appropriate;

2\. conduct studies on the boundary between the out-of-band and spurious
domains of primary radars using magnetrons taking into consideration
ITU-R Recommendation 75 (WRC-03);

3\. review and propose modifications to other ITU Recommendations and
Reports associated with radar unwanted emissions as appropriate; and

4\. make efforts to conduct the work of JRG 1A/1C/8B by correspondence
to the extent possible.

There were twenty-one contributions to the first meeting of the JRG.
These contributions were directed towards addressing items 1 and 2 of
the JRG terms-of-reference. Upon completion of the introductions and
discussions of the contributions, the JRG reached a consensus on the
following changes to the JRG Work Program (see Attachment 1):

1.  update the milestones;

2.  add specific areas requiring studies; and

3.  identify future meeting dates/locations and aims.

Several of the contributions to the JRG addressed the emission
characteristics of maritime radars. It is a requirement of the
International Convention for the Safety of Life at Sea (SOLAS) published
by the International Maritime Organization (IMO) that ships to which the
Convention applies carry radar. There are worldwide 70,000 such radars
using magnetrons which assist in the safety of persons and the ship, and
more than a million smaller magnetron-based radars in service.
Indications from these initial studies show that many such radars are
unable to meet the existing requirement of SM.1541 for short pulses, and
further work is directed towards finding solutions whereby the
20 dB/decade requirement could be met as well as work that seeks means
whereby the 40 dB/decade might be met. However, concerns were raised
that the status of this technology is unlikely to change within the time
scale of the JRG work programme. See Attachment 2 on Draft Contribution
to the report of the JRG related to maritime and mobile radars using
magnetrons.

Related to item three of the JRG terms-of-reference, it was the
consensus of the JRG that there was no need for another ITU-R
recommendation pertaining to the measurement of unwanted emissions of
primary radars using magnetrons as indicated in the further decides of
Question ITU-R 230/1. It was preferred that there only be a single ITU-R
recommendation addressing unwanted emission measurements for all types
of radar output devices. It was the views of the JRG that it may be
necessary to make revisions to Recommendation ITU-R M.1177, Techniques
for measurement of radar unwanted emissions. It was agreed that any
changes to Recommendation ITU-R M.1177 would be addressed by Working
Party 8B. Related to the necessary bandwidth formulas contained in
Recommendation ITU-R SM.1541, Annex 8; it was the views that it may be
necessary for the JRG to propose revisions to Recommendations ITU-R SM.
853 and SM.1138. Also, it was the view of the JRG that it may be
necessary to propose a change to the definition of rise time, t~r~, in
Recommendations ITU-R M.1177 and SM.1541.

Attachment 3 contains some suggested changes made at the meeting to
Recommendation ITU-R SM.1541.

**Contacts:** Jian Wang

Co-chairman, Working Party 1A

Thomas Hasenpusch

Acting Co-chairman, Working Party 1C

Robert Hinkle

Co-Chairman, Working Party 8B

## ATTACHMENT 1

## Revised work program

#### JRG 1A-1C-8B

Background

Unwanted emission masks in the out-of-band domain for primary radar
systems are contained in Recommendation ITU-R SM.1541, Annex 8. The
ITU-R out-of-band emission masks for primary radars systems are intended
to recommend an acceptable degree of electromagnetic compatibility among
radar systems, and between such systems and those of other radio
services sharing the frequency spectrum.

In the development of the out-of-band emission masks for primary radar
systems, it was the view of several administrations that there was a
need to further investigate the state-of-the-art radar systems and their
ability to suppress unwanted emissions. This review of radar unwanted
emissions in the out-of-band domain is to be completed by 2006. See
Recommendation ITU-R SM.1541, Annex 8, Note 3. The outstanding issue
concerns the "design objectives" highlighted in this document. This
"design objective" concerns the possibility of making more stringent the
requirement for radars with regard to the "roll-off\" of out‑of-band
(OOB) emissions.

The outcome of this study may result in revisions to Recommendation
ITU-R SM.1539, which addresses the boundary between the out-of-band and
spurious domains, and Recommendation ITU‑R SM.1541, which addresses
out-of-band emissions domain.

Pursuant to initiating this study, Working Party 8B revised Question
202/8 to provide guidance to administrations in conducting their
investigation.

Objectives

The objectives of this work programme are to:

a)  Review the current ITU-R limits for unwanted emissions in the
    out-of-band domain contained in Annex 8 of Recommendation ITU-R
    SM.1541, and assess the feasibility of establishing guidance to
    promote more effective and efficient use of the spectrum.

Approach

In order to accomplish the above objectives, the following tasks will be
undertaken:

a\) Develop a software tool that will provide current ITU-R emission
masks and alternative emission masks for comparison with measured radar
emission data.

b\) Identify, through measurements, characteristic radar emission
spectra considering such parameters as: waveforms (e.g. pulse shape and
modulation); types of output devices; RF filter technologies; and
antenna types.

c\) Analyse the measured emission characteristics to assess the
feasibility of establishing more spectrum efficient emission masks.

d\) Discuss draft revised emission masks, and identify state-of-the-art
capabilities which may allow radars to operate more efficiently while
recognizing economic impacts and mission requirements to achieve
efficient and effective operation.

e\) Report the results of these studies to Working Party 1A, 1C and 8B.

Milestones

Completion of the aforementioned approach should correspond to the
following task milestone dates:

a\) February 2004 (version 2 provided)\
Revisions to the program will be issued as appropriate.

b\) March 2005

c\) September 2005

d\) September 2005

e\) August 2006

Specific areas requiring studies

The following areas have been identified as key areas in which studies
are necessary in order to assess the feasibility of the "design
objective" of Recommendation ITU-R SM.1841, Annex 8.

1.  Review the --20dB bandwidth (necessary bandwidth) and --40 dB
    bandwidth formulas for FM-pulsed modulated and FMCW waveforms,
    including non-linear FM applicable across a wide range of
    time-bandwidth products. Analysis and measurements have shown that
    the current formulas FM-pulsed modulated waveforms are generous for
    large time-bandwidth products (compression ratios) (See Documents
    JRG-12, JRG-13, JRG-19 and JRG-21). Analysis indicates that the
    current --40 dB bandwidth formula for FMCW modulated waveforms may
    not be representative for all cases (see Document JRG-7).

2.  Determine if current formulas for the --20dB bandwidth (necessary
    bandwidth) and --40 dB bandwidth apply for waveforms such as stepped
    chirp, phase-coded pulses (MSK/GMSK, QPSK and Taylor quadriphase),
    step FM, multi-carrier radars and develop new formulas as
    appropriate.

3.  Investigate the --40dB bandwidth formula for non-FM pulsed radars
    using magnetrons with low pulse width to rise time ratio (see
    documents JRG-7, JRG-16).

4.  Identify through measurements the achievable roll-off from the --40
    dB bandwidth for radars with solid state output devices as a
    function of the class of amplification.

5.  Investigate the feasibility of implementing filters between solid
    state Transmit-Receive (T/R) Modules and the antenna elements. These
    studies should consider the type of platform (e.g. ground based,
    ship borne, airborne, space borne).

6.  Review the definition of rise time (Note 1 of Annex 8 of Rec. ITU-R
    SM.1541).

7.  Determine the characteristics of airborne radar systems.

8.  For radars using magnetrons, acquire additional emission spectrum
    data, especially for S Band radars, and identify factors that could
    affect the emission spectrum (e.g. temperature).

### Meeting dates / locations and aims

1.  First quarter 2005 / United Kingdom

    a.  Further data to validate the "design objectives"

    b.  Outline final report

2.  Third quarter 2005 / U.S.

    a.  Further structuring of final report

    b.  First proposed revision of Rec. ITU-R SM.1541

3.  First quarter 2006 / Germany

    a.  Complete draft of final report

    b.  Finalize proposed revision of Rec. ITU-R SM.1541

4.  Third quarter 2006 / Geneva

    a.  Agree on final report including proposed revision of Rec. ITU-R
        SM.1541

**ATTACHMENT 2**

**Contribution to the Report of the 1^st^ meeting -- 13/15 July 2004 --
Geneva**

**Mobile maritime radars using magnetrons**

## 

**Background**

The ITU-R adopted in 2001 Recommendation SM.1541. It contains in Annex 8
the requirements for OOB domain emissions for primary radars. In
Recommendation SM.1539 the requirements for the boundary between OOB
domain and the spurious domain emissions are described.

RR Appendix 3 contains Category A requirements for spurious emissions
for radiodetermination systems and these were applicable to radars
installed after 1 January 2003. At WRC-03 in Annex 1 of Appendix 3 --
Determination of the boundary between the out-of-band and spurious
domains -- in Paragraph 3 the following text was agreed.

" .....Further guidance on the boundary between the out-of-band and
spurious domains for primary radar is provided in the most recent
version of Recommendation ITU-R SM.1541."

It should be noted that SM.1541 has not been incorporated by reference
into the Radio Regulations.

Annex 8 of SM.1541 calls for a roll-off of the OOB domain emissions at
20 dB/decade for primary radars.

Since 1 January 2003 the mobile maritime radar industry has been working
to meet this roll-off requirement.

Annex 8 of SM.1541 also contains a 'design objective' for future radars
of 40 dB/decade.

It is a requirement of the International Convention for the Safety of
Life at Sea (SOLAS) published by the International Maritime Organization
(IMO) that ships to which the Convention applies carry radar. There are
worldwide 70,000 such radars using magnetrons which assist in the safety
of persons and the ship. These radars operate under extreme
environmental conditions, are required to have high reliability with
minimum maintenance and a 20-year life. Any design changes considered
for such radars should reflect the operational requirement.

In addition, there are more than a million smaller magnetron-based
radars in service.

**Input documents**

## [JRG 7, 14, 16, 17, 19, 20 and 21]{.underline}

Consideration of the input documents, in particular those containing
measured data of current technology for such radars has shown that many
such radars are unable to meet the existing requirement of SM.1541 and
current work is directed towards finding solutions whereby the
20 dB/decade requirement could be met as well as feasibility work that
seeks means whereby the 40 dB/decade might be met.

The documents that contain measured data (14, 16, 17, and 19) indicate
some samples of laboratory work beyond state of the art technology.
**[The status of this technology is unlikely to change within the time
scale of the JRG work programme.]{.underline}**

Various areas of further study have been identified which will continue
during and beyond the JRG time scale, and these are included in the work
programme.

To meet the current requirement, various possible components of a future
radar system, are being investigated, and work on improving the
magnetron emissions is continuing.

An example of such components is the use of filters. The problems in
their use in a maritime environment are extensive. They include power
loss, reduction in receiver sensitivity and adverse effects on the
magnetron emissions. All these affect detection capability. This is more
significant at this time as IMO has completed a revision of radar
performance standards that include a requirement for a more stringent
detection capability. In addition, there are many physical problems e.g.
size and weight, large costs involved, problems associated with
magnetron frequency drift over time, the impracticality of replacing
magnetrons whilst at sea, coupled with then a need to readjust filter
characteristics. (See also JRG-7 Page 78 sections A 5.3 and A 5.4)

With regard to magnetron radars operating at short pulse, shortening the
rise time can reduce occupied bandwidth in some systems, but in most
cases state of the art radars already approach the practical limit, for
optimum stability and minimum spurious emissions.

In summary, the documents considered using state of the art technology,
show that further work is required to guarantee meeting the 20 dB/decade
in 100% of cases, and very few radars would be capable of meeting the
design objective.

**Note 1 -** It is recognized that magnetron based radar equipment
similar to that used in the mobile maritime radar environment may also
be in use in airborne radars e.g. weather radars, and obstacle avoidance
radars and fixed locations on land e.g. ASMI radars at airports.

## Current findings

It is unlikely that state of the art technology will significantly
change during the lifetime of the JRG.

Future work, some of which has been identified here, may lead to a
greater assurance that all mobile maritime radars would meet the current
requirement.

Many other studies will need to be identified and completed successfully
before there is a possibility that a future design objective could be
met.

## Preliminary proposal

Mobile maritime radars using magnetrons may need to be excluded from the
design objective in this current proposal for the revision of SM.1541.
The proposed revision could include the reasons for the exclusion and
retain the need for further study for this class of radars.

# ATTACHMENT 3

# Comments on Rec. ITU-R SM.1541-1 Annex 8

[2 (first sentence)]{.underline}

Delete.

[2 (whole topic)]{.underline}

Replace by a reference to SM.1138 and SM.853, but only after making sure
all information is contained in these recommendations and they are up to
date. If this is the case: revise these other recommendations.

Alternatively: keep it also in SM.1541 because it concentrates all
information in one document and it's not too long.

[2.2 (headline)]{.underline}

Replace "other modulations" with an extra headline for each modulation.

Provide additional information on other modulations not covered here.

[3 (and whole rest of annex 8)]{.underline}

Place extra sub-headlines for each type of modulation. Agree on one term
for "unmodulated" and "non-FM" radars throughout the document.

[3.1 (formulas)]{.underline}

Specify the shorter of rise and fall times instead of rise time only.