WORKING DOCUMENT TOWARDS PRELIMIARY DRAFT REVISION OF RECOMMENDATION
ITU-R SM.1541, ANNEX 8

Unwanted emissions in the out-of-band domain

(Question ITU-R 211/1)

# 1 Introduction

The RR define "primary radar" as "A *radiodetermination* system based on
the comparison of reference signals with radio signals reflected from
the position to be determined".

Terrestrial primary radars operate in the radionavigation service (air
surveillance radars and navigation radars on aircraft and ships), the
meteorological aids service (weather radars), and the radiolocation
service (most other terrestrial radars). Space-based radars include
active remote sensing satellites operating in the SRS and EESS, and
other radars in the SRS.

The following limits are not applicable inside exclusive
radiodetermination and/or EESS and SRS bands, but do apply at the band
edges. The topic of primary radar emission limits within these exclusive
service bands will be the subject of further studies.

Several categories of primary radars are not included in the OoB
emission limits defined in this Annex. These include pulsed radars with
rated peak power of 1 kW or less, non-pulsed radars with rated average
power of 40 W or less, radars operating above 40 GHz, man-portable
radars, and expendable radars on missiles. These categories of radars
will also be the subject of further studies to establish the appropriate
limits.

Throughout this Annex, in all formulas, bandwidth (*Bc*, *Bs*, *Bd*,
*B*--40) is expressed in Hertz, while pulse duration and rise/fall time
are expressed in seconds.

# 2 Necessary bandwidth

\[Due to limitations in technology, the emission of radar systems can
not be limited to the necessary bandwidth in the sense of the definition
in the RR. A realistic 20 dB bandwidth can be calculated using the
formulas given in Recommendation ITU-R SM.853. However, because tThe OOB
emission masks for radar systems are referenced to the 40 dB bandwidth,
knowledge of the necessary and 20 dB bandwidths is not required for
determining the out of band emission mask.\]
$B_{N}\  = \ \frac{1\text{.}\text{79}}{\sqrt{t\  \cdot \ t_{r}}}\ \text{or}\ \frac{6\text{.}\text{36}}{t}$
$t_{r}$
$B_{N}\  = \ \frac{1\text{.}\text{79}}{\sqrt{t\  \cdot \ t_{r}}}\  + \ 2\ B_{c}$
$B_{N}\  = \ \frac{1\text{.}\text{79}}{\sqrt{t\  \cdot \ t_{r}}}\  + \ 2\ B_{c} + \ B_{s}$
$B_{N}\  = \ 2\ B_{d}$ (38)

## 2.3 Typical values of necessary bandwidth

Table 20 below shows typical necessary bandwidths, followed by the
ranges of the necessary bandwidth values, for four types of radars.

TABLE 20

# 

# 3 Formulas for the 40 dB bandwidth

A major difficulty in establishing general OoB domain emission limits
for primary radars is the diversity of systems and transmitted
waveforms. OoB domain emission limits for primary radars are based on
the 40 dB bandwidth of the spectrum of the transmitted waveform.

For radars with multiple waveforms, the 40 dB bandwidth should be
calculated for each individual waveform and the maximum 40 dB bandwidth
obtained shall be used to establish the shape of the emission mask.

# 

# . The following formulas for the 40 dB bandwidth (*B*--40) of primary radar transmitters have been established.

## 3.1 Unmodulatded pulse, spread spectrum, and coded pulse radars

For unmodulated pulse radars spread spectrum, and coded pulse radars,
the bandwidth is the lesser of:

$B_{- \text{40}}\  = \ \frac{K}{\sqrt{t\  \cdot \ t_{r}}}\ \text{or}\ \frac{\text{64}}{t}$
(39)

where the coefficient *K* is 6.2 for radars with output power greater
than 100 kW and 7.6 for lower‑power radars and radars operating in the
radionavigation service in the 2 900-3 100 MHz and

9 200-9 500 MHz bands[^1]. The latter expression applies if the rise
time *t~r~* is less than about 0.0094*t* when *K* is 6.2, or about
0.014*t* when *K* is 7.6.

For frequency hopping radars:

$B_{- \text{40}}\  = \ \frac{K}{\sqrt{t\  \cdot \ t_{r}}} + B_{s}$ (40)

B~s~ is the maximum range over which the carrier frequency will be
shifted.

## 3.2 FM pulse radars

For FM-pulse radars, the 40 dB bandwidth is:

$B_{- \text{40}}\  = \ \frac{K}{\sqrt{t\  \cdot \ t_{r}}} + 2\ \left( B_{c} + \frac{A}{t_{r}} \right)$\[TBD :
Refer to JRG 71, Sec. 2.2\] (41)

.

For FM-pulse radars with frequency hopping[^2]:

$B_{- \text{40}}\  = \ \frac{K}{\sqrt{t\  \cdot \ t_{r}}} + 2\ \left( B_{c} + \frac{A}{t_{r}} \right) + B_{s}$\[TBD :
Refer to JRG 71, Sec. 2.2\] (42)

$B_{- \text{40}}\  = \ \frac{K}{\sqrt{t\  \cdot \ t_{r}}} + B_{s}$ 3.3
Phase coded pulse radar

\- to be developed-

## 3.4 CW radars

For un-modulated CW radars, the 40 dB bandwidth is:

$B_{- \text{40}}\  = \ 0\text{.}\text{0003}\ F_{0}$ (43)

3.5 FM/CW radars

For FM/CW radars:

$B_{- \text{40}}\  = \ 0\text{.}\text{0003}\ F_{0}\  + \ 2\ B_{d}$\[TBD :
Refer to JRG 69 and JRG 70\] (44)

In equations (43) and (44), *F*0 is the operating frequency.

OoB masks

## 

## 

## Figure 26 shows the OoB mask for primary radars, specified in terms of psd and expressed in units of dBpp. The mask rolls off at 20 dB per decade from the 40 dB bandwidth to the spurious level specified in RR Appendix 3[^3]. Figure 27 shows the OoB mask for primary radars, specified in terms of psd and expressed in units of dBpp. The mask rolls off at 40 dB per decade from the 40 dB bandwidth to the spurious level specified in RR Appendix 3. The 40 dB bandwidth can be offset from the frequency of maximum emission level. The \[necessary bandwidth (RR No. 1.152) and preferably, the\] overall occupied bandwidth (RR No. 1.153), should be contained completely within the allocated band.

\[Editor's Note: Determination of the appropriate 40 dB bandwidth
equation, including implementation factors, is critical to determining
the applicability of a roll-off, ranging from 20 to 40 dB per decade.
The applicability of roll-off requirements to various radar types is
TBD. Figures 26 and 27 may need to be modified to show the spurious
level as defined in RR Appendix 3.\]

Figure 26

OoB mask for primary radars

![](media/image1.wmf){width="5.375in" height="3.65625in"}

## 

## 

Figure 27

OoB mask for radars

![](media/image2.wmf){width="5.375in" height="3.65625in"}

## 

## 

## 

## 

## 5 Boundary between the OoB and spurious domains

According to *recommends* 2.2 and RR Appendix 3, the spurious domain
generally begins at a frequency separation equal to 250% of the
necessary bandwidth, with exceptions for certain kinds of systems,
including those with digital or pulsed modulation. However, it is
difficult to apply the general boundary concept of 250% of the necessary
bandwidth to primary radar stations in the radiodetermination and other
services, such as the meteorological aids service, SRS and EESS.

For primary radar stations, the boundary between the OoB and spurious
domains is defined as at the frequency where the OoB domain emission
limits defined herein are equal to the spurious limit defined in [Table
II of RR Appendix 3]{.mark}.

# 

$5\ B_{- \text{40}}\  = \ 2\text{.}5\ \alpha\ B_{N}\  \rightarrow \ \alpha\  = \ 2\ \frac{B_{- \text{40}}}{B_{N}}$
6 Measurement techniques

The most recent version of Recommendation ITU-R M.1177 provides guidance
regarding the methods of measuring OoB domain emissions from radar
systems.

**ANNEX 5**

WORKING DOCUMENT TOWARDS PRELIMIARY DRAFT REVISION OF RECOMMENDATION
ITU-R SM.853

Necessary Bandwidth

**ANNEX 6**

WORKING DOCUMENT TOWARDS PRELIMIARY DRAFT REVISION OF RECOMMENDATION
ITU-R SM.1539

Variation of the boundary between the out-of-band and spurious domains\
required for the application of Recommendations ITU-R SM.1541\
and ITU‑R SM.329

(Question ITU-R 211/1)

The following are proposed changes to Item 3.3

## 3.3 Primary radars in the radiodetermination and other services

According to *further recommends* 2.3 of Recommendation ITU-R SM.329,
the spurious domain emission generally begins at a frequency separation
equal to 250% of the necessary bandwidth, with exceptions for certain
kinds of systems, including those with digital or pulsed modulation.
RR Appendix 3 includes similar provisions. However, it is difficult to
apply the general boundary concept of 250% of the necessary bandwidth to
primary radar stations in the radiodetermination and other services,
such as the meteorological aids service, the space research service, and
the Earth exploration-satellite service.

For the case of primary radar systems, the detailed definition of the
OoB/spurious domain boundary is contained in Annex 8 of Recommen­dation
ITU-R SM.1541.

# 

[^1]: ^3^ These coefficients, *K* = 6.2 or 7.6 and 64, are related to
    theoretical values that would prevail in the case of constant
    frequency trapezoidal and rectangular pulses, respectively. Also, in
    the case of the trapezoidal pulses, the coefficient *K* has been
    increased somewhat to allow for implementing output device
    characteristics. For ideal rectangular pulses, the spectrum falls
    off at 20 dB per decade leading to a 20 dB bandwidth of 6.4/*t* and
    a 40 dB bandwidth ten times as large, i.e. 64/*t*. To discourage the
    use of pulses with abrupt rise and fall times, no margin is allowed.
    The spectra of trapezoidal pulses fall off firstly at 20 dB per
    decade and then ultimately at 40 dB per decade. If the ratio of rise
    time to pulse width exceeds 0.008 the 40 dB points will fall on the
    40 dB per decade slope, in which case the *B*--40 would be:

    $$\frac{5\text{.}7}{\sqrt{t \cdot t_{r}}}$$

    Allowance for unavoidable imperfections in implementation requires
    that the mask be based on values of at least:

    $$\frac{6\text{.}2}{\sqrt{t \cdot t_{r}}}\ \text{or}\ \frac{7\text{.}6}{\sqrt{t \cdot t_{r}}}$$

    depending upon the category of radar.

[^2]: ^5^ Equations (41) and (42) yield the total composite *B*--40
    bandwidth of a frequency hopping radar as if all channels included
    within *Bs* were operating simultaneously. For frequency hopping
    radars, the OoB emission mask falls off from the edge of the 40 dB
    bandwidth as though the radar were a single frequency radar tuned to
    the edge of the frequency hopping range.

[^3]: ^6^ RR Appendix** **3 specifies a spurious attenuation of
    43  10 log* *(*PEP*), or 60 dB, whichever is less stringent. (PEP:
    peak envelope power.)