**JRG-68**

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

**4^th^ Meeting -- Mainz Germany -- 13^th^-15^th^ November 2006**

**[Spectrum emission measurements of various radars]{.underline}**

**[(Germany)]{.underline}**

# Introduction

The Joint Rapporteurs Group JRG-1A-1C-8B has to investigate the
possibility of introducing a more stringent emission mask for the
out-of-band domain of radar emissions.. This document aims to support
the work of this group by providing spectrum measurements performed in
Germany on a number of magnetron based and one clystron based radar
systems.

# Measured radars and their parameters

Measurements were made on the following radars:

1.  Fixed weather radar in Hamburg on 5919 MHz, using a coaxial
    magnetron

2.  Fixed weather radar in Hannover on 5639 MHz, using a coaxial
    magnetron

3.  Fixed maritime radar in Bremerhaven on 8959 and 9141 MHz, using a
    coaxial magnetron

4.  Fixed aeronautical radar at Deister on 1259 and 1345 MHz, using a
    clystron

Radars 3 and 4 consist of two transmitters on different frequencies
using a common antenna via directional couplers. Since they have two
different output devices with different characteristics they are
regarded as two radars and numbered radar 3a, 3b, 4a and 4b.

The following is a summary of the radar parameters relevant for this
project:

+---------+--------+---------+---------+---------+---------+---------+
| **Para  | *      | **Radar | **Radar | **Radar | **Radar | **Radar |
| meter** | *Radar | 2**     | 3a**    | 3b**    | 4a**    | 4b**    |
|         | 1**    |         |         |         |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| Re      | M.1638 | M.1638  | M.      |         |         |         |
| ference | A      | A       | \[8B\]  |         |         |         |
|         |        |         | S1      |         |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| Fr      | 5619   | 5639    | 8959.2  | 9141.2  | 1259    | 1345    |
| equency | MHz    | MHz     | MHz     | MHz     | MHz     | MHz     |
+---------+--------+---------+---------+---------+---------+---------+
| Radar   | EEC    | Gem     | AEG     |         | DASA    |         |
| Manuf   | (USA)  | atronic | Tel     |         | (GER)   |         |
| acturer |        | (GER)   | efunken |         |         |         |
|         |        |         | (GER)   |         |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| Output  | C      | Coaxial | Coaxial |         | C       |         |
| device  | oaxial | Ma      | mag     |         | lystron |         |
|         | Mag    | gnetron | netron\ |         |         |         |
|         | netron |         | CPI     |         | T       |         |
|         |        | Varian  | VMX2037 |         | hompson |         |
|         | Varian | S       |         |         | 2068A   |         |
|         | SF     | FD-341A |         |         |         |         |
|         | D-373A |         |         |         |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| Peak    | 250 kW | 250 kW  | 30 kW   | 30 kW   | 2500 kW | 1585 kW |
| Power   |        |         |         |         |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| Pulse   | 930 ns | 852 ns  | 130.6   | 130.2   | 2.0 µs  | 2.0 µs  |
| length  |        |         | ns      | ns      |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| Ri      | 51 ns  | 125 ns  | 13.6 ns | 14.4 ns | 150 ns  | 150 ns  |
| se/fall |        |         |         |         |         |         |
| time    |        |         |         |         |         |         |
+---------+--------+---------+---------+---------+---------+---------+
| PRF     | 500 -- | 500 --  | 2400 Hz | 2400 Hz | 6 x 400 | 6 x 400 |
|         | 1200   | 1200 Hz |         |         | Hz\     | Hz\     |
|         | Hz     |         |         |         | 8 x 500 | 8 x 500 |
|         |        |         |         |         | Hz      | Hz      |
+---------+--------+---------+---------+---------+---------+---------+

# Measurement setup and procedure

Radar 1 was equipped with a filter to suppress sideband emissions.
Measurements were taken after this filter, directly before the rotary
joint.

Radar 2 was also equipped with a filter. Measurements were taken both in
front of and after this filter. This enables to verify the effect of the
filter in the results.

Radar 3 and 4 were measured at the output of directional couplers,
before the combiner. Decoupling between both transmitters was about 50
dB for radar 3 and 65 dB for radar 4, so that emissions less than 50 /
65 dB below the spectrum of the transmitter under test could originate
from the other transmitter. For radar 4, pulses from both transmitters
had an offset of 4.3 µs, so that at no time both transmitters were up
simultaneously.

The spectrum was measured with an R&S FSIQ40 spectrum analyzer.

The pulse parameters were measured with a 1 GHz Infinium oscilloscope
54835A in conjunction with a broadband pulse detector.

![](media/image1.png){width="5.010416666666667in" height="3.46875in"}

**Interpretation and conclusion**

The results show that even spectra from identical types of radars differ
considerably. Especially for magnetron based radars it sometimes seems
difficult to meet the current 20 dB/decade mask (radars 1 and 2). In
most cases, the 40 dB/decade mask from the design objective could not be
met. Exception is Radar 3b that seems to meet the design objective. To
make a definite statement here, a higher measurement dynamic range would
be necessary. When looking at the effect of filters as used for the
sidebands of radars 1 and 2, it may be possible to meet this mask if the
filters were better optimized for both sidebands.

Although the clystron based radar 4b has a very clean spectrum, it can
not meet a -40 dB/decade mask, mainly because of the 40 dB bandwidth
being too wide when compared with the current formula.

The chosen radar examples, all with unmodulated pulses, show how
critical the -40 dB bandwidth formulas are when applying OoB masks.
Whereas the current formula may even be insufficient in case of radar 2,
it is much too generous in case of radar 4.

# Annex: Result radar 1 {#annex-result-radar-1 .unnumbered}

![](media/image2.wmf){width="8.709027777777777in"
height="5.951388888888889in"}

Fig. 1: The sideband emissions depend on the PRF. In the worst case,
even the 20 dB/decade mask is exceeded, in all other cases, the 40
dB/decade mask is still exceeded around 5500 MHz (offset around -120
MHz).

**Result radar 2 (full span 7 GHz)**

![](media/image3.wmf){width="8.698611111111111in"
height="5.951388888888889in"}

Fig. 2: A filter is used to suppress sideband emissions. Without this
filter, not even the -60 dB attenuation for high frequency offsets can
be met.

**Result radar 2 (span 1 GHz)**

![](media/image4.wmf){width="8.698611111111111in"
height="5.951388888888889in"}

Fig. 3: The filter cannot suppress the sideband emissions at about 100
MHz offset. Therefore, even with filter, the 20 dB/decade mask can not
be met.. The 40 dB/decade mask still seems critical, mainly due to the
very tight fit at the -40 dB bandwidth points, even if the filter would
be better optimized and/or narrower.

**Result radar 3a**

![](media/image5.wmf){width="8.698611111111111in"
height="5.951388888888889in"}

Fig. 4: The peak at 9141 MHz is from the second radar working to the
same antenna, but the peaks around 8500 MHz (offset -450 MHz) prevent
conformance with the design objective. The -40 dB bandwidth formulas are
very generous in this case. The actual bandwidth is only about 50% of
the calculated.

**Result radar 3b**

![](media/image6.wmf){width="8.698611111111111in"
height="5.951388888888889in"}

Fig. 5: The peak at 8959 MHz is from the second radar working to the
same antenna. Due to the very generous -40 dB bandwidth formulas
(measured bandwidth is only about 50% of that), the 40 dB/decade mask
from the design objective could be met.

**Result radar 4a**

![](media/image7.wmf){width="8.698611111111111in"
height="5.951388888888889in"}

Fig. 6: Neither the current nor the mask from the design objective could
be met by this radar which obviously has a problem with the transmitter,
because even the -40 dB necessary bandwidth is exceeded by nearly 100%.

**Results radar 4b**

![](media/image8.wmf){width="8.698611111111111in"
height="5.951388888888889in"}

Fig. 7: This radar can easily meet the 20 dB/decade mask, but sideband
emissions around 1285 MHz (offset around -80 MHz) make it impossible to
meet the design objective. The -40 dB bandwidth is a very critical fit.