2011 EMC Directory & Design Guide - Interference Technology

H o f f m a nn, Br aun, Frech, Rus s e r
filters
Figure 6. 1.1 - 6 GHz down-converter.
broadband subbands are consecutively down-converted
to the 1.1-6 GHz band via broadband, low-conversion loss
mixer and fed to the input of the 1.1 - 6 GHz down-converter.
HARDWARE IMPLEMENTATION
As most of the EMI in the frequency range above 1 GHz, e.g.
higher harmonics of communication systems, is low-level in
nature, high sensitivity is mandatory for frequencies above 1
GHz. Increased attenuation of cable assemblies above 1 GHz
in common test environments aggravates the problem. A low
noise figure of the input stage is critical for high sensitivity.
This correlates with a low attenuation of the first stages of
the multi-stage broadband down-converter, as (5) for the
calculation of the noise figure F of a cascaded system with
N stages [10] implies
F = 1 + F 1 + F 2 − 1
+ F 3 − 1
+ ... + F N − 1
,
G 1 G 1 G N−1
2 ∏
G k
k=1
(5)
where G i
is the available power gain of stage i and F i
is
the noise figure of stage i.
In the presented measurement system, high-gain, lownoise
InGaP/GaAs MMIC preamplifiers yield a system
noise figure of around 6-8 dB, rendering the use of external
amplifiers unnecessary. To further increase the system’s
sensitivity and dynamic range, low-noise double balanced
mixers with low conversion loss and high 1 dB compression
point are used.
The switching between the bands from 6-18 GHz is accomplished
by broadband low insertion loss, single-input,
tripleoutput (SP3T) PIN-diode switches. The low diode
junction capacitance in reverse polarity yields an excellent
isolation of -55 dB to -35 dB in the OFF-state. The switches
achieve a low insertion loss of -1.5 dB to -2 dB in the range
from 6-18 GHz.
EMISSION MEASUREMENTS
Electric household appliances radiate considerable spectral
energy density in the frequency range above 1 GHz. A
commonly found example is the microwave oven. A magnetron
generates high-power microwave energy at around
2.5 GHz. In order to characterize the radiated emission of
a microwave oven, the oven was placed in a full anechoic
chamber. An ultra-broadband quad-ridged horn antenna
with a bandwidth from 1.7-20 GHz [11] was placed in a
Figure 7. 6 - 18 GHz down-converter.
distance of 3 m to the device under test. To compensate
for cable losses and to give the electric field strength of the
EMI, the corresponding transducer factors and the antenna
factor were applied.
In Figure 8, the measured emission spectrum from 2-18
GHz is presented. The spectrum shows the magnetron’s
strong fundamental at around 2.45 GHz and several higher
harmonics up to 18 GHz. The scan time using an IF-filter
bandwidth of 9 kHz and a frequency resolution of 50 kHz
was around 120 s, while around 320 000 frequency points
were calculated.
The emission of the microwave oven is not stationary.
The amplitude spectrum cannot give any insights into the
time-behavior of the radiated emission. The time-domain
EMI Power Line Interference Filters
Reliable
U.S. Supplier
For Over
45 Years
“Your source for EMI/RFI Filter solutions”
5466 Complex St, Ste 207
San Diego, CA 92123
Be up-to-date and take advantage of
Genisco’s proven, cost effective EMI/RFI
Filters to solve your electromagnetic and
radiofrequency interference problems.
We can Provide-
• Shielded Room Filters
• Telephone Line Filters
• Communications Filters
• Signal Fire Alarms Filters
• Build to Spec Filters
• Military/Aerospace Filters
• Single & Multiple Circuit Filters
ISO 9001:2008 Certified
www.Genisco.com
Cage Code
07294
Email: Sales@Genisco.com
Ph: (858) 565-7405
interferencetechnology.com interference technology 119