Antenna elements of constant length
Antenna element of variable electrical length
Rohde & Schwarz
R&S®DDF255 Digital Direction Finder
17
Active/passive switchover with just a mouse click
The number of radio services and transmitters is continu-
ously growing, resulting in an increasing cumulative load
on the antenna input and the receiver input. Especially
digital broadcasting services such as DVB-T and DAB with
their high bandwidths represent a growing challenge to
the linearity of antennas and receivers. The problem may
intensify if the DF antenna is in the vicinity of strong trans-
mitters – which, particularly in urban areas, can hardly be
avoided.
If the number of strong signals becomes too high,
intermodulation products may become visible in the
spectrum. In the worst case, they would mask signals of
interest and make it impossible to take bearings.
Most Rohde & Schwarz DF antennas are equipped with ac-
tive antenna elements, which provide significantly higher
sensitivity than passive elements – and also have compact
dimensions. Although extremely linear, active antenna cir-
cuitry with top-quality components is used, very strong
signals may cause intermodulation.
Passive antennas provide significantly higher linearity and
therefore generate virtually no intermodulation products;
however, they are either less sensitive or considerably
larger than active antennas. In applications where only
compact antennas can be used, passive DF antennas are
substantially less sensitive in the VHF and the lower UHF
range than active models.
Up until now, users have had to decide what is more im-
portant to them: the higher sensitivity offered by active
DF antennas or the higher immunity to strong signals pro-
vided by passive DF antennas.
The R&S®ADD196/197/295 for the first time make it possi-
ble to bypass the active circuitry of the antenna elements.
The user can switch the active elements to passive mode
by a simple mouse click. These DF antennas offer the ad-
vantages of both methods.
Exceptionally high DF sensitivity
For DF antenna elements to exhibit good receive charac-
teristics, adaptation to the subsequent stage must be op-
timized and coupling to the adjacent elements minimized.
These requirements can best be met over a wide frequen-
cy range by using configurable antenna structures:
❙
At low frequencies, confi guration of antenna element for
maximum electrical length
❙
At high frequencies, selection of the most effective
antenna length to achieve the best possible compromise
between decoupled receive power and impact on the
directional pattern due to mutual coupling
Optimal results are achieved using electric switches that
connect or disconnect parts of the antenna element (see
figure, right).
The antenna elements of the R&S®ADD196, R&S®ADD197
(vertical polarization) and R&S®ADD295 DF antennas are
equipped with PIN diodes, allowing the electrically active
structure to change very quickly in the VHF/UHF range.
As a result, these elements are always optimally adapted
to the receive frequency and offer exceptionally high
sensitivity.
Commercially available DF antennas that cover a very
wide frequency range with antenna elements of constant
length (see figure, left) are usually optimized for the UHF
range and are considerably less sensitive in the VHF range
than the Rohde & Schwarz models with variable electrical
length.ency
Antenna elements of constant lengthAntenna element of variable electrical lengthRohde & SchwarzR&S®DDF255 Digital Direction Finder17Active/passive switchover with just a mouse clickThe number of radio services and transmitters is continu-ously growing, resulting in an increasing cumulative loadon the antenna input and the receiver input. Especiallydigital broadcasting services such as DVB-T and DAB withtheir high bandwidths represent a growing challenge tothe linearity of antennas and receivers. The problem mayintensify if the DF antenna is in the vicinity of strong trans-mitters – which, particularly in urban areas, can hardly beavoided.If the number of strong signals becomes too high,intermodulation products may become visible in thespectrum. In the worst case, they would mask signals ofinterest and make it impossible to take bearings.Most Rohde & Schwarz DF antennas are equipped with ac-tive antenna elements, which provide significantly highersensitivity than passive elements – and also have compactdimensions. Although extremely linear, active antenna cir-cuitry with top-quality components is used, very strongsignals may cause intermodulation.Passive antennas provide significantly higher linearity andtherefore generate virtually no intermodulation products;however, they are either less sensitive or considerablylarger than active antennas. In applications where onlycompact antennas can be used, passive DF antennas aresubstantially less sensitive in the VHF and the lower UHFrange than active models.Up until now, users have had to decide what is more im-portant to them: the higher sensitivity offered by activeDF antennas or the higher immunity to strong signals pro-vided by passive DF antennas.The R&S®ADD196/197/295 for the first time make it possi-ble to bypass the active circuitry of the antenna elements.The user can switch the active elements to passive modeby a simple mouse click. These DF antennas offer the ad-vantages of both methods.Exceptionally high DF sensitivityFor DF antenna elements to exhibit good receive charac-teristics, adaptation to the subsequent stage must be op-timized and coupling to the adjacent elements minimized.These requirements can best be met over a wide frequen-cy range by using configurable antenna structures:❙At low frequencies, confi guration of antenna element formaximum electrical length❙At high frequencies, selection of the most effectiveantenna length to achieve the best possible compromisebetween decoupled receive power and impact on thedirectional pattern due to mutual couplingOptimal results are achieved using electric switches thatconnect or disconnect parts of the antenna element (seefigure, right).The antenna elements of the R&S®ADD196, R&S®ADD197(vertical polarization) and R&S®ADD295 DF antennas areมี PIN ไดโอดได้ อนุญาตให้ใช้งานด้วยระบบไฟฟ้าโครงสร้างการเปลี่ยนแปลงอย่างรวดเร็วในช่วง VHF/UHFดัง องค์ประกอบเหล่านี้มักดัดแปลงอย่างเหมาะสมการรับความถี่สูงสุดความไวในการส่วน DF ใช้ได้ในเชิงพาณิชย์ที่ครอบคลุมการมากช่วงความถี่กว้าง มีเสาอากาศองค์ประกอบของค่าคงความยาว (ดูรูป ซ้าย) นี้มักเหมาะสำหรับ UHFช่วงและมีมากน้อยสำคัญในช่วง VHFกว่ารุ่น Rohde & โรลด์กับแปรไฟฟ้าlength.ency
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Antenna elements of constant length
Antenna element of variable electrical length
Rohde & Schwarz
R&S®DDF255 Digital Direction Finder
17
Active/passive switchover with just a mouse click
The number of radio services and transmitters is continu-
ously growing, resulting in an increasing cumulative load
on the antenna input and the receiver input. Especially
digital broadcasting services such as DVB-T and DAB with
their high bandwidths represent a growing challenge to
the linearity of antennas and receivers. The problem may
intensify if the DF antenna is in the vicinity of strong trans-
mitters – which, particularly in urban areas, can hardly be
avoided.
If the number of strong signals becomes too high,
intermodulation products may become visible in the
spectrum. In the worst case, they would mask signals of
interest and make it impossible to take bearings.
Most Rohde & Schwarz DF antennas are equipped with ac-
tive antenna elements, which provide significantly higher
sensitivity than passive elements – and also have compact
dimensions. Although extremely linear, active antenna cir-
cuitry with top-quality components is used, very strong
signals may cause intermodulation.
Passive antennas provide significantly higher linearity and
therefore generate virtually no intermodulation products;
however, they are either less sensitive or considerably
larger than active antennas. In applications where only
compact antennas can be used, passive DF antennas are
substantially less sensitive in the VHF and the lower UHF
range than active models.
Up until now, users have had to decide what is more im-
portant to them: the higher sensitivity offered by active
DF antennas or the higher immunity to strong signals pro-
vided by passive DF antennas.
The R&S®ADD196/197/295 for the first time make it possi-
ble to bypass the active circuitry of the antenna elements.
The user can switch the active elements to passive mode
by a simple mouse click. These DF antennas offer the ad-
vantages of both methods.
Exceptionally high DF sensitivity
For DF antenna elements to exhibit good receive charac-
teristics, adaptation to the subsequent stage must be op-
timized and coupling to the adjacent elements minimized.
These requirements can best be met over a wide frequen-
cy range by using configurable antenna structures:
❙
At low frequencies, confi guration of antenna element for
maximum electrical length
❙
At high frequencies, selection of the most effective
antenna length to achieve the best possible compromise
between decoupled receive power and impact on the
directional pattern due to mutual coupling
Optimal results are achieved using electric switches that
connect or disconnect parts of the antenna element (see
figure, right).
The antenna elements of the R&S®ADD196, R&S®ADD197
(vertical polarization) and R&S®ADD295 DF antennas are
equipped with PIN diodes, allowing the electrically active
structure to change very quickly in the VHF/UHF range.
As a result, these elements are always optimally adapted
to the receive frequency and offer exceptionally high
sensitivity.
Commercially available DF antennas that cover a very
wide frequency range with antenna elements of constant
length (see figure, left) are usually optimized for the UHF
range and are considerably less sensitive in the VHF range
than the Rohde & Schwarz models with variable electrical
length.ency
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