ANT-315-HETH
Data Sheet
Product Description
HE Series antennas are designed for direct PCB
mounting. Thanks to the HE’s compact size, they
are ideal for internal concealment inside a product’s
housing. The HE is also very low in cost, making it
well suited to high-volume applications. HE Series
antennas have a very narrow bandwidth; thus, care
in placement and layout is required. In addition,
they are not as efficient as whip-style antennas,
so they are generally better suited for use on the
transmitter end where attenuation is often required
anyway for regulatory compliance. Use on both
transmitter and receiver ends is recommended only
in instances where a short range (less than 30% of
whip style) is acceptable.
Outside
8.89 mm
Diameter
(0.35")
by
Inside
6.35 mm
Diameter
(0.25")
Wire
Diameter
1.27 mm
(0.05")
Features
•
•
•
•
•
Very low cost
Compact for physical concealment
Precision-wound coil
Rugged phosphor-bronze construction
Mounts directly to the PCB
38.10 mm
(1.50")
Recommended Mounting
No ground plane or traces
under the antenna
38.10 mm
(1.50")
7.62 mm
(0.30")
Ø1.52 mm
(0.060")
12.70 mm
(0.50")
3.81 mm
(0.15")
No electircal
connection on this
pad. For physical
support only.
Electrical Specifications
Center Frequency:
Recom. Freq. Range:
Wavelength:
VSWR:
Impedance:
Connection:
Oper. Temp. Range:
315MHz
305–325MHz
¼-wave
≤
2.0 typical at center
50-ohms
Through-hole
–40°C to +80°C
Electrical specifications and plots measured on a 7.62 cm x
24.13 cm (3.00" x 9.50") reference ground plane.
Ordering Information
50-ohm microstrip line
ANT-315-HETH (helical, through-hole)
Ground plane on
bottom layer for
counterpoise
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Revised 12/9/13
Counterpoise
Quarter-wave or monopole antennas require an associated ground plane
counterpoise for proper operation. The size and location of the ground
plane relative to the antenna will affect the overall performance of the
antenna in the final design. When used in conjunction with a ground
plane smaller than that used to tune the antenna, the center frequency
typically will shift higher in frequency and the bandwidth will decrease.
The proximity of other circuit elements and packaging near the antenna
will also affect the final performance. For further discussion and guidance
on the importance of the ground plane counterpoise, please refer to Linx
Application Note AN-00501: Understanding Antenna Specifications and
Operation.
VSWR Graph
VSWR
3:1
1.166
Reflected Power
25%
2:1
11%
1:1
215MHz
315MHz
0%
415MHz
What is VSWR?
The Voltage Standing Wave Ratio (VSWR) is a measurement of how well
an antenna is matched to a source impedance, typically 50-ohms. It is
calculated by measuring the voltage wave that is headed toward the load
versus the voltage wave that is reflected back from the load. A perfect
match will have a VSWR of 1:1. The higher the first number, the worse the
match, and the more inefficient the system. Since a perfect match cannot
ever be obtained, some benchmark for performance needs to be set. In
the case of antenna VSWR, this is usually 2:1. At this point, 88.9% of the
energy sent to the antenna by the transmitter is radiated into free space
and 11.1% is either reflected back into the source or lost as heat on
the structure of the antenna. In the other direction, 88.9% of the energy
recovered by the antenna is transferred into the receiver. As a side note,
since the “:1” is always implied, many data sheets will remove it and just
display the first number.
How to Read a VSWR Graph
VSWR is usually displayed graphically versus frequency. The lowest point
on the graph is the antenna’s operational center frequency. In most cases,
this will be different than the designed center frequency due to fabrication
tolerances. The VSWR at that point denotes how close to 50-ohms the
antenna gets. Linx specifies the recommended bandwidth as the range
where the typical antenna VSWR is less than 2:1.
159 Ort Lane, Merlin, OR, US 97532
Phone: +1 541 471 6256
Fax: +1 541 471 6251
www.linxtechnologies.com
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Data Sheet ANT-315-HETH
by
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