PIFA天线讲解

simon2000

【文件名】:07919@52RD_PIFA天线讲解.pdf
【格　式】:pdf
【大　小】:710K
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【目　录】:Table of Contents
Acronyms ........................................................................................................................................................... 2
Module Description ............................................................................................................................................ 3
Types of Antennas ............................................................................................................................................. 3
Stub Helix ....................................................................................................................................................... 4
Surface Mount Dielectric Chip......................................................................................................................... 4
Printed Inverted F (PIFA)................................................................................................................................ 6
Principle of Surface Mount, Printed or Patch Antennas .................................................................................. 6
Reference Design: Example........................................................................................................................... 7
Diversity Recommendation for CVM................................................................................................................... 8
Summary.......................................................................................................................................................... 10

mwo1974

National Semiconductor Confidential : Rev 0.1 Page 1 of 10
Applications Note
5th August 2003
Haroon Khan
Revision 0.2
Cordless Voice Module Antenna : Application Note
General Description
This Application Note describes some of the antennas and basics on design that can be used with the Cordless
Voice Module. PIFA antennas are explained along with information on their design and matching to the
CVM output. Diversity antennas are strongly recommended for the CVM module as they offer far better reception
quality and the principle of diversity is described.
National Semiconductor Confidential : Rev 0.1 Page 2 of 10
Revision History
Revision 0.1 12th February, 2003
Revision 0.2 5th August, 2003
Table of Contents
Acronyms ........................................................................................................................................................... 2
Module Description ............................................................................................................................................ 3
Types of Antennas ............................................................................................................................................. 3
Stub Helix ....................................................................................................................................................... 4
Surface Mount Dielectric Chip......................................................................................................................... 4
Printed Inverted F (PIFA)................................................................................................................................ 6
Principle of Surface Mount, Printed or Patch Antennas .................................................................................. 6
Reference Design: Example........................................................................................................................... 7
Diversity Recommendation for CVM................................................................................................................... 8
Summary.......................................................................................................................................................... 10
Acronyms
EMC Electro-Magnetic Compatibility
DCT Digital Cordless Telephony
DECT Digital Enhanced Cordless Telephony
PCB Printed Circuit Board
GSM Global System for Mobile communications
VSWR Voltage Standing Wave Ratio
PIFA Printed Inverted F Antenna
BER Bit Error Rate
CVM Cordless Voice Module
RSSI Receiver Signal Strength Indicator
RF Radio Frequency
TEM Transverse Electro-Magnetic
λg Wavelength of micro-strip guided wave
National Semiconductor Confidential : Rev 0.1 Page 3 of 10
Module Description
The CVM module consists of an SC14428 baseband processor, LMX4168 1.9GHz or LMX4268 2.4GHz RF
transceiver, crystal oscillator, power amplifier and diode switch as shown above. The dimensions of the module
are 26.6mm × 45.6mm and the transceiver plus power amplifier sections would be shielded from to meet
EMC requirements. The module as a whole is designed to be mounted on a motherboard that will also contain
the antenna. Different types of antennas can be used based on size and performance and a few will be
discussed in this report. This report will discuss the basics of such antennas that are vital to any designer
wishing to implement into their application.
Types of Antennas
1.9 and 2.4GHz antennas that can be used for DECT and DCT respectively are available in several different
designs, all suitable for mobile application such as printed line, inverted F, dielectric chip surface mount and
stub helix. Manufacturers that produce such antennas include Allgon, GigaAnt, Yokowo, Mitsubishi, Rangestar
and several others that will also make custom designs if the volumes are large enough.
National Semiconductor Confidential : Rev 0.1 Page 4 of 10
Stub Helix
This type of antenna is most commonly used for GSM mobile phones, but tuned to 1.9 and 2.4GHz, it has excellent
RF performance in terms of bandwidth and efficiency of radiation and has only one connection point to
the main PCB. It does not require a ground connection or a ground plane and because of its large bandwidth
it will not easily be de-tuned by user handling. But like all the antennas mentioned in this report, it does need
tuning to the individual mechanics of the application in which it is being used. Different shapes and materials
used for the chassis will distort the radiation pattern and pull the center frequency of the antenna. This is one
disadvantage of helix antennas, because they are more difficult to tune than a printed antenna where the
resonant length can be easily changed.
The negative point of course with this type of antenna is that its not low profile, it projects from the side of the
PCB. For this reason they are often not used for mobile applications.
Surface Mount Dielectric Chip
A low profile, smaller, lighter and cheaper antenna is the dielectric chip antenna, this consists of a high dk dielectric
slab with the active element printed on top. The reason for using a dielectric slab rather than printing
the element on the PCB directly is that it is smaller due to the concentrated electric field within the dielectric
material. This type of antenna is low profile and can be machine mounted during assembly, but it does not
yield as good performance as the stub helix. Being small means narrow bandwidth, worse efficiency and easily
de-tuned through handling.
Even though the antenna element is quite small (approx. 12×2mm) the size of the whole antenna is much larger
because of the ground plane required for the antenna to function correctly. In addition to this, a certain
copper free clearance needs to be maintained around the radiating element both in a horizontal plane as
shown in the diagram and some clearance in the vertical plane. The results of making the ground plane or
copper free area too small will be reduced bandwidth and as a rule of thumb, the antenna should have a
bandwidth which covers the entire DECT or DCT band with VSWR<2.5.

zca

general information on PIFA, no design information