EN 60862-2:2002

SLOVENSKI SIST EN 60862-2:2003

STANDARD
oktober 2003
Surface acoustic wave (SAW) filters of assessed quality - Part 2: Guidance on use
(IEC 60862-2:2002)
ICS 31.160 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 60862-2
NORME EUROPÉENNE
EUROPÄISCHE NORM September 2002

ICS 31.140
English version
Surface acoustic wave (SAW) filters of assessed quality
Part 2: Guidance on use
(IEC 60862-2:2002)
Filtres à ondes acoustiques de surface Oberflächenwellenfilter (OFW-Filter)
(OAS) sous assurance de la qualité mit bewerteter Qualität
Partie 2: Guide d'utilisation Teil 2: Leitfaden für die Anwendung
(CEI 60862-2:2002) (IEC 60862-2:2002)

This European Standard was approved by CENELEC on 2002-09-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60862-2:2002 E
Foreword
The text of document 49/542/FDIS, future edition 2 of IEC 60862-2, prepared by IEC TC 49,
Piezoelectric and dielectric devices for frequency control and selection, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 60862-2 on 2002-09-01.

The following dates were fixed:

– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-06-01

– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-09-01

Annexes designated "normative" are part of the body of the standard.
In this standard, annex ZA is normative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60862-2:2002 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - EN 60862-2:2002
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 60368-2-1 1988 Piezoelectric filters - -
Part 2: Guide to the use of piezoelectric
filters
Section 1: Quartz crystal filters

IEC 60862 Series Surface acoustic wave (SAW) filters of - -
assessed quality
NORME CEI
INTERNATIONALE IEC
60862-2
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2002-05
Filtres à ondes acoustiques de surface (OAS)
sous assurance de la qualité –
Partie 2:
Guide d'utilisation
Surface acoustic wave (SAW) filters
of assessed quality –
Part 2:
Guidance on use
© IEC 2002 Droits de reproduction réservés ⎯ Copyright - all rights reserved
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électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch  Web: www.iec.ch
CODE PRIX
XA
PRICE CODE
Commission Electrotechnique Internationale
International Electrotechnical Commission
ɆɟɠɞɭɧɚɪɨɞɧɚɹɗɥɟɤɬɪɨɬɟɯɧɢɱɟɫɤɚɹɄɨɦɢɫɫɢɹ
Pour prix, voir catalogue en vigueur
For price, see current catalogue

60862-2 © IEC:2002 – 3 –
CONTENTS
FOREWORD.7
INTRODUCTION.11
1 Scope.13
2 Normative references .13
3 Terms and definitions .13
3.1 General terms .13
3.2 Response characteristics .19
3.3 SAW filter related terms .27
4 Preliminary remarks of a technical nature .27
5 Fundamentals of SAW transversal filters .29
5.1 Frequency response characteristics .29
5.2 Weighting methods.31
5.3 Filter configurations and their general characteristics .39
6 Fundamentals of SAW resonator filters.67
6.1 Classification of SAW resonator filters.67
6.2 Ladder and lattice filters .67
6.3 Coupled resonator filters .71
6.4 Interdigitated interdigital transducer (lIDT) resonator filters .89
7 Application guide.89
7.1 Substrate materials and their characteristics .89
7.2 Application to electronics circuits.99
7.3 Availability and limitations .101
7.4 Input levels.105
8 Practical remarks .107
8.1 Feed-through signals.107
8.2 Impedance matching condition .109
8.3 Miscellaneous .109
9 Ordering procedure .111
Figure 1 – Frequency response of a SAW filter .31
Figure 2 – Applicable range of frequency and relative bandwidth of the SAW filter and
the other filters .33
Figure 3 – Schematic diagram showing signal flow through a transversal filter.33
Figure 4 – Basic configuration of a SAW transversal filter .35
Figure 5 – Frequency response of the SAW transversal filter shown in figure 4, where
f is the centre frequency and N is the number of finger pairs of the IDT .35
Figure 6 – Apodization weighting obtained by apodizing fingers.37
Figure 7 – Withdrawal weighting obtained by selective withdrawal of the fingers.37
Figure 8 – Series weighting obtained by the dog-leg structure .37
Figure 9 – Split-finger (double electrode) configuration .39

60862-2 © IEC:2002 – 5 –
Figure 10 – Typical characteristics of a SAW IF filter for radio transmission equipment
(nominal frequency of 70,0 MHz) .45
Figure 11 – Typical characteristics of a frequency asymmetrical SAW filter (nominal
frequency of 58,75 MHz for TV-IF use) .47
Figure 12 – SAW three-IDT filter .47
Figure 13 – Typical frequency response of a 900 MHz range SAW filter for
communication (mobile telephone use) .49
Figure 14 – Schematic of the IIDT (multi-IDT) filter.49
Figure 15 – Multi-phase unidirectional transducer .51
Figure 16 – Single-phase unidirectional transducers .53
Figure 17 – Frequency characteristics of a filter using multi-phase unidirectional
transducers.55
Figure 18 – Frequency characteristics of a filter using single-phase unidirectional
transducers.55
Figure 19 – Various reflector filter configurations .59
Figure 20 – Z-path filter configuration .61
Figure 21 – Dual-track reflector filter configuration.61
Figure 22 – SPUDT-based dual-track filter .63
Figure 23 – Frequency characteristics of Z-path filter.63
Figure 24 – Frequency characteristics of dual-track reflector filter.65
Figure 25 – Frequency characteristics of SPUDT-based reflector filter.65
Figure 26 – Structure of ladder and lattice filters.73
Figure 27 – Equivalent circuit of basic section of ladder and lattice filter .75
Figure 28 – Pattern layout of ladder filter .75
Figure 29 – Basic concept of ladder and lattice filter .77
Figure 30 – Typical characteristics of a 1,5 GHz range ladder filter.79
Figure 31 – SAW energy distribution and equivalent circuit of transversely coupled
resonator filter .81
Figure 32 – Typical characteristics of a transversely coupled resonator filter .83
Figure 33 – Basic configuration and SAW energy distribution of longitudinally coupled
resonator filter .85
Figure 34 – Typical characteristics of a longitudinally coupled resonator filter.87
Figure 35 – Schematic of IIDT resonator filter .91
Figure 36 – Frequency characteristics of a 820 MHz range IIDT resonator filter.91
Figure 37 – Minimum theoretical conversion losses for various substrates .93
Figure 38 – Relationship between relative bandwidth and insertion attenuation for
various SAW filters, with the practical SAW filters’ bandwidth for their typical
applications .103
Figure 39 – Ripples in the characteristics of a SAW filter caused by TTE or feed-
through signal: įf = 1/(2t) for the TTE, and įf = 1/t for the feed-through, where t is the
delay of the SAW main signal .105
Table 1 – Properties of typical single-crystal substrate materials .97
Table 2 – Properties of typical thin-film substrate materials.97
Table 3 – Properties of typical ceramic substrate materials.99

60862-2 © IEC:2002 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SURFACE ACOUSTIC WAVE (SAW) FILTERS
OF ASSESSED QUALITY –
Part 2: Guidance on use
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60862-2 has been prepared by IEC technical committee 49:
Piezoelectric and dielectric devices for frequency control and selection.
This second edition cancels and replaces the first edition published in 1991 and constitutes a
technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
49/542/FDIS 49/550/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.

60862-2 © IEC:2002 – 9 –
IEC 60862 consists of the following parts, under the general title Surface acoustic wave
(SAW) filters of assessed quality
1)
– Part 1: General information, standard values and test conditions
– Part 2: Guidance on use
2)
– Part 3: Standard outlines
– Part 4: Sectional specification – Capability approval (under consideration)
– Part 4-1: Blank detail specification – Capability approval (under consideration)
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged
until 2007. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
________
1)
A second edition (generic specification) is under consideration.
2)
A second edition is under consideration.

60862-2 © IEC:2002 – 11 –
INTRODUCTION
This part of IEC 60862 gives practical guidance on the use of SAW filters which are used
in telecommunications, measuring equipment, radar systems and consumer products.
IEC 60862-1 should be referred to for general information, standard values and test
conditions.
The features of these SAW filters are their small size, light weight, adjustment-free, high
stability and high reliability. SAW filters add new features and applications to the field of
crystal filters and ceramic filters. At the beginning, SAW filters meant transversal filters which
have two interdigital transducers (IDT). Although SAW transversal filters have a relatively
higher minimum insertion attenuation, they have excellent amplitude and phase
characteristics. Extensive studies have been made to reduce minimum insertion attenuation,
such as resonator filter configurations, unidirectional interdigital transducers (UDT),
interdigitated interdigital transducers (IIDT). Nowadays, various kinds of SAW filters with low
insertion attenuation are widely used in various applications and SAW filters are available in
the gigahertz range.
This standard has been compiled in response to a generally expressed desire on the part of
both users and manufacturers for guidance on the use of SAW filters, so that the filters may
be used to their best advantage. To this end, general and fundamental characteristics have
been explained here.
60862-2 © IEC:2002 – 13 –
SURFACE ACOUSTIC WAVE (SAW) FILTERS
OF ASSESSED QUALITY –
Part 2: Guidance on use
1 Scope
SAW filters are now widely used in a variety of applications such as TV, satellite
communications, optical fibre communications, mobile communications and so on. While
these SAW filters have various specifications, many of them can be classified within a few
fundamental categories.
This part of IEC 60862 includes various kinds of filter configuration, of which the operating
frequency range is from approximately 10 MHz to 3 GHz and the relative bandwidth is about
0,02 % to 100 % of the centre frequency.
It is not the aim of this standard to explain theory, nor to attempt to cover all the eventualities
which may arise in practical circumstances. This standard draws attention to some of the
more fundamental questions, which should be considered by the user before he places an
order for a SAW filter for a new application. Such a procedure will be the user's insurance
against unsatisfactory performance.
Standard specifications, given in IEC 60862, and national specifications or detail specifi-
cations issued by manufacturers, define the available combinations of nominal frequency,
pass bandwidth, ripple, shape factor, terminating impedance, etc. These specifications are
compiled to include a wide range of SAW filters with standardized performances. It cannot be
over-emphasized that the user should, wherever possible, select his SAW filters from these
specifications, when available, even if it may lead to making small modifications to his circuit
to enable standard filters to be used. This applies particularly to the selection of the nominal
frequency.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60368-2-1:1988, Piezoelectric filters – Part 2: Guide to the use of piezoelectric filters –
Section One: Quartz crystal filters
IEC 60862 (all parts), Surface acoustic wave (SAW) filters of assessed quality
3 Terms and definitions
For the purpose of this part of IEC 60862, the following terms and definitions apply.
3.1 General terms
3.1.1
surface acoustic wave (SAW)
acoustic wave, propagating along a surface of an elastic substrate, whose amplitude decays
exponentially with substrate depth

60862-2 © IEC:2002 – 15 –
3.1.2
surface acoustic wave filter (SAW filter)
filter characterized by a surface acoustic wave which is usually generated by an interdigital
transducer and propagates along a substrate surface to a receiving transducer
3.1.3
power flow vector
vector, analogous to a Poynting vector, characterizing energy propagation caused by a surface
acoustic wave
3.1.4
propagation vector
vector characterizing the phase progression of a wave
3.1.5
power flow angle
angle between the direction of the power flow vector and the direction of the propagation
vector
3.1.6
SAW beam steering
SAW propagation phenomenon in anisotropic materials described by an angle of power flow
which is not zero
3.1.7
SAW diffraction
phenomenon (analogous to diffraction of light from a source of finite aperture) which causes
SAW beam spreading and wavefront distortion
3.1.8
SAW coupling coefficient ( k )
s
SAW electromechanical coupling coefficient is defined as follows:
∆ν
s
k = 2
s
ν
s
where
∆ν /ν is the relative velocity change produced by short-circuiting the surface potential from
s s
the open-circuit condition
3.1.9
interdigital transducer (IDT)
SAW transducer made of two comb-like conductive structures deposited on a piezoelectric
substrate transforming electrical energy into acoustic energy or vice versa
3.1.10
unidirectional interdigital transducer (UDT)
transducer capable of radiating and receiving surface acoustic waves in or from a single direction
3.1.11
multiphase transducer
interdigital transducer having more than two inputs which are driven in different phases.
Usually used as a unidirectional transducer
3.1.12
finger
element of the IDT comb electrode

60862-2 © IEC:2002 – 17 –
3.1.13
dummy finger
passive finger which may be included in order to suppress wavefront distortion
3.1.14
split finger
finger formed of more than one element, so as to produce antireflection properties
3.1.15
bus bar
common electrode which connects individual fingers together and also connects the filter to
an external circuit
3.1.16
weighted-response transducer
transducer intended to produce a specified impulse response by design of the structure
(see, for example, 3.1.17 to 3.1.22)
3.1.17
finger overlap or source strength
length of a finger pair between which only electromechanical interaction is generated
3.1.18
apodization
weighting produced by the change of finger overlap over the length of the IDT
3.1.19
withdrawal weighting
weighting by removal of fingers or sources
3.1.20
capacitive weighting
weighting by change of capacitance between electrodes
3.1.21
series weighting
weighting by separation of a finger into individual elements having capacitive coupling
between them. The elements may be separated from the bus bar
3.1.22
phase weighting
weighting by change in period of finger arrangement inside the IDT
3.1.23
aperture
normalized beamwidth of the SAW generated at centre frequency and normalized to the
corresponding wavelength
3.1.24
multistrip coupler (MSC)
array of additional metal strips deposited on a piezoelectric substrate, in a direction
transverse to the propagation direction, which transfers acoustic power from one acoustic
track to an adjacent track
60862-2 © IEC:2002 – 19 –
3.1.25
reflector
SAW reflecting component which normally makes use of the periodic discontinuity provided by
a metal strip array or a grooved array
3.1.26
spurious reflections
unwanted signals caused by reflection of SAW or bulk waves from substrate edges or
electrodes
3.1.27
triple transit echo (TTE)
unwanted signals in a SAW filter which have traversed three times the propagation path
between input and output IDTs caused by reflections from output and input transducers
3.1.28
bulk-wave signals
unwanted signals caused by bulk-wave excitation, detected at the filter output
3.1.29
feed-through signals (signals of electromagnetic interference)
unwanted signals from the input appearing at the filter output due to stray capacitances and
other electromagnetic couplings
3.1.30
suppression corrugation
grooves in the non-active side of a substrate for suppressing bulk-wave signals
3.1.31
acoustic absorber
material with high acoustic loss placed on any part of the substrate for acoustic absorption
purposes
3.1.32
shielding electrode
electrode intended for the reduction of electromagnetic interference signals
3.1.33
interdigitated interdigital transducer (IIDT)
SAW transducer made of a combination of three or more interdigital transducers. Same as a
multi-IDT
NOTE  In this standard, IIDT (or multi-IDT) resonator filters are referred to as SAW resonator filters composed of a
number of IDTs for input and output in a line alternating with grating reflectors confirming the IDT structure at both
ends.
3.2 Response characteristics
3.2.1
nominal frequency
frequency given by the manufacturer or the specification to identify the filter
3.2.2
centre frequency
arithmetic mean of the cut-off frequencies

60862-2 © IEC:2002 – 21 –
3.2.3
reference frequency
frequency defined by the specification to which other frequencies may be referred
3.2.4
cut-off frequency
frequency of the pass-band at which the relative attenuation reaches a specified value
3.2.5
total power loss
logarithmic ratio of the available power at the given source to the power that the SAW filter
delivers to a load impedance under specified operating conditions
3.2.6
insertion attenuation
logarithmic ratio of the power delivered directly to the load impedance before insertion of the
filter to the power delivered to the load impedance after insertion of the filter
3.2.7
nominal insertion attenuation
insertion attenuation at a specified reference frequency
3.2.8
relative attenuation
difference between the attenuation at a given frequency and the attenuation at the reference
frequency
3.2.9
pass-band
band of frequencies in which the relative attenuation is equal to, or less than, a specified
value
3.2.10
pass bandwidth
separation of frequencies between which the relative attenuation is equal to, or less than, a
specified value
3.2.11
pass-band ripple
variation in insertion attenuation within a specified pass-band
3.2.12
TTE ripple
maximum variation in attenuation characteristics caused by TTE within a specified pass-band
3.2.13
minimum insertion attenuation
minimum value of insertion attenuation in the pass-band
3.2.14
stop-band
band of frequencies in which the relative attenuation is equal to, or greater than, a specified
value
60862-2 © IEC:2002 – 23 –
3.2.15
stop bandwidth
separation of frequencies between which the relative attenuation is equal to, or greater than,
a specified value
3.2.16
shape factor
ratio of two bandwidths at specified values of the relative attenuation
3.2.17
group delay
time equal to the first derivative of the phase shift, in radians, with respect to the angular
frequency
3.2.18
nominal group delay
group delay at a specified reference frequency
3.2.19
group delay distortion
difference between the lowest and highest value of group delay in a specified frequency band
3.2.20
trap frequency
specified frequency at which the relative attenuation is equal to, or greater than, a specified
value
3.2.21
trap attenuation
relative attenuation at a specified trap frequency
3.2.22
transition band
band of frequencies between the cut-off frequency and the nearest point of the adjacent
stop-band
3.2.23
reflection coefficient
dimensionless measure of the degree of mismatch between two impedances Z and Z , given
a b
by the expression
Z − Z
a b
Z + Z
a b
where
Z and Z represent respectively the input and source impedance or the output and load
a b
impedance
3.2.24
return attenuation
value of the reciprocal of the modulus of the reflection coefficient expressed in decibels
Quantitatively, it is equal to:
Z + Z
a b
20 log dB
Z − Z
a b
60862-2 © IEC:2002 – 25 –
3.2.25
reflected wave signal suppression
relative attenuation of unwanted signals caused by reflection of SAW or bulk waves from
substrate edges or electrodes within a specified time window
3.2.26
feed-through signal suppression
relative attenuation which implies the suppression of directly coupled signals by the
electromagnetic and electrostatic coupling between the input and output electrodes
3.2.27
unwanted response
response other than that associated with the mode of vibration intended for the application
3.2.28
input level
power, voltage or current value applied to the input terminal pair of a filter
3.2.29
output level
power, voltage or current value delivered to the load
3.2.30
nominal level
power, voltage or current value at which the performance measurement is specified
3.2.31
input impedance
impedance presented by the filter to the signal source when the output is terminated by a
specified load impedance
3.2.32
output impedance
impedance presented by the filter to the load when the input is terminated by a specified
source impedance
3.2.33
terminating impedance
either of the impedances presented to the filter by the source or by the load
3.2.34
available power
maximum power obtainable from a given source by suitable adjustment of the load impedance
3.2.35
roll-off rate
index describing the rise-up characteristics for digital communication SAW roll-off filters. It is
a ratio of the transition band to the ideal cut-off frequency, which is equal to half of the
sampling frequency, in the case of cosine roll-off frequency characteristics
3.2.36
intermodulation distortion
non-linear distortion of a SAW transducer or filter response characterized by the appearance
of frequencies at the output equal to the differences (or sums) of integral multiples of the two
or more component frequencies present at the input

60862-2 © IEC:2002 – 27 –
3.3 SAW filter related terms
3.3.1
transversal filter
filter consisting of input and output interdigital transducers on a piezoelectric substrate.
The frequency response of the filter is fundamentally given by the impulse response of the
transducer
3.3.2
frequency symmetrical filter
filter having a symmetrical frequency characteristic in relation to the reference frequency
3.3.3
frequency asymmetrical filter
filter having a specified asymmetrical pass-band or stop-band characteristic in relation to the
reference frequency
3.3.4
dispersive filter
filter designed so as to have group delay which is a function of frequency, usually by varying
the finger periodicity
3.3.5
comb filter
filter having two or more pass-bands between three or more stop-bands
3.3.6
resonator filter
filter in which two or more SAW resonators are incorporated
3.3.7
ladder filter
filter having a cascade or tandem connection of alternating series and shunt SAW resonators
3.3.8
lattice filter
filter having at least four SAW resonators connected in series to form a mesh, two non-
adjacent junction points are used as input terminals, while the remaining two junction points
are used as output terminals (bridge circuit). Preferably it can be used for balanced circuits
4 Preliminary remarks of a technical nature
It is of prime interest to a user that the filter characteristics should satisfy a particular speci-
fication. The selection of tuning networks and SAW filters to meet that specification should be
a matter of agreement between user and manufacturer.
Filter characteristics are usually expressed in terms of insertion attenuation and group delay
as a function of frequency, as shown in figure 1. A standard method for measuring insertion
1)
attenuation and group delay is described in 4.5.2 of IEC 60862-1 . In some applications, such
characteristics as phase distortion are also important.
Insertion attenuation characteristics are further specified by nominal frequency, minimum
insertion attenuation or maximum insertion attenuation, pass-band ripple and shape factor.
The specification is to be satisfied between the lowest and highest temperatures of the
specified operating temperature range and before and after environmental tests.
________
1)
To be published.
60862-2 © IEC:2002 – 29 –
SAW filters are classified roughly into two types: transversal filters and resonator filters.
Transversal filters are further classified into two types: bidirectional IDT filter and uni-
directional IDT filter. Also resonator filters are further classified into three types i.e. ladder
and lattice filters, coupled resonator filter and IIDT resonator filter. Fundamentals of SAW
transversal filters and SAW resonator filters are described in clauses 5 and 6 of this
standard, respectively. In figure 2, the applicable frequency range and relative bandwidth of
the SAW filters are shown in comparison with those of ceramic, crystal, dielectric, helical
and stripline filters.
5 Fundamentals of SAW transversal filters
5.1 Frequency response characteristics
A brief description of SAW filters is given here to help users unfamiliar with these filters to
understand their operating principles and characteristics. The SAW filter uses a surface
acoustic wave, usually the Rayleigh wave. The mechanical energy transported by the wave is
concentrated in a surface region of the order of a wavelength in depth. The wave travels on a
3 4
solid surface at a velocity, 10 m/s to 10 m/s, which offers the possibility of filtering
operations in the VHF and UHF regions in practical SAW filters. The SAW filter has a planar
structure, in which electrodes are formed on one surface of a piezoelectric substrate,
incorporating a suitable configuration of electrodes as a means of conversion between
surface acoustic waves and electrical signals.
Figure 3 is a diagram showing the signal flow through a transversal filter. The filter consists
of N taps separated by delays D . Each tap is weighted by a coefficient A . Filtering is
n n
achieved by passing the signal through a number of delay paths and adding these delayed
signals. The delays correspond to the positions of IDT fingers on a substrate. The coefficients
correspond to weighting coefficients given to the IDT fingers. The frequency response of the
filter H(f) is given by a discrete Fourier transformation, expressed as the following equation at
a frequency f:
N n
H( f ) = A exp (−j2πfT ) T = D (1)
n i
∑ n n ∑
n =1 i=1
where T is the accumulated delay at the nth tap.
n
Both amplitude and phase characteristics of the transversal filter are given by two sets of
variables: weighting coefficients A and delays D of the sampling taps.
n n
The SAW transversal filter is essentially constructed with a pair of transducers on a
piezoelectric substrate as shown in figure 4. When an electrical signal is applied to the input
IDT, the surface wave is generated by means of the piezoelectric effect and propagates in
both directions along the substrate surface. The surface wave is converted again into an
electrical signal at the output IDT. If the IDT spatial period 2d is uniform, maximum efficiency
can be achieved at the frequency for which the surface wave propagates one transducer
period synchronously in one RF signal period. The centre frequency f of the IDT is given by
this synchronization condition:
2(df = ν 2)
0 s
where ν is the SAW velocity.
s
60862-2 © IEC:2002 – 31 –
When the SAW transversal filter has two uniform identical transducers, its frequency response
is as shown in figure 5. The transfer function T(f) is approximately expressed as
⎛ sin x ⎞
T(f) = (3)
⎜ ⎟
⎝ x ⎠
where
Nπ( f − f )
x = and
f
N is the number of finger pairs.
IEC  1159/02
Figure 1 – Frequency response of a SAW filter
5.2 Weighting methods
The IDT operates as a kind of transversal filter with N taps for the weighting. A number of
weighting methods are applicable, for example apodization, withdrawal and series (dog-leg)
weighting.
a) Apodization weighting
An apodized transducer, as shown in figure 6, is most commonly used to achieve
weighting. An acoustic wave is generated or detected only in regions where adjacent
electrodes of opposite polarity overlap.
b) Withdrawal weighting
Weighting is achieved by selectively withdrawing electrodes, as illustrated in figure 7, to
equate with the desired weighting function.
c) Series (dog-leg) weighting
Weighting is achieved by dividing the voltage by segmenting each electrode pair, as
shown in figure 8.
60862-2 © IEC:2002 – 33 –
IEC  1160/02
Figure 2 – Applicable range of frequency and relative bandwidth of
the SAW filter and the other filters
Figure 3 – Schematic diagram showing signal flow through a transversal filter

60862-2 © IEC:2002 – 35 –
Figure 4 – Basic configuration of a SAW transversal filter
IEC  1161/02
Figure 5 – Frequency response of the SAW transversal filter shown in figure 4,
where f is the centre frequency and N is the number
of finger pairs of the IDT
60862-2 © IEC:2002 – 37 –
Figure 6 – Apodization weighting obtained by apodizing fingers
Figure 7 – Withdrawal weighting obtained by selective withdrawal of the fingers
Figure 8 – Series weighting obtained by the dog-leg structure

60862-2 © IEC:2002 – 39 –
5.3 Filter configurations and their general characteristics
In some cases, the split-finger (double electrode) configuration, as shown in figure 9, is used
to reduce SAW reflections at the metal electrodes. With this geometry, the individual
reflections, caused by the discontinuity in acoustic impedances on the surface, are cancelled
in each finger pair. This finger configuration is now popular in SAW TV-IF filters, etc.
Ordinary IDTs show bidirectional property. These bidirectional IDTs transmit and receive SAWs to
and from two directions respectively. For instance, a transmitting IDT converts an electric signal
into SAWs. The SAW propagates both forwards and backwards with the same intensities.
A receiving IDT will receive either of them with the same efficiency. This means that
bidirectional loss values can be estimated at 3 dB each at the transmitting and receiving IDT.
Therefore, the bidirectional loss of 6 dB is inherent and is the minimum insertion attenuation
in a bidirectional two-transducer SAW filter. Moreover, in these ordinary SAW filters
accompanying the bidirectionality, strong pass-band ripple is induced by the triple transit echo
(TTE) when the impedances of transmitting IDT and the receiving IDT are matched to the
outer loads.
In order to reduce the bidirectional loss and the triple transit echo (TTE) in SAW transversal
filters, multi-IDT (IIDT) filters (including three-IDT SAW filters) and unidirectional IDT filters
are utilized.
Additionally, reflector filters (see figures 19 and 20) can be included as one of the transversal
filters. Grating technology is widely used as a reflector which changes SAW's propagation
direction with some reflection frequency response. The reflector filters utilize not only their
own transversal filter characteristics which are derived from the transducers but also the
reflection frequency responses of the reflector in various grating constitutions in order to
actively shape the filter transfer function and to reduce their chip length by folding the SAW
propagation.
A brief summary of the configurations, the principles and/or the characteristics of individual
types of SAW filters is given in the following subclauses.
Figure 9 – Split-finger (double electrode) configuration

60862-2 © IEC:2002 – 41 –
5.3.1 Bidirectional IDT filters
5.3.1.1 Bidirectional two-IDT filters
In the ordinary bidirectional two-IDT filters, as shown in figure 4, the TTE is reduced to a
sufficiently low level at the sacrifice of the insertion attenuation, by mis-matching the IDTs to
the outer loads.
a) Frequency symmetrical band-pass filter
The centre frequency and bandwidth for an IDT are given by the periods of the fingers and
the number of finger pairs of the IDT, respectively. In phase characteristics, phase lag
increases proportionally with frequency. Therefore, group delay is invariant in the pass-
band. One typical application of a frequency symmetric band-pass filter is as an IF filter
for radio transmission equipment. Linear-phase characteristics and flat pass-band
amplitude characteristics are preferable for the system requirement. Figure 10 shows a
typical frequency response of a SAW filter whose nominal frequency is 70,0 MHz. High-
frequency SAW filters are also available with higher selectivity.
b) Frequency asymmetrical band-pass filter
In the SAW transversal filters, the amplitude and phase characteristics can be designed
independently. Asymmetrical pass-band, stop-band and/or group delay characteristics in
relation to the reference frequency are obtainable by means of a sophisticated design
technique. SAW TV-IF filters have frequency asymmetrical characteristics, as shown in
figure 11.
c) Other filter categories
Comb filters have also been proposed and are available. SAW matched filters are applied
to recent civil spread spectrum (SS) systems, for example wireless LAN, etc. SAW filters
with Nyquist characteristics have been
...