co axial switch.pdf

7/29/2019 Co axial switch.pdf

1/5

TUTORIAL SERIES

Dow-Key Microwave | www.dowkey.com | 800.266.3695 1

Your Sw itch Solution Since 1945 Rev. 0611

Guide to Selecting a Coaxial SwitchAcoaxialswitch isanelectromechanicalrelay apassivecomponent usedtodirectRFsignalsfromonepathto

anotherpath.Thistypeofswitch iswidelyused insignalroutingapplicationswherehighfrequency,highpower,

andgreatRFperformancesarerequired. It iscommonlyused inRFapplicationstestingDUT,switchingbetween

antennas,SATCOM,Telecom,base stations,avionics,or inanyother applicationswhereRF signalsneed tobe

routedfromonepointtoanother.

IdentifySwitchConfiguration: PolesandThrows

Whenwetalkaboutcoaxialswitches,wetalkabout

poles and throws where number of poles (P)

refersto

number

of

input

ports

and

number

of

throws(T) indicatestheoutputports. For instance,

oneinputandtwooutputportsaredeclaredasSPDT

switch:meaningsinglepoledoublethrow. Youmay

refertoitas1P2Taswell. So ifyouhaveoneinput

and 14 outputs, a SP14T switch will reflect this

configuration.

Hence, the first step toselectacoaxial switch is to

understand the number of paths that need to be

routed and select a coaxial switch thatmeets this

requirement.As

aresult,

it

will

quickly

narrow

down

yourchoicestofewswitchseries.

DowKeycoaxialswitchesarebidirectionalsuchthat

the same switch canbeusedforbothe.g.1x2and

2x1 applications.Also, DowKey offers SDPT up to

SP14T switches. For larger configurations, multiple

switcheswillneedtobecascaded.

IdentifySwitchParametersandCharacteristics

Letssayyourapplication is to switchbetween two

antennasignals.

Right

off

you

know

that

aSPDT

switch is needed. Although it narrows down your

selectiontoaSPDTswitch,youarefacedwithmany

typical parameters to choose from as specified by

theswitch industry.Wewilltakeacloser lookatall

of them; impedance, frequency and connector

relation, power handling, coil voltage, actuator

types, terminations, indicators, circuit control, and

otherspecial

options.

Impedance

The standard impedance in a coaxial line for RF

power transmission in theU.S. is either50ohmor

75ohm impedance(thereasonbehindthesevalues

ought to be discussed outside the scope of this

tutorialseries).These industrystandardsarewidely

used incoaxialcablesandaswellinRFapplications.

Duetotransmissiontheory,itisdesiredtominimize

reflectionsandmaximizepowertransferoverawide

bandwidth and therefore, impedance matching is

critical.Topreventreflectionofthesignalback into

thesource,theloadmustbematchedexactlytothe

source impedance. As a result, it is important to

understandwhether your transmission line isa50

ohm (most common) or a 75ohm (common in

broadcastingandvideosignals)andselectacoaxial

switch that isdesignedaccordingly.Majorityof the

coaxial switches in the microwave industry is

designedfor50ohmapplicationsandso isDowKey

switches.

DowKey switches are by default 50ohm switches

unlessstatedotherwise.


2/5

TUTORIAL SERIES



FrequencyandConnectorTypes

Nextstepinselectingtheappropriatecoaxialswitch

for your application is to specify the frequency of

yourapplication.Coaxialswitchescanhandlesignals

as high as 40 GHz, where different switch series

support different range of frequencies. Before

digging deeper into the DowKey switches, it is

critical to understand that the frequency range is

limited by the type of connector one selects. The

reverse can be said as well, that the required

frequency limits the type of RF connector one can

select.

For40GHzapplications,2.9mmconnectorsmustbe

used

as

it

is

designed

specifically

for

high

frequency

applications. SMA connectors are most commonly

used as it can handle up to 27 GHz.Next popular

connectorsareNandTNCtypeandtheyoperateup

to 12.4 GHz. Lastly, DowKey also offers BNC

connectors that go to 4 GHz. With better

understandingofthelimitationeachconnectortype

puts on the operating frequency, DowKey coaxial

switch series are offered with the following

connectoroptions:

DC4GHz (withBNCconnector) DC12.4GHz (withNorTNCconnector) DC18GHz (withSMAconnector) DC26.5GHz (withSMAconnector) DC40GHz (with2.9mmconnector)

RFPowerHandling

Powerhandingcapabilityisoftenakeyspecification

inanapplicationand inselectingcomponents.How

much power a switch can handle depends on the

mechanical design, materials, and connector type

used inaswitch.External factorssuchas frequency

ofoperation,

ambient

temperature

and

altitude

over

sea level, further limits the power capacity in a

switch.

The average power a.k.a. CW (ContinuesWave) is

summarized inthePowerChartshownbelow.Note

how the power capability decreases as the

frequency increases. This power chart is based on

ambienttemperature

(40

degree

C),

at

sea

level,

at

a

VSWRof1.0:1andnonswitchingcondition.Ifanyof

thisfactorschanges,thepowerwillbederated.

DowKey

further

offers

high

power

options

for

most

switchesandthisisindicatedbytheAoption.Note

thatNandTNCconnectorscanhandlehigherpower

compared to the SMA connector at the same

frequency. The SCconnector can handle themost

powercomparedtoallotherconnectors.

It is recommended to contact DowKeys technical

teamforpeakpowerandderatedpowerconditions.

CoilVoltage

Nowthatwehavefiguredoutthemostcriticalspecs

of a coaxial switch, we are faced with a range of

selections that solely depends on the users

preference.


3/5

TUTORIAL SERIES



Ascoaxialswitchesconsistofsolenoidcoilsandare

inpresentofmagnets,DCvoltageisneededtoforce

the relay to switch toaRFpositionusingmagnetic

field theory. Therefore, one needs to select a coil

voltage.MostcommonDowKeycoilvoltageoptions

are:

CoilVoltage VoltageRange

12Vdc 1114Vdc

15Vdc 1317Vdc

24Vdc 2028Vdc

28Vdc 2432Vdc

For other coil voltage requirements contact Dow

Keystechnicalteam.

ActuatorType

An actuator is refereeing to the electromechanical

mechanismthattransferstheRFcontacts fromone

position to another in a switch. Most DowKey

actuators use magnetic solenoids acting on a

mechanical linkage to the RF contacts. When

selectingaswitch,youare facedwithfourdifferent

actuatortypes,dependingontheswitchseries.

FailsafeType: Afailsafeswitchbydefaultconnects

the input to a known output without any power

applied to the switch. It requires continuously

appliedDCvoltagetomaintainRFconnectiontoany

other position. Hence, at power loss a failsafe

switchwillactuatetoitsdefaultposition.

Thisoption isavailablewithSPDT,2/3andTransfer

DPDTswitches.

Pulse Latching: A latching switch maintains its

positionanddrawscontinuescurrenttodoso,until

apulsedDCvoltagecommandstheswitchtochange

its position. Hence, at power loss a pulse latched

actuatorremainsinitslastposition.

Thisoption isavailablewithSPDT,2/3andTransfer

DPDTswitches.

Latching Self CutOff: Like the pulse latching

actuatortheswitchstaysinitspositionuntilapulsed

DCvoltagecommandstheswitchtochangeRFpath,

and at power loss a latching self cutoff actuator

remains in its lastposition.However,thedifference

lies in thata selfcutoff latching switchonlydraws

current when changing its position and stops

drawing current to keep its position. For power

sensitive applications, this is the best actuator

option.

Thisoptionisavailablewithmostcoaxialswitches.

NormallyOpen: In a normally open switch, all RF

pathswillremainopenbydefault.Theswitchneeds

tobecommendedthroughaDCvoltagetocloseaRF

pathand itdrawscontinuouscurrent to remains in

its position.Hence, at power loss a normally open

actuatorwillopenallitsRFpaths.

This option is available with multiposition SPnT

switches.

Suppression Diodes: Failsafe, Pulse Latching, and

Normally Open actuators are also offered with

suppressiondiodes.What itdoes is to limitvoltage

spikesorreversecurrentfromenteringtheelectrical

circuitry of the switch and therefore prevents the

switch frombeingdamaged if such incidentswould

occur.

Suppression Diodes are by default included in all

Latching SelfCutOffactuators.Thisfeaturecanbe

addedtononTTLswitches.


4/5

TUTORIAL SERIES



Terminations

DowKey offers terminated switches as an option;

eitherinternalorexternalterminations.ARFcoaxial

terminationprovidesa resistivepower termination,

to properly terminate the output port as shown

belowforaSPDTswitch.

Terminationsare

available

in

various

power

ratings

andDowKeyusuallyoffers2W50ohmand5W50

ohmterminations.

Indicators

DowKey offersmechanical indicators as an option

with all coaxial switches. This form of indicator

(asshown inbelow figure foraSPnTswitch)closes

internallyamechanicalpathwhencorrespondingRF

positionisclosed.Consequently,whentheRFpathis

off

(open)

the

indicator

opens

its

corresponding

mechanicalpath.

Thusinordertomonitortheindicationoftheswitch

position,theuserneedstocreateacircuitbetween

themechanical indicatorpaths suchwhen thepath

isclosed itclosestheexternalcircuit,andthewhen

switch position is off the external circuit will be

opened.

CircuitControl

Theuserhas theoption tocontrolacoaxial switch

withTTLlogicorCANBusinterface.

TTLlogicstandsforTransistorTransistorLogicandis

awellknowncontrolsignalinthedigitalworld.Dow

Key offersboth Low andHigh TTL logic levelswith

voltagelevelsasshownbelow.

TTLHigh

Option

TTLLow

Option

PathisON (1) 2.45.5Vdc 00.8Vdc

PathisOFF (0) 00.8Vdc 2.45.5Vdc

Suppression

Diodes

are

by

default

included

in

all

TTL

options. Naturally, this cannot be combined with

actuator types that call out suppression diodes, as

thisisalreadyincludedintheTTLoption.

CANBus (Controller area Network) switches are

designedmainlytobeusedwithourBuildYourOwn

Switch Solution Kit, but it can also be used

independently for the software savvyuser.CANBus

technology provided an easier way to integrate

switches into a system level solution compared to

TTLlogic.

CANBusisa4wiresserialbuswithCANLandCANH

sending and receiving messages (but not

simultaneously).Belowchartshowsthecontrolpins

availableonaCANBusswitch.

CANBus

Pin1 +12Vdc

Pin2 CANL

Pin3 CANH

Pin4 RTN


5/5

TUTORIAL SERIES



SpecialOptions

DowKey coaxial switches are offered with many

options tomeetany typeof specificationand to fit

mostapplication.

Extended Temperature: This option extends the

standard operating temperature from 25C to

+65 C to 25 Cto+85 C.

EpoxySeal: Itextendsthestandardnoncondensing

humidlyratingfrom90%to95%.

Immersion

Seal:

It

extends

the

non

condensing

humidlyratingfrom90%to100%(waterproof).

DsubConnector:Insteadofstandardterminalpins,

a dsub connector (9pin, 15pin, or 25pin) is

availabledependingontheswitchseries.

PowerConnector:Insteadofstandardterminalpins,

acircularplugisavailable.

Reverse Polarity: Instead of +Vdc and COM coil

voltageterminals,

the

reverse

polarity

Vdc

and

+COMisavailable.

26.5 GHz: Extends the standard DC18 GHz

bandwidth to DC26.5 GHz. This option is only

availableforsomeseries.

40GHz:ExtendsthestandardDC18GHzbandwidth

toDC40GHz.Thisoption isonlyavailableforsome

series.

FlangeMount:

Radial

switches

are

not

offered

with

mounting holes. This feature can be available by

addingaflange.

MountingBracket: Ifmountingholesrequiredother

than the ones available on a flange, this option is

offeredasanalternative.

Bypass:This

options

applies

to

transfer

DPDT

switches only. One can select to bypass a specific

path:J1J2,J2J4,J3J4,orJ1J3.

LowPIM:Extendsthestandard 110dBcPIMlevelto

160dBc.Thisoptionisavailableformostswitches.

Most specials options can be combined and it is

recommendedtoconsultwithDowKeyfordetails.

co axial switch.pdf

Documents