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Microwave MeasurementsWaveguide

Dept. of Electrical, Computer and Biomedical Engineering,University of Pavia

e-mail: [email protected]: microwave.unipv.it

1Microwave Measurements, L. Silvestri


Outline• Common types of waveguides

• Standards for rectangular waveguides

• Attenuation

• Flanges

• Waveguide/coaxial cable transitions


Waveguide: why?Waveguides are used for high quality factor microwave components such as

filters, resonant cavities, isolators, couplers, etc. Generally they are used when

high performances in terms of low losses and high power are fundamental.

Coaxial to waveguide transition

Waveguide component

Type of waveguides: rectangularWaveguides are widely used up to around 300 GHz.

Microwave Measurements, L. Silvestri 4

From: ATMmicrowaveFrom: Smithsinterconnect

Cut-off frequencyThe cut-off fequency sets the frequency limit for a specific propagating mode.

Each mode has a different cut-off frequency. The first propagating mode in a

rectangular waveguide is the TE10 mode.


From: Maurizio Bozzi, Campi Elettromagnetici e Circuiti - Propagazione Guidata

Cut-off frequency


𝛽𝛽 =𝑚𝑚𝜋𝜋𝑎𝑎

2+

𝑛𝑛𝜋𝜋𝑏𝑏

2

𝑓𝑓𝑐𝑐, 𝑚𝑚𝑚𝑚 =1

2𝜋𝜋 𝜖𝜖𝜖𝜖𝑚𝑚𝜋𝜋𝑎𝑎

2+

𝑛𝑛𝜋𝜋𝑏𝑏

2

From: Maurizio Bozzi, Campi Elettromagnetici e Circuiti - Propagazione Guidata

Waveguides are used in the monomodal band

Type of waveguides: circularCircular waveguides are waveguide where the first propagating mode is

the TE11 mode, due to two degenerate modes (with same cut-off frequency).


Less common: ridge and flexibleRidge waveguides


Flexible waveguides

From: Flann From: Flexiguide

Rectangular waveguides standars


From: everythingrf.com

EIA:US standard,The name is related to the a dimensions in inches.

RCSC:Uk standardIt uses increasingnumbers as the cut-off frequency increases.

IEC:International ElectrotechnicalCommission.Not very common.


From: everythingrf.com

Rectangular waveguides standars

Metallic loss in rectangular wav.


α = 2𝜋𝜋2𝑅𝑅𝑠𝑠(𝑏𝑏 +𝑎𝑎2

+𝑏𝑏2𝑎𝑎3

2𝜋𝜋2)/(𝜔𝜔𝜖𝜖𝑎𝑎3𝑏𝑏𝛽𝛽)

f

α

fc

Rule of thumb: waveguide should be used approximately starting from a

frequency 30% higher than the cut-off frequency.

FlangesFlanges are used to connect different waveguides together.

The number of holes, their position and the mating faces should be taken

into account when buying a new waveguide.


From: Giwaveguide

Flange terminology


Considering the mating faces different flanges can be choosen:

Plain face:The simplest of all, it can be mated with the o-ring or the choke.

O-ring:There is a groove in the face where an O-ring is placed. Not to be used withanother O-ring.

Choke:Two grooves with the outermost dedicated to the housing of the O-ring andthe innermost for a choke.

Flange terminology


From: ATMmicrowave

Flanges can have a rectangular, square or circular shape.

Wg to Wg transitions


From:Pasternack

Different waveguide to waveguide transitions can be found on the market.

They are used to change the flange type and/or the waveguides

dimensions.

Wg to Wg transitions: example


From:Pasternack

Wg to coaxial cable transitions


From: Quinstar

Different connectors can be installed, in relation with the operational

frequency and the environment they will be used in.

Alignment pin

Wg to coax transition: E-plane


Side

TE10

D

Front

Front

Wg to coax transition: H-plane


Side

D≈λ/4

Front

Front

D

Wg/coax cable transitions:example


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