EE 350 / ECE 490 Analog Communication Systems

EE 350 / ECE 490Analog Communication

SystemsCh. 15 – Waveguides &

Radar

4/20/2010R. Munden - Fairfield University 1

R. Munden - Fairfield University

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Objectives Differentiate among sending signals on transmission lines,

antennas, and waveguides based on power and distance Describe basic modes of operation for rectangular waveguides Calculate the cutoff wavelength for the dominant mode of

operation Provide a physical picture of waveguide propagation, including

the concepts of guide wavelength and velocity Describe other types of waveguides including circular, ridged,

flexible, bends, twists, tees, tuners, terminations, attenuators, and directional couples

Explain three methods for coupling energy into or out of a waveguide and the uses for cavity resonators

Calculate an object’s velocity when using a Doppler radar system Calculate the characteristic impedance for microstrip and

stripline.4/20/2010


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15-1 Comparison of Transmission Systems

Waveguides allow you to send much more power over short distances than you could with transmission lines or antennas

At long distances waveguides are less efficient than antennas

There is also a frequency dependence: transmission lines above DC, antennas above 100 kHz, waveguides above 300 MHz

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Power vs. Distance

F i g u r e 1 5 - 1 I n p u t p o w e r r e q u i r e d v e r s u s d i s t a n c e f o r fi x e d r e c e i v e r p o w e r.


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15-2 Types of Waveguides

Waveguide Operation

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Waveguide Construction

F i g u r e 1 5 - 2 Tr a n s f o r m i n g a t r a n s m i s s i o n l i n e i n t o a w a v e g u i d e .


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Waveguide Dimensions

F i g u r e 1 5 - 3 Wa v e g u i d e d i m e n s i o n d e s i g n a t i o n .

The width, a, needs to be λ/2, while b is about half that. This is why waveguide is only used for high frequencies, otherwise the size would be far too large.


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Modes

F i g u r e 1 5 - 4 E x a m p l e s o f m o d e s o f o p e r a t i o n i n r e c t a n g u l a r w a v e g u i d e s .

Multiple modes may travel down a waveguide simultaneously


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Falstad EM Waveguide Applet

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http://www.falstad.com/embox/guide.html




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Dominant Mode Operation

TE10 is the “natural” or dominant mode of operation TE10 has the lowest cut-off frequency and there is a

frequency “gap” before the next higher mode can be excited

TE10 allows the physically smallest waveguide for a given frequency

Cutoff wavelength: λco = 2a For X-band waveguide is 0.9 x 0.4 in, λco = 1.8 in or

4.56 cm fco = 6.56 GHz, with the next highest mode being

TE20 at 13.1 GHz, so the recommended range of operation is 8.2 – 12.4 GHz

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Waveguide Bands / Sizes

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Range Internal InternalGHz (inches) (mm. approx) U.S. (EIA) Narda1.12 - 1.7 6.5 x 3.25 165.0 x 83.0 WR650 L1.45 - 2.2 5.1 x 2.55 131.0 x 65.0 WR5101.7 - 2.6 4.3 x 2.15 109.0 x 55.0 WR430 LS2.2 - 3.3 3.4 x 1.7 86.0 x 43.0 WR3402.6 - 3.95 2.84 x 1.34 72.0 x 34.0 WR284 S3.3 - 4.9 2.29 x 1.145 59.0 x 29.0 WR229 A(7.5cm)3.95 - 5.85 1.872 x 0.872 48.0 x 22.0 WR187 C4.9 - 7.05 1.59 x 0.795 40.0 x 20.0 WR1595.85 - 8.2 1.372 x 0.622 35.0 x 16.0 WR137 XN7.05 - 10.0 1.122 x 0.497 29.0 x 13.0 WR112 XB8.2 - 12.4 0.9 x 0.4 23.0 x 10.0 WR90 X10.0 - 15.0 0.75 x 0.375 19.0 x 9.5 WR7512.4 - 18.0 0.622 x 0.311 16.0 x 7.9 WR62 KU15.0 - 22.0 0.510 x 0.255 13.0 x 5.8 WR5118.0 - 26.5 0.420 x 0.170 11.0 x 4.3 WR42 K22.0 - 33.0 0.340 x 0.170 8.6 x 4.3 WR3426.5 - 40.0 0.280 x 0.140 7.1 x 3.6 WR28 V33.0 - 50.0 0.224 x 0.112 5.7 x 2.9 WR22 Q40.0 - 60.0 0.188 x 0.094 4.8 x 2.4 WR1950.0 - 75.0 0.148 x 0.074 3.8 x 1.9 WR15 M60.0 - 90.0 0.122 x 0.061 3.1 x 1.6 WR12 E75.0 - 110.0 0.100 x 0.050 2.4 x 1.3 WR1090.0 - 140.0 0.080 x 0.040 2.0 x 1.0 WR8 N110.0 - 170.0 0.065 x 0.0325 1.7 x 0.82 WR7140.0 - 220.0 0.051 x 0.0255 1.3 x 0.65 WR5 A(7.5cm)170.0 - 260.0 0.043 x 0.0215 1.1 x 0.55 WR4220.0 - 325.0 0.034 x 0.017 0.87 x 0.44 WR3 R


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15-3 Physical Picture of Waveguide Propagation

You can imagine EM waves bouncing off the walls of the waveguide, much like total internal reflection. The lower the frequency the more perpendicular to the walls the waves must travel to reflect and interfere properly, eventually, below the cutoff frequency the waves travel entirely perpendicular, and no energy propagates down the wavegude.

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Wave paths

F i g u r e 1 5 - 5 P a t h s f o l l o w e d b y w a v e s t r a v e l i n g b a c k a n d f o r t h b e t w e e n t h e w a l l s o f a w a v e g u i d e .


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Wavefront propagation Group Velocity:

Guide Wavelength:

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2

21sin

ac

Vg

F i g u r e 1 5 - 6 Wa v e f r o n t r e fl e c t i o n i n a w a v e g u i d e .

As frequency goes down, wavelength goes up. As this approaches the cutoff wavelength, the wave must be travelling more perpendicular (theta near zero), which lowers the group velocity, eventually stopping propagation of energy when theta = 0 and Vg =0. At this condition in TE10 mode you have one half wavelength of E field across the a direction of the guide.

sin1

space in wavelengthguide in wavelength

g



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Wavefront Reflection


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15-4 Other Types of Waveguides

Rectangular is by far the most common, but special applications may require use of special waveguide configurations

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Circular Waveguide

F i g u r e 1 5 - 8 C i r c u l a r - t o - r e c t a n g u l a r t a p e r.

F i g u r e 1 5 - 7 C i r c u l a r w a v e g u i d e r o t a t i n g j o i n t . Circular waveguide

Advantages:Simple to manufactureRotationally symmetric – ideal for rotating radar installationsDisadvantages:Twice the cross-section necessaryExpensiveOnly 15% bandwidth as opposed to 50% BW for dominant mode


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Ridged Waveguide

F i g u r e 1 5 - 9 R i d g e d w a v e g u i d e s .

Allow longer wavelengths (lower frequencies) with smaller outside dimensions. Allow larger bandwidth. More expensive to manufacture, so only used when space is a premium (i.e. satellites).


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Flexible Waveguide

F i g u r e 1 5 - 1 0 F l e x i b l e w a v e g u i d e .

Spiral wound ribbons of metal allow continuous flexing for special applications. Usually coated with rubber to maintain seal, and are often pressurized to prevent water or dust buildup or are coated with silver or gold to prevent corrosion


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15-5 Other Waveguide Considerations

Waveguide Attenuation Waveguides can propagate up to 1 MW at 1.5 fco in

air. Generally waveguide losses are highest below fco Above fco, the waveguide supports some travelling

waves which have attenuation due to skin effect of walls and the dielectric losses.

Generally attenuation drops approaching fco, then is a broad minimum, and gradually rises as frequency increases

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Waveguide Bends and Twists

F i g u r e 1 5 - 1 1 Wa v e g u i d e b e n d s a n d t w i s t s .

H lines are bent E lines are bent E lines polarization plane is changed

These are used to mechanically move the wave around corners, or to change its polarization. Often governed by “plumbing” considerations.


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Waveguide Tees

F i g u r e 1 5 - 1 2 S h u n t , s e r i e s , a n d h y b r i d t e e s .

Shunt – A+B add in phase to C, or C splits equally into A & B

Series – D splits equally, but opposite phase, into A and B. D can be used with a piston for a short circuit stub.

Hybrid or Magic Tee – combines the two previous forms, many interesting applications


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Magic Tee

F i g u r e 1 5 - 1 3 H y b r i d - t e e T R s w i t c h .


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Tuners

F i g u r e 1 5 - 1 4 Tu n e r s .

Similar to shorted stub in a transmission line.If less than ¼ wave it looks capacitive, if longer it looks inductive.

Can be used to match loads.a) Is like a single-stub tuner

b) Is like a double-stub tuner


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15-6 Termination and Attenuation

Characteristic Wave Impedance (depends on frequency):

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377)2/(1 20

L

La

Z



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Termination

F i g u r e 1 5 - 1 5 Te r m i n a t i o n f o r m i n i m u m r e fl e c t i o n s .

Graphite Sand or a high resistance rod or wedge at the end will serve to dissipate the energy as heat, preventing reflections back up the waveguide


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Attenuators

F i g u r e 1 5 - 1 6 A t t e n u a t o r s .

a) Flap attenuator, insertion of a resistive card causes attenuation, this is varied by how much the card is inserted.

b) Vane attenuator positions the vanes near the edges for low attenuation or the center for high attenuation


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15-7 Directional Coupler Power moving from left to right couples into the

secondary, while power moving from right-to-left is dissipated in the secondary’s vane.

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F i g u r e 1 5 - 1 7 Tw o - h o l e d i r e c t i o n a l c o u p l e r.

out

in

PPdBcoupling log10)(



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15-8 Coupling Waveguide Energy and Cavity Resonators

Coupling into the waveguide is accomplished by Probe, Loop, or Aperture coupling.

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Probe Coupling

F i g u r e 1 5 - 1 8 P r o b e , o r c a p a c i t i v e , c o u p l i n g .

The coax probe should be at the center of a and a ¼ wavelength from the end of the guide for maximum coupling


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Loop Coupling

F i g u r e 1 5 - 1 9 L o o p , o r i n d u c t i v e , c o u p l i n g .


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Aperture Coupling

F i g u r e 1 5 - 2 0 A p e r t u r e , o r s l o t , c o u p l i n g .

Provide electric, magnetic, or EM field coupling


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Cavity Resonators

F i g u r e 1 5 - 2 1 R e c t a n g u l a r w a v e g u i d e r e s o n a t o r.

Cavity Resonators are used at microwave frequencies in place of standard LC resonant circuits, just like transmission lines can be used in place of LC resonators in RF applications.


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Cavity Tuning

F i g u r e 1 5 - 2 2 C a v i t y t u n i n g b y v o l u m e .

Cavity volume can be tuned. Decreasing d increases f, and increasing d decreases f

Tuning can also be accomplished by inserting a non-ferrous screw or paddle near maximum H to increase or decrease the inductance inversely decreasing or increasing f.


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15-9 Radar

Radio Detection and Ranging Fundamentally a microwave transmitter and

receiver Measures waves reflected from an object such as a

plane Uses a directional antenna to determine range and

distance to the object Generally the larger the antenna, the better the

resolution

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Radar Waveform and Range Determination

F i g u r e 1 5 - 2 3 R a d a r p u l s e s .

Speed of light, c = 186000 mi/s or 162000 nautical mi/s (6076 ft/s)Radar mile is 2000 yards (6000 ft). Range found from time, 6.18us to travel 1 radar mile. Range = t/12.36Can be calculated from speed of light


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Radar System Parameters

F i g u r e 1 5 - 2 4 S e c o n d r e t u r n e c h o .

Max unambiguous range = PRT/12.2Minimum Range = 150 PWDuty cycle = PW / PRT


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F i g u r e 1 5 - 2 5 D o u b l e r a n g e e c h o .

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F i g u r e 1 5 - 2 6 R a d a r s y s t e m b l o c k d i a g r a m .

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15-10 RFID - Radio Frequency Identification

Powering the Tag Frequency of Operation Communications (Air Interface) Protocol

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F i g u r e 1 5 - 2 7 B a s i c b l o c k d i a g r a m o f a n R F I D s y s t e m .

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F i g u r e 1 5 - 2 8 E x a m p l e s o f ( a ) s i n g l e - d i p o l e a n d ( b ) d u a l - d i p o l e R F I D i n l a y s . ( 2 0 0 7 S y m b o l Te c h n o l o g i e s , I n c . Re p r i n t e d w i t h p e r m i s s i o n . )

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F i g u r e 1 5 - 2 9 T h e G 2 C 5 0 1 a c t i v e R F I D t a g f r o m G 2 M i c r o s y s t e m s . ( C o u r t e s y o f G 2 M i c r o s y s t e m s . )

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F i g u r e 1 5 - 3 0 T h e f r e q u e n c y b a n d s u s e d b y R F I D t a g s .

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15-11 Microintegrated Circuit Waveguiding

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F i g u r e 1 5 - 3 1 S t r i p l i n e a n d m i c r o s t r i p .

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F i g u r e 1 5 - 3 2 C h a r a c t e r i s t i c i m p e d a n c e .

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F i g u r e 1 5 - 3 3 M i c r o s t r i p c i r c u i t e q u i v a l e n t s .

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F i g u r e 1 5 - 3 4 D i e l e c t r i c w a v e g u i d e a n d d i e l e c t r i c - fi l l e d w a v e g u i d e .

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15-12 Troubleshooting

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F i g u r e 1 5 - 3 5 V S W R t e s t .

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F i g u r e 1 5 - 3 6 L o s s t e s t .

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15-13 Troubleshooting w/ Multisim

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F i g u r e 1 5 - 3 7 T h e c i r c u i t e x a m p l e o f a l o w - l o s s w a v e g u i d e s e c t i o n c o n n e c t e d t o a n e t w o r k a n a l y z e r.

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F i g u r e 1 5 - 3 8 T h e s i m u l a t i o n o f a l o w - l o s s w a v e g u i d e a s v i e w e d w i t h t h e n e t w o r k a n a l y z e r.

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F i g u r e 1 5 - 3 9 T h e s i m u l a t i o n o f a v e r y l o s s y w a v e g u i d e .

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F i g u r e 1 5 - 4 0 A n e x a m p l e o f a t e s t o n t h e M u l t i s i m s a m p l e l o s s y t r a n s m i s s i o n l i n e .

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F i g u r e 1 5 - 4 1 T h e s i m u l a t i o n r e s u l t s o f t h e l o s s y t r a n s m i s s i o n l i n e p r o v i d e d b y E W B M u l t i s i m .

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EE 350 / ECE 490 Analog Communication Systems

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