July, 19985 - 1RF100 (c) 1998 Scott Baxter Antennas for Wireless Systems Antennas for Wireless...

July, 1998 5 - 1RF100 (c) 1998 Scott Baxter

Antennas for Wireless Systems

Antennas for Wireless Systems

Chapter 5

Dipole

Typical WirelessOmni Antenna

Isotropic


Introduction toAntennas for Wireless

Introduction toAntennas for Wireless

Chapter 5 Section A


Understanding Antenna RadiationThe Principle Of Current Moments

An antenna is just a passive conductor carrying RF current

• RF power causes the current flow• Current flowing radiates

electromagnetic fields• Electromagnetic fields cause

current in receiving antennas The effect of the total antenna is the sum

of what every tiny “slice” of the antenna is doing

• Radiation of a tiny “slice” is proportional to its length times the current in it

• remember, the current has a magnitude and a phase!

TX RX

Width of banddenotes current

magnitude

Zero currentat each end

Maximum currentat the middle

Current induced inreceiving antennais vector sum of

contribution of everytiny “slice” of

radiating antenna

each tiny imaginary “slice”of the antennadoes its share

of radiating


Different Radiation In Different Directions

Each “slice” of the antenna produces a definite amount of radiation at a specific phase angle

Strength of signal received varies, depending on direction of departure from radiating antenna

• In some directions, the components add up in phase to a strong signal level

• In other directions, due to the different distances the various components must travel to reach the receiver, they are out of phase and cancel, leaving a much weaker signal

An antenna’s directivity is the same for transmission & reception

TX

MaximumRadiation:contributions

in phase, reinforce

MinimumRadiation:contributionsout of phase,

cancel

MinimumRadiation:contributionsout of phase,

cancel


Antenna Polarization

To intercept significant energy, a receiving antenna must be oriented parallel to the transmitting antenna

• A receiving antenna oriented at right angles to the transmitting antenna is “cross-polarized”; will have very little current induced

• Vertical polarization is the default convention in wireless telephony• In the cluttered urban environment, energy becomes scattered and “de-

polarized” during propagation, so polarization is not as critical• Handset users hold the antennas at seemingly random angles…..

TX

ElectromagneticField

currentalmost

nocurrent

Antenna 1VerticallyPolarized

Antenna 2Horizontally

Polarized

RX

RF current in a conductor causes electromagnetic fields that seek to induce current flowing in the same direction in other conductors.

The orientation of the antenna is called its polarization.

Coupling between two antennas is proportional to the cosine of the angle of their relative orientation


Antenna Gain

Antennas are passive devices: they do not produce power

• Can only receive power in one form and pass it on in another, minus incidental losses

• Cannot generate power or “amplify” However, an antenna can appear to have “gain”

compared against another antenna or condition. This gain can be expressed in dB or as a power ratio. It applies both to radiating and receiving

A directional antenna, in its direction of maximum radiation, appears to have “gain” compared against a non-directional antenna

Gain in one direction comes at the expense of less radiation in other directions

Antenna Gain is RELATIVE, not ABSOLUTE

• When describing antenna “gain”, the comparison condition must be stated or implied

Omni-directionalAntenna

DirectionalAntenna


Reference Antennas

Isotropic Radiator• Truly non-directional -- in 3 dimensions• Difficult to build or approximate physically, but

mathematically very simple to describe• A popular reference: 1000 MHz and above

– PCS, microwave, etc. Dipole Antenna

• Non-directional in 2-dimensional plane only• Can be easily constructed, physically practical• A popular reference: below 1000 MHz

– 800 MHz. cellular, land mobile, TV & FM

IsotropicAntenna

(watts or dBm) ERP Effective Radiated Power Vs. Dipole

Effective Radiated Power Vs. Isotropic

Gain above Dipole reference

Gain above Isotropic radiator

(watts or dBm) EIRP

dBd

dBi

Quantity Units Dipole Antenna

Notice that a dipolehas 2.15 dB gaincompared to an isotropic antenna.


Effective Radiated Power

An antenna radiates all power fed to it from the transmitter, minus any incidental losses. Every direction gets some amount of power

Effective Radiated Power (ERP) is the apparent power in a particular direction

• Equal to actual transmitter power times antenna gain in that direction

Effective Radiated Power is expressed in comparison to a standard radiator

• ERP: compared with dipole antenna

• EIRP: compared with Isotropic antennaAB

ERP B A (ref)

100w275w

ReferenceAntenna

TX100 W

A

DirectionalAntenna

TX100 W

B

Example: Antennas A and B each radiate 100 watts fromtheir own transmitters. Antenna A is our reference, ithappens to be isotropic.Antenna B is directional. In its maximum direction, itssignal seems 2.75 stronger than the signal from antennaA. Antenna B’s EIRP in this case is 275 watts.


Antenna Gain And ERPExamples

Many wireless systems at 1900 & 800 MHz use omni antennas like the one shown in this figure

These patterns are drawn to scale in E-field radiation units, based on equal power to each antenna

Notice the typical wireless omni antenna concentrates most of its radiation toward the horizon, where users are, at the expense of sending less radiation sharply upward or downward

The wireless antenna’s maximum radiation is 12.1 dB stronger than the isotropic (thus 12.1 dBi gain), and10 dB stronger than the dipole (so 10 dBd gain).

Isotropic

Dipole

Omni

12.1 dBi

10dBd

Gain Comparison

Isotropic

Dipole

Typical WirelessOmni Antenna

Gain 12.1 dBi or 10 dBd


Radiation PatternsKey Features And Terminology

An antenna’s directivity is expressed as a series of patterns

The Horizontal Plane Pattern graphs the radiation as a function of azimuth (i.e..,direction N-E-S-W)

The Vertical Plane Pattern graphs the radiation as a function of elevation (i.e.., up, down, horizontal)

Antennas are often compared by noting specific landmark points on their patterns:

• -3 dB (“HPBW”), -6 dB, -10 dB points

• Front-to-back ratio• Angles of nulls, minor lobes, etc.

Typical Example

Horizontal Plane Pattern

0 (N)

90 (E)

180 (S)

270 (W)

0

-10

-20

-30 dB

Notice -3 dB points

Front-to-back Ratio

10 dBpoints

MainLobe

a MinorLobe

nulls orminima


In phase

Out of phase

How Antennas Achieve Their Gain

Quasi-Optical Techniques (reflection, focusing)• Reflectors can be used to concentrate

radiation– technique works best at microwave frequencies,

where reflectors are small

• Examples:– corner reflector used at cellular or higher

frequencies– parabolic reflector used at microwave frequencies– grid or single pipe reflector for cellular

Array techniques (discrete elements)• Power is fed or coupled to multiple antenna

elements; each element radiates• Elements’ radiation in phase in some

directions• In other directions, a phase delay for each

element creates pattern lobes and nulls


Types Of Arrays

Collinear vertical arrays• Essentially omnidirectional in

horizontal plane• Power gain approximately

equal to the number of elements

• Nulls exist in vertical pattern, unless deliberately filled

Arrays in horizontal plane• Directional in horizontal plane:

useful for sectorization• Yagi

– one driven element, parasitic coupling to others

• Log-periodic– all elements driven– wide bandwidth

All of these types of antennas are used in wireless

RF power

RF power

CollinearVerticalArray

Yagi

Log-Periodic


Omni AntennasCollinear Vertical Arrays

The family of omni-directional wireless antennas:

Number of elements determines• Physical size• Gain• Beamwidth, first null angle

Models with many elements have very narrow beamwidths

• Require stable mounting and careful alignment

• Watch out: be sure nulls do not fall in important coverage areas

Rod and grid reflectors are sometimes added for mild directivity

Examples: 800 MHz.: dB803, PD10017, BCR-10O, Kathrein 740-198

1900 MHz.: dB-910, ASPP2933

beamwidth

Angleof

firstnull

-3 dB

Vertical Plane Pattern

Number of Elements

PowerGain

Gain, dB

Angle

0.00 n/a3.01 26.57°4.77 18.43°6.02 14.04°6.99 11.31°7.78 9.46°8.45 8.13°9.03 7.13°9.54 6.34°10.00 5.71°10.41 5.19°10.79 4.76°11.14 4.40°

1234567891011121314

1234567891011121314 11.46 4.09°

Typical Collinear Arrays


Sector AntennasReflectors And Vertical Arrays

Typical commercial sector antennas are vertical combinations of dipoles, yagis, or log-periodic elements with reflector (panel or grid) backing

• Vertical plane pattern is determined by number of vertically-separated elements

– varies from 1 to 8, affecting mainly gain and vertical plane beamwidth

• Horizontal plane pattern is determined by:

– number of horizontally-spaced elements

– shape of reflectors (is reflector folded?)

Vertical Plane PatternUp

Down

Horizontal Plane PatternN

E

S

W


Example Of Antenna Catalog Specifications

Frequency Range, MHz.Gain - dBd/dBiVSWR

Beamwidth (3 dB from maximum)Polarization

Maximum power input - WattsInput Impedance - OhmsLightning ProtectionTermination - StandardJumper Cable

Electrical DataAntenna Model ASPP2933 ASPP2936 dB910C-M

1850-1990 1850-1990 1850-19703/5.1

<1.5:1

32Vertical

40050

Direct GroundN-Female

Order Sep.

6/8.1<1.5:1

15Vertical

40050


Order Sep.

10/12.1<1.5:1

5Vertical

40050


Order Sep.

Mechanical DataAntenna ModelOverall length - in (mm)Radome OD - in (mm)

Wind area - ft2 (m2)Wind load @ 125 mph/201 kph lb-f (n)Maximum wind speed - mph (kph)

Weight - lbs (kg)Shipping Weight - lbs (kg)

Clamps (steel)

ASPP293324 (610)

1.1 (25.4)

.17 (.0155)4 (17)

140 (225)

4 (1.8)11 (4.9)

ASPA320

ASPP293636 (915)

1.0 (25.4)

.25 (.0233)6 (26)

140 (225)

6 (2.7)13 (5.9)

ASPA320

dB910C-M77 (1955)

1.5 (38)

.54 (.05)14 (61)

125 (201)

5.2 (2.4)9 (4.1)

Integral


Example Of Antenna Catalog Radiation Pattern

Vertical Plane Pattern

• E-Plane (elevation plane)

• Gain: 10 dBd

• Dipole pattern is superimposed at scale for comparison (not often shown in commercial catalogs)

• Frequency is shown

• Pattern values shown in dBd

• Note 1-degree indices through region of main lobe for most accurate reading

• Notice minor lobe and null detail!


Other RF ElementsOther RF Elements

Chapter 5 Section B


Antenna Systems

Antenna systems include more than just antennas Transmission Lines

• Necessary to connect transmitting and receiving equipment Other Components necessary to achieve desired system function

• Filters, Combiners, Duplexers - to achieve desired connections• Directional Couplers, wattmeters - for measurement of performance

Manufacturer’s system may include some or all of these items• Remaining items are added individually as needed by system operator

F R

Duplexer

Combiner

BPF

TX

RX

TXTransmission LineJumper

Jumpers

DirectionalCoupler

Antenna


Characteristics Of Transmission Lines

Physical Characteristics Type of line

• Coaxial, stripline, open-wire

• Balanced, unbalanced Physical configuration

• Dielectric:– air– foam

• Outside surface– unjacketed– jacketed

Size (nominal outer diameter)• 1/4”,1/2”, 7/8”, 1-1/4”,

1-5/8”, 2-1/4”, 3”Foam

DielectricAir

Dielectric

Typical coaxial cablesUsed as feeders in wireless applications


Transmission LinesSome Practical Considerations

Transmission lines practical considerations• Periodicity of inner conductor

supporting structure can cause VSWR peaks at some frequencies, so specify the frequency band when ordering

• Air dielectric lines– lower loss than foam-dielectric; dry air

is excellent insulator – shipped pressurized; do not accept

delivery if pressure leak• Foam dielectric lines

– simple, low maintenance; despite slightly higher loss

– small pinholes and leaks can allow water penetration and gradual attenuation increases

FoamDielectric

AirDielectric


Characteristics Of Transmission Lines, Continued

Electrical Characteristics Attenuation

• Varies with frequency, size, dielectric characteristics of insulation

• Usually specified in dB/100 ft and/or dB/100 m

Characteristic impedance Z0 (50 ohms is the usual standard; 75 ohms is sometimes used)

• Value set by inner/outer diameter ratio and dielectric characteristics of insulation

• Connectors must preserve constant impedance (see figure at right)

Velocity factor• Determined by dielectric characteristics

of insulation. Power-handling capability

• Varies with size, conductor materials, dielectric characteristics

dD

Characteristic Impedance of a Coaxial Line

Zo = ( 138 / ( 1/2 ) ) Log10 ( D / d )

= Dielectric Constant = 1 for vacuum or dry air


Transmission LinesSpecial Electrical Properties

Transmission lines have impedance-transforming properties

• When terminated with same impedance as Zo, input to line appears as impedance Zo

• When terminated with impedance different from Zo, input to line is a complex function of frequency and line length. Use Smith Chart or formulae to compute

Special case of interest: Line section one-quarter wavelength long has convenient properties useful in matching networks

• ZIN = (Zo2)/(ZLOAD)

Zo=50ZLOAD=

50ZIN = 50

Matched condition

Zo=50ZLOAD=

83-j22

ZIN = ?

Mismatched condition

Zo=50ZLOAD=

100ZIN=25

/4

ZIN= ZO2

/ ZLOAD

Deliberate mismatchfor impedance transformation


Transmission LinesImportant Installation Practices

Respect specified minimum bending radius!

• Inner conductor must remain concentric, otherwise Zo changes

• Dents, kinks in outer conductor change Zo

Don’t bend large, stiff lines (1-5/8” or larger) to make direct connection with antennas

Use appropriate jumpers, weatherproofed properly.

Secure jumpers against wind vibration.

ObserveMinimumBendingRadius!


Transmission LinesImportant Installation Practices, Continued

During hoisting

• Allow line to support its own weight only for distances approved by manufacturer

• Deformation and stretching may result, changing the Zo

• Use hoisting grips, messenger cable

After mounting

• Support the line with proper mounting clamps at manufacturer’s recommended spacing intervals

• Strong winds will set up damaging metal-fatigue-inducing vibrations

200 ft~60 mMax.

3-6 ft


RF FiltersBasic Characteristics And Specifications

Types of Filters

• Single-pole:– pass

– reject (notch)• Multi-pole:

– band-pass– band-reject

Key electrical characteristics

• Insertion loss• Passband ripple• Passband width

– upper, lower cutoff frequencies

• Attenuation slope at band edge• Ultimate out-of-band attenuation

Typical bandpass filters have insertion loss of 1-3 dB. and passband ripple of 2-6 dB.

Bandwidth is typically 1-20% of center frequency, depending on application. Attenuation slope and out-of-band attenuation depend on # of poles & design

Typical RF bandpass filter

0

Att

enu

atio

n,

dB

Frequency, megaHertz

passband rippleinsertion loss

-3 dB passbandwidth


RF FiltersTypes And Applications

Filters are the basic building blocks of duplexers and more complex devices

Most manufacturers’ network equipment includes internal bandpass filters at receiver input and transmitter output

Filters are also available for special applications

Number of poles (filter elements) and other design variables determine filter’s electrical characteristics

• Bandwidth rejection

• Insertion loss

• Slopes

• Ripple, etc.

Notice construction: RF input excites one quarter-wave element and electromagnet fields propagate from element to element, finally exciting the last element which is directly coupled to the output.

Each element is individually set and forms a pole in the filter’s overall response curve.

Typical RF Bandpass Filter

/4


Basics Of Transmitting Combiners

Allows multiple transmitters to feed single antenna, providing

• Minimum power loss from transmitter to antenna

• Maximum isolation between transmitters

Combiner types• Tuned

– low insertion loss ~1-3 dB– transmitter frequencies must be

significantly separated• Hybrid

– insertion loss -3 dB per stage– no restriction on transmitter frequencies

• Linear amplifier– linearity and intermodulation are major

design and operation issues

Typical tuned combiner application

TX TX TX TX TX TX TX TX

Antenna

Typical hybrid combiner application

TX TX TX TX TX TX TX TX

Antenna

~-3 dB

~-3 dB

~-3 dB


Duplexer Basics

Duplexer allows simultaneous transmitting and receiving on one antenna

• Nortel 1900 MHz BTS RFFEs include internal duplexer

• Nortel 800 MHz BTS does not include duplexer but commercial units can be used if desired

Important duplexer specifications

• TX pass-through insertion loss

• RX pass-through insertion loss

• TX-to-RX isolation at TX frequency (RX intermodulation issue)

• TX-to-RX isolation at RX frequency (TX noise floor issue)

• Internally-generated IMP limit specification

fR fT

RX TX

Antenna

Duplexer

Principle of operation

Duplexer is composed of individualbandpass filters to isolate TX fromRX while allowing access to antennafor both. Filter design determinesactual isolation between TX and RX,and insertion loss TX-to-Antenna and RX-to-Antenna.


Directional Couplers

Couplers are used to measure forward and reflected energy in a transmission line; it has 4 ports:

• Input (from TX), Output (to load)

• Forward and Reverse Samples Sensing loops probe E& I in line

• Equal sensitivity to E & H fields• Terminations absorb induced

current in one direction, leaving only sample of other direction

Typical performance specifications• Coupling factor ~20, ~30,

~40 dB., order as appropriate for application

• Directivity ~30-~40 dB., f($)– defined as relative

attenuation of unwanted direction in each sample

Principle of operation

ZLOAD= 50

Input

Reverse Sample

Forward Sample

RT

RT

Typical directional coupler

Main line’s E & I induce equal signals in sense loops. E is direction-independent, but I’s polarity depends on direction andcancels sample induced in one direction.Thus sense loop signals are directional.One end is used, the other terminated.


Return Loss And VSWR Measurement

A perfect antenna will absorb and radiate all the power fed to it

Real antennas absorb most of the power, but reflect a portion back down the line

A Directional Coupler or Directional Wattmeter can be used to measure the magnitude of the energy in both forward and reflected directions

Antenna specs give maximum reflection over a specific frequency range

Reflection magnitude can be expressed in the forms VSWR, Return Loss, or reflection coefficient

• VSWR = Voltage Standing Wave Ratio

Transmission line

AntennaDirectionalcoupler Fwd

Refl

RFPower


Return Loss and VSWR

Forward Power, Reflected Power, Return Loss, and VSWR can be related by these equations and the graph.

• Typical antenna VSWR specifications are 1.5:1 maximum over a specified band.

• VSWR 1.5 : 1

= 14 db return loss

= 4.0% reflected power

VSWR vs. Return Loss

VSWR

0

10

20

30

40

50

1 1.5 2 2.5 3

VSWR =

Reflected PowerForward Power

Reflected PowerForward Power

1 +

1 -Reflected PowerForward Power

ReturnLoss, dB = 10 x Log10 ( )


Swept Return Loss Measurements

It’s a good idea to take swept or TDR return loss measurements of a new antenna at installation and to recheck periodically

• maintain a printed or electronically stored copy of the analyzer output for comparison

• most types of antenna or transmission line failures are easily detectable by comparison with stored data

What is the maximum acceptable value of return loss as seen in sketch above?Given: Antenna VSWR max spec is 1.5 : 1 between f1 and f2 Transmission line loss = 3 dB.Consideration & Solution: From chart, VSWR of 1.5 : 1 is a return loss of -14 dB, measured at the antenna Power goes through the line loss of -3 db to reach the antenna, and -3 db to return Therefore, maximum acceptable observation on the ground is -14 -3 -3 = - 20 dB.

Transmission Line

AntennaDirectionalCoupler Fwd

Refl

Network Analyzer-10

-20

-30f1 f2

A Network Analyzer can also display polar plots, Smith Charts, phase response

A Spectrum Analyzer and tracking generator can be used if Network Analyzer not available


Some Antenna Application Considerations

Some Antenna Application Considerations

Chapter 5 Section C


Near-Field/Far-Field Considerations

Antenna behavior is very different close-in and far out Near-field region: the area within about 10 times the

spacing between antenna’s internal elements • Inside this region, the signal behaves as

independent fields from each element of the antenna, with their individual directivity

Far-field region: the area beyond roughly 10 times the spacing between the antenna’s internal elements

• In this region, the antenna seems to be a point-source and the contributions of the individual elements are indistinguishable

• The pattern is the composite of the array Obstructions in the near-field can dramatically alter the

antenna performance

Near-field

Far-field


Local Obstruction at a Site

Obstructions near the site are sometimes unavoidable

Near-field obstructions can seriously alter pattern shape

More distant local obstructions can cause severe blockage, as for example roof edge in the figure at right

• Knife-edge diffraction analysis can help estimate diffraction loss in these situations

• Explore other antenna mounting positions

Diffractionover

obstructing edge

Local obstruction example


Estimating Isolation Between Antennas

Often multiple antennas are needed at a site and interaction is troublesome

Electrical isolation between antennas• Coupling loss between isotropic

antennas one wavelength apart is 22 dB

• 6 dB additional coupling loss with each doubling of separation

• Add gain or loss referenced from horizontal plane patterns

• Measure vertical separation between centers of the antennas

– vertical separation usually is very effective

One antenna should not be mounted in main lobe and near-field of another

• Typically within 10 feet @ 800 MHz• Typically 5-10 feet @ 1900 MHz


Visually Estimating Depression Anglesin the field

Before considering downtilt, beamwidths, and depression angles, do some personal experimentation at a high site to gain a sense of the angles involved

Visible width of fingers, etc. can be useful approximate benchmark for visual evaluation

Measure and remember width of your own chosen references

Standing at a site, correlate your sightings of objects you want to cover with angles in degrees and the antenna pattern

distance

width

angle = arctangent (width / distance)

Visually estimating angleswith tools always at hand

Typical Angles

Thumb width

Nail of forefinger

All knuckles

~2 degrees

~1 degree

~10 degrees“Calibrate” yourself using the formula!


Antenna DowntiltWhat’s the goal?

Downtilt is commonly used for two reasons

1. Reduce Interference• Reduce radiation toward a

distant co-channel cell• Concentrate radiation within

the serving cell 2. Prevent “Overshoot”

• Improve coverage of nearby targets far below the antenna

– otherwise within “null” of antenna pattern

Are these good strategies? How is downtilt applied?

Scenario 2

Cell A

Scenario 1

Cell B


Consider Vertical Depression Angles

Basic principle: important to match vertical pattern against intended coverage targets

• Compare the angles toward objects against the antenna vertical pattern -- what’s radiating toward the target?

• Don’t position a null of the antenna toward an important coverage target!

Sketch and formula

• Notice the height and horizontal distance must be expressed in the same units before dividing (both in feet, both in miles, etc.)

= ArcTAN ( Vertical distance / Horizontal distance )

Horizontaldistance

Verticaldistance

Depression angle


Types Of Downtilt

Mechanical downtilt

• Physically tilt the antenna

• The pattern in front goes down, and behind goes up

• Popular for sectorization and special omni applications

Electrical downtilt

• Incremental phase shift is applied in the feed network

• The pattern “droops” all around, like an inverted saucer

• Common technique when downtilting omni cells


Reduce Interference Scenario 1

The Concept: Radiate a strong signal toward

everything within the serving cell, but significantly reduce the radiation toward the area of Cell B

The Reality: When actually calculated, it’s

surprising how small the difference in angle is between the far edge of cell A and the near edge of Cell B

• Delta in the example is only 0.3 degrees!!

• Let’s look at antenna patterns

Cell AConcept

Cell B

weakstrong

1 = ArcTAN ( 150 / ( 4 * 5280 ) ) = -0.4 degrees

2 = ArcTAN ( 150 / ( 12 * 5280 ) ) = -0.1 degrees

Reality

12 miles4

height difference

150 ft 21


Reduce Interference Scenario 1 , Continued

It’s an attractive idea, but usually the angle between edge of serving cell and nearest edge of distant cell is just too small to exploit

• Downtilt or not, can’t get much difference in antenna radiation between 1 and 2

• Even if the pattern were sharp enough, alignment accuracy and wind-flexing would be problems

– delta in this example is less than one degree!

• Also, if downtilting -- watch out for excessive RSSI and IM involving mobiles near cell!

Soft handoff and good CDMA power control is more important

-0.4-0.1

1 = -0.4 degrees

2 = -0.1 degrees


Avoid Overshoot Scenario 2

Application concern: too little radiation toward low, close-in coverage targets

The solution is common-sense matching of the antenna vertical pattern to the angles where radiation is needed

• Calculate vertical angles to targets!!

• Watch the pattern nulls -- where do they fall on the ground?

• Choose a low-gain antenna with a fat vertical pattern if you have a wide range of vertical angles to “hit”

• Downtilt if appropriate

• If needed, investigate special “null-filled” antennas with smooth patterns

Scenario 2


Other Antenna Selection Considerations

Before choosing an antenna for widespread deployment, investigate:

Manufacturer’s measured patterns• Observe pattern at low end of band, mid-band, and high end of band• Any troublesome back lobes or minor lobes in H or V patterns?• Watch out for nulls which would fall toward populated areas• Be suspicious of extremely symmetrical, “clean” measured patterns• Obtain Intermod Specifications and test results (-130 or better)• Inspect return loss measurements across the band

Inspect a sample unit• Physical integrity? weatherproof? • Dissimilar metals in contact anywhere?• Collinear vertical antennas: feed method?

• End (compromise) or center-fed (best)?• Complete your own return loss measurements, if possible• Ideally, do your own limited pattern verification

Check with other users for their experiences

July, 19985 - 1RF100 (c) 1998 Scott Baxter Antennas for Wireless Systems Antennas for Wireless...

Documents

Transcript of July, 19985 - 1RF100 (c) 1998 Scott Baxter Antennas for Wireless Systems Antennas for Wireless...