Larsen Basic Antenna Types

Larsen® is a leader in the design, development and manufacture of technologically advanced antenna systems for wireless applications. Larsen has provided mobile, portable and base antennas for two-way radio, public safety and military markets for over 40 years.

 

Basic Antenna Types

The following discussion of antenna types assumes an “adequate” ground plane is present.

1/4 Wave
A single radiating element approximately 1/4 wavelength long. Directivity 2.2 dBi, 0 dBd.

Loaded 1/4 Wave
The loaded 1/4 wave antenna looks electrically like a 1/4 wave antenna but the loading allows the antenna to be physically smaller than a 1/4 wave antenna. Quite often this is implemented by placing a loading coil at the base of the antenna. Gain depends upon the amount of loading used. Directivity 2.2 dBi, 0 dBd.

1/2 Wave
A single radiating element 1/2 wavelength long. Directivity 3.8 dBi, 1.6 dBd. A special design is the end fed 1/2 wave.

5/8 Wave
A single radiating element 5/8 wavelength long. Directivity 5.2 dBi, 3.0 dBd.

Collinear
Two or three radiating elements separated by phasing coils for increased gain. Four styles are common:

  1. 5/8 over 1/4: top element is 5/8 wave and bottom element is 1/4 wave. Directivity 5.4 dBi, 3.2 dBd.
  2. 5/8 over 1/2: top element is 5/8 wave and the bottom is 1/2 wave. Directivity 5.6 dBi, 3.4 dBd.
  3. 5/8 over 5/8 over 1/4: the top 2 elements are 5/8 wave and the bottom element is 1/4 wave. Directivity 7.2 dBi, 5.0 dBd.
  4. 5/8 over 5/8 over 1/2: the top 2 elements are 5/8 wave and the bottom element is 1/2 wave. Directivity 7.6 dBi, 5.4 dBd.

Using more than three radiating elements in a base-fed collinear configuration does not significantly increase gain. The majority of the energy is radiated by the elements close to the feed point of the collinear antenna so there is only a small amount of energy left to be radiated by the elements which are farther away from the feed point.

Please note the directivity is given above for common antenna configurations. The gain depends upon the electrical efficiency of the antenna. Here is where the real difference between antenna manufacturers is seen. If you cut corners in building an antenna, the gain may be significantly lower than the directivity. Larsen uses low-loss materials to minimize the difference between the gain and the directivity in our antennas.

Whip
The vertical portion of the antenna assembly acting as the radiator of the radio frequency.

GPS
Global Positioning Satellite or Global Positioning System.

  • Active GPS antennas include an amplifier circuit in order to provide better reception of the satellite signal. This active stage generally includes a low noise amplifier and a power amplifier.
  • Combi GPS/Cellular structures include several antennas in one radome to allow reception and transmission in different frequency bands.Dipole
    An antenna – usually 1/2 wavelength long – split at the exact center for connection to a feed line. Dipoles are the most common wire antenna. Length is equal to 1/2 of the wavelength for the frequency of operation. Fed by coaxial cable.
  • Sleeve Dipoles are realized by mean of the addition of a metallic tube on a coaxial structure.
  • Printed Dipoles have a radiation structure supported by a printed circuit.Embedded Omni
    These antennas are generally integrated on a base for applications such as access points. This structure could be externally mounted (ex: sleeve dipole) or directly integrated on the PC board of the system (ex: printed dipole).Yagi
    A directional, gain antenna utilizing one or more parasitic elements. A yagi consists of a boom supporting a series of elements which are typically aluminum rods. Named after one of the Japanese inventors (Yagi and Uda).Panel
  • Single Patch describes an elementary source obtained by means of a metallic strip printed on a microwave substrate. These antennas are included in the radiating slot category.
  • Patch Arrays are a combination of several elementary patches. By adjusting the phase and magnitude of the power provided to each element, numerous forms of beamwidth (electric tilt, sectoral, directional …) can be obtained.
  • Sectoral antennas can be depicted like a directive antenna with a beamwidth greater than 45°. A 1 dB beamwidth is generally defined for this kind of radiating structure.Omni-ceiling Mount
    Omni-ceiling mount antennas are used for the propagation of data in an in-building environment. In order to provide good coverage, these antennas are vertically polarized and present an omnidirectional pattern in the horizontal plane and a dipolar pattern in the vertical plane.Parabolic
    An antenna consisting of a parabolic reflector and a radiating or receiving element at or near its focus.
  • Solid Parabolics utilize a dish-like reflector to focus radio energy of a specific range of frequencies on a tuned element
  • Grid Parabolics employ an open-frame grid as a reflector, rather than a solid one. The grid spacing is sufficiently small to ensure waves of the desired frequency cannot pass through, and are hence reflected back toward the driven element.

 

Antenna Solutions for Portable/Terminal Applications
Nearly half the commercial communications radios sold today are portables. With the installed base increasing at an extraordinary rate, the demand for replacement antennas is growing fast. Unlike mobile and base antennas, portable radio antennas are subject to a variety of abuses leading to premature failure. Antennas are twisted off, sat on, slammed in the door and used to pull the radios out of their holsters! The result is an average need for replacement every four years.

Portable radio antennas cover a broad range of applications including:

  • Cellular/PCS fixed and telescoping masts
  • LMR/SMR fixed, flexible rubber antennas
  • Rigid, rotating, flexible and telescoping antennas for portable data terminals
  • Various other communications and telemetry applications.

There are several antenna types to fit a specific radio. The type selected depends on exact customer requirements including:

  • Radio model
  • Connector type
  • Frequency range
  • Performance desired
  • Size constraints
  • Budget

A proper replacement can restore or improve radio performance. With a good understanding of portable radio antennas, a sales associate or technician can make the right choice the first time and assure a happy customer.

Kulduckies

Spots!

Stealth Blades

LINKS:

    • Kulduckies
    • Spots!
    • Stealth Blades
    • Spots Dipoles
    • SPWB Wide Bands
    • Dual Wide Band

 

Antenna Solutions for Mobile Applications
At Larsen we want our customers to be confident they can find the right antenna for the right application. For this reason, we have provided some guidelines for mobile antenna selection.

Factors to consider to ensure the maximum performance from a mobile antenna installation:

  • Gain requirements
  • Electrical type
  • Ground plane availability
  • Mounting style and placement
  • Coaxial type and loss ratings
  • Physical size, appearance and surrounding environment

Larsen provides a complete selection of permanent and temporary mounting alternatives, using only the highest quality materials to ensure superior electrical performance and mechanical durability.

  • Magnetic mounts (MM, MMR, MS)
  • Trunk lid mounts (TLM, TLP)
  • Trunk gutter brackets (TMB)                    Mounts/Brackets
  • Mirror mount brackets (MB)
  • Window clip mounts (KGK)
  • Traditional permanent hole mounts
Low Profiles Broadband Mobile Mobiles

NMO High Frequency Mounts

NMO High Frequency Mount
– Gold plated contact pin and conductor
– Zinc alloy body plated with copper and nickel
– Nickel plated brass ring
Convert from low frequency applications to high frequency applications and back simply by pulling or replacing the center pin and insulator. NMO High Frequency
Thick Mount

LINKS:

      • Low Band / Mid Band
      • VHF (136 – 174 MHz)
      • UHF (406 – 512 MHz)
      • Multi Band VHF / UHF
      • Tunable ¼ Wave (136 – 512 MHz)
      • Cellular, SMR, Data 700/800/900
      • Cellular / PCS Multi Band Cellular PCS
  • Amateur Products
  • Low Profile Transit
  • Low Profile
  • NMO HF Mounts
  • Broadband Mobile

 

Antenna Solutions for Base Station Applications
Cellular, PCS, Data, ISM and WLL are technologies migrating to completely wireless systems. Base station antennas provide the critical link between the user and the system provider. They also provide connectivity within the system without being directly accessed by the user. Base station antennas, as their name implies, are usually fixed in a specific location in the network and provide connectivity over a geographic area or from point-to-point. Base station antennas can be broken into two general categories; omni-directional and directional.

Larsen manufactures a variety of small base station antennas to meet many of today’s demanding requirements. Our versatile product line offers selection and performance to meet your system needs. In addition to our standard product offering, Larsen ’s engineering staff can work with you to design antennas to your exact specifications.

Base Stations

Broadband

Broadband Multi Band

LINKS:

  • Base Station Antennas – Antenna SourceBook
  • Broadband Antennas – Antenna SourceBook
  • Multi Band Broadband Antennas – Antenna SourceBook
  • Yagis
  • Broadband Product Matrix

 

Antenna Solutions for GPS Applications
Larsen Antenna Technologies is proud to present a complete line of GPS antennas designed for asset tracking and AVL applications. These antennas are intended for use in trucking, commercial fleet, utility, public safety, search and rescue, GIS and survey and mapping markets. Larsen antennas provide exceptional performance with high-gain GPS modules. The small footprints and low profiles make for more flexible mounting options.

Our GPS development competency leverages tri-band technology that enables continuous GPS signal reception when the co-located communications antennas are transmitting. All tri-band GPS antennas can work on either 3 VDC or 5 VDC.

Larsen makes a GPS antenna for virtually any application.

GPS:

  • GPS NMO Mount
  • GPS Glass Mount
  • GPS Mag Mount
  • GPS Direct Mount (GPS Direct Mount or GPS Combi Whip)

GPS Tri-Bands:

  • Roof Mount
  • Interior Glass Mount
  • Direct Mount

LINKS:

  • GPS Solutions for Mobile Applications
  • Broadband Muti Band Antenna
  • Telematics Product Matrix

 

Antenna Solutions for Broadband Applications
WLAN and Wi-Fi deployment is growing rapidly, and so is the need for advanced technologies. In response to these demands, Larsen has developed antenna solutions to cover 802.11 a/b/g as well as 4.9 GHz while delivering superior electrical performance through efficient signal coverage. Larsen covers virtually every requirement from the router to complete indoor coverage.

Terminal & Infrastructure

Broadband Product Matrix

Broadband Mobiles

4.9 GHz Public Safety

Multi-Band Solutions Covering 2.4 and 4.9 – 5.9 GH

LINKS:

    • Broadband Multi Band Section of the Antenna SourceBook
    • Broadband Section of the Antenna SourceBook
    • 4.9 GHz Solutions
    • 4.9 GHz Products
    • Dual/Wide Band Products (2.4 and 4.9-5.9 GHz)
    • Broadband Product Matrix

 

ABOUT US
OUR HISTORY

  • Founded in 1965 as Larsen Electronics
  • Founded on a passion for innovation and excellence
  • Purchased by Radiall SA in 1999 – became Radiall/Larsen Antenna Technologies
  • Acquired by Pulse, a Technitrol Company, in 2006. Larsen became a Pulse brand.

QUALITY

  • ISO certified since 1996
  • ISO 9001:2000 standard certification by Underwriters Laboratories (UL)
  • Automotive Division ISO/TS 16946 certification by Underwriters Laboratories (UL)
  • RoHS compliant

OPERATIONS

  • Located in Vancouver, WA, in the heart of the Pacific Northwest high tech sector
  • Complete knowledge of high-precision manufacturing operations

 

Ordering
For your convenience, we’ve made ordering from Larsen® as easy as 1 – 2 – 3

  1. Contact one of our distributors USA or IL-WI Manufacturer’s Representative >>> Apogee Industries
  2. Order via phone by dialing 1-800-ANTENNA (268-3662) ~ or Apogee Industries @ 1-888-280-5290
  3. Fax your order 24 hours a day, 7 days a week to 800-525-6749  Apogee Industries @ 1-815-363-6056

Service & Support

US Distributors

 

AMATEUR PRODUCT DISTRIBUTORS

To order Larsen® amateur products, contact our preferred dealers

  • HRO (Ham Radio Outlet)
  • AES (Amateur Electronic Supply)

Larsen Amateur Antenna Products Catalog

Larsen is proud to announce the return of the Amateur Antenna Products catalog. The Amateur catalog contains a selection of the most popular Larsen portable radio, Low/Mid Band, VHF, UHF and small base station antennas along with cable assemblies, mounting brackets, replacement parts and accessories to support them.

The catalog also includes a Technical Guide explaining amateur frequency bands, an explanation of electrical types and a glossary of common terms used in the catalog plus a full description of the electrical types of portable radio antennas – helicals, helical ¼ waves, 2/70 dual bands and more.

Click here for an electronic copy of the Larsen Amateur Antenna Products catalog.

MINIMUM ORDER POLICY

  • US$250 on domestic orders (net value after all discounts)
  • US$1000 on international orders (net value after all discounts)

CHANGES/CONDITIONS: Continual research and development make it necessary for Pulse to reserve the right to make exceptions to or changes in policies, specifications and prices without notice.

 

Technical Reference
Larsen offers complete customer support on all of our products. The technical information listed below provides a means to answer many general antenna application questions. If you are unable to find the information you are seeking, please don’t hesitate to contact our customer support staff.

LINKS:

  • Cutting Charts
  • Pattern Data
  • Antenna Basic Concepts
  • FAQs
  • Antenna Glossary
  • Feedback Form
  • Custom Design Request
  • Spectrum Allocation – US
  • Spectrum Allocation – CA
  • NMOHF White Paper

 

Catalogs/Brochures
The complete Larsen Antenna SourceBook™ (ASB) (Volume 10) is available for for download from our website:

Larsen Antenna SourceBook™ (ASB) (Volume 10)

ASB Volume 10 by Section

Visitors using a dialup modem should visit the Antenna SourceBook™ Sections page — we have divided the entire book into sections for easier downloading. To view the ASB by section, please click here.

Larsen M2M/AMR Antennas Products

Larsen is pleased to bring you the latest in our series of catalogs – M2M/AMR Antenna Products. The goal of this catalog is to provide a “go to” source for your Machine to Machine and Automatic Meter Reading antenna needs.

Larsen LMR/Public Safety Catalog, Volume 1

In a continuing effort to support our customers in the Public Safety market, we are pleased to announce the release of a new catalog designed specifically to present Larsen’s most popular public safety products. This 32-page catalog showcases these products in a clear, concise format.

Larsen Broadband Catalog

Larsen is pleased to bring you the latest in our series of catalogs – Broadband Antenna Products. The goal of the catalog is to provide you with a “go to” source for your Broadband antenna needs. Here you will find the most popular Larsen antennas for 802.11a, b and g applications – including Mesh networks.

Larsen Amateur Antenna Products Catalog

Larsen is proud to announce the return of the Amateur Antenna Products catalog. The Amateur catalog contains a selection of the most popular Larsen portable radio, Low/Mid Band, VHF, UHF and small base station antennas along with cable assemblies, mounting brackets, replacement parts and accessories to support them.

The catalog also includes a Technical Guide explaining amateur frequency bands, an explanation of electrical types and a glossary of common terms used in the catalog plus a full description of the electrical types of portable radio antennas – helicals, helical ¼ waves, 2/70 dual bands and more.

Click here for an electronic copy of the Larsen Amateur Antenna Products catalog.

Sales Sheets

Larsen provides detailed sales sheet on many of our products. To view a list of sales sheets, please click here.

To order a price book or hard copies catalogs/brochures, please send us an email at: marketing@larsen.pulseeng.com.

Application Brochures:

  • Antenna Solutions for In-Building Applications
  • Antenna Solutions for Public Safety Applications
  • Antenna Solutions for Telematics Applications
  • Antenna Solutions for Machine-to-Machine Applications
  • Antenna Solutions for Custom OEM Applications – Coming Soon!

 

FOR ILLINOIS AND WISCONSIN CUSTOMERS

 

 

AVAILABLE FROM

 

P.O. Box 323 

McHenry, IL 60051

Phone: 815-344-4808 

Fax: 815-363-6056

 

Dan Noncek   E-Mail: dan@apogeeindustriesinc.com

 

Bryan Wadsworth  E-Mail: bryan@apogeeindustriesinc.com

  

Toll Free# (888)-280-5290

 

 

ADDITIONAL ANTENNA INFORMATION

 

Antenna Basic Concepts
Why Larsen Antennas Are The Best

For more than 30 years Larsen has produced antennas which are electrically efficient and mechanically rugged. Technical achievement and the use of advanced materials play a major role in electrical efficiency and mechanical strength. Larsen ‘s dedication to research and development places us in the forefront of the industry for producing innovative antennas.

Antenna

An antenna is a device to transmit and/or receive electromagnetic waves. Electromagnetic waves are often referred to as radio waves. Most antennas are resonant devices, which operate efficiently over a relatively narrow frequency band. An antenna must be tuned (matched) to the same frequency band as the radio system to which it is connected otherwise reception and/or transmission will be impaired.

Wavelength

We often refer to antenna size relative to wavelength. For example: a 1/2 wave dipole is approximately half a wavelength long. Wavelength is the distance a radio wave travels during one cycle. The formula for wavelength is:

Where:
is the wavelength expressed in units of length, typically meters, feet or inches
is the speed of light (11,802,877,050 inches/second)
is the frequency

For example, wavelength in air at 825 MHz is:
11.803 X 109 in./sec = 14.307 inches
825 x 106 cycles/sec. Note: The physical length of a half-wave dipole is slightly less than a half-wavelength due to end effect. The speed of propagation in coaxial cable is slower than in air, so the wavelength in the cable is shorter. The velocity of propagation of electromagnetic waves in coax is usually given as a percentage of free space velocity, and is different for different types of coax.

Impedance Matching

For efficient transfer of energy, the impedance of the radio, the antenna and the transmission line connecting the radio to the antenna must be the same. Radios typically are designed for 50 Ohms impedance, and the coaxial cables (transmission lines) used with them also have a 50 Ohm impedance. Efficient antenna configurations often have an impedance other than 50 Ohms. Some sort of impedance matching circuit is then required to transform the antenna impedance to 50 Ohms. Larsen antennas come with the necessary impedance matching circuitry as part of the antenna. We use low loss-components in our matching circuits to provide the maximum transfer of energy between the transmission line and the antenna.

VSWR and Reflected Power

Voltage Standing Wave Ratio (VSWR) is an indication of the quality of the impedance match. VSWR is often abbreviated as SWR. A high VSWR is an indication the signal is reflected prior to being radiated by the antenna. VSWR and reflected power are different ways of measuring and expressing the same thing.

A VSWR of 2.0:1 or less is often considered acceptable. Most commercial antennas, however, are specified to be 1.5:1 or less over some bandwidth. Based on a 100 watt radio, a 1.5:1 VSWR equates to a forward power of 96 watts and a reflected power of 4 watts, or the reflected power is 4.2% of the forward power.

Bandwidth

Bandwidth can be defined in terms of radiation patterns or VSWR/reflected power. The definition used is based on VSWR. Bandwidth is often expressed in terms of percent bandwidth, because the percent bandwidth is constant relative to frequency. If bandwidth is expressed in absolute units of frequency, for example MHz, the bandwidth is then different depending upon whether the frequencies in question are near 150 MHz, 450 MHz or 825 MHz.

Decibels

Decibels (dB) are the accepted method of describing a gain or loss relationship in a communication system. The beauty of dB is they may be added and subtracted. A decibel relationship (for power) is calculated using the following formula. dB = 10 log     Power A
dB = 10 log     Power B
“A” might be the power applied to the connector on an antenna, the input terminal of an amplifier or one end of a transmission line. “B” might be the power arriving at the opposite end of the transmission line, the amplifier output or the peak power in the main lobe of radiated energy from an antenna. If “A” is larger than “B”, the result will be a positive number or gain. If “A” is smaller than “B”, the result will be a negative number or loss.

Example: At 1700 MHz, one fourth of the power applied to one end of a coax cable arrives at the other end. What is the cable loss in dB?

 

Loss in dB = 10 log  1  = 10 X (-) 0.602
  4  
Loss = (-) 6.02 dB    

In the above case, taking the log of 1/4 (0.25) automatically results in a minus sign, which signifies negative gain or loss.

It is convenient to remember these simple dB values which are handy when approximating gain and loss:

 

Power Gain

3 dB = 2X power
6 dB = 4X power
10 dB = 10X power
20 dB = 100X power

Power Loss

-3 dB = 1/2 power
-6 dB = 1/4 power
-10 dB = 1/10 power
-20 dB = 1/100 power

In the case of antennas, passive structures cannot generate power. dB is used to describe the ability of these structures to focus energy in a part of space.

Directivity and Gain

Directivity is the ability of an antenna to focus energy in a particular direction when transmitting or to receive energy better from a particular direction when receiving. There is a relationship between gain and directivity. We see the phenomena of increased directivity when comparing a light bulb to a spotlight. A 100-watt spotlight will provide more light in a particular direction than a 100-watt light bulb and less light in other directions. We could say the spotlight has more “directivity” than the light bulb. The spotlight is comparable to an antenna with increased directivity.

Gain is the practical value of the directivity. The relation between gain and directivity includes a new parameter h which describes the efficiency of the antenna.

For example, an antenna with 3dB of directivity and 50% of efficiency will have a gain of 0 dB.

Gain Measurement

One method of measuring gain is to compare the antenna under test against a known standard antenna. This is known as a gain transfer technique. At lower frequencies, it is convenient to use a 1/2-wave dipole as the standard. At higher frequencies, it is common to use a calibrated gain horn as a gain standard with gain typically expressed in dBi.

Another method for measuring gain is the 3-antenna method. Transmitted and received powers at the antenna terminal are measured between three arbitrary antennas at a known fixed distance. The Friis transmission formula is used to develop three equations and three unknowns. The equations are solved to find the gain expressed in dBi of all three antennas.

Larsen uses both methods for measurement of gain. The method is selected based on antenna type, frequency and customer requirement.

Use the following conversion factor to convert between dBd and dBi: 0 dBd = 2.15 dBi. Example: 3.6 dBd + 2.15 dB = 5.75 dBi

Radiation Patterns

Radiation or antenna pattern describes the relative strength of the radiated field in various directions from the antenna at a constant distance. The radiation pattern is a “reception pattern” as well, since it also describes the receiving properties of the antenna. The radiation pattern is three-dimensional, but it is difficult to display the three-dimensional radiation pattern in a meaningful manner. It is also time-consuming to measure a three-dimensional radiation pattern. Often radiation patterns measured are a slice of the three-dimensional pattern, resulting in a two-dimensional radiation pattern which can be displayed easily on a screen or piece of paper. These pattern measurements are presented in either a rectangular or a polar format.

Antenna Pattern Types

Omnidirectional Antennas

For mobile, portable and some base station applications the type of antenna needed has an omnidirectional radiation pattern. Omnidirectional antenna radiate and receive equally well in all horizontal directions. The gain of an omnidirectional antenna can be increased by narrowing the beamwidth in the vertical or elevation plane. The net effect is to focus the antenna’s energy toward the horizon.

Selecting the right antenna gain for the application is the subject of much analysis and investigation. Gain is achieved at the expense of beamwidth. Higher-gain antennas feature narrow beamwidths while the opposite is also true. Omnidirectional antennas with different gains are used to improve reception and transmission in certain types of terrain. A 0dBd gain antenna radiates more energy higher in the vertical plane to reach radio communication sites located in higher places. Therefore they are more useful in mountainous and metropolitan areas with tall buildings. A 3dBd gain antenna is a good compromise for use in suburban and general settings. A 5dBd gain antenna radiates more energy toward the horizon compared to the 0 and 3dBd antennas to reach radio communication sites further apart and less obstructed. Therefore they are best used in deserts, plains, flatlands and open farm areas.

Directional Antennas

Directional antennas focus energy in a particular direction. Directional antennas are used in some base station applications where coverage over a sector by separate antennas is desired. Point-to-point links also benefit from directional antennas. Yagi and panel antennas are directional antennas.

Auto Glass Thickness

Tempered auto glass varies in thickness between .138″ and .158″. Larsen optimized at .157″ when designing our KG on-glass series. Windshields are laminated safety glass and are considerably thicker.

Beamwidth

Beamwidth describes the angular aperture where the most important part of the power is radiated. In general, we talk about the 3db beamwidth which represents the aperture (in degrees) where more than 90% of the energy is radiated.

For example, for a 0 dB gain antenna, 3 db beamwidth is the area where the gain is higher than –3 dB.

Value of q in degree = 3 dB beamwidth.

Near-Field and Far-Field Patterns

The radiation pattern in the region close to the antenna is not exactly the same as the pattern at large distances. The term “near-field” refers to the field pattern existing close to the antenna; the term “far-field” refers to the field pattern at large distances. The far-field is also called the radiation field, and is what is most commonly of interest. The near-field is called the induction field (although it also has a radiation component).

Ordinarily, it is the radiated power that is of interest so antenna patterns are usually measured in the far-field region. For pattern measurement it is important to choose a distance sufficiently large to be in the far-field, well out of the near-field. The minimum permissible distance depends on the dimensions of the antenna in relation to the wavelength. The accepted formula for this distance is:

 

Antenna Polarization

Polarization is defined as the orientation of the electric field of an electromagnetic wave. Two often-used special cases of elliptical polarization are linear polarization and circular polarization. Initial polarization of a radio wave is determined by the antenna launching the waves into space. The environment through which the radio wave passes on its way from the transmit antenna to the receiving antenna may cause a change in polarization.

With linear polarization the electric field vector stays in the same plane. In circular polarization the electric field vector appears to be rotating with circular motion about the direction of propagation, making one full turn for each RF cycle. The rotation may be right- hand or left-hand.

Choice of polarization is one of the design choices available to the RF system designer. For example, low frequency (< 1 MHz) vertically polarized radio waves propagate much more successfully near the earth than horizontally polarized radio waves because horizontally polarized waves will be cancelled out by reflections from the earth. Mobile radio system waves generally are vertically polarized. TV broadcasting has adopted horizontal polarization as a standard. This choice was made to maximize signal-to-noise ratios. At frequencies above 1 GHz, there is little basis for a choice of horizontal or vertical polarization, although in specific applications there may be some possible advantage in one or the other. Circular polarization has also been found to be of advantage in satellite applications such as GPS. Circular polarization can also be used to reduce multipath.

Determining Whip Length
In general, whip length is defined as a fraction of the wavelength and depends on the electrical characteristics you want to achieve. Theoretically, a whip provides an omnidirectional pattern in the horizontal plane and a dipolar pattern in the elevation plane. When you increase the whip length by a fraction of a wavelength (commonly ¼ wavelength), you increase the gain of the structure by reducing the aperture in the elevation plane.

Determining Ground Plane Size

For many types of antennas the theoretical analysis is based on the use of an infinite ground plane. In practice, this condition is never achieved. Different effects of reduction of the size of the ground plane are commonly:

  • Electrical tilt: The maximum energy is not radiated in the expected direction.
  • Beamwidth Increased: The aperture of the radiating element is modified and the gain of the antenna is decreased.In conclusion, we could say the bigger the ground plane, the better the control of the electrical performances of the antenna.