Sigma Wireless Technologies Ltd McKee Avenue Finglas, Dublin 11 Ireland Phone: Fax:

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1 Sigma Wireless Technologies Ltd McKee Avenue Finglas, Dublin 11 Ireland Phone: Fax: info@sigma.ie ANTENNA SYSTEM DESIGN 800MHZ

2 Contents 1 INTRODUCTION FUNDAMENTALS OF ANTENNA DESIGN GAIN Polar Plots ANTENNA POSITION RELATIVE TO MAST Omnidirectional Offset Omnidirectional Sectoral Arrays RF DOWNTILT SELECTING THE APPROPRIATE TYPE OF ANTENNA Medium / Low Traffic Density High Traffic Density DIVERSITY Diversity Gain Explained Experimental Results Different Diversity Schemes Described How does Space Diversity work? How Does Polarisation Diversity Work? GOOD TETRA ANTENNA SYSTEM DESIGN PRACTICE RECEIVER ISOLATION FROM TRANSMITTERS ANTENNAS USED IN EXAMPLES Omni Antennas...18 Panel Antennas OMNIDIRECTIONAL DIVERSITY APPLICATIONS Introduction Sample Link Budget Calculation Covering Traffic Corridors Top of Mast Omni plus Two Offsets Side Mount Omnidirectional Diversity Array Two Sector Hybrid Sector System MOUNTING CRITERIA FOR OPTIMUM PERFORMANCE PHYSICAL MOUNTING CRITERIA Sectored Panel array ANTENNA / SYSTEM INTEGRATION LOW DENSITY SYSTEM MEDIUM DENSITY HIGH DENSITY...31 Sigma Wireless Technologies 2 March 2002.

3 Figures Figure 1 - Effect of Gain...6 Figure 2 -Antennas on One Metre Mast at various Spacings...7 Figure 3- Illustration of Offset Antenna when compared with Omni...8 Figure 4 - Build up Of Sectored Site Coverage...9 Figure 5 - Illustration of Interference in Re-Using Frequencies...10 Figure 6 - An Electrically Down-Tilted Panel Antenna Mechanically Up-Tilted...11 Figure 7 - Illustration Of difference between Electrical and Mechanical Down-Tilt...12 Figure 8 - Variability of the Signal Strength coming from a mobile transmitter over time...13 Figure 9 - Illustration of Dual Polarisation Diversity...16 Figure 10 - Covering a Traffic Corridor...22 Figure 11 - 'Top of Mast' Omni Plus Two Offsets Figure 12 - Side Mount Omnidirectional Diversity Array...25 Figure 13 - Side Mount Omnidirectional Diversity Array Gain...26 Figure 14 - Two-Sector Hybrid Sector System...27 Figure 15 - Two Sector Hybrid Sector System Gain...27 Sigma Wireless Technologies 3 March 2002.

4 1 Introduction The design criteria used in the traditional PMR environment differ significantly from those required by Digital PMR. The difference between the two platforms demand that a higher priority be given to the shape and control of the antenna s radiation pattern. The use of antennas in the 800MHz-frequency band for cellular operation has been well documented in relation to cellular systems, however, cellular operators seldom use omni antennas. In instances where they do, the areas are where users do not require good coverage. Thus, very little information is reported in relation to the use of omni antennas in cellular type applications. Antenna systems, when properly designed, will yield reduced costs to the network operator / owner and clear communication to network users. The following document is divided into five sections aimed at describing the fundamentals of antenna design at TETRA frequencies, highlighting the key trade-off s when designing a TETRA antenna system and finally to pass over some tips on good antenna system design. This document will not focus on antennas for hand portables or mobile transceivers. 2 Fundamentals of Antenna design The main challenges of antenna design are concerned with defining and controlling the shape of the radiation pattern. The ability to do this well ensures that RF signals are directed into the right area and at the appropriate signal strength. It also ensures the minimisation of unwanted signals in key areas. The TETRA standard requires that a 19dB differential be maintained between carrier and the interference level i. In a frequency re-use scenario, it is important to be able to plan the network using realistic antenna patterns, which may be used to: 'Amplify' signals for range or building penetration purposes. Direct radiation in a controlled manner, omni, sectored, directional. Reduce/enlarge coverage using gain and diversity. Optimise performance in a range of mast fixing arrangements. The key factors affecting the shape of the RF envelope are as follows: Omnidirectional: Gain, mast position and down-tilt. Sigma Wireless Technologies 4 March 2002.

5 Sectoral: Gain, beamwidth, front-to-back ratio and down-tilt. The antenna patterns used to characterise an antenna are the E-Plane and H-Plane. The E-plane is a crosssection of the antenna pattern and is a side on view. The main information given is the depth of the main beam plus any side lobes produced. These side lobes may be a source of interference to other sites and need to be controlled. Panel antennas invariably have unwanted lobes at the rear of the panel. These need to be minimised and controlled. Failure to control this may result in interference to some other site. The H-Plane is the top down view of the radiation pattern and defines the direction of the pattern in relation to the antenna. Omnidirectional antennas have a circular pattern, while panel and directional antennas tend to focus the RF energy in a particular manner. The focussing of this energy results in gain. 2.1 GAIN An Omnidirectional antenna is used in circumstances where frequency re-use is not a major issue due to medium to low traffic density requirements. This type of antenna is constructed using a spiral dipole array or a collinear design and generates a circular pattern when viewed from above. All antenna gains are expressed in db which is always expressed in terms of the relationship of the gain of the two antennas. The first reference antenna is the Isotropic antenna which radiates signals equally in all directions (up, down, left right etc.). This ideal radiator can never actually be realised. It is frequently used to express an antennas gain and it will always be expressed as dbi. The second reference antenna type is the dipole and the suffix used will be dbd. It is worth noting that the gain of a dipole is approximately 2.2dB higher than that of an an isotrope (or 0dBd = 2.2dBi). The following diagram is an E-Plane view of an omni-directional antenna and shows the effect of gain on the shape of the main lobes. When the gain level is increased from 3dB gain, using two dipoles, to 6dB, using four dipoles, the distance covered is increased and the lobes become thinner. The Figure 1 - shows the effect of gain in any frequency band. Sigma Wireless Technologies 5 March 2002.

6 0 Simplified 3dB Gain Antenna Simplified 6dB Gain Antenna db Figure 1 - Effect of Gain Polar Plots Sigma uses log-db polar plots to display their antenna patterns. The ARRL (the American Radio Relay League, the US national organisation of Amateur Radio operators) log-db scale is widely used in amateur publications. It provides a convenient scale to compare the patterns of antennas with those of existing designs. It also yields patterns with familiar shapes. The ARRL log-db scale dedicates approximately half of the area of the plot to the first 10dB. This emphasises the detail of the pattern near the full-gain point and causes the lower level side-lobes to be compressed toward the centre of the pattern without hiding them completely. The log-db plot is normalised so that the outer 0dB circle represents the maximum gain of the antenna in that plane. The centre of the plot is minus infinity db, but there isn't much area below -40 db. 2.2 ANTENNA POSITION RELATIVE TO MAST Omnidirectional The position of an antenna in relation to the mast can affect the radiation pattern and care needs to be taken to ensure that the appropriate antenna type is selected for specific masts and position on that mast. The main impact is on the H-Plane pattern (also known as the Azimuth Pattern). Figure 2(A) shows the ideal H-plane pattern represented by the thick circle. This scenario is realised when the antenna is placed at the top of a mast, free from close obstructions. The other patterns are the result of placing the same antenna at varying distances from a one-metre mast. The smaller the tower, the more effect it has on the pattern distortion. (This is counter-intuitive and is because each leg of the tower has current Sigma Wireless Technologies 6 March 2002.

7 induced in them by coupling with the antenna. This current then re-radiates from the tower leg and interferes with the antenna pattern. When the tower legs are in close proximity to each other, they couple to one another, increasing the amount of current which flows in each leg, thus increasing the interference potential). To minimise the effect of towers on omni antenna patterns, the antennas should be placed at least one metre away from the towers in the 800 to 960MHz band Antenna to 1M Tower Spacing Free Space Antenna to 1M Tower Spacing Free Space db mm 750mm db mm 750mm 1250mm 1250mm 180 (A) - Omni Antennas Figure 2 -Antennas on One Metre Mast at various Spacings 180 (B) - Offset Antennas Offset Omnidirectional On the other hand, a different result is achieved for an Offset antenna placed at the front of a triangular mast. When the antenna is placed in front of the apex of the mast with the dipoles arranged in the offset configuration, the H-plane radiation pattern is less susceptible to the effects of positioning at different distances from the mast. The H-plane is reasonably circular, but is offset towards the front of the antenna. Figure 2 (B) shows how the pattern remains relatively consistent even when mounted on the side of a mast, at varying electrical distances. As the distance increases, this effect is reduced. The consistency of RF patterns makes network planning more reliable. A positive side effect of the offset pattern is higher gain in one direction. This offset shape can easily be incorporated into overall network planning by choosing sites with this in mind and directing the main lobe in an appropriate direction to form a suitable total coverage pattern. Offset antennas can be substituted directly for omni antennas. Figure 3 shows the pattern of Sigma s Swift omni antenna as a dotted line. On the same plot, shown as a solid line, is the pattern of an overlaid omni antenna. The centre of the both plots is marked with a point mark. When it comes to placing an omni site on a coverage map, there is little scope for moving the site s location without affecting the location of most (if not all) adjacent sites. However, if an offset antenna is used, then the planner can consider many more locations that are possible. If we consider the situation where the offset Sigma Wireless Technologies 7 March 2002.

8 pattern's centre is moved down the graph to the blue square point-mark, then the offset pattern will exactly overlay the omni pattern. If the antenna were to be placed anywhere along the red circle in the centre and oriented correctly a perfect omni pattern is obtained, offset by 2.5dB from the centre of the omni pattern. When the system designer considers omni and offset antennas then an area represented by a circle with a diameter equivalent to 5dB on the link budget is available for consideration as possible locations of the sites. This level of flexibility is available to the system designer without needing to change the overall cellular pattern, by choosing either omni antennas or offset antennas pointing in a suitable direction db 90 Figure 3- Illustration of Offset Antenna when compared with Omni Sectoral Arrays Drawing from the cellular experience, capacity is increased by having sectored sites with three panel antennas per site, each panel radiating on different RF channels. Sigma Wireless Technologies 8 March 2002.

9 -3dB -10dB -3dB -10dB Single Sector Figure 4 - Build up Of Sectored Site Coverage Three Sectors at a Single Site Figure 4 shows how a sectored site is built up to optimise channel capacity. These sites are typically used in urban environments where traffic density is higher than in rural areas. As vehicles or people move from coverage of one antenna to another, the system takes care of the hand-over to the appropriate available channel. The interleaving of site patterns ensures hand-over between sites without causing interference between them Frequency Re-Use As the number of sectors increases an antenna s front-to-back ratio becomes important. The 'spillage' of signal from the back of the antenna can interfere with cells some distance away, particularly if the back lobes are directed at the horizon. Good design ensures that the back lobes are small and tilted down. In Figure 5, if you imagine the two cells being separated by the cell re-use distance, you can see that the energy radiated off the back of the bottom right dotted cell could interfere with a mobile in the coverage area of the top left dotted cell. This is how front-to-back ratio affects the frequency re-use of a system. The TETRA standard sets limits on the maximum distance a mobile can access a site from (See reference ii, which states "This distance may be used to prevent MS from grossly exceeding the planned cell boundaries"). However, this does not affect the levels of interference created by back lobes, which still must be taken into consideration. Sigma Wireless Technologies 9 March 2002.

10 -3dB -10dB -3dB -10dB Figure 5 - Illustration of Interference in Re-Using Frequencies The frequency re-use policy dictates whether this is a major design concern or not. Networks that have low frequency re-use, for example those which have a large separation between sites, will be less concerned about RF spillage from the back of the panel antenna. A method for controlling the back lobe is to use electrical down-tilt (See RF DOWNTILT on Page 11) with mechanical up-tilt (See Figure 6 on page 11 to see the effects of this arrangement on the back lobe at the horizon). One possible option for an antenna user is to purchase all sectored antennas with the maximum amount of down tilt (say 6 o ). If another down-tilt value is required at a particular site, then all that needs be done is to reverse the mounting brackets (bottom clamp at the top and vice versa) and the antenna is tilted UP. So that for a 2 o down tilt, we would tilt a 6 o antenna up by 4 o. Thus the antennas to be delivered to all sites would be the same and the down tilt is decided at the installation time and can easily be changed subsequently. The benefits for this type of arrangement is that the purchaser will have all the logistical advantages of having only one sectored antenna type with maximum front-to-back ratio. Sigma Wireless Technologies 10 March 2002.

11 Figure 6 - An Electrically Down-Tilted Panel Antenna Mechanically Up-Tilted Combining Radiation Patterns from Multiple Antennas It is not normally practical to combine the radiation patterns of multiple antennas to give an omni pattern from, for example, three panel antennas. This is because there is a single source of signal (the transmitter) and the relative phases of the radiated signals from each antenna will determine the final radiation pattern of the antenna system. Both the relative lengths of the feeder cables and the distance between the antenna centres (i.e. where each antenna is mounted) control these phases. The resultant pattern contains many nulls, the number of which depends on relative spacing. The phasing of the antennas (relative cable lengths) only moves the position of the nulls around the pattern, but does not affect the number or their depth. This is in contrast to diversity (See DIVERSITY on Page 13) which is used for the receive path only and uses up to three separate receivers to achieve the gain. In this case, the phases of the RF signals do not matter, as they are processed in the receivers before the gain is achieved by aggregating the demodulated outputs using an additive or selective process. 2.3 RF DOWNTILT The effect of down-tilt applies to both Sectored and Non-Sectored antenna arrays. Omnidirectional and sectoral antennas use pattern tilting to regulate the size of cells and control the signal strength in overlap areas. The tilt may be provided using either mechanical or electrical tilt and in some cases a combination of both. Figure 7 shows the difference between mechanical and electrical down-tilt. The dotted pattern is a cross section of the radiation pattern for our SPA Series panel antenna, with no electrical down-tilt, but which has been mechanically tilted down. The solid pattern shows the same antenna type but with 5 degrees of electrical down-tilt. As you can see the electrically down-tilted pattern has two larger secondary lobes, but more importantly, the back lobe is also down-tilted. This provides a powerful and positive means of preventing unwanted spillover into cells some distance away. (See also Frequency Re-Use above and Figure 6 - An Electrically Down-Tilted Panel Antenna Mechanically Up-Tilted above) Sigma Wireless Technologies 11 March 2002.

12 Figure 7 - Illustration Of difference between Electrical and Mechanical Down-Tilt 2.4 Selecting the Appropriate Type of Antenna The role of an antenna system is driven by the need to balance the conflicting requirements of electrical performance (gain, pattern, tilt), physical dimensions (restricted space available on masts) and product costs. The choice of antenna type will be driven first by the predicted traffic density. Traffic density will be determined by the potential number of users per square kilometre, the area to be covered by the cell and the average call duration. From this information, the system designer will classify cells into two or more traffic density classes, which in turn will determine the network configuration and the antenna configuration on each site. Diversity is recommended where at all practical Medium / Low Traffic Density Omni (and offset) antennas will be chosen where there is a large area to be covered with low traffic density. The choice of omni or offset depends on the network configuration and the availability of sites at optimum locations. (See also on page 7). An optimum antenna pattern can be obtained if a top of mast position is available. Many of the examples in section 3 are used to illustrate this configuration. Generally, Public-Safety system owners Public Safety bodies will have more Low to Medium traffic-density cells using the omni / offset antenna configuration. They may need some sectored antennas in cities. Private systems will usually have similar antenna requirements. Public Access Operators will have relatively few cells of this configuration High Traffic Density Panel antennas will be used where there is high traffic density. A sectored site can be viewed as three sites in one location, sharing a single site controller. This reduces costs in selecting and obtaining permission to use sites. As mast space is at a premium at sites, care needs to be taken to ensure that the panel antennas have the Sigma Wireless Technologies 12 March 2002.

13 smallest dimensions possible while delivering good electrical performance. Key parameters at risk as you try to reduce the overall dimensions include, gain (length), front to back ratio (width), bandwidth (depth) and horizontal beamwidth. On the inbound side, receiver diversity is used to balance the system. Cell sizes can be maximised using dual polarised antennas or arrays of space diversity antennas. Space diversity may be used with Omni and panel antenna arrays and offers the maximum electrical performance possible. However, from a practical point of view the current practice is to use dual polar panel antennas in high-traffic-density sites. The use of arrays is usual only in legacy situations. Generally, Public Access Operators will have more High-Traffic-density cells using the Panel antenna configuration. Public Safety Bodies will have relatively few of this configuration. 2.5 DIVERSITY Figure 8 illustrates the variability of the strength of a received signal coming from a mobile transmitter over time, in to both polarisations of a dual slant polarised antenna. Signals usually arrive at the receiver via multiple paths (see below). This receiver diversity can be used to enhance systems performance. This is particularly useful when the system requires talkback from low powered handheld devices. This technique ensures that the network receives the same signal at least twice (dual receiver mode) which is then manipulated either by an additive or a selective process to ensure a better net received signal to noise ratio. Signal Strength In Dual Polar Antenna with Distance Travelled Signal Strength -60 Left Polar Right Polar Time Travelling Figure 8 - Variability of the Signal Strength coming from a mobile transmitter over time Quoting from reference iii may help to understand the complexities of propagation in the mobile radio environment: - "Radio wave propagation in the mobile radio environment is described by dispersive multi- Sigma Wireless Technologies 13 March 2002.

14 path caused by reflection, diffraction and scattering. Different paths may exist between a BS and a MS due to large distant reflectors and/or scatterers and due to scattering in the vicinity of the mobile, giving rise to a number of partial waves arriving with different amplitudes and delays. Since the mobile will be moving, a Doppler shift is associated with each partial wave, depending on the mobile's velocity and the angle of incidence. The delayed and Doppler shifted partial waves interfere at the receiver causing frequency and time selective fading on the transmitted signal." The available antenna diversity options are: - Space -Vertical. Space - Horizontal Polarisation (Usually dual polarisation) The principle is the same for each, in that the receiving base station has a choice of two signals on the incoming path. The process on average yields a gain on the receive path Diversity Gain Explained Diversity gain only operates on the up-link (Mobile Station to Base Station). It is required because portables usually have one watt transmit power towards the base, but bases can be up to 40-Watts back to the mobile. The measurement test involves a mobile and a base station with special test software in it. A typical test route is driven; the mean bit-error rate is measured at the base, using a vertically polarised antenna of equivalent gain to the antenna under test. The route is then driven again, using either two vertically polarised antennas spaced apart, or the two halves of a cross polarised antenna (as two separate tests) each being fed into separate receivers. The mobile transmit power is reduced in steps until the same bit error rate is achieved at the base as was measured in the reference drive. The amount by which the power is reduced is the equivalent Diversity Gain of the base antenna configuration chosen for the test Experimental Results Most cellular operators have, over the years, done experiments to assess the gain obtained with different diversity schemes, and some have published the results. The findings are generally similar, but never identical. One set of results is given here iv. Sigma Wireless Technologies 14 March 2002.

15 Area Type Estimated Diversity Gain with 45 Slanted Antenna Estimated Diversity Gain with Space Diversity Urban, Indoor 3.7 db 5.0 db Urban, Outdoor 4.7 db 3.3 db Suburban, Indoor 4.0 db 3.7 db Suburban, Outdoor 5.7 db 4.7 db Rural 2.7 db 5.3 db Table 1 - Diversity Gain as a Function of Operating Environment Different Diversity Schemes Described Horizontal space diversity requires that two antennas be placed some distance apart horizontally. It is generally regarded that approximately 3 meters should horizontally separate the two antennas. Reducing this space reduces the gain and the final gain obtained depends on the antenna height above surrounding terrain as well as the spacing between the antennas. The spacing of the antennas is not as critical as one would expect and spacing down to as little as 1.5 metres give good results. If optimum diversity techniques are used in the base station design, expect an absolute minimum of 3dB diversity gain for two antennas and 4.7dB gain from three antennas. Vertical space diversity can be easier to implement, but again the requirement is for approximately 4 metres vertical separation between two antennas to give the best improvement over a single antenna (similar to that given by horizontal spacing). Most of the diversity advantage is lost at 2metres. One reason for this failure is that the coverage area of the two antenna systems is very different at the 4 metre spacing. This will cause many problems trying to balance the signal quality received at the base with that received at the mobile / portable. Another disadvantage of this type of diversity is that the two received signal are not the same strength at the antenna, causing a reduction in diversity gain. Dual-polar diversity is achieved using a single antenna structure with two sets of dipoles positioned at +/- 45 degrees to each other. The dipoles positioned in this manner typically produce 3 to 4.5dB better than a single vertically polarised antenna of similar dimensions. The gain of these antennas is usually specified as Co-Polar gain i.e. the gain measured at ±45 Degrees. The 2 to 4dB gain improvement is relative to this gain. If, however, you measure the antenna gain vertically polarised, it will be 3dB less than that measured at ±45 o. The vertical space occupied by a dual polarised antenna of a given Co-Polar gain is the same as for a vertically polarised antenna of the same gain. Sigma Wireless Technologies 15 March 2002.

16 Red Feed Blue Feed Figure 9 - Illustration of Dual Polarisation Diversity How does Space Diversity work? To achieve diversity at least two receivers are required. These will receive signals from diverse sources - two antennas. These antennas will provide a separate signal to each receiver, this signal comes from the same original source - the portable / mobile (called a mobile in the following discussion) but via different paths. These antennas will need to be positioned on a mast in a suitable position to allow them to appear as two separate diverse sources of the same signal. The greater the distance between the antennas horizontally, the less likely that a signal fade (received from a moving mobile) from one antenna will occur at the same time as a signal fade from the other antenna. Thus, the diversity gain (reducing the effect of these fades) increases as the separation increases and relies on the concept that the strength of the two signals should be nearly equal on average. On average, if the two signal strengths are not equal, then the full diversity gain cannot be achieved. At 850 MHz, antennas are generally regarded as being at optimum separation at 2.75 metres (9 feet). The required separation is in fact a function of effective antenna height and does not have too much affect on diversity gain of a particular configuration. Using one method of calculating diversity gain v, reducing the spacing on a 20m tower from 2.75m to 2m reduces the diversity gain by 0.3dB. The correlation coefficient between the amplitude envelope of the received signals depends on the antenna spacing. To give an adequately low coefficient (0.7), the antennas should be at the same height and spaced at least 2.75 metres apart. In other words, the long-term correlation between the amplitude of the received signals should be high, but the instantaneous value of the correlation should be very low. (The lowest short term correlation coefficient achievable with two antennas is approximately 0.5, which is adequate to achieve expected diversity gain. The lower the short-term correlation coefficient, the better the diversity gain). If Sigma Wireless Technologies 16 March 2002.

17 these criteria are met by the antenna system, (and the receivers receive equal amplitude signals on average in the long term), the gain achieved by two receivers over one can be up to 5dB and by three receivers is up to 7dB, depending on the surrounding propagation environment. Generally, it is best to design a system for 3dB gain for two-receiver systems and 4.7dB for three antenna systems How Does Polarisation Diversity Work? As a RF signal travels from a moving mobile towards the base antenna, it will follow multiple paths. The obvious one is directly from the mobile antenna to the base antenna. However, since this path is often obstructed, a more indirect path may give a better signal. There will be many paths and each will be due to reflections. These reflections will change the polarisation of the signal. The amount by which the signal's polarisation is changed depends on the angle of incidence at the reflection point. In most instances, the signal will be partly reflected and partly refracted at the surface of the 'reflecting' material. There will be multiple signals propagating from the mobile to the base and, as it moves, the points at which the signals are reflected will be constantly changing. Thus, the polarisation and strength of the incident signals at a single base antenna will be constantly changing in a similar manner. If two receiving base antennas occupy the same space, but receive signals at different polarisations (+/- 45 o ), the RF signals coming from these antennas will be diverse or different (see Figure 8 on page 13) as the signals incident on the two base antennas from the mobile are of different polarisations. One antenna characteristic of importance in this regard is Cross-Polar Discrimination, which quantifies the ability of the antenna to discriminate between the polarisations of the signals impinging on them. If this is at 15dB or better the correlation coefficient is at 0.58 and it falls rapidly below this value. Thus an antenna with the ability to discriminate between opposite polarisations at better than 15dB across the field-of-view of the antenna, will have an adequately low correlation coefficient to achieve the 3 to 5dB diversity gain improvement. 3 Good Tetra Antenna System Design Practice Good design practice ensures that the antenna system is compatible with the infrastructure and offers additional benefits through delivery of: - 1. Lower Costs 2. Higher redundancy 3. Optimum channel usage (capacity) Sigma Wireless Technologies 17 March 2002.

18 These benefits can be derived using a combination of good mounting practices and infrastructure enhancement. The following outlines some possible antenna configurations, along with possible explanations for choice of configuration. These are only examples and the final choices taken will be determined by the system designer. The diversity gain shown in the examples is 3.5 for illustration purposes only. It is up to the system designer to avail of the currently available information on diversity and the radio environment to decide on the value to apply in a particular circumstance. The examples are given primarily to stimulate thought and not to be final solutions. 3.1 Receiver Isolation from Transmitters In the TETRA standard vi, the level of blocking for a base station receiver is -45dBm. With a transmitter level of +47 dbm, the isolation between two antennas with transmitter into one antenna and receiver into the other will need to exceed 92dB (+47 (-45) = 92dB). This does not take into account any additional filtering, or the fact that some manufacturer's equipment will exceed minimum TETRA requirements. In fact many system designers use a band-pass duplexer on the transmit / receive antenna and use a separate band-pass filter for each receiver. In all antenna configurations given below this requirement for isolation must be taken into account as must any additional insertion losses in the receiver and transmitter paths. 3.2 Antennas Used in Examples The following two antenna types have been used for the examples in this section. The antennas have been designed so that the available down-tilt will put the 3dB point on the horizon. This assures the system designer that the co-channel interference is minimised without compromising the coverage Omni Antennas The SWIFT Series has been specifically developed to offer a simple Solution for multiple applications, combining an aesthetically pleasing design with excellent performance. Typical applications are TETRA 800, MIRS, AMPS, CDMA and GSM. Models are available for top of mast and side-mount positioning. The omni-directional model offers pure omni coverage with controlled down-tilt. The offset version is suited to side of mast positioning, offering offset omni coverage and higher gain The Swift series offers network planners maximum flexibility within a Compact design. Sigma Wireless Technologies 18 March 2002.

19 Electrical Specifications Offset Omnidirectional Frequency Range MHz MHz Gain 7.5dBd (9.7dBi) 6dBd (8.2dBi) Polarisation Vertical Vertical Electrical Downtilt 0, 8 0, 8 H-plane beamwidth 3dB Points Circular to within ±0.5dB E-plane beamwidth ±9 ±9 Mechanical Overall Length 1700mm 2000mm Radiator housing Diameter 65mm 65mm Support Tube 90mm Diameter 90mm Diameter Table 2 - Omni Antenna Characteristics used in Examples Panel Antennas This broadband antenna is designed to offer a simple solution for multiple applications. It can be used either as a single band panel, dual-band or tri-band antenna. Typical applications are TETRA 800 and GSM, and CDMA. Both the 6 Bay and 8 Bay antennas deliver exceptional performance in a slim and narrow housing, reducing visual impact and wind-loading, thereby assisting the site acquisition process. Electrical Specifications SP65X8096G16 SP65X8096G17 Frequency Range MHz MHz Gain 16dBi (13.8dBd) 17dBi (14.8dBd) Polarisation ±45 0 ±45 0 Isolation between Ports 25 30dB 25 30dB Front to Back Ratio Better than 22dB Better than 22dB Electrical Downtilt 0, 6 0, 4 H-plane beamwidth 3dB Points 3dB Points E-plane beamwidth 12 9 Mechanical Dimensions (W x H X D) 260 x 1450 x 100mm 260 x 1930 x 100mm Table 3 Cross-Polar Antenna Characteristics used in Examples Sigma Wireless Technologies 19 March 2002.

20 3.3 Omnidirectional Diversity Applications Introduction Cellular networks give priority to site capacity. Thus, the use of cellular sectored sites using panel antennas is widespread and has led to the use of polarisation diversity, in preference to space diversity. In contrast to cellular, many TETRA networks will place a lower emphasis on capacity and will seek to maximise cell size (and minimise the use of frequencies) using Omnidirectional antenna arrays. The examples given below are presented to show that there are many different ways to achieve omni coverage from towers. They will give the designer some idea of how to go about obtaining an optimum design for the network under consideration. Most system designers will use some form of propagation software to predict to coverage achieved by a particular site. To allow this software to perform the calculations, it needs a Link Budget to be input. The Link Budget will take into account items such as transmit power, receiver sensitivity, cable losses, antenna gain(s), and a propagation margin. The propagation margin is used to increase the probability that the signal will be above the threshold of the receiver. Table 4 below illustrates the relationship between the propagation margin and the probability that the received signal will be above the threshold level. Margin Probability Margin Probability 5dB 73% 15dB 97% 10dB 90% 20dB 99.4% Table 4 - Propagation 'Margin' Sample Link Budget Calculation Table 5 below shows an example non-diversity Link Budget calculation for a system with a single omni antenna of 6dBd gain (such as the SWIFTOM840) connected to a TETRA reference base station. (Note that all antenna gains are expressed as dbi. If an antenna s gain is specified in dbd, add 2.2dB for the isotropic gain, giving a gain of 8.2dBi for this example). There is no diversity gain in this example. It assumes a 1- Watt class 'B' portable worn on the users' belt (giving an assumed for these examples antenna gain of - 15dBi). It should be noted that the Reference base station is 3dB more sensitive than the Reference mobile in the TETRA standard. In the table below BS is the Base Station and MS is the Mobile Station. A 25Watt base station has been used and it is clearly visible that there is a significant imbalance in the paths. This is one of the major reasons for using diversity gain at the base station. Sigma Wireless Technologies 20 March 2002.

21 Tx Rx BS -> MS MS->BS Tx Power 44 dbm 30 dbm Portable Antenna Gain -15 dbi -15 dbi Base Antenna Gain 8.2 dbi 8.2 dbi Base Cable Losses -2 db -2 db Diversity Gain 0 db 0 db Faded Rx Sensitivity -103 dbm (MS) -106 dbm (BS) Isotropic Link Gain (db) db db Useable Link Budget 127.2dB Table 5- Link Budget in Reference Example Combiner / Filter Base Station Specified at this Point Duplexer Main Antenna Covering Traffic Corridors Directional antenna patterns are used to establish communication or up/down traffic corridors. A typical example would be a highway in a sparsely populated area. Sigma has developed an antenna system especially for this application - called the 'Autorouter'. It consists of two by 6 or 8-element ±45 0 slant polarised diversity antennas fitted to a pole with special cabling. The two antennas are fed through phasing harnesses providing one transmit / receive connection and a second receive-only connection, providing diversity. The pattern shown below in Figure 10 shows the resulting pattern using two panel antennas (one pointing East and the other pointing West ). As the front to back ratio on these antenna types is high, there is little interference between the back of one pattern and the front of the other. The configuration also allows the antennas to be rotated until the angle between the antennas is If rotated closer than this, the patterns start to 'break up' because of the mutual interference as mentioned in section on page 11. If the 6-element antenna type SP65X8096G16 with a gain of 16dBi is used in this application and the two antennas are fed from the same transmitter, it is apparent that the transmitter power is divided equally between them. (If we imagine that the antennas are 50Ω loads, instead of antennas, this is easier to envisage). Thus the power being delivered into each antenna is reduced by 3dB (½ expressed as db is 3dB). This reduction will give a net antenna 'system' gain of 13dBi (-3dB + 16dBi) for a system of two antennas of the type cited at the beginning of this discussion. On the receive-path where the receiver is being fed from one Antenna, some of the power coming from this Antenna is also fed into the other antenna. It is not possible to limit this power division without affecting the transmit path. In fact, the antenna matching harness is a 3-way matched system with power being fed from one arm into the other two. This gives rise to Sigma Wireless Technologies 21 March 2002.

22 the reduction of the apparent extra gain of the antenna system, which is also directed in the specific direction of the two antennas. The reduction in gain gets larger as the angle is decreased from to At the net antenna gain is reduced by 4dB. Tx Rx1 Rx2 BS -> MS MS->BS Tx Power 44 dbm 30 dbm Portable Antenna Gain -15 dbi -15 dbi Base Antenna Gain 13 dbi 13 dbi Base Cable Losses -2 db -2 db Diversity Gain 0 db 2.7 db Faded Rx Sensitivity -103 dbm (MS) -106 dbm (BS) Isotropic Link Gain (db) 143 db db Useable Link Budget 134.7dB Combiner / Filter Base Station Specified at this Point Duplexer Left Polarisation. Optional Filter Right Polarisation. Table 6 Link Budget for two by 6-Bay Cross Polar antennas in Autorouter Configuration Diversity Gain in this configuration In this type of application, it should be noted that the diversity gain achievable is still very dependent on the environment (see Table 1 on page 15) and could be as low as 2.7dB in a rural setting. This is the diversity gain figure used in Table 6. The diversity gain is obtained around the whole pattern, which results from the combination of the two antenna patterns into a single pattern Single 60 Degree XP Antenna db 90 2 XP Antennas at 180 Degrees 2 XP Antennas at 120 Degrees 180 Figure 10 - Covering a Traffic Corridor Sigma Wireless Technologies 22 March 2002.

23 3.3.4 Top of Mast Omni plus Two Offsets This method uses a single omni at the top of the mast and two offset antennas positioned so that their tops are positioned below the omni and are mounted at 1 metre off each side of the mast. Table 7 shows the resultant link budget. This configuration will suit virtually all masts. Smaller towers will distort the offset patterns more than large towers. The patterns shown in Figure 11 are based upon offset antennas spaced at 1m from a 300mm tower. The exact amount of distortion depends on how far away from the tower the antennas are mounted and the exact nature of the tower's construction. (See ANTENNA POSITION RELATIVE TO MAST on Page 6). Tx Rx1 Rx2 Rx3 BS -> MS MS->BS Tx Power 44 dbm 30 dbm Portable Antenna Gain -15 dbi -15 dbi Base Antenna Gain 9.7 dbi 9.7 dbi Base Cable Losses -2 db -2 db Diversity Gain 0 db 5 db Faded Rx Sensitivity -103 dbm (MS) -106 dbm (BS) Isotropic Link Gain (db) db db Useable Link Budget 133.7dB Combiner / Filter Duplexer Main Omnii Antenna. Base Station Specified at these Pointe Optional Filter Other Two Offset Antennas. Optional Filter Table 7 Link Budget for Two Offsets plus an omni Diversity Gain in this configuration The pattern of the omni antenna at the top of the mast is shown as a solid black line in Figure 11(A) below. The two offset antennas are shown as red and green lines. In the centre is shown the layout of the antennas in relation to the tower, with arrows illustrating the direction in which the offset is pointed. However, these are ideal antennas patterns, without taking the effect of the distortion of the patterns created by the proximity of the tower. Figure 11(B) shows the patterns of the antennas with this distortion taken into account as well as showing the pattern of the resulting diversity gain. This comes from considering the three real patterns. This diversity pattern is, on average, 6.5dB above the gain of the omni, never less than 5.2dB and never more than 7dB at any point. This is in part due to the fact that the offset antennas are spaced far enough apart ( m = 2.3m total spacing). As we sweep around towards the 0 o and the 180 o positions, we see Sigma Wireless Technologies 23 March 2002.

24 three antennas with nearly equal gains, giving best diversity gain. As we rotate away from this the gains of the antennas become markedly different, so the diversity gain will be reduced in these directions but the gain one of the three antennas increases. In such a configuration, consideration should be given to providing sufficient isolation between the transmit antenna at the top of the tower and the receive antennas on the side of the tower. (See 3.1 Receiver Isolation from Transmitters on page 18) Omni at Top Offset to Right db db 90 Offset to Left Diversity Composite (A) Ideal Patterns (B) Patterns on 0.3m Tower Spaced at 1m from Tower. Figure 11 - 'Top of Mast' Omni Plus Two Offsets Side Mount Omnidirectional Diversity Array This antenna array comprises a pair of four stack antennas, one of which is used for Tx while both are used for receiving to achieve space diversity gain. The antenna system functions identically to and has the advantages of the Offset omni (See page 7). The Link Budget would be similar to the one shown in Table 7. The antenna configuration has the radiation pattern described below. Network planners would direct the pattern peak in the appropriate direction. Sigma Wireless Technologies 24 March 2002.

25 First Antenna Second Antenna Duplex Filter Tx Combiner Rx Multicoupler A Rx Multicoupler B 1 2 n 1A 2A na 1B 2B nb N by 4 Voice Channels N by RF Channels Two Diverse antennas shown Figure 12 - Side Mount Omnidirectional Diversity Array Diversity Gain in this configuration Figure 13 (A) shows the antenna patterns in the ideal situation. The solid line in the centre is the Transmit pattern (which is also the ideal pattern). The offset antennas should be pointed in the same direction. The diversity gain of the antennas will yield at least a 3dB improvement in all directions around the mast compared with a single offset antenna, shown as the dotted line around the outer edge of the patterns. Figure 13 (B) shows the antenna patterns in a real situation. The antennas are mounted at 1metre on either side of a 400mm triangular tower. This shows the patterns of the antennas with this distortion taken into account as well as showing the pattern of the resulting diversity gain. This comes from considering the three real patterns. (For illustration purposes the ideal, free space, patterns is shown as a solid line in the figure). Sigma Wireless Technologies 25 March 2002.

26 db db 90 Ideal Offset Red Antenna Blue Antenna Diversity Composite 180 (A) Ideal Patterns Figure 13 - Side Mount Omnidirectional Diversity Array Gain 180 (B) Patterns on 0.4m Tower Spaced at 1m from Tower. In such a configuration, consideration should be given to providing sufficient isolation between the transmit antenna and the receive antennas on the other side of the tower, especially receiver 'B'. (See 3.1 Receiver Isolation from Transmitters on page 18) Two Sector Hybrid Sector System In some circumstances, it may be appropriate to install a hybrid sector array which operates as two discretely separate sectors. The first part of the sector uses a cross-polarised panel antenna in one direction and the second part of the sector uses two separate stacked dipole arrays using space diversity. The pair of stacked dipoles is used in the classic way, one antenna Tx/Rx with a duplexer and the other antenna providing the second Rx path. The stacked dipole in its offset configuration is Omnidirectional but skewed in one direction. This should be pointed in the opposite direction to the panel antenna. The resulting coverage is egg shaped and slightly offset in the direction of the panel. It has been used where a high traffic density is required and where this shape of coverage is not a disadvantage (Such as at Motorway Junctions, with the heavier traffic in the direction of the Panel). Sigma Wireless Technologies 26 March 2002.

27 First Sector - Panel Second Sector Two Offset Half of First Antenna Second Half not Illustrated for Clarity Second Antenna Third Antenna Duplex Filter Duplex Filter Tx Combiner A Rx Multicoupler A Tx Combiner B Rx Multicoupler B A 2A 4A 1B 2B 3B 4B 1B 2B 4B Example shows two sector cell One Offset and one panel system Rx Multicoupler C 1C 2C 4C Figure 14 - Two-Sector Hybrid Sector System Diversity Gain in this configuration The radiation pattern for the stacked array is shown in black as both the Tx and Rx patterns overlap completely, as in the two offset mode. The dipole arrays of these two antennas need to be pointed in the same direction (note that they are shown in the centre of the radiation pattern and it is worth noting their directions). The diversity gain of the antennas will yield a 3dB improvement in all directions, for this antenna pair over a single antenna of the same type. The solid line represents the combination of two offset patterns. On the opposite side of the mast, a single cross-polarised panel antenna is mounted on a different set of channels. This also has a diversity gain of 3dB relative to the nominal gain of the antenna. This antennas radiation pattern is shown as a green line Figure 15 - Two Sector Hybrid Sector System Gain 90 Sigma Wireless Technologies 27 March 2002.

28 4 Mounting Criteria for Optimum Performance 4.1 Physical Mounting Criteria The antenna system most appropriate for a given application is governed by: Mast type and position. Traffic Density Radio system configuration Sectored Panel array 1. Pole mount This approach involves the three antennas mounted at the same height, each arranged at 120 degrees to each other. Either the antennas may be vertically polarised or dual polarised where diversity gain is required. 2. Mast mount The panel may be mounted on each leg of a triangular tower, again at the same level as before. Sigma Wireless Technologies 28 March 2002.

29 3. Building mount The panel antennas may be mounted at the edge of a building giving sufficient clearance from the rooftop and held in position by a steel structure. The positioning of the panels should be as with a mast, in terms of level and orientation. Free space in front of the antenna should be provided for at least 20M extending down at an angle of 30 degrees. Avoid roof edge obstructions. 5 Antenna / System Integration 5.1 Low Density System. This type of system uses a simple approach to radio coverage and shows how a single antenna may be used to allow two-way communication with four RF channels. The duplex filter allows simultaneous Tx/Rx operation and is only restricted by the RF power requirements dictated by the number of channels in use. Below is a representation of how a non-diversity system functions, using one antenna. This antenna could be Omnidirectional, sectored panel or directional. The use of one antenna in this arrangement reduces the cost of antennas, plus the cost of mast space. Sigma Wireless Technologies 29 March 2002.