Measurements of antenna radiation patterns
PawełKryszkiewicz
Faculty of Electronics and Telecommunications Poznan University of Technology
Poznan, Poland
Email: pawel.kryszkiewicz@put.poznan.pl
Adrian Kliks
Faculty of Electronics and Telecommunications Poznan University of Technology
Poznan, Poland
Email: akliks@et.put.poznan.pl
Abstract—Effective conducting of measurements of various
antenna parameters is one of the skills expected from the wireless communication engineers. This paper concentrates on the mea-surements of transmit/receive radiation patterns of the selected directional antenna. Moreover, the antenna system installed on the building of the Faculty of Electronics and Telecommunica-tions, Poznan, Poland, has been presented in details, showing its potential for development of further laboratory exercises.
I. INTRODUCTION
Having in mind the rapid development of wireless commu-nications systems being in effect the response to continuous traffic growth, the role of passive or active antennas cannot be underestimated. The transmit characteristic (radiation pattern) of the applied antenna determines the amount of interference that will be induced to the other users or systems, and defines the signal gain, achieved by input power condensation in the specified direction. Should the so-called back- and side-lobes be minimized, the interference observed by the neighboring users will be minimized as well. It is then usually desired to provide expected (e.g., of the specified 3dB width) shape of the main-lobe in the radiation pattern, and to maximize antenna energy efficiency.
The aerial manufacturers offer great variety of products de-pending on their expected target application, starting from om-nidirectional antennas, through sector120◦ antennas, finishing on very narrow pencil-beam solutions. Furthermore, beside interference minimization, the application of highly advanced antenna solutions, such as distributed antenna systems, smart antennas, or MIMO techniques, allows for significant usage optimization of available resources. Real-time adaptation of the transmit antenna characteristics provides great opportunity of dynamic tracking of the user position. One can easily state that the advantages of the application of modern antenna solutions are quite significant as well as promising, and the future bachelor or master study graduates should be aware of such great possibilities.
The theoretical radiation pattern characteristic, delivered by the antenna manufacturer together with their products, can even highly differ from one achieved by the measurements in the location, where the aerials are mounted. As the pa-rameters of the antenna will not change and are in general not dependent from the location of the antenna, the radiation pattern characteristic observed by second antenna would be different from the theoretical one. This is of course due to the
fact that the influence on the whole environment cannot be in practice omitted, i.e., the reflected waves (from the pavement, buildings, small infrastructure) can add destructively to the main signal reducing the amount of energy/power collected by the end-user. It is then worth performing the detailed yet simple method for verification of the equivalent characteristics of the already deployed antennas to observe the influence of the surrounding elements on the signal transmission. Clearly, if the measurements will be carried out in an anechoic chamber, the measured radiation patter shall be identical to the charac-teristic provided by the manufacturer in the data-sheet.
In this work we discuss the features of the antenna system installed at the Faculty of Electronics and Telecommunica-tions that can be utilized for the laboratory purposes, both scientific and didactic, such as the measurement of the real transmission/reception characteristics of the given antenna. Please notice that although we concentrate in this paper on the radiation pattern measurements, many more laboratory exercises can be realized by means of that system.
The paper is organized as follows; first, the fundamentals of the antenna parameters will be revised. It is succeeded by the illustration of the built antenna system and by the discussion of the potential laboratory exercise, where the equivalent antenna characteristic will be measured. The whole paper is concluded at the end in Section IV.
II. ANTENNA FUNDAMENTALS
In general, an antenna is an element that converts there and back the electric signals to its electro-magnetic form. Various parameters can be specified for the antenna description, the selected set of them are listed below [1], [2]:
• Energy efficiency: is the ratio between the power deliv-ered to the antenna and radiated from it; this term has no units;
• Directivity is an ability of the antenna to concentrate the power in a specific 3D area; this term is expressed in dB; • Gain is the product of the energy efficiency and
direc-tivity, this term is also specified by dB
• Radiation pattern is the graphical representation of the antenna ability to concentrate the power on specified directions; it is usually presented in the form of circular graph, where typically the main-, back- and side lobes are presented. The main lobe defined the direction, in which the radiation is the strongest. The sidelobes are
separated from the main-lobes and between themselves by the so-called ”zeros”, or radiation minimums. In fact, the radiation pattern requires the 3D representation. It is usually expressed in terms of θ and φ, denoting the angle in the z-axis and counterclockwise in the x-axis, respec-tively. The planar graphs represents the cross-section of the 3D representation. In this work we concentrate on the measurements of the power in one horizontal plane, resulting in the 2D radiation pattern. In order to make the radiation pattern independent from the distance from the antenna, the measured values of electric field are divided by the maximum value of the measured energy field. The normalized radiation characteristics F (θ, φ) can be represented as:
F (θ, φ) = Eθ(θ, φ)
Eθ,max . (1)
Finally, please note that although the radiation pattern is presented in form of circular or 3D plot, its representation in the Cartesian coordinate system is also possible, as it will be shown later in that paper.
• Side Lobe Level (SSL) - represents the ratio between the maximum side-lobe radiation value and the overall maximum radiation value, i.e.,
SSL[dB] = 20 log 10F (SSLmax)
Fmax . (2)
• half-power points / -3dB points - represents the points in the radiation pattern, where the observed power is two times (3dB) smaller than the maximum observed power; the angle betweem these points on the radiation pattern is known as the half power beam width (HPBW).
HP BW = |θleft− θright|, (3) where θleft and θright represent the angle between the -3dB points on the left and right sides and the direction of maximum power radiation.
III. INSTALLATION
In order to provide the lecturers the opportunities for performing various laboratory exercises in wireless commu-nications, the dedicated antenna system has been deployed in the building belonging to the Faculty of Electronics and Telecommunications. Its schematic diagram is depicted in Fig 1.
One can observe that the laboratory room is located on the ground floor, and is connected via various types of cables with the set of antennas mounted on the rooftop. Although the location of the place where the antennas are installed is exactly above the laboratory room, still the direct-line distance between these two places is relatively high and equals approximately 12 meters. Since the cables can be mounted only in the dedicated cable ducts, the effective cable length is significantly greater. In the current configuration of our antenna system three antennas can be mounted at the rooftop, according to the schematic presented in Fig. 2.
Groundfloor 1st floor 2nd floor rooftop laboratory room antenna masts panel box cable beam
in the cable duct
steering panel
Fig. 1. Schematic of the antenna installation - side view
top view
panel box antenna 1 antenna 2 antenna 3 ca. 3m ca. 12mcable duct entry
Fig. 2. Schematic of the antenna installation - top view
Thus, three antenna cables have been installed: one H155 (typical and relatively cheap cable with the attenuation equal to around 49.6dB/100m at 2.4 GHz) and two H1000 (advanced cable of greater diameter comparing to H155, with the atten-uation of 23.2dB/100, at 2.4 GHz). In order to protect the devices in the laboratory from any potential supertensions, the concentric cables at the rooftop are connected to the surge arresters with gas capsule (Rosenberger 53BK501-S00N1 [3]) mounted in the dedicated panel box. The connection between the box and the antennas are guaranteed by the short-length jumpers. All of the connections are realized with the N-type connectors. The photograph of the panel box mounted on the roof is presented in Fig. 3.
At the laboratory side, the cables are also connected to the dedicated panel box (please see Fig. 4 ), from which the user can connect a given antenna with the computer or any measuring device, such as spectrum analyzer.
One of the assumptions was to provide the functionality of real time measurements of the antenna radiation patter. It will be only possible if one of two antennas in a set can be rotated around its own axis over 360 degrees. Thus, the rotor HYGAIN AR35/303X [4]has been installed on the mast, allowing for steering the position of the antenna (or the entire mast) from the laboratory room. Moreover, in order to visualize the current position of the antenna, the IP camera
Low Noise Amplifier
Surge protector (for rotor)
Fuse (for Ethernet) Surge protector (for power supply)
Fig. 3. Photograph of the panel box
Power strip
Connection panel with four N sockets
Ethernet Socket Rotor steering
Fig. 4. Photograph of the inside panel box
APTI-1C3-40W [5] has been also installed on that mast (please see the Fig. 5). Application of these two elements required the installation of two additional cables: one for the power supply cables (for rotor steering) and Ethernet cable (for camera). As shown in Fig 3, the Ethernet and power cables are also protected against any supertensions (coming from e.g. the lighting) using the AXON-NET/PROF [6] module.
IV. RADIATION PATTERN MEASUREMENTS
In order to measure in real time the radiation pattern of the transmit antenna, two aerials have been used for experiment, i.e. the directional WiFi antenna Westa 17 HV [7], and the omnidirectional antenna AOR DN753 [8] (Fig. 6).
It is the WiFi antenna that can be rotated around its axis. The measurements have been conducted on the center frequency equal to 2.45GHz. In the first phase of the experiment, the signal generated by R&S SMBU 100A with the transmit power set to 25dBm has been delivered to the directional antenna. On the other hand, the omnidirectional antenna has been connected with the R&S FLS6 spectrum analyzer. The setup of the latter was the following:
1) the preamplifiers was active, attenuation was then set to 0
IP Camera
Westa 17 HV directional 2.4 GHz antenna
Rotor
Fig. 5. Mast with the IP camera, rotor and directional antenna
Antenna 1 Antenna 2
Fig. 6. Two antennas used for experiment
2) resolution and video bandwidth were set as 100 kHz, and 300 kHz
3) trace mode was set to average mode
4) zero-span mode has been selected in order to capture the signal changes in time domain
5) it has been stated that the full rotation of the antenna lasts for 80 seconds, thus, in order to store the measure-ments over the 360 Celsius degrees the sweep time has been set to 80s as well
6) finally, the number of points per one sweep was set to 501 (i.e. the sampling period was equal to 80/501 = 0.16 seconds).
In the second phase of the experiment the roles of the antennas have been interchanged, i.e. the omnidirectional antenna was used for signal transmission, while the directional one for signal detection. It can be noticed that in the first phase the transmit radiation patter was measured, while in the second the reception pattern. Clearly, these two patters shall more or less overlap some discrepancies can be observed due to the changing propagation characteristics.
The measured signal (in absolute logarithmic values) are presented in Fig. 7, while its circular representation is shown in Fig. 8.
0 50 100 150 200 250 300 350 −105 −100 −95 −90 −85 −80 −75 −70 −65 −60 −55 Degrees Observed power [dBm] receive pattern transmit pattern
Fig. 7. Radiation patterns achieved when the tested antenna acted as the transmitter and receiver
0.2 0.4 0.6 0.8 1 30 210 60 240 90 270 120 300 150 330 180 0 transmit pattern reeive pattern
Fig. 8. Radiation patterns achieved when the tested antenna acted as the transmitter and receiver, logarithmic scale, normalized
Analysis of the circular representation of the radiation patter allow as to state that the HPBW is equal to around 10 Celsius degrees, while SSL (after analysis of the linear logarithmic plot) equals around 10dB
One can observe the following:
1) as expected, there is a perfect match between the trans-mit and reception radiation patterns.
2) The achieved pattern is in line with the characteristic provide by the manufacturer
3) The whole measurement process is quite fast
4) Knowing the attenuations of the cables, as well as the transmit and received power, the path-loss between the antennas can be also calculated
V. CONCLUSION
In this paper the antenna system has been presented, fo-cusing on the technical aspects as well as installation
de-tails. Moreover, an exemplary laboratory exercise has been proposed, showing high potential of the built system.
ACKNOWLEDGMENT
This work has been supported by the Polish Ministry of Science and Higher Education funds for the status activity project DS-MK (DS/81/147/MK).
REFERENCES [1] J. Szostka, ”Fale i anteny”, WK 2000
[2] http://www.antenna-theory.com/antennas/main.php
[3] Access online, Product datasheets: http://www.kabeltechnika.pl/ produkt/1690/odgromnik-gazowy-n-mz-panelowy.html, and http: //www.rosenberger.com/0 documents/de/catalogs/ba communication/ COM Surge 2006.pdf, accessed: 17 November 2014
[4] http://www.inradio.pl/index.php/akcesoria-antenowe/rotory-antenowe/ 949/rotor-antenowy-hy-gain-ar-35-detail [5] https://sklep.delta.poznan.pl/ip-camera-apti-1c3-40w---720p-3.6-mm c0 p6112.html?ps session=1c4a5bce1a6b55ddfcaae3b2c2204e13 [6] https://sklep.delta.poznan.pl/ogranicznik-przepi-axon-net-prof c549 p4939.html [7] http://yagi.pl/antena-mikropaskowa-westa-p-1300.html [8] http://www.aorja.com/antennas/da753g.html
