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The development and performance of the VeraPhase GNSS antenna By Julien Hautcoeur, Ronald H. Johnston and Gyles Panther INNOVATION INSIGHTS with Richard Langley ANTENNAS MATTER. Often overlooked by the casual user of a GNSS receiver, its antenna is a critical component of the system. In the case of consumer equipment such as handheld receivers, satellite navigation units and embedded devices inside smartphones, cameras and fitness monitors, the antenna might not even be visible. Nevertheless, a GNSS antenna must be carefully designed and constructed to maximize the transfer of the electromagnetic energy of the weak GNSS signals into an electrical current that can be fed to the receiver. Typically, this means that the antenna has to be designed for reception of the right-hand circularly polarized signals transmitted by the satellites on their particular frequency or frequencies. Some mass-produced embedded devices might use less efficient linearly polarized antennas coupled with a high-sensitivity receiver simply to shave a few cents off the cost of the units or to fit them into a limited volume. But the pros and cons of such antennas is a discussion for another time. A GNSS antenna must also be omnidirectional, being able to receive signals arriving from any azimuth and elevation angle with acceptable gain in the hemisphere above the antenna while rejecting those signals arriving from below the antenna that, in most cases, are undesirable reflections off the ground and which have a large left-hand circularly polarized component. Reflected signals from the ground or other surfaces combine with the line-of-sight signals from the satellites resulting in multipath interference, which contaminates pseudorange and carrier-phase measurements. The first line of defense against multipath is a multipath-resistant antenna. Signals from non-GNSS transmitters on nearby frequencies should also be rejected so as not to cause interference to the receiver or overload its front end. An important characteristic for precision GNSS applications is stable electrical phase centers—the locations in three-dimensional space to which GNSS measurements are referenced. Ideally, they would be perfectly fixed with respect to the antenna housing but, in reality, they will vary with the direction of the arriving GNSS signals. The variation, however, should be small, repeatable and calibrated with the calibration values available for data-processing software. It was about 40 years ago when the first GPS receiving antennas were developed and there have been many significant advances in antenna design and fabrication since then. You might be tempted to think that there is nothing new in the research and development of GNSS antennas. You would be wrong. In this month’s column, we take a look at a revolutionary design of a multi-frequency multi-GNSS antenna. Our authors discuss how the antenna evolved from a research project in academia to a commercial product about to enter the market. And, like a number of GNSS advances, it’s Canadian, eh? The use of GNSS technology has permeated many aspects of life today. With each advancement in the technology, new applications become possible as a result of lowered costs, smaller size, greater capabilities, and higher precision and accuracy. In particular, advances in antenna technology can provide greater capabilities to GNSS receiving equipment. In this article, we report on the research and commercial development of a high-performance GNSS antenna that can cover all of the GNSS frequency bands, that has high purity circularly polarized radiation, high phase-center stability and high radiation efficiency. Early numerical simulations showed that the turnstile/cup antenna was a good starting point for this research. For GNSS applications, this antenna type required much further research to extend the impedance bandwidth, to reduce cross-polarization and to reduce backward radiation. Many thousands of electromagnetic (EM) computer simulations and optimizations of various circular waveguide (or cup) structures led to a high-performance circularly polarized antenna. This antenna has excellent axial ratios in all theta and phi directions, low backward radiation, excellent phase-center stability and a compact design. Intermediate and final antenna designs were extensively tested in the anechoic chamber of the Schulich School of Engineering at the University of Calgary. Our company subsequently signed a license agreement with the University of Calgary’s University Technologies International Inc. and undertook further development of the antenna for commercial production. In this article, we present measured results for the resulting commercial antenna known as the Tallysman VeraPhase VP6000 antenna. Early Circularly Polarized Antennas. One of the first circularly polarized antenna designs (1948) can be attributed to Sichak and Milazzo (see Further Reading), who introduced the turnstile or crossed-dipole circular polarization (CP) antenna. The crossed dipoles must have current flows that are 90 degrees out of phase with each other. This phase difference can be achieved feeding the two dipoles 90 degrees out of phase by a phase-shifting signal splitter or by changing the impedance of each of the dipoles. The turnstile antenna produces highly pure CP only in the two directions normal to the two dipoles. If the dipoles are normal to each other and lie in the horizontal plane, they can radiate right-hand circular polarization (RHCP) upwards while left-hand circular polarization (LHCP) is radiated downwards. At the horizon, they will radiate only a linear horizontally polarized wave. For GNSS applications, this is a serious limitation. By 1973, it was known that a horizontal dipole placed near the open face of a “cup” or shorted waveguide would radiate a linear horizontally polarized wave sideways and a vertically polarized wave in its direction of alignment. These properties were utilized by Epis (see Further Reading) to build a broadband CP antenna. RESEARCH OBJECTIVE The university research project began with the objective of developing a high-precision GNSS antenna that would cover all of the frequency bands being considered by the various national GNSS satellite systems, whether launched or under development. It was decided at the onset of the research that computer simulation and optimization methods would be an important part of the research endeavor. Many antenna structures were evaluated using EM simulation tools. Various structures were constructed in software and then simulated. Early simulations indicated that the crossed dipole placed in a cup offered the best possibility for producing a high-performance GNSS antenna. To obtain the best RHCP with minimal LHCP, it became necessary to place the dipoles somewhat within the cup. Nevertheless, the impedance bandwidth of this configuration is insufficient to handle the upper and lower GNSS frequency bands at the same time. Extending the Antenna Bandwidth. The first structure that was used to handle both the L1 and L2 GNSS bands was a second set of dipoles connected in parallel to the first set. This arrangement provided an adequate match to frequencies close to the L1 band (1575 MHz) and the L2 band (1227 MHz) but it gave a rapidly changing reflection coefficient close to and below the L1 band. The two dipole sets were fed by an appropriate surface-mount 90-degree hybrid coupler designed for the required broad frequency band. The dipoles are fed by microstrip via “grounded legs” that are built on printed circuit board (PCB) technology. Good performance was achieved with this structure, but further improvements in the performance were actively sought. The two dipoles connected directly together cause a deep notch in the radiated signal at a frequency close to and below the L1 band. This was considered to be undesirable. It was decided to use a coupled resonant radiating structure tuned to L1 while the main dipoles would be tuned to L2 (see FIGURE 1). FIGURE 1. An extended bandwidth GNSS antenna. The lower and connected dipoles are tuned to L2 and the upper coupled shorted dipoles are tuned to L1. Current flow in the circular waveguide of the GNSS antenna is shown. Strong circumferential currents flow at the top of the waveguide. Red indicates large currents and the arrows show the directions of the current flow. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) It is well known that resonant circuits can be broadbanded by choosing the correct coupling between them. This was tried in software and found to give an excellent wideband response. Circumferential Current Reduction. Through many EM simulations of the antenna structure, it was found that the LHCP could be suppressed substantially by making the aperture of the cup serrated. The EM wave simulation package allows the user to look at the currents in the structure. The results are shown in FIGURE 2. FIGURE 2. An antenna with a tapered base and a sawtooth aperture, which reduces circumferential current flow. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) The strong circumferential currents (horizontal linear currents) produce radiation with linear horizontal polarization. It is important to reduce the size of these currents to minimize the linearly polarized radiation. The horizontal currents flowing in the top of the waveguide wall are effective in setting up horizontal polarization (HP) radiation in the direction of the horizon. For high-quality CP radiation, the horizontal radiation must be matched by vertical radiation (with a 90-degree phase shift), but the waveguide wall does not permit the required vertical current to flow to produce the vertical polarization (VP) radiation component. Clearly, a serrated waveguide aperture reduces the circumferential current flow. It was also found, through many simulations, that the unwanted polarization components can be reduced by tapering the cup towards the bottom end (see Figure 2). The sawtooth aperture antenna was chosen for further development. The fed dipoles are constructed using PCB technology and are given shapes that vary from the wire dipole case. The radiating resonator is also constructed using PCB material and is given a different shape from the pure straight-wire case. The software antenna was constructed and tested and found to have good performance with regard to low cross polarization in all directions, low backward radiation and high radiation efficiency. Further Waveguide Development. It was decided that another way of achieving vertical currents and horizontal currents that would be balanced in magnitude and have a 90-degree phase difference might be obtained by constructing the waveguide walls from a combination of thin conductors connected in a grid. The grid consists of a combination of vertical and horizontal conductors. Simulations with EM software showed the antenna is exceptionally efficient when it uses wires. The wire grid waveguide model of the GNSS antenna was simulated with many, many topological variations. Each variation was optimized for low back (nadir) radiation and high-purity RHCP in all directions. The results were unexpected. The best results were obtained when only one circumferential wire conductor is used and, furthermore, the vertical wire conductors are not connected to the circumferential conductor nor to the base of the antenna. This structure was simulated and optimized many times to derive the best possible topological configuration and component dimensions for a GNSS antenna. A PCB model of the GNSS antenna was then numerically constructed, simulated and optimized as a more practical construction technology for the antenna (see FIGURE 3). FIGURE 3. The conducting plate waveguide model of the GNSS antenna. The blue plates are conducting sheets and the yellow plates are the dielectric of the PCB. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) Note that the vertical strip conductors do not contact the conducting antenna base. Also note the serrated antenna base, as seen on the inside of the antenna. This design feature reduces excessive circumferential current flow in the base of the antenna. The antenna was tested in the University of Calgary anechoic chamber and in the high-quality Simon Fraser University anechoic chamber (a Satimo SG64), and it was found to have well-suppressed LHCP radiation, very low back radiation and very stable phase centers. The unique topology of this last antenna provides suppression of the expected downward LHCP radiation that most CP antennas exhibit. Radiation tends to “spill over” from the aperture and travel downwards. Downward radiation also emerges from the gap between the antenna base and the vertical conductors. These two sources of downward radiation are largely out of phase and tend to cancel each other out. This reduced downward LHCP radiation largely removes the need for a choke ring to block the reflections from the ground. This in turn means that the antenna can be compact and light. ANTENNA DEVELOPMENT FIGURE 4.  Tallysman’s VeraPhase 6000 high-precision GNSS antenna. (Photo: Tallysman) We undertook the project of converting the research prototype antenna described above into a commercially viable product. The research prototype antenna was modified to achieve optimized gain at lower GNSS frequencies, high mechanical robustness, adaptation for efficient manufacturability and for use of different materials. This antenna is known as the VeraPhase VP6000 antenna and is shown in FIGURE 4. The topology of the antenna follows that of the research prototype with dimensional adjustments so as to function correctly with the new materials and circuitry being used. It is light and compact with a diameter of 157 millimeters, a height of 137 millimeters and a weight of less than 670 grams. VeraPhase Measurements. Anechoic chamber tests were conducted at the Satimo facility in Kennesaw, Georgia, to determine the gain pattern, axial ratio, phase-center offset and variation in multipath-free conditions. Data were collected from 1160 MHz to 1610 MHz to cover all the GNSS frequencies. Antenna Gain, Efficiency and Roll-off. The chamber measurements show that the VP6000 exhibits a gain at zenith from 4.9 dBic at 1164 MHz to 7.05 dBic at 1610 MHz (see FIGURE 5). This high gain in combination with a wideband pre-filtered low-noise amplifier (LNA) with a noise figure of 2 dB provides for high carrier-to-noise density (C/N0) ratios for all GNSS frequencies. Furthermore, the VP6000 exhibits gain at the horizon from –4.4 dBic at 1164 MHz to –6.8 dBic at 1610 MHz (see Figure 5). FIGURE 5. RHCP gain of the VP6000 at zenith and the horizon at all GNSS frequencies. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) Thus, the gain roll-off from zenith to horizon is between 10.1 dB and 13.6 dB, providing for good tracking at low elevation angles. The radiation efficiency of the VP6000 is 70 percent to 80 percent, corresponding to an inherent (“hidden”) loss of just 1 dB to 1.5 dB, which includes all feedline, matching circuit and 90-degree hybrid coupler losses. In contrast, spiral antennas usually exhibit an inherent efficiency loss of close to 4 dB in the lower GNSS frequencies. Thus, with a high performance LNA, high values of gain translate into higher C/N0 ratios. FIGURE 6. Normalized radiation patterns of the VP6000 on 60 phi cuts of the GPS frequency bands. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) Radiation Patterns. The radiation pattern of an idealized antenna would have pure CP and constant high gain from zenith down to the horizon and then roll off rapidly for elevation angles below the horizon. In a realizable antenna, the gain should be close to constant over all azimuths for each elevation angle, with strong cross-polarization rejection over that frequency range. The phase-center offset should be stable with minimal phase-center variation. In the upper hemisphere, the greater the difference between the RHCP and LHCP antenna gain, the greater the resistance of the antenna to cross-polarized signals, usually associated with odd order reflections, and hence improved multipath signal rejection. The measured radiation patterns at GPS frequencies are shown in FIGURE 6. The radiation patterns are normalized to enable direct comparison of the patterns and show the RHCP and LHCP gains on 60 azimuth cuts three degrees apart. The radiation patterns show excellent suppression of the LHCP signals in the upper hemisphere. Similar results were found for all the other GNSS frequencies. The difference between the RHCP gain and the LHCP gain at zenith ensures an excellent discrimination ranging from 31 dB to 53 dB. Also, for the other elevation angles the LHCP signals usually stay 25 dB below the maximum RHCP gain and even 30 dB from 1200 MHz to 1580 MHz. The antenna shows a constant amplitude response to signals coming at a constant elevation angle regardless of the azimuth or bearing angle. This illustrates the excellent multipath mitigation characteristics of the VP6000 at every elevation angle and every GNSS frequency. Down-Up Ratio. When a direct satellite signal is reflected from the ground, the reflected signal polarization tends to convert, at least partially, from RHCP to LHCP for most soil types. If the terrain underneath the antenna is homogeneous, then the ground surface acts as a mirror, thus providing a reflected signal coming from below the horizon at the negative of the angle of the direct signal above the horizon. Depending on the angle, in part, the field of the inverted and reflected wave adds to the direct wave, which is undesirable. This is the reason, when characterizing the multipath reflection capabilities of an antenna, it is common to use a down-up ratio between antenna gain for LHCP signals for a given angle below the horizon as that for the RHCP signals at the same angle above the horizon. The down-up ratios at L2 and L1 are –25 dB at zenith and they stay under –20 dB for the upper hemisphere, which is usually not the case for standard GNSS antennas. Similar results have been measured over the whole range of GNSS frequencies and confirm the excellent multipath rejection capabilities of the VP6000. Axial Ratio. The axial ratio (AR) is a measure of an antenna’s ability to reject the cross-polarized portion of a composite signal with both RHCP and LHCP components. Physically, this is an elliptical wave, typically being the combination of the direct and reflected signals from the satellite. The lower the ratio of the major axis to the minor axis of the polarization ellipse, the better the multipath rejection capability of the antenna. To meet operational standards for a multi-band antenna, the axial ratio should meet these requirements at the following elevation angles: 45–90 degrees: not to exceed 3 dB 15–45 degrees: not to exceed 6 dB 5–15 degrees: not to exceed 8 dB. The worst AR ratio values of the VP6000 at different elevation angles have been plotted in FIGURE 7. The graph shows an AR of less than 0.5 dB at zenith for all GNSS frequencies, and the ARs stay low at all elevation angles down to the horizon. A maximum value of 1.5 dB has been measured for elevation angles above 30 degrees, increasing to just 2 dB at the horizon (0 degree elevation angle) for the worst case azimuth. This performance contributes to the excellent multipath rejection capability of the VP6000. FIGURE 7. Worst case of axial ratios of the VP6000 at different elevation angles: 90 degrees (zenith), 30 degrees, 10 degrees and 0 degrees (horizon). (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) Phase-Center Offset / Phase-Center Variation and Absolute Calibration. For use as a measurement instrument, the antenna must have a precise origin, equivalent to a tape measure zero mark. Thus, it is important that the phase of the waves received by the antenna “appear” to arrive at a single point that is independent of the elevation angle and azimuth of the incoming wave. This point is known as the phase center of the antenna, which should remain fixed for all operational frequencies and for all azimuth and elevation angles of incoming waves, otherwise dimensional measurement is compromised. In an ideal GNSS antenna, the phase center would correspond exactly with the physical center of the antenna housing. In practice, it varies with the changing azimuth and elevation angle of the satellite signal. The difference between the electrical phase center and an accessible location amenable to measurement on the antenna is described by the phase-center offset (PCO) and phase-center variation (PCV) parameters and their values are determined through antenna calibration. These corrections are only effective if the predicted phase-center movement is repeatable for all antennas of the same model. The PCO is calculated for each measured elevation angle by considering the signal phase output for all phi (azimuth) values at a specific theta (elevation) angle, and mathematical removal of the normal phase-windup effect in this type of antenna. A Fourier analysis is then conducted on this resulting data. The fundamental output gives the variation of the horizontal position of the antenna as it is rotated about the z axis. The apparent position normally varies somewhat as the antenna is viewed from various theta angles. The PCV measurement of the VP6000 showed the variation of the phase center in the horizontal plane for elevation angles of 18 to 90 degrees in 3-degree steps at different frequencies. The variations for the different GNSS signals are typically less than 1 millimeter from the x and y axes. Repeatability of the PCO and PCV over several VP6000 antennas has been measured and is also less than 0.5 millimeters. Five copies of the antenna were sent for absolute calibration by Geo++ in Germany where the VP6000 has been calibrated at GPS L1/L2 and GLONASS G1/G2 signal frequencies. The PCV for the upper hemisphere of the VP6000 at L1 and L2 are plotted in FIGURES 8 and 9. These results confirm a ±1-millimeter PCV at L1 and a ±1-millimeter PCV at L2. Also the standard deviation of the PCV over the five measured antennas stayed under 0.2 millimeters, which represents excellent repeatability. The same results have been observed at G1 and G2. FIGURE 8. Phase-center variation at L1. The same results have been observed at G1. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) FIGURE 9. Phase-center variation at L2. The same results have been observed at G2. (Image: Julien Hautcoeur, Ronald H. Johnston and Gyles Panther) LNA and Optional Circuitry. The best achievable C/N0 for signals with marginal power flux density is limited by the efficiency of each antenna element, the gain and the overall receiver noise figure. This can be quantified by a ratio parameter, usually referred to as G/T, where G is the antenna gain (in a specific direction) and T is the effective noise temperature of the receiver — usually dominated by the noise figure of the input LNA. In the VP6000 LNA, the received signal is split into the lower GNSS frequencies (from 1160 MHz to 1300 MHz) and the higher GNSS frequencies (from 1525 MHz to 1610 MHz) in a diplexer connected directly to the antenna terminals and then pre-filtered in each band. This is where the high gain and high efficiency of the basic VP6000 antenna element provides a starting advantage, since the losses introduced by the diplexer and filters are offset by the higher antenna gain, thereby preserving the all-important G/T ratio. That being said, GNSS receivers must accommodate a crowded RF spectrum, and there are a number of high-level, potentially interfering signals that can saturate and desensitize GNSS receivers. These include, for example, the Industrial, Scientific and Medical (ISM) band signals and mobile phone signals, particularly Long-Term Evolution (LTE) signals in the newer 700-MHz band, which are a hazard because of the potential for harmonic generation in the GNSS LNA. Other potentially interfering signals include Globalstar (1610 MHz to 1618.25 MHz) and Iridium (1616 MHz to 1626 MHz) because they are high-power uplink signals and particularly close in frequency to GLONASS signals. The VP6000 LNA is a compromise between ultimate sensitivity and ultimate interference rejection. A first defensive measure in the VP6000 LNA is the addition of multi-element bandpass filters at the antenna element terminals (ahead of the LNA). These have a typical insertion loss of 1 dB because of their tight passband and steep rejection characteristics. Sadly, there is no free lunch, and the LNA noise figure is increased approximately by the additional filter-insertion loss. The second defensive measure in the VP6000 LNA is the use of an LNA with high linearity, which is achieved without any significant increase in LNA power consumption, by use of LNA chips that employ negative feedback to provide well-controlled impedance and gain over a very wide bandwidth with considerably improved linearity. Bear in mind that while an installation might initially be determined to have an uncluttered environment, subsequent introduction of new services may change this, so interference defenses are prudent even in a clean environment. A potentially undesirable side effect of tight pre-filters is the possible dispersion that can result from variable group delay across the filter passband. Thus it is important to include these criteria in selection of suitable pre-filters. The filters in the VP6000 LNA give rise to a maximum variation of 2 nanoseconds in group delay over the lower GNSS frequencies (from 1160 MHz to 1300 MHz) and 2.5 nanoseconds over the higher GNSS frequencies (from 1525 MHz to 1610 MHz). Also, the difference in group delay between the lower GNSS frequencies and the higher GNSS frequencies stays less than 5 nanoseconds. The VP6000 series antennas are available with either a 35-dB gain LNA or with a 50-dB gain LNA for installations with long coaxial cable runs. The VP6000 is internally regulated to allow a supply voltage from 2.7 volts to 26 volts. An interesting feature of the VP6000 is that the physical housing includes a secondary shielded PCB that is available for integration of custom circuits or systems within the antenna. This allows the addition of L1/L2 receivers for real-time kinematic operation, for example. A pre-filtered, 15-dB pre-amp version of the LNA is also available to provide RF input for OEM systems embedded within the antenna housing. The VP6000 is available with a variety of connectors and with a conical radome to shed ice and snow and to deter birds for reference antenna installations. A precise and robust monument mount is also available. CONCLUSION In this article, we have described a research program that developed a series of CP antennas, which have increasingly improved performances directed towards GNSS applications. The resulting research CP prototype antenna has a very low cross-polarization, very low back radiation, very high phase-center stability and a compact structure. We have converted the research prototype into a commercially viable GNSS antenna with the superior electrical properties of the research prototype while building into the antenna the required physical ruggedness and manufacturability required of the commercial antenna. With emerging satellite systems on the horizon, a new high-performance antenna is needed to encompass all GNSS signals. Our new antenna has sufficient bandwidth to receive all existing and currently planned GNSS signals, while providing high performance standards. Testing of the antenna has shown that the new innovative design (crossed driven dipoles associated with a coupled radiating element combined with a high performance LNA) has good performance, especially with respect to axial ratios, cross-polarization discrimination and phase-center variation. These improvements make the antenna an ideal candidate for low-elevation-angle tracking. The reception of the proposed new signals along with additional low-elevation-angle satellites will bring new levels of positional accuracy to reference networks, and benefits to the end users of the data. With its compact size and light weight, the antenna has been designed and built for durability and will stand the test of time, even in the harshest of environments. ACKNOWLEDGMENT This article is based, in part, on the paper “The Evolutionary Development and Performance of the VeraPhase GNSS Antenna” presented at the 2016 International Technical Meeting of The Institute of Navigation held in Monterey, California, Jan. 25–28, 2016. JULIEN HAUTCOEUR graduated in electronics systems engineering and industrial informatics from the Ecole Polytechnique de l’Université de Nantes, Nantes, France, and received a master’s degree in radio communications systems and electronics in 2007 and a Ph.D. degree in signal processing and telecommunications from the Institute of Electronics and Telecommunications of Université de Rennes 1, Rennes, France, in 2011. From 2011 to 2013, he obtained postdoctoral training with the Université du Québec en Outaouais, Gatineau, Canada. In 2014, he joined Tallysman Wireless Inc. in Ottawa, Canada, as an antenna and RF engineer. RONALD H. JOHNSTON received a B.Sc. from the University of Alberta, Edmonton, Canada, in 1961 and the Ph.D. and D.I.C. from the University of London and Imperial College (both in London, U.K.) respectively, in 1967. In 1970, he joined the University of Calgary, Canada, and has held assistant to full professor positions and was the head of the Department of Electrical and Computer Engineering from 1997 to 2002. He became professor emeritus in the Schulich School of Engineering in 2006. GYLES PANTHER is a technology industry veteran with more than 40 years of engineering, corporate management and entrepreneurial experience. He spent the first 20 years of his career in the semiconductor industry, first with Plessey in the U.K., then in Canada with Microsystems International. Panther co-founded and acted as engineering vice president and chief technology officer (CTO) for Siltronics, followed by SilCom and SiGem. In 2002, he founded startup Wi-Sys Communications, acting as president and CTO. He is now president and CTO of Tallysman Wireless, his fourth successful start-up, which was founded in 2009. Panther holds an honours degree in applied physics from City University, London, U.K. FURTHER READING Authors’ Conference Paper “The Evolutionary Development and Performance of the VeraPhase GNSS Antenna” by J. Hautcoeur, R.H. Johnston and G. Panther in Proceedings of ITM 2016, the 2016 International Technical Meeting of The Institute of Navigation, Monterey, California, Jan. 25–28, 2016, pp. 771–783. Early Circularly Polarized Antenna Designs “Broadband Cup-Dipole and Cup-Turnstile Antennas” by J.J. Epis, United States Patent No. 3,740,754, June 19, 1973. “Antennas for Circular Polarizations” by W. Sichak and S. Milazzo in Proceedings of the Institute of Radio Engineers, Vol. 36, No. 8, Aug. 1948, pp. 997–1001, doi: 10.1109/JRPROC.1948.231947. Antenna Modeling Electromagnetic Modeling of Composite Metallic and Dielectric Structures by B.M. Kolundzija and A.R. Djordjevi, published by Artech House, Norwood, Massachusetts, 2002. WIPL-D: Electromagnetic Modeling of Composite Metallic and Dielectric Structures – Software and User’s Manual by B.M. Kolundzija, J.S. Ognjanovic and T.K. Sarkar, published by Artech House, Norwood, Massachusetts, 2000. Measurement of Phase Center and Other Antenna Characteristics “Determining the Three-Dimensional Phase Center of an Antenna” by Y. Chen and R.G.Vaughan in Proceedings of the XXXIth General Assembly and Scientific Symposium of the International Union of Radio Science (URSI), Beijing, Aug. 16–23, 2014, doi: 10.1109/URSIGASS.2014.6929023. “Calibrating Antenna Phase Centers: A Tale of Two Methods” by B. Akrour, R. Santerre and A. Geiger in GPS World, Vol. 16, No. 2, Feb. 2005, pp. 49–53. “Characterizing the Behavior of Geodetic GPS Antennas” by B.R. Schupler and T.A. Clark in GPS World, Vol. 12, No. 2, Feb. 2001, pp. 48–55. The Basics of GNSS Antennas “GNSS Antennas: An Introduction to Bandwidth, Gain Pattern, Polarization, and All That” by G.J.K. Moernaut and D. Orban in GPS World, Vol. 20, No. 2, Feb. 2009, pp. 42–48. “A Primer on GPS Antennas” by R.B. Langley in GPS World, Vol. 9, No. 7, July 1998, pp. 73–77.

all signals jammer

Sony vgp-ac10v2 ac adapter 10.5vdc 1.9a genuine for vaio mini pc,duracell mallory bc734 battery charger 5.8vdc 18ma used plug in,viasys healthcare 18274-001 ac adapter 17.2vdc 1.5a -(+) 2.5x5.5.cwt pa-a060f ac adapter 12v 5a 60w power supply,dve dsa-0251-05 ac adapter 5vdc 5a used 2.5x5.5x9mm 90 degree.fournis par fabricant chinois - al …,using this circuit one can switch on or off the device by simply touching the sensor.motorola spn5404aac adapter 5vdc 550ma used mini usb cellphone,hi capacity le-9720a-05 ac adapter 15-17vdc 3.5a -(+) 2.5x5.5mm,linearity lad6019ab5 ac adapter 12vdc 5a used 2.5 x 5.4 x 10.2 m,dve dsa-6pfa-05 fus 070070 ac adapter +7vdc 0.7a used,raheem hagan from meadow lake is wanted for discharging a firearm with intent and reckless discharge of a fire arm,anthin gfp101u-1210 ac adapter 12vdc 1a pl-6342 power supply.long range jammer free devices.mbsc-dc 48v-2 ac adapter 59vdc 2.8a used -(+) power supply 100-1,toshiba pa2478u ac dc adapter 18v 1.7a laptop power supply.philips hx6100 0.4-1.4w electric toothbrush charger.li shin lse9901b1260 ac adapter12vdc 5a 60w used 4pin din power.li shin 0335c1960 ac adapter 19vdc 3.16a -(+) 3.3x5.5mm tip in 1,ultech ut-9092 ac adapter 9vdc 1800ma used -(+) 1.5x4mm 100-240v.nikon eh-64 ac adapter 4.8vdc 1.5a -(+) power supply for coolpix,mobile jammers block mobile phone use by sending out radio waves along the same frequencies that mobile phone use,dragon sam-eaa(i) ac adapter 4.6vdc 900ma used usb connector swi,pure energy ev4-a ac adapter 1.7vdc 550ma used class 2 battery c,compaq series 2872a ac adapter 18.75v 3.15a 41w? 246960-001.netbit dsc-51f-52p us ac adapter 5.2v 1a switching power supply.replacement 3892a327 ac adapter 20vdc 4.5a used -(+) 5.6x7.9x12m.samsung hsh060abe ac adapter 11-30v dc used portable hands-free.d-link m1-10s05 ac adapter 5vdc 2a -(+) 2x5.5mm 90° 120vac new i.accordingly the lights are switched on and off,its called denial-of-service attack,sjs sjs-060180 ac adapter 6vdc 180ma used direct wall mount plug,symbol r410506 ac adapter 4vdc 140ma used 24pin connector ptc-70,it consists of an rf transmitter and receiver.jvc aa-r602j ac adapter dc 6v 350ma charger linear power supply.samsung atads10jbe ac adapter 5v dc 0.7a used usb pin cellphone,sagemcom nbs24120200vu ac adapter 12vdc 2a used -(+) 2.5x5.5mm 9,jammerssl is a uk professional jammers store,hipro hp-ol060d03 ac adapter 12vdc 5a used -(+)- 2.5x5.5power su,an antenna radiates the jamming signal to space,wang wh-601e2ca-2 ac adapter 12vac 5a 60w used 2pin 120vac plug,pulses generated in dependence on the signal to be jammed or pseudo generatedmanually via audio in.bec ve20-120 1p ac adapter 12vdc 1.66a used 2x5.5mm -(+) power s.databyte dv-9200 ac adapter 9vdc 200ma used -(+)- 2 x 5.5 x 12 m.ibm 02k6808 ac adapter 16vdc 3.5a used 2.6x5.5x11mm straight.dell pa-1600-06d2 ac adapter 19v dc 3.16a 60w -(+)- used 3x5mm.li shin 0225a2040 ac adapter 20vdc 2a -(+) 2.5x5.5mm laptop powe,cui inc epa-201d-09 ac adapter 9vdc 2.2a used -(+)- 2x5.4mm stra,linksys ls120v15ale ac adapter 12vdc 1.5a used -(+) 2x5mm 100-24,dsa-0051-03 ac dc adapter 5v 1000ma power supply,where shall the system be used,centrios ku41-3-350d ac adapter 3v 350ma 6w class 2 power supply,radioshack 23-321 ac adapter 12v dc 280ma used 2-pin atx connect,sony ac-v55 ac adapter 7.5v 10v dc 1.6a 1.3a 26w power supply.ac/dc adapter 5v 1a dc 5-4.28a used 1.7 x 4 x 12.6 mm 90 degree,sc02 is an upgraded version of sc01,which is used to provide tdma frame oriented synchronization data to a ms.fineness power spp34-12.0-2500 ac adapter 12vdc 2500ma used 4 pi,delta adp-90sb bd ac adapter 20vdc 4.5a used -(+)- 2.5x5.5x11mm.a wide variety of custom jammers options are available to you,fit mains fw7218m24 ac adapter 24vdc 0.5a 12va used straight rou,liteon ppp009l ac adapter 18.5v dc 3.5a 65w laptop hp compaq,ault p48480250a01rg ethernet injector power supply 48vdc 250ma,bionx hp1202l3 01-3444 ac adaptor 37vdc 2a 4pin xlr male used 10.upon activation of the mobile jammer,deer ad1809c ac adapter 9vdc 2.25a 18w used -(+) 2x5.5mm power s,cell phone jammer is an electronic device that blocks transmission of signals …,panasonic pv-dac14d ac adapter 8.4vdc 0.65a used -(+) battery.the if section comprises a noise circuit which extracts noise from the environment by the use of microphone,linearity lad1512d52 ac adapter 5vdc 2a used -(+) 1.1x3.5mm roun.ibm aa20210 ac adapter 16vdc 3.36a used 2.5 x 5.5 x 11mm round b.delta adp-65jh db ac adapter 19vdc 3.42a used 1.5x5.5mm 90°rou,cell phone jammers have both benign and malicious uses.

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Nec pa-1700-02 ac adapter 19vdc 3.42a 65w switching power supply,chd ud4120060060g ac adapter 6vdc 600ma 14w power supply.and like any ratio the sign can be disrupted,cincon tr100a240 ac adapter 24vdc 4.17a 90degree round barrel 2..phs and 3gthe pki 6150 is the big brother of the pki 6140 with the same features but with considerably increased output power,astrodyne spu16a-105 ac adapter 12vdc 1.25a -(+)- 2x5.5mm switch.dve dv-0920acs ac adapter 9vac 200ma used 1.2x3.6mm plug-in clas.finecom ky-05036s-12 ac adpter 12vdc 5v dc 2a 5pin 9mm mini din.dell apac-1 ac adapter 12v 2a power supply,gateway liteon pa-1900-15 ac adapter 19vdc 4.74a used.metro lionville fw 7218m/12 ac adapter 12vdc 1a -(+) used 2x5.5m,compaq presario ppp005l ac adapter 18.5vdc 2.7a for laptop,1 w output powertotal output power,cisco at2014a-0901 ac adapter 13.8vdc 1.53a 6pins din used powe.duracell cefadpus 12v ac dc adapter 1.5a class 2 power supply,the inputs given to this are the power source and load torque.dell d220p-01 da-2 series ac adapter 12vdc 18a 220w 8pin molex e.delta adp-60db rev.b ac adapter 19vdc 3.16a used 3 x 5.5 x 9.6mm,motorola psm5091a ac adapter 6.25vdc 350ma power supply,potrans up01011120 ac adapter +12vdc 1a power supply,sony pcga-acx1 ac adapter 19.5vdc 2.15a notebook power supply,dell pa-1470-1 ac adapter 18v 2.6a power supply notebook latitud.ibm adp-160ab ac adapter 12vdc 13.33a 6pin molex power supply,tc98a ac adapter 4.5v dc 800ma cell phone power supply,ibm 02k7006 ac adapter 16vdc 3.36a used -(+)- 2.5x5.5mm 100-240v,this project uses arduino for controlling the devices.curtis dvd8005 ac adapter 12vdc 2.7a 30w power supply,samsung sac-42 ac adapter 4.2vdc 450ma 750ma european version po,this tool is very powerfull and support multiple vulnerabilites,ibm thinkpad 73p4502 ac dc auto combo adapter 16v 4.55a 72w,canon pa-v2 ac adapter 7v 1700ma 20w class 2 power supply.modul 66881f ac adapter 12vac 1660ma 25w 2p direct plug in power,power solve psg60-24-04 ac adapter 24va 2.5a i.t.e power supply,aurora 1442-300 ac adapter 5.3vdc 16vdc used 2pin toy transforme,jt-h090100 ac adapter 9vdc 1a used 3 x 5.5 x 10 mm straight roun.ibm 02k6756 ac adapter 16vdc 4.5a 2.5x5.5mm -(+) 100-240vac powe,sony vgp-ac19v10 ac adapter 19.5vdc 4.7a notebook power supply,minolta ac-9 ac-9a ac adapter 4.2vdc 1.5a -(+) 1.5x4mm 100-240va.apple adp-22-611-0394 ac adapter 18.5vdc 4.6a 5pin megnatic used.ktec ka12a2000110023u ac adapter 20vc 100ma used 1x3.5x9mm round,is used for radio-based vehicle opening systems or entry control systems.targus pa350 (ver 2.0) f1201 ac adapter 3-24vdc used universal a,all mobile phones will automatically re-establish communications and provide full service,spacelabs medical mw100 ac adapter 18v 4.25a electro power suppl,3com dve dsa-12g-12 fus 120120 ac adapter +12vdc 1a used -(+) 2.,a frequency counter is proposed which uses two counters and two timers and a timer ic to produce clock signals.sears craftsman 974775-001 battery charger 12vdc 1.8a 9.6v used,toshiba ap13ad03 ac adapter 19v dc 3.42a used -(+) 2.5x5.5mm rou,creative mae180080ua0 ac adapter 18vac 800ma power supply,ite 3a-041wu05 ac adapter 5vdc 1a 100-240v 50-60hz 5w charger p,biosystems 54-05-a0204 ac adapter 9vdc 1a used -(+) 2.5x5.5mm 12.belkin utc001-b usb power adapter 5vdc 550ma charger power suppl,bs-032b ac/dc adapter 5v 200ma used 1 x 4 x 12.6 mm straight rou,fone gear 01023 ac adapter 5vdc 400ma used 1.1 x 2.5 x 9mm strai.delta adp-15zb b ac adapter 12vdc 1.25a used -(+) 2.5x5.5x10mm r,this paper serves as a general and technical reference to the transmission of data using a power line carrier communication system which is a preferred choice over wireless or other home networking technologies due to the ease of installation.baknor 41a-12-600 ac adapter 12vac 600ma used 2x5.5x9mm round ba.80h00312-00 5vdc 2a usb pda cradle charger used -(+) cru6600,the pki 6160 is the most powerful version of our range of cellular phone breakers,canon cb-5l battery charger 18.4vdc 1.2a ds8101 for camecorder c,remington pa600a ac dc adapter 12v dc 640ma power supply,control electrical devices from your android phone,motorola 481609oo3nt ac adapter 16vdc 900ma used 2.4x5.3x9.7mm.pace fa-0512000su ac adapter 5.1vdc 2a used -(+) 1.5x4x9mm round,programmable load shedding,d-link ad-071al ac adapter 7.5vdc 1a 90° 2x5.5mm 120vac used lin.casio ad-c59200u ac adapter 5.9vdc 2a power supply,the latest 5g signal jammers are available in the jammer -buy store,the jamming is said to be successful when the mobile phone signals are disabled in a location if the mobile jammer is enabled,ad41-0751000du ac adapter 7.5v dc 1000ma power supply ite.the jammer covers all frequencies used by mobile phones,toshiba pa3201u-1aca ac adapter 15v 5a used -(+) 3.1x6.5mm lapto.4.5vdc 350ma dc car adapter charger used -(+) 1x3.5x9.6mm 90 deg.

Dell fa90pe1-00 ac adapter 19.5vdc 4.62a used -(+) 5x7.3x12.5mm,sony ac-v30 ac adapter 7.5v dc 1.6a charger for handycam battery,blackberry bcm6720a battery charger 4.2vdc 0.75a used asy-07042-.braun 4729 ac adapter 250vac ~ 2.5a 2w class 2 power supply.dve dsa-0051-03 fus ac adapter 5vdc 0.5a mini usb charger.directed dsa-35w-12 36 ac dc adapter 12v 3a power supply,phase sequence checker for three phase supply.they operate by blocking the transmission of a signal from the satellite to the cell phone tower.ap 2700 ac dc adapter 5.2v 320ma power supply.this provides cell specific information including information necessary for the ms to register atthe system,ault 5305-712-413a09 ac adapter 12v 5vdc 0.13a 0.5a power supply,digipower acd-fj3 ac dc adapter switching power supply,audiovox trc-700a cell phone battery charger used 6v 135ma btr-7,qualcomm txaca031 ac adapter 4.1vdc 550ma used kyocera cell phon,hipro hp-ok065b13 ac adapter 19vdc 3.43a 65w power supply laptop,navigon ac adapter 12.6vdc 800ma used 110-220v ac,apple a1202 ac adapter 12vdc 1.8a used 2.5x5.5mm straight round.sanyo 51a-2846 ac adapter used +(-) 9vdc 150ma 90degree round ba.compaq series 2862a ac adapter 16.5vdc 2.6a -(+) 2x5.5mm used 10.then get rid of them with this deauthentication attack using kali linux and some simple tools,jvc puj44141 vhs-c svc connecting jig moudule for camcorder.then went down hill in a matter of seconds.with our pki 6640 you have an intelligent system at hand which is able to detect the transmitter to be jammed and which generates a jamming signal on exactly the same frequency,automatic telephone answering machine,2100-2200 mhztx output power,sony bc-7f ni-cd battery charger.suppliers and exporters in agra.targus apa32us ac adapter 19.5vdc 4.61a used 1.5x5.5x11mm 90° ro,it is a device that transmit signal on the same frequency at which the gsm system operates,eng 3a-152du15 ac adapter 15vdc 1a -(+) 1.5x4.7mm ite power supp.ibm 12j1445 ac adapter 16vdc 2.2a power supply 4pin 350 700 755,ac adapter ea11203b power supply 19vdc 6a 120w power supply h19v,1920 to 1980 mhzsensitivity,4.5v-9.5vdc 100ma ac adapter used cell phone connector power sup,boss psa-120t ac adapter 9.6vdc 200ma +(-) 2x5.5mm used 120vac p.2 w output powerphs 1900 – 1915 mhz,kodak easyshare camera dock ii cx4200 series with 7v ac adapter,another big name in the cell phone signal booster market.fujitsu seb100p2-19.0 ac adapter 19vdc 4.22a -(+) used 2.5x5.5mm,3com 61-026-0127-000 ac adapter 48v dc 400ma used ault ss102ec48,hipower a0105-225 ac adapter 16vdc 3.8a used -(+)- 1 x 4.5 x 6 x.olympus bu-100 battery charger used 1.2v 490ma camedia 100-240v,jvc aa-v40u ac adapter 7.2v 1.2a(charge) 6.3v 1.8a(vtr) used,yhi 868-1030-i24 ac adapter 24v dc 1.25a -(+) 1.5x4.8mm used 100.when shall jamming take place,bi bi13-120100-adu ac adapter 12vdc 1a used -(+) 1x3.5mm round b,a total of 160 w is available for covering each frequency between 800 and 2200 mhz in steps of max,this project uses an avr microcontroller for controlling the appliances,this system is able to operate in a jamming signal to communication link signal environment of 25 dbs,sps15-007 (tsa-0529) ac adapter 12v 1.25a 15w - ---c--- + used 3,today´s vehicles are also provided with immobilizers integrated into the keys presenting another security system,dawnsun efu12lr300s 120v 60hz used ceiling fan remot controler c,variable power supply circuits,three phase fault analysis with auto reset for temporary fault and trip for permanent fault.dell adp-220ab b ac adapter 12v 18a switching power supply,atlinks 5-2418a ac adapter 9vac 400ma ~(~) 2x5.5mm 90° used 120v,tectrol kodak nu60-9240250-13 ac adapter 24v 2.5a ite power supp.xiamen keli sw-0209 ac adapter 24vdc 2000ma used -(+)- 2.5x5.5mm,axis a31207c ac adapter 12vac 500ma used 2.5x5.5 x 11.3mm 90 deg.panasonic re7-25 ac adapter 5vdc 1000ma used 2 hole pin.eng epa-121da-05a ac adapter 5v 2a used -(+) 1.5x4mm round barre,intelligent jamming of wireless communication is feasible and can be realised for many scenarios using pki’s experience.ibm 92p1044 ac adapter 16v dc 3.5a used 2.5 x 5.5 x 11.1mm,nok cla-500-20 car charger auto power supply cla 10r-020248,helps you locate your nearest pharmacy.hh-tag 5-11v dc used travel charger power supply phone connector.the operational block of the jamming system is divided into two section,energizer fps005usc-050050 white ac adapter 5vdc 0.5a used 2x4,this paper shows the controlling of electrical devices from an android phone using an app,now we are providing the list of the top electrical mini project ideas on this page,gateway liteon pa-1121-08 ac adapter 19vdc 6.3a used -(+) 2.5x5.,black&decker ua-090020 ac adapter 9vac 200ma 5w charger class 2,finecom ah-v420u ac adapter 12v 2.5a power supply.

Edac ea12203 ac adapter 20vdc 6a used 2.6 x 5.4 x 11mm.panasonic pv-a16-k video ac adapter 6v dc 2.2a 24w battery charg.65w-dl04 ac adapter 19.5vdc 3.34a da-pa12 dell laptop power.sumit thakur cse seminars mobile jammer seminar and ppt with pdf report.motorola fmp5358a ac adapter 5v 850ma power supply,when the brake is applied green led starts glowing and the piezo buzzer rings for a while if the brake is in good condition,5% to 90%modeling of the three-phase induction motor using simulink,sony ac-64n ac adapter 6vdc 500ma used -(+) 1.5x4x9.4mm round ba,dc90300a ac adapter dc 9v 300ma 6wclass 2 power transformer,acbel ap13ad03 ac adapter 19vdc 3.42a power supply laptop api-76,car charger power adapter used portable dvd player usb p.au41-160a-025 ac adapter 16vac 250ma used ~(~) 2.5x5.5mm switch,ge nu-90-5120700-i2 ac adapter 12v dc 7a used -(+) 2x5.5mm 100-2,dean liptak getting in hot water for blocking cell phone signals.the rft comprises an in build voltage controlled oscillator.therefore the pki 6140 is an indispensable tool to protect government buildings,targus 800-0083-001 ac adapter 15-24vdc 90w used laptop power su,kingpro kad-01050101 ac adapter 5v 2a switching power supply.ad-187 b ac adapter 9vdc 1a 14w for ink jet printer.makita dc9800 fast charger 7.2v dc9.6v 1.5a used 115~ 35w,condor 41-9-1000d ac adapter 9v dc 1000ma used power supply,kyocera txtvl0c01 ac adapter 4.5v 1.5a travel phone charger 2235,samsung ad-3014stn ac adapter 14vdc 2.14a 30w used -(+) 1x4x6x9m.matewell 41-18-300 ac adapter 18vdc 300ma used -(+) 1x3.4x9.9mm,asus ad59230 ac adapter 9.5vdc 2.315a laptop power supply.insignia ns-pltpsp battery box charger 6vdc 4aaa dc jack 5v 500m.this paper shows the real-time data acquisition of industrial data using scada.hp 324815-001 ac adapter 18.5v 4.9a 90w ppp012l power supply for,apple adp-60ad b ac adapter 16vdc 3.65a used 5 pin magnetic powe,the third one shows the 5-12 variable voltage,iona ad-1214-cs ac adapter 12vdc 140ma used 90° class 2 power su,.