ANTENNA MODULES OF GNSS USER EQUIPMENT: INNOVATIVE APPROACHES

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Introduction. In our days in the world practice standard antenna module design approaches and methods are formed. In the paper our methods and solutions, which differ from the conventional ones, are presented. During the navigation antennas design a trend of integrating of antenna element, filters, low noise amplifier (LNA) and also a receiver chipset into a union device, named active navigation antenna or navigation antenna module (NAM) is seen. Usually a microstrip (or patch) antenna (MSA) acts as an antenna element of a NAM, as a mostly compact [1-3]. Navigation antenna modules design innovative approaches. An original conception of the NAM was suggested by our company, according which a dielectric substrate of the antenna element is made of a ceramic in the form of turned cup provided with the patch on its top and metalized inner hollow, in which all active elements are placed [4; 5]. This technology of NAM production was named “uncased” or “full-ceramic”. A cup-shape antenna element and navigation natenna module, made basing on it and using uncased technology, are presented on fig. 1. As a result of this way of NAM design, their strength was significantly increased and size was optimized, as well the production cost was reduced for a module because of its high manufacturability. Also, turned-cup shape antenna has additional advantages comparing with traditional patch antenna. It has 1.5-2 times wider working band, its radiation efficiency is about 6 % higher, wider radiation pattern and wider (up to 1.5 times) meridian angle range in which circle field polarization persists (fig. 2). These advantages give an opportunity of the total NAM miniaturization. Besides, parameters of cup-shaped antenna elements depend much less on the additional shield size, on which they can be placed [2; 5]. Consequently, NAM, made using uncased technology, can be used even without additional shield. Usage of metamaterials in antenna element and total full-ceramic antenna module construction gives additional advantages. Basically, usage of metamaterials in the elements of antenna technique improve such parameters as coupled bandwidth, gain, selectivity, back radiation reductions and others. Корпус_3.jpg a b Fig. 1. A cup-shape antenna element construction (a) and navigation natenna module ASNK-1, based on it (b), having dimentions 48×44×19 mm a b Fig. 2. Amplitude (a) and polarization (b) radiation patterns of traditional (1) and uncased (2) antenna modules a b Fig. 3. A metamaterial-based antenna element construction (a) and navigation natenna module ASNK-3, based on it (b), having dimentions 30×30×12 mm On fig. 3 a construction of a metamaterial-made antenna element and an uncased type antenna module, based on it are presented. This antenna element construction allows using substrates with the lower value of permittivity, what provides higher radiation efficiency. Also presented metamaterial-made antenna element has a meridian angle range with the axial ratio of less than 5 dB up to -80º…+80º (fig. 4), which only quadrifillar antennas also have [6]. Due to usage of low permittivity materials for the substrate, the presented antenna module has a lower weight and cost value. The antenna module has a flat and compact planar construction and due to this fact it can be implemented into any compact onboard or even on-body devices. On fig. 5 an embedded receiving antenna module with a receiver chipset, made using uncased technology (fig. 5, a) and an analog of the module made using traditional technologies (fig. 5, b) are presented. Advantages of the uncased module are its complete tightness, simultaneous operation in L1 GLONASS/GPS, E1 GALILEO and B1 BEYDOU bands and better navigation signal reception, what is caused by the cup-shaped antenna element. In our days the number of GNSS systems increases because of GALILEO and BEYDOU operation start, and also number of GNSS operating bands increases. Thus appears a necessity of creation of multifunctional devises, which simultaneously work with maximum number of GNSS in various (ideally in all) bands. It forces creation of patch antennas with extended operating band or multiband MSA. Usually the bandwidth of coupling with low noise amplifier is achieved by using the so called proximity antenna feeding [7; 8]. But this method forces multilayer PCB design. For operation in widened bend (with more number of operating GNSS) we have proposed an antenna element, which has two planar segments with symmetry around the center of MSA [9; 10]. The first segment is a patch located in the center of the ceramic surface, while the second one is a square frame surrounding the first segment. Two segments have a distributed mutual coupling, what allows achieving antenna element matching with 50-Ohm feeding and invariable radiation pattern in L1 GLONASS/GPS, E1 GALILEO and B1 BEYDOU bands. The proposed antenna element can be also designed to work in 2 bands, for example L1 and L2 GLONASS/GPS or L1 and L2 GPS/GALILEO. The designed active GNSS module based on the proposed antenna element which also contains a low noise amplifier with filters and overload protection for operation in L1, GLONASS/GPS, E1 GALILEO and B1 BEIDOU bands is presented on fig. 6. It can be seen, that the antenna element VSWR is lower than 3 in the band 1504-1631 MHz (fig. 6, b) and its axial ratio is not higher than 3 in the band 1540-1600 MHz (fig. 6, c). The designed antenna module can be used as an independent embedded element of GLONASS/GPS/GALILEO navigation receivers, and also as a basic part of external antennas and antenna arrays. During design of an antenna module, which is able to work simultaneously in all GLONASS/ GPS/ GALILEO/ BEYDOU GNSS operating bands it is possible to implement more complicated antenna element - a stacked MSA [11]. In the stacked antennas antenna elements for different bands are placed one above another in the way that antenna for higher frequencies are placed above antennas for lower frequencies. Each mentioned antenna serves as a ground plane for the antenna, placed above. The main deficiency of multi frequency stacked MSA antennas is a high mutual influence of the antenna elements what causes radiation pattern distortion in each band and low mutual isolation of the antenna inputs. The mutual isolation of antenna inputs can be sometimes improved when using the special multi frequency MSA feeding nets, but the problem is not solved generally. We have suggested a multi frequency stacked antenna design method with cross feeding of the antenna elements (fig. 7), which provides the antenna element isolation more than 25 dB and identical radiation patterns in separated bands (fig. 8). Рис_4_b a b Fig. 4. Measured amplitude (a) and polarization (b) radiation patterns of navigation antenna module ASNK-3 a b Fig. 5. Full-ceramic antenna module PAM-2 (30×30×10 mm) (a) and similar traditionally made ceaseless module (22×22×8) (b) a b c Fig. 6. Dual band navigation antenna module ASNP-8 (30×30×10 mm) (a), the antenna element VSWR (b) and axial ratio (c) Fig. 7. Stacked patch antenna with cross feeding of antenna elements a b Fig. 8. Radiation patterns of the module AA2-KKS, based on stacked antenna with antenna elements cross feeding on the frequencies 1600 (a) and 1247 (b) MHz In especial GNSS antenna application it is very impotent not to receive multipath signals. Multipath signal is a signal from the satellite, which was received by the antenna not directly, but after some reflections from earth or any constructions, which surround the antenna. This is the cause of a phase noise, which increases the mistake in determining co-ordinates. Usually choke ring ground planes are used for multipath mitigating. But these constructions have a disadvantage of big size and weight. EBG metamaterials allow obtaining compact ground planes for GNSS antenna multipath mitigating [12-14]. But all multipath mitigating ground planes have a common deficiency - they spoil the antenna element phase center stability. In our antenna module ASNG-3 a special type of a EBG metamaterial (fig. 9) and a special method of EBG metamaterial multipath mitigating ground plane mounting is used, which has no such a deficiency [15]. The antenna module radiation patterns, taken on the frequencies 1590 MHz and 1236 MHz are presented on fig. 10. Diagrams show the wide radiation pattern in the top hemisphere and the maximum down-up ratio value minus 40 dBi in L1 band and minus 35 dBi in L2 band. Using two antenna modules, installed stationary with the base between them 0.538 m, measurements of router point coordinates within 24 hours were made. On fig. 11 router point latitude and longitude deviations are presented as well. It is seen from the diagram that most part of deviations are within ±2 mm what means that antenna phase center stability is not greater than 2 mm. Conclusion. Thus, navigation antenna module design innovative approaches, provided in the paper, allow with the use of their combination obtaining devises with almost any characteristics collection for implementation in various GNSS equipment. Fig. 9. EBG metamaterial ground plane a b Fig. 10. Radiation patterns of the module ASNG-3 on the frequencies 1236 (a) and 1590 (b) MHz Router deviation.jpg Fig. 11. Router point latitude and longitude deviations

作者简介

S. Boyko

Branch of United Rocket and Space Corporation Institute of Space Device Engineering

Email: npk6@mail.ru
53, Aviamotornaya Str., Moscow, 111250, Russian Federation

A. Isaev

Branch of United Rocket and Space Corporation Institute of Space Device Engineering

53, Aviamotornaya Str., Moscow, 111250, Russian Federation

S. Kosyakin

Branch of United Rocket and Space Corporation Institute of Space Device Engineering

53, Aviamotornaya Str., Moscow, 111250, Russian Federation

A. Kukharenko

Branch of United Rocket and Space Corporation Institute of Space Device Engineering

53, Aviamotornaya Str., Moscow, 111250, Russian Federation

Y. Yaskin

Branch of United Rocket and Space Corporation Institute of Space Device Engineering

53, Aviamotornaya Str., Moscow, 111250, Russian Federation

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