Antenna system and antenna module with reduced interference between radiating patterns

An antenna system comprises a first antenna element adapted to a first frequency band and a second antenna element adapted to a second frequency band different from the first frequency band. The first antenna element includes a radiating structure having a planar radiating element and configured to radiate at a frequency in the first frequency band and a band-stop filter having a planar conductive element and configured to attenuate a current flow at a frequency in a second frequency band different from the first frequency band. The planar conductive element is arranged in a meander pattern, has an end electrically connected to the planar radiating element, extends in a direction substantially parallel to the planar radiating element, and has an electrical length substantially equal to ¼ of a wavelength of the frequency in the second frequency band.

FIELD OF THE INVENTION

The present invention relates to an antenna system and, more particularly, to an antenna system having a first antenna element and a second antenna element.

BACKGROUND

Antenna systems in the prior art having a first antenna element and a second antenna element have various structural advantages. The assembly of the antenna system as a single structural module allows mechanical and electrical components to be shared between the plural antenna elements. The plural antenna elements may be arranged within and share a same housing, a same base, may share same PCB circuitry, and may share a same electrical connection for transmitting/receiving electrical signals from the outside to/from the plural antenna elements within the antenna system. The arrangement of plural antenna elements in an antenna system, however, suffers from mutual interference effects with their respective radiating patterns.

In PCT International Application No. WO 98/26471 A1, frequency selective surfaces are applied in an antenna system to reduce mutual interference effects between two antenna elements. The disclosed antenna system comprises a first and a second antenna element. The first antenna element is capable of transmitting in a first frequency range and the second antenna element is capable of transmitting in a second—i.e. non-overlapping—frequency range.

In order to reduce interference effects, the antenna system additionally includes a frequency selective surface which is conductive to radio frequency energy in the first frequency range and reflective to radio frequency energy in the second frequency range. The frequency selective surface comprises repetitive metallization pattern structures that display quasi band-pass or quasi band-reject filter characteristics to radio frequency signals impinging upon the frequency selective surface.

U.S. Pat. No. 6,917,340 B2 also relates to an antenna system comprising two antenna elements. In order to reduce the coupling and hence interference effects, one of the two antenna elements is subdivided into segments which have an electrical length corresponding to ⅜ of the wavelength of the other antenna element. Further, the segments of the one antenna element are electrically interconnected via electric reactance circuits which possess sufficiently high impedance in the frequency range of the other antenna element and sufficiently low impedance in the frequency range of the one antenna element.

Even though the above described approaches allow for a reduced inference in the radiation patterns of two antenna elements, the design of the antenna system comprising the two antenna elements becomes more complicated in view of the incorporation of additional components, namely the manufacturing and arrangement of the incorporation of electric reactance circuits. In particular, the design of the electric reactance circuits and their arrangement on the respective antenna element is complex and necessitates additional development steps. Further the components of the electric reactance circuit as well as the, for instance soldered, electrical connection to the antenna elements introduces unacceptable variances to the frequency characteristic.

SUMMARY

An antenna system according to the invention comprises a first antenna element adapted to a first frequency band and a second antenna element adapted to a second frequency band different from the first frequency band. The first antenna element includes a radiating structure having a planar radiating element and configured to radiate at a frequency in the first frequency band and a band-stop filter having a planar conductive element and configured to attenuate a current flow at a frequency in a second frequency band different from the first frequency band. The planar conductive element is arranged in a meander pattern, has an end electrically connected to the planar radiating element, extends in a direction substantially parallel to the planar radiating element, and has an electrical length substantially equal to ¼ of a wavelength of the frequency in the second frequency band.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

An antenna system100according to an embodiment of the invention is shown inFIGS. 1A and 1B. The antenna system100comprises a first antenna element110and a second antenna element120which are arranged within the near-field to each other. Accordingly, the radiation pattern of the second antenna element120is exposed to interference effects from the first antenna element110and vice-versa.

In the context of the invention, the term “near-field” is to be understood as the region around each of the first and second antenna element110and120where their radiating pattern is dominated by interference effects from the respective other of the first and second antenna element110and120. For example, in case the first and second antenna elements110and120are shorter than half of the wavelength λ they are adapted to emit, the near-field is defined as the region with a radius r, where r<λ.

The first antenna element110is adapted to transmit/receive electromagnetic waves of a first frequency band. In other words, the first antenna element110is adapted to the first frequency band. In the shown embodiment, the first antenna element110is a monopole antenna. In other embodiments, the first antenna element110may be, for instance, a dipole antenna, a planar inverted-F antenna (PIFA), or a multi-band antenna.

The second antenna element120is adapted to transmit/receive electromagnetic waves of a second frequency band. In other words, the second antenna element120is adapted to the second frequency band. In the shown embodiment, the second antenna element120is a planar antenna element, in an embodiment, a corner-truncated patch antenna. In other embodiments, the second antenna element120may be any other form of antenna known to those with ordinary skill in the art.

The first frequency band, to which the first antenna element110is adapted, and the second frequency band, to which the second antenna element120is adapted, are different from each other. In an embodiment, the first frequency band is lower than the second frequency band; the first frequency band includes frequencies which are smaller than that of the second frequency band. This includes cases where the first and the second frequency band have no overlap in frequency with each other. Furthermore, if one or both antenna elements110and120is/are multi-band antenna(s), the first frequency band may also encompass the second frequency band.

The first antenna element110, as shown inFIG. 1A, has at least one radiating structure112configured to radiate at a frequency in the first frequency band. In the shown embodiment, the first antenna element110is a single radiating structure112. In other embodiments, the first antenna element110is a multi-band antenna and comprises a plurality of radiating structures each of which radiates at a different frequency in the first frequency band.

The at least one radiating structure112, as shown inFIG. 1A, has at least one planar radiating element114and is formed of segments of at least one or plural planar radiating elements114. In the shown embodiment, the single radiating structure112has five planar radiating elements114, but one with ordinary skill in the art would understand that the radiating structure112may have a number of planar radiating elements114other than five. In the embodiment shown inFIG. 1A, the five planar radiating elements114of the single radiating structure112are arranged on two parallel planes in an interleaved manner, such that the first, the third and the fifth radiating element114extend along a first plane of the two parallel planes and the second and the fourth radiating element114extend along a second of the two parallel planes. Each of the electrically interconnected planar radiating elements114has an electrical length of less than or equal to ⅜ of the wavelength of the frequency in the second frequency band.

The single radiating structure112can be manufactured by folding the radiating structure112so as to form the different planar radiating elements114. Alternatively, the radiating structure112may be manufactured by printing/etching consecutive planar radiating elements114on opposite surfaces of a dielectric substrate. In the latter case, the consecutive planar radiating elements114can be electrically connected by means of a through connection (e.g. via) in-between the opposite surface of the dielectric substrate.

The first antenna element110, as shown inFIG. 1A, further comprises at least one band-stop filter structure116configured to attenuate a current flow at a frequency in the second frequency band within the first antenna element110. In other words, the at least one band-stop filter structure116suppresses current from flowing within the at least one radiating structure114which has a frequency in the second frequency band.

The at least one band-stop filter structure116, as shown inFIG. 1A, comprises at least one planar conductive element118which is electrically connected at one end (which is the case for antenna system100) or at both ends (which is the case for the antenna system200, and300described below) to the at least one planar radiating element114of the at least one radiating structure112. In the shown embodiment, each of the at least one band-stop filter structures116has one planar conductive element118. In other embodiments, the at least one band-stop filter structure116may comprise a plurality of planar conductive elements118, for instance, two planar conductive elements118, and each of these two planar conductive elements118is electrically connected at one end to the same planar radiating element114at different portions thereof. The at least one planar conductive element118has a predetermined electrical length which corresponds to a quarter of a wavelength ( 2/4) of the frequency in the second frequency band.

The at least one planar conductive element118, as shown inFIG. 1A, is arranged in a meander pattern. In the context of the invention, the at least one planar conductive element118is said to be arranged in a meander pattern provided it has consecutive loops of conductive segments pointing in opposite traverse directions. The meander pattern of the at least one planar conductive element118allows for an excessive electrical length compared to the dimension (i.e. length and width) of the area in which it extends. In the shown embodiment, the at least one planar conductive element118has three consecutive loops of conductive segments pointing in opposite traverse directions.

The at least one planar conductive element118, as shown inFIG. 1A, extends in a direction substantially in parallel to a direction of the at least one planar radiating element114of the at least one radiating structure112. In other words, the at least one planar conductive element118extends in the same direction as the at least one planar radiating element114. Thereby, the at least one planar conductive element118and the at least one radiating element114are both exposed to a same radiating pattern of the second antenna element120inducing a current of a same magnitude and directivity therein.

The at least one planar conductive element118and the at least one planar radiating element114are arranged facing each other in two parallel planes. This arrangement of the at least one planar conductive element118and at least one planar radiating element114advantageously increases the coupling therebetween. The coupling between the at least one planar conductive element118and at least one planar radiating element114enhances the filtering effect of the at least one band-stop filter structure116. The at least one planar conductive element118is shaped such that it covers the width of the at least one planar radiating element114of the at least one radiating structure112; the overlap between the at least one planar conductive element118and the at least one planar radiating element114is increased, further enhancing the coupling therebetween. In another embodiment, the at least one planar conductive element118and the at least one planar radiating element114are disposed on two opposing surfaces of a dielectric substrate where a suitably small relative permittivity of the dielectric substrate further enhances the coupling therebetween.

In the embodiment shown inFIG. 1A, one radiating structure112of the first antenna element110has five electrically interconnected planar radiating elements114and two band-stop filter structures116each of which includes one planar conductive element118. The one planar conductive element118of each of the two band-stop filter structures16is electrically connected to every other of the five electrically interconnected planar radiating elements114. Due to this configuration of the at least one planar conductive element118and of the at least one planar radiating element114to which it is electrically connected, the at least one band-stop filter structure116act as a band-stop filter for an induced current at the frequency in the second frequency band, thereby attenuating a current flow at a frequency in the second frequency band. A current which is induced in the at least one planar conductive element118is reflected at the not electrically connected end of the at least one planar conductive element118and hence is exposed to an electrical length of twice a quarter of the wavelength (2·λ/4=λ/2) of the frequency of the second frequency band compared to a current induced in the at least one planar radiating element114. With a phase offset of half of the wavelength (λ/2) of the frequency of the second frequency band, both currents destructively interfere (i.e. cancel each other out). Accordingly, even if the second antenna element120induces a current in the first antenna element110, the at least one planar conductive element118of the band-stop filter structure116suppresses the induced current at the frequency of the second frequency band.

The first antenna element110is configured to reduce interference effects at the frequency of the second frequency band, namely the frequency to which the second antenna element120is adapted. The first antenna element110can be said to be transparent to the second antenna element120. Accordingly, the radiating pattern of the second antenna element120is exposed to a reduced amount of interference from the first antenna element110, even if the first antenna element110is arranged within the near-field thereof.

A same effect of a reduction in interference to the radiating pattern of the second antenna element120can also be appreciated from the simulation radiating pattern results shown inFIG. 1B. The radiating pattern of the second antenna element120is nearly concentric and only marginal deformations are with respect to the x-axis, i.e. the direction in which the first antenna element110was arranged for simulation purposes.

A two-port scattering pattern or s-parameter simulation is shown inFIG. 2B. For the simulation, the left and the right section of the first antenna element110shown inFIG. 2Aare the ports to the two-port s-parameter simulation. As can be appreciated from the simulation results, the forward gain and the reverse gain coefficients S12and S21show a high attenuation at the frequency of 2.3014 GHz corresponding to the frequency of the second frequency range for which each of the at least one band-stop filter structure116is configured. The reflection coefficients S11and S22show an inverse behavior.

An antenna system200and an antenna system300according to other embodiments of the invention are shown inFIGS. 3A and 3B. Each of the antenna systems200and300comprises a first antenna element210,310and a second antenna element120such as that shown inFIG. 1A. The antenna systems200and300are based on the antenna system100ofFIG. 1where corresponding parts are given corresponding reference numerals and terms. Only the differences with respect to the embodiment shown inFIG. 1Awill be described in detail herein.

The antenna systems200and300ofFIGS. 3A and 3Bdiffer from the antenna system100in that the number of planar radiating elements114comprised in the radiating structure112of the first antenna element210and310is two, and four, respectively; and the number of band-stop filter structures216of the first antenna element210, and310is one, and two, respectively. The at least one band-stop filter structure216has at least one planar conductive element218which also has a different shape and structure.

The first antenna element210,310is adapted to a first frequency band and the second antenna element120is adapted to a second frequency band which is different from the first frequency band. In an embodiment, the first frequency band is lower than the second frequency band. The first frequency band includes frequencies which are smaller than that of the second frequency band.

Each of the first antenna elements210,310, as shown inFIGS. 3A and 3B, includes at least one radiating structure112and at least one band-stop filter structure216. The following description of the at least one band-stop filter structure216equally applies to that comprised in the first antenna element210of the antenna system200and to that comprised in the first antenna element310of the antenna system300.

The least one band-stop filter structure216, as shown inFIGS. 3A and 3B, is configured to attenuate a current flow at a frequency in the second frequency band within the first antenna element210; the at least one band-stop filter structure216suppresses current from flowing within the at least one radiating structure114which has a frequency in the second frequency band. The at least one band-stop filter structure216comprises at least one planar conductive element218which is electrically connected at both ends to the at least one planar radiating element114of the at least one radiating structure112such that it forms a parallel circuit therewith. In the shown embodiment, each of the at least one band-stop filter structures216has one planar conductive element218. In other embodiments, the at least one band-stop filter structure216may have a plurality of planar conductive elements218. In embodiments in which the at least one band-stop filter structure216comprises, for instance, two planar conductive elements218, each of these two planar conductive elements218is electrically connected at both ends to the same portions of the at least one planar radiating element114such that both form a parallel circuit therewith.

As shown inFIGS. 3A and 3B, the at least one planar conductive element218of the at least one band-stop filter structure216is arranged in form of a meander pattern. The meander pattern of the at least one planar conductive element218allows for an excessive electrical length compared to the dimension (i.e. length and width) of the area in which it extends. In the shown embodiment, the at least one planar conductive element218has three consecutive loops of conductive segments pointing in opposite traverse directions. The at least one planar conductive element218has an electrical length which exceeds the electrical length of the at least one planar radiating element114to which it is connected in parallel by a half of a wavelength (λ/2) of the frequency in the second frequency band.

The at least one planar conductive element218, as shown inFIGS. 3A and 3B, extends in a direction substantially parallel to a direction of the at least one planar radiating element114. The at least one planar conductive element218and the at least one radiating element114are both exposed to a same radiating pattern of the second antenna element120inducing a current of a same magnitude and directivity therein. The at least one planar conductive element218and the at least one planar radiating element114are both arranged facing each other in two, parallel planes. This arrangement of the at least one planar conductive element218and least one planar radiating element114advantageously increases the coupling there-between. The coupling between the at least one planar conductive element218and least one planar radiating element114enhances the filtering effect of the at least one band-stop filter structure216. The at least one planar conductive element218, as shown inFIGS. 3A and 3B, is shaped such that it covers the width of the at least one planar radiating element114of the at least one radiating structure112. The overlap between the at least one planar conductive element218and the at least one planar radiating element114is increased, further enhancing the coupling there-between.

Due to the configuration shown inFIGS. 3A and 3Bof the at least one planar conductive element218and of the at least one planar radiating element114to which it is connected in parallel, the at least one band-stop filter structure216acts as a band-stop filter for an induced current at the frequency in the second frequency band, thereby attenuating a current flow at a frequency in the second frequency band. A current which is induced in the at least one planar conductive element218is exposed to an excessive electrical length of half of the wavelength (λ/2) of the frequency of the second frequency band compared to a current induced in the at least one planar radiating element114. With a phase offset of half of the wavelength (λ/2) of the frequency of the second frequency band both currents destructively interfere (i.e. cancel each other out).

The structure, dimension and arrangement of the at least one planar conductive element218provide for the band-stop filter structure216which attenuates a current flow at a frequency in the second frequency band. Accordingly, even if the second antenna element120induces a current in the first antenna element210or310, the at least one planar conductive element218of the band-stop filter structure216suppresses the induced current at the frequency of the second frequency band. The first antenna elements210and310are also configured to reduce interference effects at the frequency of the second frequency band, namely the frequency to which the second antenna element120is adapted. Accordingly, the radiating pattern of the second antenna element120is exposed to a reduced amount of interference from either one of the first antenna elements210and310, even if the first antenna element210or310is arranged within the near-field thereof.

A two-port scattering pattern or s-parameter simulation is shown inFIG. 4B. For the simulation, the left and the right section of the first antenna element210shown inFIG. 4A, which applies equally to the first antenna element310, are the ports to the two-port s-parameter simulation. As can be appreciated from the simulation results, the forward gain and the reverse gain coefficients S12and S21show a high attenuation at the frequency of approximately 2.3 GHz corresponding to the frequency of the second frequency range for which each of the at least one band-stop filter structure216is configured. The reflection coefficients S11and S22show an inverse behavior.

An antenna system according to another embodiment of the invention having a first antenna element410is shown inFIG. 5A. In this embodiment, the at least one planar conductive element218of the at least one band-stop filter structure216and the at least one planar radiating element414of the radiating structure412are both arranged in a same plane such that the at least one planar conductive element218is adjacent to the at least one planar radiating element414to which it is electrically connected in parallel. Even in this less complex structure of the first antenna element410, due to configuration of the at least one planar conductive element218and of the at least one planar radiating element414to which it is connected in parallel, the at least one band-stop filter structure216acts as a band-stop filter for an induced current at the frequency in the second frequency band, thereby attenuating a current flow at a frequency in the second frequency band.

A two-port scattering pattern or s-parameter simulation is shown inFIG. 5B. For the simulation, the left and the right section of the first antenna element410shown inFIG. 5Aare the ports to the two-port s-parameter simulation. As can be appreciated from the simulation results, the forward gain coefficient S12shows a high attenuation at the frequency of approximately 2.3 GHz corresponding to the frequency of the second frequency range for which each of the at least one band-stop filter structure216is configured. The reflection coefficients S22show an inverse behavior.

An antenna system500according to another embodiments of the invention is shown inFIGS. 6A and 6B. The antenna system500comprises a first antenna element510and the second antenna element120which are both arranged within the near-field to each other. Accordingly, the radiation pattern of the second antenna element120is exposed to interference effects from the first antenna element510and vice-versa.

The first antenna element510is adapted to transmit/receive electromagnetic waves of a first frequency band; the first antenna element510is adapted to the first frequency band. In the shown embodiment, the first antenna element510is a multi-band planar inverted-F antenna (PIFA). The first antenna element510includes a feeding point which is indicated as “P2E”. The second antenna element120includes a feeding point which is indicated as “P1E”.

The first antenna element510, as shown inFIGS. 6A and 6B, has at least one radiating structure512-1,512-2configured to radiate at a frequency in the first frequency band. In the shown embodiment, the first antenna element510has three interconnected radiating structure512-1,512-2. The first antenna element510includes a first antenna structure512-1which includes a branch (a) extending along the ground plane of the first antenna element510and another branch (b) pointing away from the ground plane, a second antenna structure512-2which includes branch (c) extending away from the ground plane and branches (d) and (e) forming a semi-circle pointing towards the ground plane, and a third antenna structure which includes the two above antenna structures512-1,512-2with the branches (a), (b), (c), (d) and (e). Each of the three shown antenna structures512-1,512-2of the first antenna element510is configured to radiate at a different frequency in the first frequency band.

The at least one radiating structure512-1,512-2, as shown inFIGS. 6A and 6B, comprises at least one planar radiating element514. In the shown embodiment, the multi-band radiating structure512-1,512-2has one planar radiating element514. In other embodiments, the radiating structure512-1,512-2may have a plurality of planar radiating elements514.

The first antenna element510, as shown inFIGS. 6A and 6B, further comprises at least one sleeve structure516configured to attenuate a current flow at a frequency in the second frequency band within the first antenna element510. The at least one sleeve structure516suppresses current from flowing within the at least one radiating structure514which has the frequency in the second frequency band to which the at least one sleeve structure516is configured. The sleeve structure516can be regarded as an open-short transmission resonator, which is one form of a band-stop filter.

The at least one sleeve structure516, as shown inFIGS. 6A and 6B, has at least two planar conductive elements518-1,518-2which are electrically connected at one end to the at least one planar radiating element514of the at least one radiating structure512-1,512-2. In the shown embodiment, the at least one sleeve structure516has two planar conductive elements518-1,518-2. However, in other embodiments, the at least one band-stop filter structure516may also have four sleeve structures which are arranged in the front and back and to the left and right of the at least one radiating structure512-1,512-2.

Each of the at least two planar conductive elements518-1,518-2of the at least one sleeve structure516has an electrical length which correspond to substantially a quarter of a wavelength (λ/4) of the frequency in the second frequency band. Each of the least two planar conductive elements518-1,518-2has an individual electrical length which deviates from a quarter of a wavelength (λ/4) of the frequency in the second frequency band, for instance, in the region of 0-5%. It has proven advantageous to individually configure the electrical length of the at least two planar conductive elements518-1,518-2since their adjacent arrangement on both sides of the at least one planar radiating element514results in a highly-coupled resonant behavior. This highly-coupled resonant behavior may mistune the at least one sleeve structure516.

The at least two planar conductive elements518-1,518-2of the at least one sleeve structure516, as shown inFIGS. 6A and 6B, extend in a direction substantially in parallel to a direction of the at least one planar radiating element514of the at least one radiating structure512-1,512-2. The at least two planar conductive elements518-1,518-2extend in the same direction as the at least one planar radiating element514. In the shown embodiment, the at least one planar radiating element514has an inverted-L shape and hence extends in two directions, namely in a horizontal and a lateral direction with respect to a ground plane. The at least two planar conductive elements518-1,518-2also extend in two directions; both directions are substantially in parallel to the respective of the horizontal and lateral direction in which the at least one planar radiating element514extends. The at least two planar conductive elements518-1,518-2of the at least one sleeve structure516and the at least one planar radiating element514of the at least one radiating structure512-1,512-2are both arranged in a same plane. In the shown embodiment, the at least one planar radiating element514and the at least two planar conductive elements518-1,518-2are provided on a same surface of a dielectric substrate (for instance by printing/etching).

The at least one planar radiating element514and the at least two planar conductive elements518-1,518-2not only extend in directions which are substantially in parallel to each other but further, each of the at least two planar conductive elements518-1,518-2of the at least one sleeve structure516is arranged equidistantly to the at least one planar radiating element514of the at least one radiating structure512-1,512-2. Both the at least one planar radiating element514and the at least two planar conductive elements518-1,518-2have opposing edges; on the inside of the at least two planar conductive elements518-1,518-2of the at least one sleeve structure516and on the outside of the at least one radiating element514of the at least one radiating structure512-1,512-2. Hence, electric current which flows on both the at least one planar radiating element514and the at least two planar conductive elements518-1,518-2counteract with each other.

Between each of the at least two planar conductive elements518-1,518-2of the at least one sleeve structure516and the at least one planar radiating element514of the at least one radiating structure512-1,512-2, a respective slit is formed as shown inFIGS. 6A and 6B. The at least two slits are defined by the area which is surrounded (or enclosed) by each of the at least two planar conductive elements518-1,518-2and the at least one planar radiating element514. Each of these at least two slits extends laterally from the tip of the at least one planar radiating element of the at least one radiating structure514to the electrical connection between the respective one of the at least two planar conductive elements518-1,518-2and the at least one planar radiating element514. At the tip, each of the at least two planar conductive elements518-1,518-2and the at least one radiating element514are flush with each other.

Due to the configuration of the at least two planar conductive elements518-1,518-2and of the at least one planar radiating element514to which both are electrically connected, the at least one sleeve structure516suppresses current from flowing at the frequency in the second frequency band, thereby attenuating—in the far-field—the radiation power in the second frequency band. The at least two planar conductive elements518-1,518-2of the at least one sleeve structure516act as a transmission line which is short circuited at the end. By applying Gauss' Law any current which flows on the inside of the at least two planar conductive elements518-1,518-2has to be opposite of another current which flows on the outside of the at least one planar radiating element514. The terms inside and outside refer to the opposing edges of the at least two planar conductive elements518-1,518-2and the at least one planar radiating element514. Hence, the current which flows on the outside of the at least one planar radiating element514also sees a short-circuited transmission line.

Since the at least two planar conductive elements518-1,518-2of the at least one sleeve structure516have an electrical length which correspond to substantially a quarter of a wavelength (λ/4) of the frequency in the second frequency band, the impedance at the frequency which the current sees that flows on the outside of the at least one planar radiating element514is infinity. Hence, due to this configuration of the at least two planar conductive elements518-1,518-2and of the at least one planar radiating element514to which both are electrically connected, the at least one sleeve structure516suppresses current from flowing at the frequency in the second frequency band.

An antenna system600according to another embodiment of the invention is shown inFIGS. 7A and 7B. The antenna system600is similar to the antenna system500ofFIGS. 6A and 6B, where corresponding parts are given corresponding reference numerals and terms. Only the differences with respect to the embodiment ofFIGS. 6A and 6Bwill be described in detail.

The antenna system600differs from the antenna system500in that the first antenna element610comprises three interconnected radiating structures612-1,612-2each of which includes at least one sleeve structure616-1,616-2. Each of the at least one sleeve structure616-1,616-2is configured to attenuate a same frequency in the second frequency band and includes two planar conductive elements618-1,618-2,618-3,618-4. Additionally, each of the at least one sleeve structure616-1,616-2is electrically connected to one planar radiating element614in each of the three radiating structures612-1,612-2. Due to this configuration of the at least two planar conductive elements618-1,618-2,618-3,618-4and of the at least one planar radiating element614to which both are electrically connected, the at least one sleeve structure616-1,616-2suppresses current from flowing at the frequency in the second frequency band, thereby attenuating—in the far-field—the radiation power in the second frequency band.

Simulation results of an interference effect on the second antenna element120, a filtering effect by the first antenna element610, and a decoupling effect between the first antenna element620and the second antenna element120of the antenna system600are shown inFIGS. 7C-7E. The results for the antenna system600are provided in form of a two-port scattering parameter (or s-parameter) simulation where the two ports are connected to the feeding line of the second antenna element120(denoted P1E in theFIG. 7A) and to the feeding line of the first antenna element610(denoted P2E), respectively. As can be appreciated from the simulation results, the reflection coefficient S11shows the reduced interference effect where the attenuation corresponds to the frequency of the second frequency range for which each of the at least one sleeve structure616-1,616-2is configured, the reflection coefficient S22showing the filtering effect by the first antenna element610, and reverse gain coefficient S21show a decoupling effect at the frequency of approximately 2.3 GHz. The reflection coefficients S11and S22show an inverse behavior.

Each of the above discussed antenna systems of the various embodiments can be included in an antenna module for use on a vehicle rooftop. For this purpose, an antenna module, in addition to the antenna system, comprises a housing for protecting the antenna system from outside influences, a base for arranging the antenna system thereon, an antenna matching circuit, and an electrical connection for transmitting/receiving electrical signals from the outside to/from the first antenna element and the second antenna elements of the antenna system. Further, the vehicle rooftop provides for a ground plane to the first planar antenna element and the second antenna element of the antenna system.