Planar antenna

The invention relates to a planar antenna 1 having surface resonators 5, which are connected via a supply network 6 to a supply point 7, the supply point 7 of the planar antenna 1 being connected via a coupling element 13 to an electronic circuit 12, particularly a converter, the coupling element 13 being a coaxial conductor in which the ratio, between the outer diameter of the inner conductor and the inner diameter of the outer conductor 17, changes between the supply point 7 of the supply network 6 and the terminal 11 of the electronic circuit 12.

FIELD OF THE INVENTION 
The invention relates to a planar antenna. 
BACKGROUND 
The presently known antenna systems for the reception of satellite signals, 
especially TV, Astra and DSR signals, within the DBS band (direct 
broadcasting satellite) of 11.70 GHz to 12.50 GHz for electronic 
communication means, are based upon the electromagnetic excitation of 
dipole groups, which are respectively supplied with power in specific 
phases with respect to each other and thereby generate linearly or 
circularly polarized radiation fields. Such planar antennas are 
implemented mostly in triplate technology or microstrip technology. 
Downstream of the planar antenna, there is connected an electronic device, 
particularly a converter, which processes the signals, according to the 
particular application. 
Coupling of the planar antenna and the electronic parts is in most cases by 
means of a hollow waveguide with capacitive coupling-in of the radiation 
summation signal. 
In this type of planar antenna with electronics connected downstream, the 
required dimensions of the individual subassemblies are disproportionately 
large, in order to obtain a sufficiently large reception and transmission 
power, with the result that the antenna becomes unnecessarily heavy in 
weight and unwieldy, thus making such radio systems unsuitable for 
hand-held applications. Further, manufacturing requirements, with respect 
to dimensions of the individual parts for the hollow waveguide used, are 
very great, and the coupling of signals between the planar antenna, the 
hollow waveguide and the electronics is problematical, with the result 
that, in case of even small manufacturing-tolerance deviations, the 
signals, from one component to the next, become insufficiently coupled. 
Further, noise matching or compensation using such a hollow waveguide 
conductor is not possible. 
JP-A-62-048103, assigned MATSUSHITA, discloses a securing element for a 
microstrip-conductor-antenna, by means of which the antenna is connectable 
to a coaxial conductor. It is based on a microstrip conductor antenna, 
which comprises a dielectric material, onto whose first surface, the 
microstrip conductor is secured and onto whose other surface, the 
grounding conductor is secured. The grounding conductor has, compared to 
the dielectric material, a significantly greater thickness. The 
generically defined microstrip conductor antenna of JP-A-62-048103 has a 
securing element which is fastened onto the grounding conductor by means 
of screws. In the securing element is a central pin, which is held in 
position by means of a cylindrical dielectric body. The central pin has a 
region of smaller diameter and a region of larger diameter, the region of 
smaller diameter penetrating the dielectric material and the microstrip 
conductor and being connected to the latter by solder. Such a construction 
of the central pin has advantages and disadvantages. advantages are that 
the soldering, first, of the free end of the part with the microstrip 
conductor and, secondly, through the thicker region of the central pin, 
makes easier the connection to the external circuit (not shown). As set 
forth in the JP-A-62-048103 discussion of prior art, the structure of 
small and large diameters in the central pin leads to problems, since the 
jump in external diameter of the central pin, adjacent the interface 
region between grounding conductor and the dielectric body, leads to a 
mismatch of impedance of the microstrip conductor antenna. A mismatch of 
impedance has the consequence that reflection- and radiation-losses occur. 
The avoidance of such reflection- and radiation-losses is the object of 
JP-A-62-048103. For solution of the above-described problem, 
JP-A-62-048103 proposes to lengthen the region of the central pin in the 
direction of the grounding conductor, and, in the region of the grounding 
conductor, to surround the pin with a bushing consisting of a dielectric 
material, thereby creating an additional characteristic impedance and 
permitting a matching of impedance among the regions of differing 
diameters on the central pin. The JP-A-62-048103 suggests for this purpose 
suitable diameters D1 and D2. In order to make a connection to the 
electronics, one must insert, into the fastening element, a coaxial 
bushing not disclosed in the JP-A-62-048103. From JP-A-62-048103, it is 
thus known to match impedance in the fastening element. The fastening 
element of JP-A-62-048103 is, however, in its dimensions, large relative 
to the dimensions of the planar antenna, which means the connection of 
planar antenna and downstream electronics would consume a 
disproportionately large space. Further, the transmission losses of the 
fastening element are great, whereby the performance of the antenna would 
be detrimentally influenced, since an impedance matching of the planar 
antenna and downstream electronics is not possible. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a compact radio 
system with planar antenna coupling element and downstream electronics 
which consists of parts which are simple and cost-effective to make, and 
by means of which an impedance matching among the planar electronics and 
the downstream electronics is possible. 
This object is achieved, in accordance with the invention. The coupling 
element thus comprises, advantageously, only a few parts, which are easy 
to manufacture. As a result of the fixed galvanic coupling by means of an 
electromagnetic element or aperture of this type, the radio system is 
particularly robust against mechanical forces and also against dirt, and 
is thus outstandingly adapted for portable applications or uses. By means 
of the radio system in accordance with the invention, depending on the 
formation of the surface resonators, linearly and circularly polarized 
waves can be received or transmitted, whereby advantageous signals from 
the most varied satellites can be received and transmitted. The surface 
resonators are either square- or rectangle-shaped. The impedance matching 
of the components by means of the coupling element can be performed 
advantageously relatively easily by altering the lengths and/or diameters 
of segments A1, A2 and A3 of inner- and outer-conductors. Advantageous 
dimensions can be determined with the aid of suitable numeric 
approximation methods, the changes in dimension and changes in material of 
one part having an effect on the dimensions or material constants of the 
other parts to be selected. One obtains a good impedance and noise 
matching, using the values specified in subclaim 11 for the coupling 
element. On the basis of the values described, the radio system is 
optimized for a frequency range of 11.70-12.50 GHz. 
As a result of the stepwise variation in outer diameter of the inner 
conductor and its two-part structure, the radio system can be assembled 
easily and quickly. No additional parts are required in order to hold the 
inner conductor parts and ring disks in place. Furthermore, the numerical 
process is simplified, as a result of the subdivision of the coupling 
element into the three segments A1, A2 and A3, since only three 
characteristic impedances need to be factored into the calculation. 
As the outer ends of the inner conductor of the coupling piece are soldered 
to the feedpoint, or to the connection point, respectively, a durable 
electrical connection between the individual components is obtained. 
Impedance matching can also be achieved by selecting the inner diameter of 
the outer conductor and the outer diameter of the inner conductor to be 
constant, while, simultaneously, contiguous dielectric ring elements, 
having differing dielectric constants, are arranged between the baseplates 
of the planar antenna and the downstream electronics. The thickness of the 
respective annular element and its material determine the characteristic 
impedance of the segment. By means of a suitable numeric process, optimum 
values can be calculated. 
Due to the method of construction using microstrip technology, the planar 
antenna and downstream electronics can be produced relatively economically 
and simply, which provides a great cost advantage, particularly at high 
production rates. 
The mechanical carrier plate stabilizes the radio system and advantageously 
seals off the coupling element and also the ground planes from the 
outside. 
To receive or transmit circularly polarized electromagnetic waves by means 
of the planar antenna, rectangular or square-shaped surface resonators can 
be used; in the case of the square-shaped resonators, additional parasitic 
radiating elements, in the form of strip conductors, are arranged parallel 
to two opposite edges of a surface resonator, at a specific spacing 
therefrom. The spacing, to be selected for each, varies, depending upon 
which frequencies, or oscillation conditions, the surface resonator is 
being optimized for. The surface resonators and the parallel strip 
conductors can be advantageously produced using a laser beam, a 
rectangular shape having first been produced by a lithographic process. 
Using a laser beam, an exact matching of the surface resonators or a 
selective frequency displacement of surface resonators of a group with 
respect to each other can then be carried out. 
Instead of the parallel strip conductors, which are producible by means of 
a laser beam or the lithographic process, frequency matching can also be 
performed by two identical mimic elements, e.g. capacitive reactances, for 
the square surface resonator, these elements being connected by one pole 
in the intersection of the surface diagonals and by their other pole to 
one edge of the surface resonator; the two edges must be opposing each 
other, in order to obtain symmetry sufficient for oscillation conditions. 
Using the mimic elements (e.g. capacitors), one can achieve cost-effective 
adjustment, which can easily be performed manually. 
Furthermore, slots can be made in square-shaped surface resonators in the 
centers of two opposite edges by means of a laser or by the etching 
method, which make it possible to transmit or receive circularly polarized 
waves by square-shaped surface resonators too. At a slot width of 0.025 of 
the line wavelength, mode superposition is achieved, to obtain a circular 
polarization with ellipticity of less than 1 dB over the frequency range 
of the planar antenna. The dimensions of the slots must be identical here. 
The length of the slots, in the direction of the midpoint of the surface 
resonator, determines the frequency which is received/transmitted by the 
surface resonator. 
Due to an additional thin dielectric film, impedance matching between the 
surface resonators and the radiation space is also obtained, by means of 
which the gain of the antenna is increased advantageously. The surface 
resonators, the supply system and the coupling element are also protected 
advantageously from external influences, such as dirt and water.

DETAILED DESCRIPTION 
FIG. 1 shows a top view of a planar antenna (1). The planar antenna (1) is 
manufactured using microstrip technology and the baseplate (2) is made of 
RT/duroid 5880, which is coated on its flat sides with a thin copper film 
(3, 8), the film thickness being 17.5 micrometers. The planar antenna (1) 
has several surface resonators (5), which are connected, with identical 
phase, to a feed point (7) by means of a supply network (6). Surface 
resonators (5), supply network (6) and the feed point (7) are produced 
using a current photolithographic process. The side of the planar antenna 
(1), remote from the radiation space, forms the ground plane (8) of the 
planar antenna (1). The supply network (6) and the surface resonators are 
adapted in impedance to each other by thin strip conductors (9) and are 
connected to the edges of the surface resonators (5) at an angle of 45 
degrees to the extended surface resonator edges (10). 
Coupling of the feed point (7) of the planar antenna (1) and the connection 
point (11) of the downstream electronics (12) is performed by a coupling 
element (13), as shown in FIGS. 2 and 3. The downstream electronic device 
(12) is likewise produced using the microstrip technique and has its 
ground plane (14) on the side adjacent the planar antenna (1) and the 
soldered electronics (15) on the side facing away from the planar antenna, 
and also a connection point (11). 
The coupling element (13) consists of the three segments A1, A2 and A3, 
having respective lengths LA1, LA2 and LA3 shown in FIG. 3, which form 
characteristic wave impedances Z1, Z2 and Z3. The outer conductor (17) is 
a bushing, which comes into electrical contact on its front faces (18) 
with the ground planes (8,14) by means of a press connection, during 
assembly of the radio system. A mechanical carrier plate (19) is located 
between the ground planes (8, 14), and it surrounds the outer conductor 
(17). The inner conductor comprises two rotationally symmetrical elements 
(20, 21). The outer diameter (D3) of the inner conductor element (21) 
shown lowermost is equal to the inner diameter of the bore (22) of the 
central segment (A2, 23). The other inner conductor element (24), shown 
uppermost, has a smaller diameter (D1) than the central inner-conductor 
segment (23). Onto both axially-outer inner-conductor elements (21,24), 
ring wheels or disks (R1, R2), preferably of quartz or 
polytetrafluoroethylene (PTFE), are slid; their inner diameters are equal 
to the appropriate outer diameter (Dl, D3) of the inner-conductor segments 
(21, 24) and their outer diameters are equal to the inner diameter (DA) of 
the outer conductor (17). A ring air gap (28) is provided between the 
central inner-conductor segment (23) and the outer conductor (17). The sum 
of the lengths LA1, LA2, LA3 of segments A1, A2 and A3 equals the spacing 
between the two baseplates (2,29). The two outer inner-conductor segments 
(21, 24) extend through the baseplates (2, 29) and are soldered 
respectively to the feedpoint (7) and to the connection point (11). 
The bore (22) of the center inner conductor part (23) is deep enough that, 
taking into account manufacturing tolerances, there is always an air gap 
(L) between the front face of the outer inner-conductor segment (21) and 
the bottom of the bore (22). 
Above the surface resonators (5), at a spacing of half a free-space 
wavelength, a thin dielectric film (35) is arranged parallel. Its 
dielectric constant is so selected that the radiation space and planar 
antenna (1) are matched to each other in impedance. This is achieved if 
the thickness of the dielectric film is approximately 0.6 to 0.9 mm and 
the dielectric constant is equal to 2.05 to 4. 
Specific embodiments of surface resonators (5) are shown in FIGS. 4 and 5. 
Thus, FIG. 4 shows a square surface resonator (5), which has, at its edges 
(30) running parallel to the Y axis, at a spacing (A), parallel-arranged 
strip conductors (31), which represent parasitic radiation elements. The 
purpose of the strip conductors (31) is mode matching. 
FIG. 5 shows a square surface resonator (5), at the midpoint (32) of which 
two capacitive mimic elements (33) (capacitors) are connected. The mimic 
elements (33) are connected to opposite edges (30) of the surface 
resonator (5) by their other poles (34). 
FIG. 6 shows a square surface resonator (5), at the edges (30) of which, 
two slots (36) are formed, in line with the midpoint (32), and having the 
length (SA) and the width (SB).