Waveguide apparatus

Waveguide apparatus in which a dielectric substrate is placed between sections of a waveguide. The dielectric substrate incorporates slots arranged in a linear fashion and having extended portions, there being a narrow gap between adjacent slots. This enables accurate control of radiation losses through the dielectric layer sandwiched between the sections of the waveguide to be achieved.

BACKGROUND OF THE INVENTION 
This invention relates to waveguide apparatus and in particular, but not 
exclusively, to apparatus comprising a waveguide consisting of two or more 
sections. 
With the advent of modern transceiver/receiver technology, often operating 
at millimeter wavelengths, it is sometimes necessary to use what is 
commonly referred to as E-plane technology. 
E-plane technology refers to the technique of mounting devices in the 
E-plane or electric field plane of the dominant mode of the waveguide. 
This plane usually extends along the waveguide perpendicular to the 
broadwall of the waveguide at the position where the radio frequency 
current is a minimum, normally in the plane bisecting the broadwall. 
In a known configuration, when using the above technology, components are 
mounted on a dielectric substrate as shown in FIG. 1 of the accompanying 
drawings, where the dielectric 1 is held in position by being sandwiched 
between the mating surfaces 2 of sections 3 and 4 which comprise the 
waveguide. 
Unfortunately, by inserting the substrate between the sections of the 
waveguide there is a discontinuity of the metallic inner wall of the 
waveguide at the dielectric. This results in power losses from the guide 
through the substrate layer and is detrimental to the performance of the 
waveguide. 
In order to reduce losses through the substrate layer the apparatus shown 
in FIG. 2 of the accompanying drawings has been proposed. The dielectric 
substrate 5, normally in the form of a PCB, is located in detents 6 in the 
waveguide 7. As the substrate does not extend across the whole width of 
the waveguide walls there is thus a continuous inner metallic wall and 
therefore no escape path for the signal being propagated along the 
waveguide. However, this technique requires precise machining of the guide 
and substrate and leads to problems in connecting components carried by 
the substrate to apparatus outside the waveguide. 
An alternative apparatus is shown in FIG. 3. The dielectric substrate 8 may 
have components mounted on it, prior to assembly, which can be connected 
via conductors carried by the substrate to the external wall 9. 
Construction tolerances are not so critical, as the substrate is simply 
sandwiched between the sections 10 and 11 of the waveguide, and can 
therefore be produced more cheaply than the apparatus shown in FIG. 2. To 
reduce the losses from the waveguide cavity 12 via the dielectric 
substrate 8, the substrate extends into secondary cavities 13 and 14 on 
either side of the waveguide. These behave as radio frequency chokes 
limiting power losses from the central cavity 12. However, there may still 
be an appreciable power loss from the waveguide and the bulk of the 
structure is considerably increased. 
British patent application GB No. 2 207 009, published Jan. 18th, 1989, 
describes apparatus as shown in FIGS. 4A, 4B and 4C, for reducing the 
above-mentioned power losses without increasing the bulk of the waveguide. 
Slots 15 are incorporated within the dielectric 17 separated by gaps d as 
shown in FIG. 4A. These slots 15 are through-plated so as to have a 
conductive layer 16 on their inner surfaces. When the substrate is 
assembled between two sections of the waveguide 18 and 19 as shown in FIG. 
4B, and FIG. 4C. (which is a transverse cross-sectional view of the 
waveguide), the inner conductive surfaces 16 of the slots 15 bridge the 
gap between the sections 18 and 19. This effectively continues the 
metallic wall of the waveguide across the dielectric region 17, except in 
the regions of the gaps between adjacent slots, d, which still permit some 
power loss from the guide. 
The object of the present invention is to control further these power 
losses. 
BRIEF SUMMARY OF THE INVENTION 
According to the present invention, there is provided a waveguide apparatus 
comprising a waveguide having partly sandwiched in one or more walls of 
the waveguide a dielectric substrate incorporating a plurality of slots, 
each slot comprising a first elongate portion with second and third 
elongate portions respectively extending to one side from both ends of the 
first elongate portion each slot having a conductive layer upon at least 
part of its inner surface, and substantially the same orientation as those 
adjacent to it. Further, first portions of adjacent slots are 
substantially co-linear, and at least part of the conductive surface of 
the slots is so positioned as to form part of the inner surface of the 
waveguide. 
The dielectric substrate, when suitably located, enables E-plane technology 
to be employed and permits components to be mounted on the dielectric 
prior to assembly. The conductive coatings on the inner surfaces of the 
slots effectively form a continuation of the inner metallic wall across 
the thickness of the dielectric, parallel to the wall of the waveguide 
which the dielectric intersects, and controls the power losses. The power 
losses through the regions between the slots, where there is no conductive 
material, are controlled by the second and third elongate portions of the 
slots, which can be arranged so that the region between adjacent slots 
function as waveguides. 
By configuring the slots so that they include said second and third 
portions, the coupling factor can be controlled. This is a measure of the 
ratio of coupling between the field within the waveguide cavity and that 
outside the waveguide, and is dependent upon: the width of the gap between 
the second portion of each slot and the third portion of the adjacent 
slot: the angle between these second and third portions; the length of 
said second and third portions; the thickness of the substrate and the 
value of the dielectric constant of the substrate material. It is 
therefore possible, by selecting suitable dimensions and configurations of 
the slots, to control the coupling factor and accurately control power 
losses through the gaps. 
If attenuation of the waveguide is to be optimized it is preferable to have 
waveguide apparatus wherein the slots are arranged so as to minimize power 
losses from the waveguide. This can be achieved by having waveguide 
apparatus in which the slots are arranged such that the second and third 
portions are extending perpendicular to the longitudinal axis of the 
waveguide, the adjacent slots being arranged with a relatively small 
spacing between them and having relatively long second and third portions. 
Arranging the apparatus in this manner, providing long narrow gaps between 
the slots perpendicular to the waveguide, causes high attenuation in these 
areas by acting as a waveguide with a cut-off frequency below that of the 
wave being propagated along &he main waveguide cavity. This greatly 
reduces losses, whilst still providing an electrically non-conductive 
structure for supporting components within the waveguide which is of 
sufficient strength for assembly purposes and which is physically robust. 
In another alternative embodiment, it may be beneficial to have waveguide 
apparatus in which the configuration of slots is arranged such that the 
waveguide apparatus functions as an antenna, that is,.in which, rather 
than reducing losses, it is arranged so that radiation escapes from the 
waveguide in a controlled fashion. Preferably, the second and third 
portions of the adjacent slots are arranged non-parallel to each other and 
have a minimum separation at their ends adjoining the first portions. The 
arrangement of the slots in this manner enables accurate control of power 
losses through each gap, and angling said second and third portions 
enables each gap to effectively act as a two-dimensional horned antenna. 
However, it is possible to use slots with parallel adjacent second and 
third portions as a phased array antenna by choosing a large enough gap 
between adjacent slots. As the positioning and dimensions of the slots may 
be accurately achieved, for example, by stamping, use of the invention 
enables millimetric wave array antennas to be fabricated more cheaply and 
easily than has previously been possible. At present, most production 
techniques for producing such antennas involve expensive CNC machining of 
slots in a waveguide body, but at millimetric wavelengths it is difficult 
to achieve the required tolerances which may make prediction of radiation 
levels difficult. 
Advantageously, where the apparatus in accordance with the invention is 
arranged to act as an antenna, an electrical component is arranged to 
connect conductive layers extending from facing walls of the waveguide, 
enabling modification of a signal transmitted along the waveguide to be 
achieved. Advantageously, a plurality of said components are included to 
control the phase and/or amplitude of a signal as it is transmitted along 
the waveguide. The waveguide may thus be arranged to act as an active 
phased array antenna. 
Construction of a phased array antenna in the above manner offers 
considerable advantages over conventional construction techniques already 
described and enables appropriate components to be sub-assembled upon the 
substrate prior to assembly within the waveguide itself, providing a very 
efficient way of manufacturing compact steerable phased array antennas. In 
some applications it may be a further advantage if several such waveguides 
are cascaded together to form a rectangular array antenna. This may be 
achieved by applying a signal in parallel to a plurality of waveguides 
which are physically located adjacent to one another and the phase of the 
signal applied to each guide may be controlled such that the rectangular 
array is steerable.

Detailed Description of the Preferred Embodiments 
With reference to FIG. 5A, a dielectric substrate 20, for use in waveguide 
apparatus and shown shaded for reasons of clarity, has slots 21 in it. 
Each slot has three portions A, B and C, which correspond to first, second 
and third portions respectively. The slots 21 are linearly arranged with 
the first portions A of adjacent slots being substantially co-linear. The 
second and third .portions B and C of each slot are arranged at right 
angles to the first portion A. Each slot has a metallized inner surface 22 
which is continuous with a metallic area 22A on one of the surfaces of the 
dielectric substrate 20. This substrate 20 is shown assembled within a 
waveguide 24 in FIG. 5B, the metallized area 22A being extending within 
the waveguide to form a fin-line waveguide. This illustrated arrangement 
has lower power losses than a conventional fin-line waveguide because the 
portions B and C of the slots extend from portion A in a direction away 
from the central cavity of the waveguide 24. The metallized coating 22 of 
the end portions B and C causes the gaps 23 between adjacent slots to 
function as waveguides, the dimensions being such that the cut-off 
frequency of the gap is less than that of the signal being propagated, 
causing attenuation of the wave in the gaps 23 and thereby reducing losses 
from the waveguide 24 itself. Broken lines indicate the location of 
different parts of the substrate 20 illustrated in FIG. 5A when it is 
positioned in the waveguide 24. 
In another waveguide apparatus in accordance with the invention as shown in 
FIG. 6A, adjacent slots 21 in a dielectric substrate 20 are more widely 
spaced than those in the substrate of FIG. 5A, enabling the regions 23 
between slots to act as propagation paths for the signal. Thus the 
waveguide apparatus in FIG. 6B which incorporates the substrate 20 of 
FIGS. 6A, functions as a phased array antenna. The size of the gap between 
the slots 21 is determined empirically. 
With reference to FIG. 7A which schematically illustrates another substrate 
20, the portions B and C of adjacent slots 21 are non-parallel such that 
the gaps 23 between slots 21 act as miniature two-dimensional waveguide 
horns. 
When the substrate 20 is incorporated in the waveguide 24, as shown in FIG. 
7B, the waveguide apparatus functions as a horned phased array antenna, 
permitting energy to be radiated through the gaps 23 between the slots 21. 
With reference to FIG. 8A, another dielectric substrate 25 is shown, which 
includes two parallel rows 26 and 27 of slots. Each slot is similar to 
those illustrated in FIG. 5A, and the two rows 26 and 27 are arranged so 
that the second and third portions B and C of one row of slots extend from 
the corresponding first portions A in the opposite direction to those of 
the other row. Each slot is covered with a metallic layer 28 on its inner 
surface. There are also two metallized areas 29 and 30 which surround the 
slots of the upper surface as shown of the dielectric substrate 25. FIG. 
8B shows the substrate 25 of FIG. 8A located within a waveguide 31 which 
is formed from two sections 32 and 33. The metallized coating 28 on the 
slot surfaces effectively extends the waveguide inner wall 34 across the 
boundary between the two sections 32 and 33. The portions B and C of the 
slots function as described with reference to FIGS. 5A and 5B. The 
portions B and C of the slots in both rows 26 and 27 extend from portion A 
in a direction away from the central cavity 35 of the waveguide 31. The 
metallized coating 28 of the end portion B and C causes the gaps 36 
between adjacent slots to function as waveguides, the dimensions being 
such that the cut-off frequency of the gap is less than that of the signal 
being propagated causing attenuation of the wave in the gaps 36 and 
thereby reducing losses from the waveguide 31 itself. The metallized areas 
29 and 30 extend within the central cavity 35 of the waveguide 31, and 
function as a fin-line waveguide. 
In another embodiment of this invention, the waveguide apparatus is 
arranged to act as a phased array antenna. FIG. 9 schematically shows a 
conventional slotted array antenna. It comprises a waveguide 37 having 
slots 38 machined in it, these slots usually being produced by expensive 
CNC machining techniques which are not capable of producing the tolerances 
required for millimetric systems, as are possible using the present 
invention. FIGS. 10A and 10B schematically show a phased array antenna in 
accordance with the present invention. FIG. 10A illustrates in plan view a 
dielectric substrate 39 having two rows 40 and 41 of slots through it. The 
lower row 40, as illustrated, is designed to reduce losses from the 
waveguide to a minimum, the first portion A of the slots being as long as 
practicable and the gaps 42 between adjacent slots the minimum possible 
whilst ensuring that the substrate 39 is physically robust enough for 
assembly purposes and to withstand physical shocks it is likely to receive 
in service. The narrow gaps 42 between the slots allow very little 
radiation to escape from the waveguide. 
The slots of the upper row 41, as shown, are arranged to have a 
substantially wider gap 43 between adjacent slots. The second and third 
portions are angled with respect to the first portions so as to form what 
are effectively two-dimensional antenna horns between adjacent slots. This 
enables radiation to escape from the waveguide in a controlled manner. 
A component 44 is mounted between two conductive areas 45 and 46 
surrounding the slots, and may be a PIN diode or other such device to 
enable the phase and/or amplitude of a signal travelling along the guide 
to be modified. Although only one component is shown, in practical 
applications there would be many such components. When the substrate 39 is 
assembled in the waveguide 47 as shown in FIG. 10B, where two such 
substrates have been incorporated, one row 40 of slots limits radiation 
from the bottom section of the waveguide 47 whilst the other row 41 of 
slots permits radiation to escape from the waveguide through its upper 
face. The component 44, (not shown in FIG. 10B) is used to control the 
phase and/or amplitude of the signal in the waveguide, enabling the 
waveguide apparatus to act as a steerable phased array antenna. Insulating 
layers 48, shown in FIG. 10B, enable a potential difference to be applied 
between two regions 49 and 50 of the waveguide 47 thereby providing a 
potential difference between the metallized areas 45 and 46 of FIG. 8A. 
This provides a potential difference across component 44 and therefore a 
means of controlling the component. 
With reference to FIG. 11A in another embodiment of the invention, a 
dielectric substrate 51 includes two rows 52 and 53 of slots arranged to 
reduce power losses from a waveguide. Each slot is filled with conductive 
material 54, which, when the substrate 51 is located in a waveguide 55, 
forms part of the inner surface of the waveguide wall, as shown in FIG. 
11B. In this embodiment the slots are set back from the waveguide cavity 
56 so that the effective inner surface of the waveguide is indented. One 
advantage of having the slots completely filled with conductive material 
is that it ensures that there are no discontinuities in the metallic 
surface around the edge of the slot. 
FIG. 12 shows a rectangular array antenna consisting of sections of 
waveguide apparatus 57, 58 and 59, each of which is similar to the 
waveguide apparatus shown in FIG. 10B, but having only a single dielectric 
layer 60. 
The input signal to all the guides may be applied to them in parallel, and 
the phase of the waves in each section may be controlled such that a 
steerable array may be produced.