Microwave connector

A microwave connector comprises two substrates arranged in orthogonal planes. A first substrate (2) is formed as a microstrip system (8) with a microstrip component (3) connected via a quarter wavelength taper (4) to a parallel transmission line (5). This transmission line terminates in a short circuit (15) to a ground electrode (7) on the back of the microstrip. A second substrate (10) is formed as a slotline system (9) having a slotline (13) between two sheet electrodes (14). In this slotline is a slot (16) of dimensions slightly less than the slotline width and sufficient length to accommodate the microstrip. The microstrip and slotline are electrically unconnected. Energy transfer between microstrip and slotline, or vice versa, takes place by electromagnetic coupling between the transmission line and the edges of the slotline. The slotline may be formed with an additional substrate and slotline electrode in a triplate configuration. Several microstrip components (8.sub.1 to 8.sub.n) may be connected in a single slotline substrate (10, 13).

BACKGROUND OF THE INVENTION 
1. Field of the Invention This invention relates to a microwave connector 
for connecting microwave energy between two substrates in orthogonal or 
near-orthogonal planes that are not electrically connected. 
2. Discussion of Prior Art 
Such a connector finds use for example in phased array radar systems where 
a large number of antenna modules must be driven from a single local 
oscillator with equal or near equal amplitude and phase. This is achieved 
by successive dividers. If the divider network is manufactured from 
stripline (triplate) or microstrip, it is necessary to use surface launch, 
right angle, connectors from the stripline to each of the modules. This is 
expensive, time consuming, and at times difficult to implement. 
Microstrip circuits are a known type of device. They comprise a flat 
plate-like insulating substrate carrying conducting tracks on one surface 
with a ground electrode covering the opposite face. The conducting track 
can be shaped into many standard forms to give couplers, circulators, 
dividers, etc. Slotline circuits are a known type of device. They comprise 
a plate-like insulating substrate covered on one surface with a sheet 
electrode that is selectively removed to provide a narrow slot of exposed 
substrate; it is similar to but the inverse of microstrip. A variation on 
microstrip is triplate which is effectively two microstrip circuits glued 
face to face. Triplate comprises two insulating substrates face to face 
with a conducting strip circuit between them. The reverse faces carry 
sheet ground electrodes. Known microwave connectors include simple surface 
launch connectors. These need to be firmly fixed onto the stripline 
substrate, requiring the use of screws or bolts, and so can be an 
expensive construction method in production. This structure is very rigid 
and allows no stress relief. Another known connector uses a customized 
surface launch connector as described in Microwaves and RF, August, 1989, 
pages 137-143, S. S. Horwitz and G. W. Bull. It employs a pin connection 
requiring a connecting pin and welding of a gold ribbon from the stripline 
track to the pin. The connector has a horseshoe shaped body that passes 
through a shaped aperture in the stripline track and is fixed by a single 
nut. Both of these connectors output the microwave signal in a coaxial 
line, requiring the use of another connector if the signal is to be 
launched into microstrip. They can also require a large amount of 
expensive metal work. 
SUMMARY OF THE INVENTION 
The connector of the present invention provides a simple microwave 
connector not requiring electrical connection, and is insensitive, in 
amplitude and phase to vibration and strain. 
According to this invention a microwave connector comprises a first 
substrate and a second substrate arranged with the first substrate within 
an aperture in the second substrate in substantially orthogonal, or within 
45.degree. of being orthogonal, planes; the first substrate being a 
microstrip circuit including a taper section leading from a microstrip 
component to a pseudo parallel plate transmission line having a length of 
approximately half wavelength long terminating in a short circuit to the 
ground plane; the second substrate being a slotline circuit having a 
slotline component terminating in a short circuit element, and a slot 
aperture adjacent to the short circuit element of length approximately 
half the slotline wavelength long sufficient to accommodate the first 
substrate pseudo parallel plate transmission line and width less than the 
slotline width; the arrangement being such that the two substrates are 
electrically unconnected and that energy transfer occurs between the two 
substrates due to electromagnetic coupling between the parallel plate 
transmission line and the slotline. 
The two substrates preferably lie in orthogonal planes but may be up to 
plus or minus 45.degree. from this condition with consequential loss in 
performance. 
The second substrate may further include a conventional slotline to 
microstrip or triplate transition so that the whole microwave connector 
may be inserted into a microstrip system. The second substrate may further 
include a second slotline component on its reverse face to form a triplate 
structure around the conventional slotline to microwave transition. 
The relative sizes of the first substrate and the slot aperture may be 
arranged so that the two substrates are held together with a slight 
interference fit, i.e. the two substrates can be readily assembled and 
separated but are self supporting.

DETAILED DISCUSSION OF PREFERRED EMBODIMENTS 
As shown in the figures a microwave connector 1 comprises a first substrate 
2 carrying a microstrip component 3 connecting to a quarter wavelength 
taper section 4 and a pseudo parallel plate transmission line 5. The 
length of the transmission line is about one half wavelength and 
terminates in a wrap around short circuit 6 to a ground sheet electrode 7 
on the rear face of the substrate 2. 
Typically the substrate 2 is a ceramic in plastic matrix material plate 
0.71 mm thick, 7 mm wide, with a dielectric constant between 2.5 to 10. 
For example the substrate 2 may be RT/Duroid (Registered Trade Mark). The 
microstrip is an 18 um thick shaped layer of gold or copper etched out 
onto the substrate 2. Operating frequency is about 8.5 GHz so that length 
of the taper 4 is about 2.8 mm, the length of the transmission line 5 is 
about 5.8 mm, and the width of the transmission line 5 about 5.25 mm. The 
substrate 2 with microstrip components 3 etc forms a microstrip line 8. 
A slotline system 9 comprises a second substrate 10 and carries a slotline 
circuit on its upper face. The slotline is formed by a slot 13 in a sheet 
electrode 14. Both ends of the slotline terminate in a slotline short 
circuit 15. Adjacent short circuit 15 is a slot 16 through the thickness 
of the substrate 10. Spaced from the other end of the slot 16 is a 
microstrip line 12 arranged on the bottom of the substrate 10 to form a 
conventional transmission feed. The gap between feed 12 and the adjacent 
end of slot 13 is about a quarter slotline wavelength; the distance 
between the free end of the feed 12 and centre of slot line 13 is about a 
quarter stripline wavelength. The first substrate 2 fits into this slot 
with a slight interference, or sliding, fit sufficient to enable easy 
assembly and remain self supporting. Small changes in the dimensions of 
the slot 16 do not seem to affect the performance of the transition. The 
first substrate may be inserted into the slot 16 in any one of the four 
possible orientations. 
typically the substrate 10 is an RT/Duroid (TM) plate, 1.26 mm thick, and 
any convenient width with a dielectric constant between 2.5 and 10. The 
electrodes 14 are 18 .mu.m thick layers of copper or gold. The slotline is 
photolithographically defined and etched out to a width of 1 mm. The slot 
16 is 7.2 mm long and 0.8 mm wide. This means that the microstrip 
transmission lie 5 and back electrode 7 are spaced from the slotline 
electrodes 14 by a gap of about 0.145 mm. There is therefore no electrical 
connection between the microstrip 8 and slotline 9 circuits. Many 
slotlines may be formed on a large substrate, particularly when feeding 
many elements in a phased array. 
The coupling of energy between microstrip 8 and slotline 9 is by 
electromagnetic coupling. As indicated in FIG. 5 microstrip feed 
transmission line 12 excites the slot 13 in the slotline 9 in a 
conventional microstrip to slotline transition. The length of the slot 13 
is given as L. The electric vector in the slot forms an approximately half 
cosine pattern. The parallel plate transmission line 5 intercepts a 
fraction of this field; the position of the line 5 is given as x. 
##EQU1## 
i.e. the amount of energy transferred varies with the value (L-u), the 
width of the parallel plate transmission line 5. 
The energy transfer, or transmission, between the microstrip 8 and the 
slotline 9 is the ratio of these two quantities, assuming an otherwise 
perfectly match system, i.e. 
##EQU2## 
As shown in FIG. 6 the second substrate 10 of FIG. 1 may be replaced by a 
triplate structure 20 which is effecitvely two slotline substrates 21, 22 
and back electrodes 23, 24 glued face to face enclosing a common 
transmission feed 25. In this configuration a slot 26 is made in both 
substrates 21, 22 and material removed from both back electrodes 23, 24. 
The microstrip transmission line 8 passes through both triplate 
substrates. By selectively covering one of the quarter wavelength slotline 
short circuits (i.e. covering one of the slots 13 in the electrodes 23 or 
24 adjacent to feed 25 by a strip of electrically conducting material), 
the transition can be made to pass a narrower band of frequencies and will 
severely attenuate frequencies outside this range. 
The connector 1 can be excited by using either microstrip or slotline both 
having a similar performance. 
Microstrip and triplate versions of the connector have been found to 
perform satisfactorily at frequencies between 800 MHz and 10 GHz. 
The following tables give typical results: 
TABLE 1 
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Maximum transmission -1.8 dB 
Centre frequency 8.5 GHz 
3 dB frequency bandwidth 
1.0 GHz 
Maximum reflections: 
with microstrip 8 as input 
-15.0 dB 
with slotline 9 as input 
-10.0 dB 
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TABLE 2 
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Characteristic impedances: 
of microstrip 8 50 ohms 
of slotline 9 100 ohms 
Substrate thickness: 
microstrip 8 0.71 mm 
slotline 9 1.26 mm 
Parallel Plate line width 
5.25 mm 
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In the modification shown in FIG. 7 the second substrate 10 and slotline 13 
are extended in length. Within the slot line 13 several slots 16.sub.1 to 
16.sub.n are formed, each similar to that of slot 16 in FIG. 1. Microstrip 
circuits 8.sub.1, 8.sub.2 . . . 8.sub.n are fitted into these slots 
16.sub.1, 16.sub.2 . . . 16.sub.n. Power for the slot line 13 is from a 
microstrip feed 12 as before. Each microstrip circuit 8.sub.1 to 8.sub.n 
extracts a proportion of energy from the slot line 13. 
The slot line 13 may be straight or curved so that the microstrips 8.sub.1 
to 8.sub.n may be in line or staggered. The microstrips 8.sub.1 to 8.sub.n 
may be similar or be different circuits. 
An alternative manner of connecting several circuits together is shown in 
FIGS. 8, 9, 10. A slot line second substrate 30 carries several microstrip 
lines 8.sub.1 to . . . 8.sub.n. Each microstrip 8.sub.n comprises a 
substrate 2 which has a narrowed end 31. This substrate 2 carries a 
microstrip component 3 connecting to a quarter wavelength taper section 4 
and a pseudo parallel plate transmission line 5 terminating in a wrap 
round circuit 6 to a rear mounted ground electrode. 
The second substrate 30 comprises several slot lines 13.sub.1, 13.sub.2 . . 
. 13.sub.n each fed by a common microstrip feed 12. Within each slot line 
13.sub.1 to 13.sub.n is a slot 16.sub.1 to 16.sub.n for carrying a 
microstrip line 8.sub.1 to 8.sub.n. The slot liens 13.sub.1 to 13.sub.n 
may be aligned as shown or staggered as required.