Waveguide-microstrip transition for millimeter waves and Microwaves

Abstract: A waveguide-microstrip line transition with low transition losses is provided by shaping the wider walls of the ridge waveguide so as to spread out toward the end. Since doing this increases the degree of freedom in design parameters, the width and the height of the ridge can be fitted to that of the microstrip line and that of the waveguide. The above elements is applicable to HF circuits, antennas and communication systems.

Description: The present invention relates to a high frequency (HF) circuit in a communication device and more specifically to a waveguide-microstrip line transition. Recently, as frequency resources in communications technology are running dry, frequency bands available for building a new communications system have been and are shifting to higher bands. In this situation, the government and the people are jointly promoting a development to milliwave and microwave communication systems domestically and internationally. For example, it has been decided that extremely high frequency bands ranging from some GHz to hundreds GHz are assigned as available frequency bands to various communication systems under development for wireless LAN (local area network) and ITS (Intelligent Transport System). Since available frequencies are rising as described above, antennas and HF (high frequency) circuits are desired which satisfactorily work in milliwave and microwave bands. However, design and manufacturing techniques that have been believed to be available may not work satisfactorily with an increase in frequency. For this reason, there is a need for novel design and manufacturing techniques. FIG. 1 is a diagram showing an arrangement of a prior art array antenna assembly 1. In FIG. 1, the antenna assembly 1 comprises an dielectric substrate 10, a circuit pattern 20, a chassis 30 that holds the dielectric substrate 10 and serves as the ground, and a waveguide-microstrip line transition 40. The circuit pattern 20, which constitutes an array antenna, includes a T branch circuit 50. A signal transmitted through a waveguide (not shown) is passed by the transition 40 to a microstrip line of the circuit pattern 20, and further passed by the T branch circuit 50 to the right and the left portions of the array antenna. FIG. 2 is a schematic diagram showing an arrangement of the transition 40 of FIG. 1. In FIG. 2, the transition 40 comprises a ridge waveguide 42, a ridge 41 formed inside the ridge waveguide 42, and a microstrip line 21 which is formed on the dielectric substrate 10 and which is extending to (or a part of) the circuit pattern 20. As described above, the signal transmitted through the not-shown waveguide is converted into a transmission mode of the microstrip line 21 by the ridge 41 provided inside the waveguide 42 and transmitted to the array antenna 20. GB 763,894 relates to a transducing arrangement for connecting a hollow waveguide to a two-conductor transmission line type waveguide with a least one of the conductors having a flat strip formation. The transducing arrangement comprises means conductively coupling a first conductor of the transmission line to one part of the hollow waveguide, and a ramp conductor disposed on the inner surface of another part of the hollow waveguide, and means conductively coupling the ramp conductor to a second conductor of the transmission line. Problems exist in conjunction with working if an antennae with the just described arrangements are to be implemented for milliwave or microwave. With an increase in frequency, dielectric materials available for the dielectric layer 10 are limited to substances lacking mechanical strength, e.g., ceramics, quartz, silicon, etc. Further, if an antenna that radiates a beam of two degrees in mesial width in a 76 GHz band is to be fabricated, the dielectric substrate 10 for the antenna will be approximately 100 to 300 µm thick and 15cm long in one side. Bonding such a thin and wide substrate 10 to the chassis 30 often results in a breakage of the dielectric substrate 10. Also as the frequency increases, the characteristics of the antenna 20 depends strongly on the earthing state of the dielectric substrate 10. For this reason, a sufficient electrical contact is indispensable for the junction of the dielectric substrate 10 and the circuit pattern 20. However this is hard to be achieved by conventional techniques. Since the degree of freedom is very low in designing a waveguide-microstrip line transition, i.e. the design parameters are limited only to the width, the length and the height of the ridge 41, this sometimes causes the width of ridge for a milliwave band to be extremely narrow. Accordingly, the height of the ridge 41 of the transition 40, which is manufactured through machining of a brass material, becomes higher as compared with the ridge 41 width, making the work difficult. The lack of degree of freedom in design may disable the conversion into a microstrip line with a lower characteristic impedance and cause the problem that a too great difference between the widths of the designed ridge 41 and the microstrip line 21 leads to an unexpected deterioration in the line conversion characteristics. The invention is directed to solving these and other problems and disadvantages of the prior art. It is an aim of the invention to provide a waveguide-microstrip transition that has a high degree of freedom in design. According to an aspect of the invention, there is provided a waveguide-microstrip line transition according to claim 1. In one embodiment, at least part of each longitudinal side of the tube is linear. However, at least a part of each longitudinal side may accord substantially with an exponential function or a trigonometric function. The features and advantages of the present invention will be apparent from the following description of an exemplary embodiment of the invention and the accompanying drawings, in which: FIG. 1 is a diagram showing an arrangement of a prior art array antenna assembly 1; FIG. 2 is a diagram showing an arrangement of the waveguide-microstrip line transition 40 of FIG. 1; FIG. 3 is a schematic diagram showing an exemplary arrangement of an array antenna assembly according to an illustrative embodiment of the invention; and FIG. 4 is a schematic diagram showing an exemplary arrangement of the wave guide-microstrip line transmission 140 of FIG. 3. Throughout the drawings, the same elements when shown in more than one figure are designated by the same reference numerals. FIG. 3 is a schematic diagram showing an exemplary arrangement of an array assembly 100 according to an illustrative embodiment of the invention. In FIG. 3, the antenna assembly 100 comprises a dielectric substrate 10, a circuit pattern or an array antenna 120 formed by patterning a metal film on the dielectric substrate 10 through photocopying, etching, etc., a chassis 130 that holds the dielectric substrate 10 and serves as the ground, and a waveguide-microstrip line transition 140 formed in the edge of the chassis 130. A signal transmitted through a waveguide (not shown) is passed by the transition 140 to a microstrip line coupled to the circuit pattern 120, and further passed by the T-branch circuit 150 to the right and the left portions of the array antenna 120. Waveguide-Microstrip Line Transmission FIG. 4 shows an exemplary arrangement of the waveguide-microstrip line transition 140 of FIG. 3. In FIG. 4 the transition 140 comprises an extension 42 of a waveguide (not shown), a fanwise tube (i.e. a tube spreading out toward the end) 142, a ridge 144 so formed as to protrude inside the fanwise tube 142, and a microstrip line 121 formed on the dielectric substrate 10 and extending to (or forming part of) the circuit pattern 120. The fanwise tube 142 has a horn-like structure with a rectangular cross section perpendicular to the current direction. The two openings of te fanwise tube 142 differ in dimensions from each other. The transition 140 serves as a transition between the waveguide extension 42 and the microstrip line 121. The transition 140 is a so called ridge waveguide converter provided, in the center of the fanwise tube 142, with a ridge 144 of a wedge shape. Specifically, the electromagnetic fields distributed all over the opening of the waveguide extension42 is gradually converged in the head of the ridge 144 and finally made resemble the electromagnetic transmission mode of the microstrip line 121 thereby to be power-transmitted to the microstrip line 121. According to the present invention, the line conversion characteristics of the transition 140 are a function of (i.e., can be controlled by) not only the dimensions of the ridge 144 but also the shape of fanning of the fanwise tube 142. That is, using a tube spreading out like an unfolded fan has increased the degree of freedom in designing the ridge 144. Since the designer can freely select the width and the height of the ridge 144, the transition 140 can be so designed as to have desired line conversion characteristics with a reduced parasitic impedance near the interface between the ridge 144 head and the microstrip line 121. In this way, the inventive transition 140 is easy to work, relatively lower in conversion loss and better in conversion characteristics. Also, since the height of the ridge 144 can be set identical to that of the fanwise tube 142, the fanwise tube 142 with a high precision in the dimensions is provided, which contributes to better line conversion characteristics of the resultant transition 140. The fanwise tube 142 has been shown as linearly shaped in FIG 4. However, the tube 142 may have any non-linear shape that spreads out toward the end. The side of the tube 142 may be curved according to, e.g. an exponential function, a trigonometric function, etc. The two openings of the tube 142 may have any suitable geometric shape different from each other to exhibit different characteristic impedance. Though the transition 140 has been described as a waveguide-microstrip transition provided in path to an antenna, the transition 140 according to the invention can be applied to an ordinary high frequency circuit. Many widely different embodiments of the present invention may constructed without departing from the scope of the present invention. It should be understood theat the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.

Claims: A waveguide-microstrip line transition (140) with low transition loss, comprising: a fanwise tube (142) having a first opening coupled with a waveguide and a second opening; said fanwise tube (142) comprising a first and a second wider wall; and an end portion of a microstrip line (121) formed on a dielectric substrate (10) arranged near said first wider wall, said end portion being situated a little inside said second opening; and a ridge (144) formed on said second wider wall, said ridge protruding gradually from the first opening side toward the second opening side to be connected, at the end thereof, with said end portion of said microstrip line (121) characterised in that said second opening is larger in size than said first opening, and said fanwise tube is such that said first and second wider walls spread from said first opening toward said second opening. A waveguide-microstrip line transition as defined in claim 1, wherein at least a part of each longitudinal side of said fanwise tube (142) is curved such that the spread is substantially linear. A waveguide-microstrip line transition as defined in claim 1 , wherein at least a part of each longitudinal side of a said fanwise tube (142) is curved such that the spread accords substantially with an exponential function. A waveguide-microstrip line transition as defined in claim 1, wherein at least a part of each longitudinal side of said fanwise tube (142) is curved such that the spread accords substantially with a trigonometric function.

Inventors: FUJITA SUGURU, SANGAWA USHIO, FUJITA, SUGURU, SANGAWA, USHIO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1999
Main classification: H01P5
IPC codes: H01Q1, H05K1, H01Q13, H01P5, H05K3, H01P11