GB2238665A

GB2238665A - Microstrip antenna

Info

Publication number: GB2238665A
Application number: GB9025672A
Authority: GB
Inventors: Kazunori Takeuchi; Masayuki Yasunaga; Takayasu Shiokawa
Original assignee: Kokusai Denshin Denwa KK
Current assignee: KDDI Corp
Priority date: 1989-11-27
Filing date: 1990-11-26
Publication date: 1991-06-05
Anticipated expiration: 2010-11-26
Also published as: CA2030886C; JPH03166803A; CA2030886A1; GB9025672D0; GB2238665B

Abstract

A microstrip antenna of two-frequency separate-feeding type for circularly polarized waves, in which four radiation conductors (111 to 114) are disposed on a dielectric plate (15) mounted on a conducting ground plane (14) and each radiation conductor has its marginal portion partly short-circuited via a short-circuiting conductor (121 to 124) to the conducting ground plane and is supplied at its feeding point with power via a feeder (161) passing through the conducting ground plane and the dielectric plate. The four radiation conductors are composed of two pairs of radiation conductors of different sizes adjusted so that two desired frequencies can simultaneously be used for transmission and for reception, respectively, the conductors of each pair being arranged to generate a circularly polarized wave. <IMAGE>

Description

MICROSTRIP ANTENNA OF TWO FREQUENCY SEPARATE-FEEDING TYPE FOR CIRCULARLY POLARIZED WAVES The present invention relates to a microstrip antenna of two-frequency separate-feeding type for circularly polarized waves which is employed for various radio communications.

A microstrip antenna is of wide application as an antenna for various communications, because it has a planar structure of a thickness sufficiently small as compared with the wavelength used, and it is lightweight. With a phased array antenna using a plurality of such microstrip antennas it is possible electrically to change a beam of radio waves by controlling the phase shift amount of a phase shifter connected to each antenna element. Such a phased array antenna features its thin, small and lightweight structure, and hence is expected to be applied to mobile communications and the like.

As is well-known in the art, the microstrip antenna is narrow-band. For example, assuming that a voltage standing wave ratio of the antenna, i.e. a criterion upon which to determine whether or not the antenna can be put to practical use, is 2 or below, the bandwidth of the microstrip antenna which satisfies the ratio is as small as several percent with respect to the centre frequency, though it depends on the characteristic of a dielectric plate used. This means that an ordinary microstrip antenna cannot be used for communications which transmit and receive radio waves higher than such a bandwidth as mentioned above. To solve this problem, microstrip antennas of various structures have been proposed so far.

However, conventional art has defects such as complicated structure and difficulty in fabrication.

An object of the present invention is to provide a microstrip antenna of two-frequency separate-feeding type for circularly polarized waves which is small in size and easy to manufacture.

With a view to solving the above-noted problems, the microstrip antenna of the present invention features a structure in which four radiation conductors are disposed on a dielectric plate mounted on a conducting ground plane and each radiation conductor has its marginal portion partly short-circuited via a short-circuiting conductor to the conducting ground plane and is supplied at its feeding point with power via a feeder passing through the conducting ground plane and the dielectric plate, and in which the four radiation conductors are composed of two pairs of radiation conductors of different sizes adjusted so that two desired frequencies can simultaneously be used for transmission and for reception, respectively, the conductors of each pair being arranged to generate a circularly polarized wave.

Embodiments of the present invention will now be described in detail below, by way of example, by comparison with prior art and with reference to accompanying drawings, in which: Figs. 1A and 1B are a plan view and a sectional view taken on the line A-A' therein, both illustrating an embodiment of the present invention; Figs. 2, 3A and 3B are plan views illustrating other embodiments of the present invention; Fig. 4A is a block diagram showing transmitting-receiving equipment in which a transmitting device and a receiving device are connected to the microstrip antenna of two-frequency separate-feeding type for circularly polarized waves according to those embodiments shown in Fig. 1, 2, 3A, or 3B;; Fig. 4B is a block diagram illustrating a phased array antenna which is formed, as antenna elements, by the use of the microstrip antenna of two-frequency separate-feeding type for circularly polarized waves of the form shown in Fig. 1, 2, 3A or 3B; Figs. 5A and 5B are a plan view and a sectional view taken on the line B-B' illustrating a conventional microstrip antenna for circularly polarized waves designed for wide-band use; Figs. 6A and 6B are a plan view and a sectional view taken on the line C-C' for illustrating a conventional microstrip antenna of two-frequency separate feeding type for circularly polarized waves; Figs. 7A and 7B are a plan view and a sectional view taken on the line D-D', showing a conventional one-point feeding type microstrip antenna for circularly polarized waves; and Fig 8. is a block diagram showing a phased array antenna employing the conventional wide-band microstrip antenna for circularly polarized waves depicted in Fig. 3.

To make differences between prior art and the present invention clear, examples of prior art will first be described.

Figs. 5A and 5B show in combination examples of the structure of a conventional microstrip antenna intended for enhanced bandwidth, Fig. 5A being a plan view and Fig. 5B a sectional view taken on the line B-B' in Fig. 5A. Reference numeral 51 indicates a radiation conductor, 52 a passive radiation conductor, 53 and 53' feeding points, 54 a grounded conductor, 55 dielectric substrate, and 56 a feeder. The feeding point 53 is connected to the feeder 56 feeding via a connector provided on the grounded conductor 54. With the structure of this example, an antenna which resonates in the transmitting or receiving frequency band can be obtained by adjustment of the sizes of the radiation conductor 51 and the passive radiation conductor 52.

Fig. 8 is a block diagram showing a conventional phased array antenna using microstrip antennas exemplified in Fig. 5.

Reference numeral 81 indicates each antenna element, 82 a directional coupler for generating a circularly polarized wave, 83 a phase shifter, 84 a power divider, 85 a diplexer, 86 a transmitter, 87 a receiver, and 88 a dummy load. By changing the phase of a feed signal by the phase shifter 83 for each antenna element 81, the direction of the beam can be controlled electrically.

Figs. 6A and 6B show in combination another example of the conventional antenna structure which is simultaneously operable for transmission and for reception, Fig. 6A being its plan view and Fig. 6B its sectional view taken on the line C-C' in Fig. 6A.

Reference numeral 61 indicates an annular microstrip antenna (a radiation conductor for reception), and 62 a circular microstrip antenna (a radiation conductor for transmission). These antennas are fed from their back sides independently of each other through a transmitting feeder 66 and a receiving feeder 68 to a transmitting feeding point 63 and a receiving feeding point 67, respectively. With this structure, the annular microstrip antenna 61 and the microstrip antenna 62 resonate in receive and transmit frequency bands, respectively. In this example, reference numeral 64 is a conducting ground plane, and 65 a dielectric substrate.

The antenna for circularly polarized waves usually employed in mobile communication can be implemented by feeding at two points as mentioned above in connection with Figs. 5A, 5B and 6A, 6B, and there has also been well known a circular polarized antenna of one-point feeding which has only one feeding point as shown in Figs. 7A and 7B. In Figs. 7A and 7B the function of an antenna for circularly polarized waves which has only one feeding point 73 is obtainable by the additional provision of protrusions 72 on a radiation conductor 71. In this example, reference numeral 74 is a conducting ground plane, 75 a dielectric plate, and 76 a feeder.

In case of constructing a phased array antenna through use of the above-described prior art, the wide-band microstrip antenna or dual-frequency resonance type microstrip antenna shown in Figs. 5A and 5B poses a problem as they are complex in design and construction.

In addition, since the feeding portion is common to transmission and reception and the phases of transmission and reception are controlled by the same phase shifter 83 as shown in Fig. 8, the prior art possesses a shortcoming in that transmission and received beams do not correspond to each other owing to a difference in frequency therebetween, and the diplexer 85 which must be provided between the phase shifters 83 and the transmitter 86 and the receiver 87 for separating transmission and received signals makes the feeding portion bulky. Reference numeral 81 indicates antenna elements, 82 directional couplers, 84 a power combiner/divider, 85 a diplexer, and 88 a dummy load.

The antenna structure having an annular microstrip antenna and a circular microstrip antenna disposed thereon, shown in Figs. 6A and 6B, does not call for a diplexer or circulator, because a feeding point for transmission 63 and a receiving feeding point 67 are sufficiently isolated from each other electrically. However, this antenna structure is two-layer and hence is more complex in construction and heavier than an antenna of a one-layer structure, and the manufacture of this antenna involves many steps and requires high machining accuracy.

The circular polarized antenna of one-point feeding depicted in Figs. 7A and 7B is not suitable as an antenna for wide-band communications, because it is narrow-band rather than the usual microstrip antenna and has frequency dependence of its axial ratio.

The present invention is intended to solve the abovementioned problems of the prior art and therefore to provide a microstrip antenna of two-frequency separate feeding type which is small in size and easy to manufacture.

The present invention will now be described with reference to embodiments thereof.

Figs. 1A and 1B illustrate in combination an embodiment of the present invention as applied to a microstrip antenna in which one side of each radiation conductor is short-circuited. Fig. 1A is a plan view of the antenna and Fig. 1B a sectional view taken on the line A-A' in Fig. 1A. As shown, four radiation conductors 111 to 114 are disposed on a dielectric plate 15 and are shortcircuited to a conducting ground plane 14 via short-circuiting conductors 121 to 124, respectively. Reference numerals 131 to 134 denote feeding points of the radiation conductors 111 to 114, respectively, which are fed with power from its back side through feeders (a feeder 161 at a feeding point 131).The radiation conductors 111 and 112 are of the same size and have the same resonance frequency tuned to a frequency of a transmitting wave, whereas the radiation conductors 113 and 114 are of the same size and have the same resonance frequency tuned to a frequency of a receiving wave. Consequently, the radiation conductors 111 and 113 are different in size.

As regards transmission, signals fed in phase to the radiation conductors 111 and 112 are thereby rendered into a circularly polarized wave, which must be formed within the half wavelength of the frequency used, as is well-known in the art.

The same is true of reception, because of reversibility of the antenna and the receiving antenna is formed by the radiation conductors 113 and 114 for receiving the circularly polarized wave. The radiation conductors 111, 112 for transmission and the radiation conductors 113, 114 for reception are disposed in such a manner as not to interfere with each other. To meet with these requirements, the radiation conductors 111, 112, 113 and 114 are disposed as shown in Fig. 1, and for each radiation conductor, a plane passing through its feeding point and perpendicular to the corresponding short-circuiting conductor (a plane A-A' for the conductor 111, for instance) forms a rectangle or square on the dielectric plate 15.

By limiting the sizes of the radiation conductors 111 to 114 to the bandwidths necessary for transmission and reception it is possible to prevent the coupling between transmission and reception from constituting an obstacle to communications. The feeding points 131 and 132 are each connected from the back side of the conducting ground plane 14 to a transmitter via a feeder and a directional coupler. Since the radiation conductors 111 and 112 generate linearly polarized waves perpendicularly intersecting each other, a transmitting circularly polarized wave can be generated by feeding from a directional coupler 421 through feeder 463 and 464 to feeding points as shown in Fig. 4A so that the phases of feeding are displaced 90 apart from each other.Whether the polarized wave is right-handed or left-handed is determined by the direction of connection of the directional coupler. For reception as well, a circularly polarized wave is received via radiation conductors 411 and 412, feeders 461 and 462 and a directional coupler 420 on the same principle as mentioned above to a receiver. A phased array antenna with a plurality of such antennas arrayed as shown in Fig. 4B has a wide-angle radiation characteristic, dispenses with the diplexer and the circulator, and is free from disagreement between transmission and reception beams. In this case, reference numeral 42 is a directional coupler and 43 a phase shifter. A transmitter 47 is connected to phase shifters 43 through a power divider 44b.

For reception, the outputs of phase shifters are applied to a receiver 66 after combining by a power combiner 44a.

The one side-shorted microstrip antenna for use in the present invention has already been proposed (Haneishi, et al., "On Radiation Characteristics of One Side Shorted Microstrip Antenna," 83 National Convention of Institute of Electronics and Communication Engineers of Japan, Proceedings No. 3, pp 743, the Institute of Electronics and Communication Engineers of Japan, March 5, 1983). In this antenna the radiation conductors used are as small as about one-half the size of ordinary microstrip antennas, and consequently, the microstrip antenna of the present invention can be miniaturized.

Fig. 2 illustrates another embodiment of the present invention, in which short-circuiting conductors 281 to 284 are provided between rectangular one side shorted microstrip radiation conductors 211 to 214 and a conducting ground plane (a plane 24 not shown but provided at the back side of the dielectric plane similarly to the conducting ground plane 14 in Fig. 1B), in addition to short-circuiting conductors 221 to 224.

Reference numerals 231 to 234 are feeding points feeding through feeders not shown. The short-circuiting conductors 281 to 284 shown to be pin-type but may also be replaced by short-circuiting plates, solder, or electrolytic plating. With the shortcircuiting pins, a microstrip antenna of excellent impedance matching can easily be implemented. When the influence of mutual coupling is present, the axial ratio may sometimes be degraded, but the provision of the short-circuiting pins permits correction of phase, and hence makes it possible to obtain a microstrip antenna of an excellent axial ratio.

Fig. 3A illustrates another embodiment in which the radiation conductors 111 to 114 in the embodiment shown in Figs 1A and B are partly cut away to provide radiation conductors 311 to 314. The present invention is also applicable to such radiation conductors. In this case, reference numerals 331 to 334 are feeding points feeding from its back side by feeders not shown; and 35 a dielectric plate.

Fig. 3B illustrates another embodiment in which short circuiting pins 381 to 384 are provided in the embodiment shown in Fig 3A. The present invention is equally applicable to such a configuration.

As described above, according to the present invention, a small, lightweight and easy-to-manufacture microstrip antenna which is capable of simultaneously transmitting and receiving circularly polarized waves of two frequencies can be implemented by arranging two pairs of one side shorted microstrip antennas of different sizes, that is, a total of four microstrip antennas, on the same plane.

By employing such an antenna as one element of a phased array antenna, a small, two-frequency separate feeding type antenna for circularly polarized waves, which has a wide-angle radiation characteristic, can be implemented on the same plane.

Incidentally, if the short-circuiting sides of the microstrip antenna by electrolytic plating or the like, then the antenna according to the present invention could easily be fabricated through use of a conventional printed-board manufacturing step.

Claims

CLAIMS:

1. A microstrip antenna of two-frequency separate-feeding type for circularly polarized waves in which four radiation conductors are disposed on a dielectric plate mounted on a conducting ground plane and each radiation conductor has its marginal portion partly short-circuited via a shortcircuiting conductor to the conducting ground plane and is supplied at its feeding point with power via a feeder passing through the conducting ground plane and the dielectric plate, and in which the four radiation conductors are composed of two pairs of radiation conductors of different sizes adjusted so that two desired frequencies can simultaneously be used for transmission and for reception, respectively, the conductors of each pair being arranged to generate a circularly polarized wave.

2. A microstrip antenna of two-frequency separate-feeding type according to claim 1, wherein each of the four radiation conductors is provided with shortcircuiting means whereby a portion of the radiation conductor adjacent other portion thereof short-circuited by the short-circuiting conductor is shortcircuited to the conducting ground plane at a position different from that of the short-circuiting conductor.

3. A microstrip antenna of two-frequency separate-feeding type according to claim 2, characterized in that the shortcircuiting means is one or more short-circuiting pins.

4. A microstrip antenna of two-frequency separate-feeding type according to claim 2, characterized in that the shortcircuiting means is provided by soldering or electrolytic plating in a plurality of through holes extending through the radiation conductors and the conducting ground plane.

5. A microstrip antenna of two-frequency feeding type for circularly polarized waves substantially as herein described with reference to Figure 1A and B with or without reference to any of Figures 2 to 4B of the accompanying drawings.

6. A transmitting-receiving equipment comprising a microstrip antenna according to any preceeding claim.

7. A phased array antenna comprising a plurality of microstrip antennas according to any of claims 1 to 5.