JPS6243906A - Microstrip antenna - Google Patents

Abstract

PURPOSE:To attain a broad band for an applied frequency band as an antenna by causing impedance mismatching between a radiation element formed by a microstrip pattern and a feeding circuit to the element. CONSTITUTION:A circular conductor pattern of a diameter 64.72mm as the radiation element 2 is formed on the surface of a 'Teflon(R)' base 1 in a thickness of 4mm and a conductor pattern 3 as an earth is formed to the entire rear face to constitute a radiator 4. Then an antenna feeding circuit 9 where a full face earth pattern 6 is formed on one face of a 'Teflon(R)' base 5 in a thickness of 0.8mm and a 3dB hybrid circuit 7 comprising the microstrip line pattern and an impedance matching circuit 8 are formed on the other side, and the radiation element 2 of the radiator 4 are overlapped while contacting the earth faces 3 and 6. Then the impedance of the radiator input and the feeding circuit output are made different by intention, the transmission characteristic of the impedance conversion circuit of the strip line is lowered slightly to cause slight mismatching thereby ensuring a broad band.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a microstrip antenna, and particularly to a microstrip antenna that achieves a wide band in a circularly polarized wave system.

(Prior art) Microstrip antenna (Micro 5trip
Antenna (hereinafter abbreviated as M 8 A) is a transmitting/receiving antenna that utilizes the radiation loss of a planar circuit, and its structure has the advantages of being thin and lightweight, and the antenna button has a low profile. In the 8HF band to 8HF band, it is attracting attention especially as an antenna mounted on an aircraft or the like, or as an antenna for receiving television broadcasting via a satellite.

However, in principle, MSA has an extremely narrow frequency band as an antenna, and widening the frequency band is an important issue in order to use it as an antenna for each of the above-mentioned systems.

Various proposals have been made in the past as methods for widening the band, but they can be roughly divided into those that aim to widen the band of the antenna element itself, and those that aim to widen the band by arranging multiple elements and combining their signals.

Of the two, methods using multi-element arrays can relatively easily achieve a wide band, but have the drawbacks of complicated control and large size, making them unsuitable for installation on aircraft, and requiring the antenna elements themselves to have a wide band. be.

In general, the frequency bandwidth BW of an MSA is calculated using the following formula (8%). However, BW: Antenna frequency band S: Standing wave ratio Q at the antenna feeding point: Given by the Q factor of the antenna element itself, increasing the bandwidth BW For this purpose, the Q factor of the antenna element itself can be reduced.

It is also known that the Q of M8A is proportional to the dielectric constant (sr) of the substrate and inversely proportional to the thickness of the substrate, that is, the distance between the antenna baton and the ground plate.

Therefore, based on this theory, as a method for widening the band of conventional MSA, a paper honeycomb plate is inserted between the antenna baton and the ground plate to reduce the weight, lower the dielectric constant of the substrate, and increase its thickness. It has been proposed to increase the antenna frequency band by decreasing Q'.

Figure 4 (al) is a diagram showing a specific structural example of a circularly polarized MSA using a conventional paper honeycomb substrate, and the results of evaluating its characteristics, especially impedance matching, in terms of return loss (dB) are shown in the figure. (It is bl.

That is, the usage conditions for this antenna are that the reception frequency band is 1.
545 (G) Iz) ~ 1.650 (mlz), the transmission frequency is 1.647 ((3) - h) ~ 1.650 (Gll
z), that is, about 100 (M
It is designed as an antenna for use in the frequency band llz), and the dimensions of each part are as shown in the figure.

The return loss (TLL) of an antenna is the ratio of the reflected power to the power supplied to the radiating element, and the relationship between this and the commonly used standing wave ratio of 8 (8WR) is expressed by the following equation, as is well known. It will be done.

R,L = -101og(8-1/S+t)"
(dB) -・-=121 As is clear from the same figure, the conventional microstrip antenna using a honeycomb substrate has a litter of 7 ox -33 dB (S?1) at the center frequency f o = 1.6 (OHz). .05), but near both ends of the desired band (1,545 to 1.650 GHz) there is a large difference of V-10 dB (S!-12), making it impossible to obtain uniform and sufficient characteristics within the desired band. It was something.

Furthermore, if the thickness of the paper honeycomb substrate is increased, it becomes difficult to obtain stable characteristics due to the influence of higher-order modes. In wave antennas, the axial ratio characteristic, which is an important factor in circularly polarized antennas, deteriorates.

Therefore, not only is there a limit to the substrate thickness in a method using such paper honeycomb material, but also the wavelength shortening ratio on the microstrip is naturally reduced due to the lower dielectric constant of the substrate material. This also comes with the secondary disadvantage that the antenna volume at the same frequency is increased due to the increased size of the antenna panel and thickened substrate.

(Object of the invention) The present invention was made in view of the above-mentioned nine circumstances, and includes:
The purpose of the present invention is to provide an MSA with an improved frequency bandwidth without impairing the original characteristics of M8A, such as being thin, small, lightweight, and having a low profile. An impedance mismatch is created between the radiating element (antenna element) formed by the antenna element and a feeding circuit for the element, thereby widening the applicable frequency band as an antenna.

(Example) The present invention will be described in detail below based on an illustrated example.

FIG. 1 (at and (b)) shows a circularly polarized MSA according to the present invention.
It is a substrate with a diameter of 64 mm on its surface as a radiating element 2.
A radiator 4t is constructed by forming a circular conductive button with a length of 72 m (designed at f o = 1.5975 GHz) and a conductive pattern 3 as a ground on the entire back surface thereof.

Similarly, 5 is a Teflon substrate with a thickness h = 0.8 m, with a full-surface grounding button 6 on one side and a branch line type 3 (I B hybrid circuit 7) with a microstrip line pattern on the other side. An antenna feeding circuit 9 formed with an impedance matching circuit 8,
The feeding circuit 9 and the radiating element 2 of the radiator 4 are overlapped with their respective ground planes 3 and 6 in contact with each other, and a terminating resistor 11 is connected to one of the two input terminals IO of the feeding circuit 9. The other end 12t is used as the input/output end of the antenna, and the two output ends 13 and 14 are provided with a bottle 15 that passes through the respective substrates 1, 5 and the ground button 3.6.
．． A microstrip antenna is constructed by connecting it to a desired position of the radiating element 2 formed on the opposite surface of the radiator 4 via 16'i.

At this time, the through-hole pins 15 and 16 and the ground pattern of each board
3 and 6, and the feeding point to the radiating element 2 is set at an advantageous point (offset point) where the input impedance is 1000.

When viewed from the side of the above-mentioned microstrip annular column, it is as shown in FIG. 1 (bl).

The 3 dB hybrid circuit 7 can be easily obtained based on conventionally known techniques, so a detailed explanation will be omitted. For example, as shown in FIG.
12 The input impedance of both sides is 500, and the output signals appearing at the two output terminals 13 and 14 are patterned symmetrically about their central axes so that their levels are divided into two and have a phase difference of 90° from each other. Bye.

In this case, the important thing is that the difference in the matching state between the impedance Zout of the output terminal 13.14 of the hybrid circuit 7 and the input impedance ZR of the radiating element 2 of the antenna radiator 4 is extremely It makes a big difference.

That is, when trying to match the input impedance ZR of 100Ω of the radiating element 2 as described above and the output power/beadance of 50Ω of the 3dB hybrid circuit 7, conventionally, a strip line with a length of 70.70Ω is used as shown in FIG. 1 (dl). After 500 to 1000 impedance conversion by
00Ω stripline is added, and the input impedance of the radiating element 2 to be fed on the microstrip line, that is, the feeding point impedance ZR (=1000)
After converting to , power was supplied.

The reason for this is the characteristic impedance MS of the strip line.
This seems to be because the physical characteristics are different from the feeding point impedance of the radiating element 2 in A.

In other words, the characteristic impedance of a microstrip line does not theoretically change with frequency, but the feeding point impedance of a radiating element has meaning only at its resonant frequency.

Therefore, when attempting impedance matching in such an antenna in the past, it seems that a matching circuit as shown in FIG. 1 (dl) was used based on the knowledge of the above-mentioned reasons from experience.

In other words, it is common sense to make the impedance of the radiator input and the feed circuit output as similar as possible at the feeding point of the antenna, to stabilize the transmission characteristics of the strip line impedance conversion circuit, and to achieve ideal matching. As mentioned above, attempts have been made to reduce Qt by reducing other elements, such as the dielectric constant (εγ) of the substrate material, in order to create a broadband antenna.

The present invention focuses on this point, and intentionally shifts the impedance of the radiator input and feeder circuit output, slightly lowering the transmission characteristics of the stripline impedance conversion circuit and creating a slight mismatch. It is closed.

That is, the hybrid circuit 7 in FIG. 1 (3 dB of cl)
is 70. to convert from 500 to 1000 at the output end.
70 strip lines λg/4 length (λg is substrate wavelength)
How to directly feed power to the radiating element 2 of the radiator 4 by simply adding ? I took it.

This is the impedance (Zin) of the 3dB hybrid circuit 7 of 50Ω and the impedance of the radiator (ZR).
100Ω, and as is well known, Z o = v' - stone 1 capacity = V15000' - = 70
．． 7p...Z calculated based on the formula (3)
λg/ where o (=70.70) is the characteristic impedance
4 length strip line impedance conversion circuit i3
It is inserted between the dB hybrid circuit and the radiating element.

If such a feeding circuit is used to construct the microstrip antenna shown in FIG. It is possible to obtain wideband antenna characteristics as shown by the solid line in FIG. 2 due to a slight mismatch that differs from the normal type of dl in FIG.

For reference, the same figure shows the return loss characteristics of a similar microstrip antenna using the conventional feeder circuit shown in FIG. 1 (dl) by a broken line.

According to the figure, the difference in the applicable bandwidth of both antennas is clear, and the microstrip antenna MSA according to the present invention can obtain an extremely wide applicable frequency band compared to the conventional antenna.

Furthermore, as shown in Fig. 3, the axial ratio characteristic in the boresight direction of the antenna according to this embodiment is less than 1 over a wide range of about 100 MHz from 1.54 GHz to 1.65 GHz, so it is different from that of the conventional honeycomb substrate. It is clear that this antenna has better axial ratio characteristics than that of the antenna of 2000, and can be used in practical use as a wideband antenna.

In the above-described embodiment, it is important to note that the presence of the through-hole 15.16 interposed between the two output ends 13.14 of the feed circuit 9 and the feed point of the radiating element 2 has some characteristics. It is to have an impact on the

That is, the penetrating pins 15 and 16 are simply conductive rods of about 5n that pass through the radiator 40 board.

Since it slightly disturbs the impedance, this should be considered in the impedance mismatch at the feeding point of the radiating element, which is deliberately caused in the present invention.

Although various embodiments of the present invention are conceivable in addition to the embodiments described above, the key point is to widen the applicable frequency band by making the input/output impedance of the antenna radiator input and the feeder circuit output slightly different. Any means may be used as long as it can be used, so there is no need to explain that it can be applied to all types of antenna devices.

(Effects of the Invention) Since the present invention is configured as described above, it is extremely effective in achieving a wide band using an extremely simple method without impairing the characteristics of the thin and low-profile MSA.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, in which (a) is a plan view, (b) is a side view, (C) and (dl are 3 dB hybrid circuit button diagrams, and FIGS. The figure shows actual measurement results of an embodiment of the MSA of the present invention, and Fig. 4 (al and (b)) shows the external structure of the conventional MSA and its characteristic diagram.・・・・－Conductive button for ground, ４．・・・－・－Radiator, ７．・・・－・
....3dB hybrid circuit, 8-.Bright...matching circuit. 9...--Power supply circuit, 15 and 16...
・−・・Through-through bottle. Patent applicant Toyo Tsushinki Co., Ltd. Freq, CQsz) ('Io')

Claims (2)

[Claims] (1) A microstrip antenna characterized in that its frequency characteristics are broadened by slightly shifting the impedance matching between the feeding point of the radiating element of the microstrip antenna and the feeding circuit. (2) Claim 1 characterized in that the applicable frequency band of the antenna is arbitrarily set by appropriately changing the impedance mismatch state.
Microstrip antenna as described in section.