1. Field of the Invention
The present invention generally relates to an antenna and bandwidth increasing and resonant frequency tuning method thereof.
2. Description of the Prior Art
Dielectric resonators made of low-loss and high-permittivity material have been used to implement antenna. They have higher radiation efficiency than printed antennas at higher frequency due to the absence of ohmic loss and surface wave, in addition to compact size, light weight, and low cost.
Many efforts have been devoted to developing multi-band or wideband DRAs. For example, make the feeding aperture radiate like a slot antenna to incur another band, induce parasitic effects with attached metal strips.
In [C. S. D. Young and S. A. Long, “Investigation of dual mode wideband rectangular and cylindrical dielectric resonator antennas,” IEEE APS Int. Symp., vol. 4, pp. 210-213, July 2005.], specific higher-order modes with the electric field distribution on the top surface of the DR similar to that of the fundamental mode are intentionally excited. In [A. A. Kishk, “Wide-band truncated tetrahedron dielectric resonator antenna excited by a coaxial probe,” IEEE Trans. Antennas Propag., vol. 51, no. 10, pp. 2913-2917, October 2003.] and [A. A. Kishk, Y. Yin, and A. W. Glisson, “Conical dielectric resonator antennas for wide-band applications,” IEEE Trans. Antennas Propag., vol. 50, no. 5, pp. 469-474, April 2002.], higher-order modes of truncated conical or tetrahedral DR are excited to obtain wide impedance bandwidth.
DRs of different sizes have been placed vertically to form a stacked DRA, or at close proximity to form a multi-element DRA to attain wideband or dual-band features.
Therefore, in accordance with the previous summary, objects, features and advantages of the present disclosure will become apparent to one skilled in the art from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.
An antenna and resonant frequency tuning method thereof are disclosed. The antenna comprises a substrate, a microstrip line, a ground plane and a resonator structure. The microstrip line and the ground plane are formed on the opposite surfaces of the substrate, and the ground plane comprises an aperture. The resonator structure is placed on the ground plane, and a first resonator and a second resonator of the resonator structure are separated by a gap, wherein the first resonator comprises a first bottom surface and a first side surface, and the second resonator comprises a second bottom surface and a second side surface. The resonant frequency of the TE111y mode of the antenna can be tuned by adjusting the width of the gap, and the bandwidth can be increased by increasing the width of the gap.
A first tunnel is engraved at the corner where the gap and the first bottom surface meet, and a second tunnel is engraved at the corner where the gap and the second bottom surface meet, wherein the resonant frequency of the TE112y mode of the antenna can be tuned by adjusting the dimensions and the positions of the first and second tunnel. Moreover, a first notch is engraved at the first side surface, and a second notch is engraved at the second side surface, wherein the bandwidth of the TE111y, TE112y and TE113y modes of the antenna can be increased by adjusting the dimensions and the positions of the first and second notch. Signals can be transmitted via the microstrip line, the aperture and the resonator structure in turn.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the disclosure. In the drawings:
The present disclosure can be described by the embodiments given below. It is understood, however, that the embodiments below are not necessarily limitations to the present disclosure, but are used to a typical implementation of the invention.
Having summarized various aspects of the present invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims.
It is noted that the drawings presented herein have been provided to illustrate certain features and aspects of embodiments of the invention. It will be appreciated from the description provided herein that a variety of alternative embodiments and implementations may be realized, consistent with the scope and spirit of the present invention.
It is also noted that the drawings presented herein are not consistent with the same scale. Some scales of some components are not proportional to the scales of other components in order to provide comprehensive descriptions and emphases to this present invention.
In this invention, a dual-band DRA (Dielectric Resonator Antenna) is proposed by splitting a rectilinear DR evenly. The electric field over the gap in between is significantly enhanced, hence reducing the Q-factor. Two notches are also engraved in each piece to tune the resonant frequencies and increase the impedance bandwidth as well. The effect of the gap and notches on the resonant frequencies are carefully disclosed, and the resonant bands associated with the TE111y and TE113y modes can be adjusted to cover the WiMAX (3.3-3.7 GHz) and the WLAN (5.15-5.35 GHz) bands.
The resonant frequency is mainly determined by the dimensions a, b, d and permittivity ∈0∈r of the resonators 150, 170. The carved notches change the electric field distribution in the original resonators 150, 170, hence the resonant frequencies. Since the gap 142 is perpendicular to the electric field of the TE111y mode of the otherwise intact resonators 150, 170, the electric field is enhanced within the gap 142. Thus, the resonant frequency of the TE111y mode and impedance are significantly affected. The input impedance can be fine tuned by adjusting the resonator offset ds, the length of the extended microstrip line 120, and the aperture 132 length La.
The electric field Ē0 and the magnetic field
−∇×Ē0=jω0μ
∇×
where ω0 is the resonant frequency. When the shape of dielectric resonator is modified by engraving gap 142, tunnels 156, 176, and notches 158, 178, the dielectric constant in the space V becomes a function of location ∈′(
which indicates that the resonant frequency is affected by the reaction between the field distributions of the original and the modified DR structures. It also implies that the resonant frequency can be more accurately predicted if the perturbed field can be approximated with reasonable accuracy. For example, if a small gap is carved off a DR, the electric field normal to the air-dielectric interface will be significantly enhanced, which can be observed by simulation.
A DR of dimension d×b×a on an infinite ground plane can be viewed as a single block of rectangular dielectric with height 2d in free space, as shown in
where A is an arbitrary constant, kx=π/2d, kz=mπ/a, and ky is determined from [Y. M. M. Antar, D. Cheng, G. Seguin, B. Henry, and M. G. Keller, “Modified waveguide model (MWGM) for rectangular resonator antenna (DRA),” Microwave Opt. Tech. Lett., vol. 19, no. 2 pp. 158-160, October 1998.]
The resonant frequency can thus be calculated as
The field expressions of the TE11ny modes with even n can be derived as
where B is an arbitrary constant, kx=π/2d, kz=nπ/a, ky and the resonant frequency can be determined from (5) and (6), respectively.
By image theory, the structure in
E
z
=m
1
k
x
A sin(kxx)cos(kyy)cos(kzp/2)
Ex=Ey≅0
{tilde over (H)}={tilde over (H)}0 (8)
Note that the Ez component is enhanced by a factor m1. For the TE111y mode, m1 approaches ∈r as the gap 142 width is very small. For the TE111y mode, it is observed that the E component is only slightly enhanced, incurring a small m1 of about 2 to 3. Hence, the resonant frequency of the TE113y mode is slightly increased. In contrast, the fields of the TE112y modes in the air gap 142 are approximately
E
x
=k
x
B cos(kyy)cos(kxx)
Ez=Ey≅0
{tilde over (H)}={tilde over (H)}0 (9)
Substituting (4), (8) with kz=π/a and kz=3π/a, respectively, into (3), the resonant frequencies of the TE111y and TE113y modes can be estimated. Substituting (7), (9) with kz=2π/a into (3), the resonant frequency of the TE112y mode can be estimated.
The radiation patterns can be determined from the tangential electric fields on the DR surfaces. Since the electric field distribution of the TE112y mode, Ez∝ sin(2πz/a), has opposite directions on different portions of the DR top surface, a null in the E0 pattern occurs in the {circumflex over (x)}-direction. The resonant frequencies of the TE111y and TE112y modes move closer as p is increased, and the two bands are merged at p=0.5 mm. However, due to the difference of radiation pattern, it is preferred to separate the band associated with the TE112y mode from that with the TE111y mode.
Based on (3), the resonant frequency of the TE112y mode can be shifted away from that of the TE111y mode if an air tunnel 146 is engraved at where the electric field of the TE112y mode is strong while that of the TE111y mode is negligible. As shown in
As for the TE112y mode, the tunnel 146 is located at where the electric field reaches the maximum. The Ex component is enhanced in the tunnel 146, and can be approximated as
E
x
=k
z
αB cos(kxd1)cos(kyy)cos(βz)
Ez=Ey≅0
{tilde over (H)}={tilde over (H)}0 (10)
Substituting (7), (10) with kz=2π/a into (3), the resonant frequency shift of the TE112y mode is predicted. The tunnel 146 has stronger effect on the resonant frequency of the TE112y mode than that of the TE111y and TE113y modes. It is observed that the Ex is strongly enhanced by a fold as the tunnel 146 is thin. The resonant frequency fr of the TE112y mode is 3.646 GHz.
Since the Ex component of the TE111y, T112y and TE113y modes reaches maximum at z=±a/2, their resonant frequencies should be affected by notches 158, 178 near z=±a/2.
By image theory, the grounded resonator structure 140 with two notches 158, 178 is equivalent to an isolated DR with four notches on its edges. First consider only one notch, the second notch 178, of dimensions d2×b×s2 engraved off the resonator structure 140 in free space, as shown in
E
x
=−k
z
αB cos(kxd1)cos(kyy)cos(βz),
for TE111y and TE113y modes (11)
E
x
=m
2
k
z
B cos(kxd1)cos(kyy)cos(kzz),
for TE112y mode (12)
With d2=4 mm, m2 is about 1.5. Substituting (4) and (11) into (3), the resonant frequencies of the DR with notches is obtained.
The design begins with a rectangular DR of dimension 10 mm×9 mm×29 mm, ds=7 mm, Ls=8 mm, Wa=2 mm and La=10 mm. The resonant frequencies of the TE111y, TE112y, and TE113y modes are 2.92 GHz, 3.58 GHz, and 4.62 GHz, respectively. In order to tune the resonant frequencies of the TE111y and TE113y modes to cover the WiMax (3.4-3.7 GHz) and the WLAN (5.15-5.35 GHz) bands, the resonator structure 140 is modified to the shape as shown in
The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Hence, an antenna 100 disclosed in the present invention can comprise a substrate 110, a microstrip line 120, a ground plane 130 and a resonator structure 140. The microstrip line 120 and the ground plane 130 are formed on the opposite surfaces of the substrate 110, and the ground plane 130 comprises an aperture 132. The resonator structure 140 is placed on the ground plane 130, and a first resonator 150 and a second resonator 170 of the resonator structure 140 are separated by a gap 142.
Referring to
When radio signals are input via the microstrip line 120, radio signals can be coupled to the resonator structure 140 through the aperture 132. The electric field over the gap 142 is enhanced to radiate the radio signals more efficiently, reducing the Q-factor and increasing the bandwidth because the flux density at the interface between the dielectric resonator structure 140 and the air must be continuous, and the permittivity of the dielectric resonator structure 140 is much higher than that of the air. Hence, the width of the gap 142 can be adjusted to tune the resonant frequency of the TE111y mode of the antenna 100 for covering the WiMax (3.3-3.7 GHz) and the WLAN (5.15-5.35 GHz) bands, as shown in
Similarly, a first tunnel 156 can be engraved at the corner where the gap 142 and the first bottom surface 152 meet, and a second tunnel 176 can be engraved at the corner where the gap 142 and the second bottom surface 172 meet, as shown in
Referring
Referring
Referring
By combining the gap 142 with the first tunnel 156 and the second tunnel 176, the resonant frequencies of the TE111y and TE112y modes of the antenna 100 can be tuned, and the bandwidth of the TE111y and TE112y modes of the antenna 100 can be increased. By combining the gap 142 with the first tunnel 156, the second tunnel 176, the first notch 158 and the second notch 178, the resonant frequencies of the TE111y, TE112y and TE113y modes of the antenna 100 can be tuned, and the bandwidth of the TE111y, TE112y and TE113y modes of the antenna 100 can be increased. In addition, the resonant frequencies of the antenna 100 can be tuned by adjusting the dimensions of the resonator structure 140.
Referring to
To cover the WiMAX and the WLAN bands, the resonant frequencies of the TE111y and TE113y modes of the antenna 100 are adjusted to cover 3.375-3.93 GHz and 5.08-5.415 GHz, with a=28 mm, b=9 mm, d=10 mm, p=1 mm, d1=4 mm, s1=2 mm, d2=4 mm, s2=2 mm, ∈r=20, ωa=2 mm, La=10 mm, Ls=2.5 mm, ds=4 mm, Wg=Lg=70 mm, t=0.6 mm and ωm=1.15 mm.
According to the above-mentioned, the electric field distributions vary with the resonant modes. Hence, the resonant frequencies of different modes can be adjusted to cover the required bandwidth or remove the non-applicable bandwidth due to notches and tunnels engraved at the resonator structure. Referring to
Referring to
The foregoing description is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. In this regard, the embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the inventions as determined by the appended claims when interpreted in accordance with the breath to which they are fairly and legally entitled.
It is understood that several modifications, changes, and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.