The proposed tunable compact tag antenna is designed according to these requirements. The PIFA antenna design makes the antenna compact than normal microstrip antenna. With an open stub feed, the antenna can be conjugate impedance matched with the chip easily by tuning the inset depth and the open stub length [ 15 ].
Moreover, with the open stub as tuning structure, the working frequency of the tag can be tuned even after the tag has been manufactured. The antenna bandwidth, radiation pattern, and metal stability also keep with good performance. The structure and dimensions of the proposed antenna are illustrated in Figure 2. It is a planar inverted antenna with a shorting wall to reduce size. The radiation patch has dimensions of 20?
The open stub feed line is inset into the patch to decrease the input impedance of the patch [ 27 ]. The inset structure has a length of and a width of 8? The open stub feed line has a length of and a width of 3? The chip is attached on the feed port composed by the open stub line and the radiation patch.
The antenna is attached on a ? The parameters and are used as variables for impedance matching. The transmission line model of the antenna is shown in Figure 3. From the antenna model, it is easy to know that the radiation patch and the CPW open stub feed lines are in series.
Therefore, the input impedance of the feed port of the antenna can be calculated as where is the input impedance of the radiation patch of the PIFA antenna, is the input impedance of the CPW open stub feed line. According to the basic RF circuit theory [ 28 ], the input impedance of the open stub can be simplified as where is the characteristic impedance of the CPW open stub feed line, is the wave number, is the length of the CPW open stub feed line.
The input impedance of the open stub only has imaginary part and its function of line length is shown in Figure 4.
It shows that the reactance of the CPW open stub feed line is capacitive when the length is less than 0. The reactance of the CPW open stub is a function of cotangent, which means that when the length of the open stub changes from 0 to 0. Therefore, the imaginary part of the input impedance of the antenna can be tuned freely by the length of the open stub in a large scale. For the UHF RFID tags, the chips generally have complex impedance, whose imaginary part is large and negative because of the rectifier and energy storage capacitor.
In order to achieve the maximum energy transfer between the antenna and the chip, the input impedance of the antenna and the chip should be conjugate matching.
That is, the real part is equal, and the imaginary part is opposite. As the imaginary part is much larger than the real part of the impedance, the impedance matching is mainly determined by the imaginary part matching.
So, the antenna should be designed to have a structure easy for impedance tuning, especially for imaginary part tuning. MHz , the tag antenna should have good impedance matching at this bandwidth. O at the frequency of ? The structure of the antenna is shown in Figure 2.
According to the relative permittivity of the substrate, the length of the radiation patch of the PIFA antenna is chosen as 37? The impedance matching between the antenna and the chip is tuned by and. For patch antennas with the inset feed structure, increasing the depth of the inset could decrease the input impedance of the antenna [ 27 ]. Therefore, the length of the inset can be used to tune the real part of the antenna impedance. Figure 5 a shows the resistance tuning of the proposed antenna with different inset depths.
The resistance of the antenna decreases with the increase of the inset depth. As we analyze above, the CPW open stub feed line can be used to tune the imaginary part of the input impedance of the antenna, which is shown in Figure 5 b. The reactance of the antenna increases with the increases of the CPW open stub length. The imaginary part of the input impedance of the antenna could be tuned freely from to by changing the length of the CPW open stub from 0 to 0.
Therefore, for conjugate impedance matching of the proposal antenna, the resistance and the reactance could be tuned freely by the depth of the inset and the length of the CPW open stub , respectively.
Through simulation and optimization, the parameters of the antenna are finalized as? With this dimension, the antenna input impedance and the reflection coefficient are calculated as shown in Figures 6 a and 6 b , respectively. The imaginary parts of the impedance of the antenna and the chip are matched well at the frequency of ? And the real parts of the impedance are matched at the frequency of ? However, as the imaginary part of the impedance is much larger than the real part, the impedance matching is dominated by the imaginary part.
Under this matching condition, the reflection coefficient is located at the ? MHz with a value of ? The 3? MHz ? Moreover, with the decreases of the length of the open stub, the working frequency of the antenna is tuned from low to high. Based on the above-optimized parameters, the antenna sample was produced with an FR4 dielectric plate, as shown in Figure 7. The chip was attached to the antenna feed port with the traditional bonding technology. The bandwidth of the reader is ?
The output power of the reader can be tuned from 15? The antenna of the reader is CSR with a gain of 6? Combining the output power of the reader and the reader antenna gain, the maximum radiation power is 36? W EIRP. According to the tag performance parameters and test methods of EPCglobal, the performance of the tag was measured based on the back-scattering method [ 30 ].
The proposed antenna was verified through both electromagnetic simulation and measurement which indicate that it presents very good impedance matching, stable radiation patterns and good gain within the tuning bandwidth. AB - This paper presents a reconfigurable microstrip patch antenna for cognitive radio applications.
Tunable slot-loaded patch antenna for cognitive radio G. Mansour, P. Hall, P. Polski English Login or register account. Sheta, A. Abstract In this letter, we propose a tunable patch antenna made of a slotted rectangular patch loaded by a number of posts close to the patch edge. The posts are short circuited to the ground plane via a set of PIN diode switches. Simulations and measurements verify the possibility of tuning the antenna in subbands from to MHz.
Good matching has been achieved over most of the bands. Other performed designs show that more than one octave can be achieved using the proposed structure. Authors Close. Assign yourself or invite other person as author. Two rings of segmented concentric tuning strips and are used to lower the resonant frequency of the antenna Another configuration of a circular antenna including the present invention is shown in FIG.
The antenna has a central feed and concentric tuning rings and surrounding the patch The antenna therefore has no means to vary the polarization or the antenna pattern, the tuning rings and only being useful in reducing the resonant frequency of the antenna The antenna of FIG.
The feeds , and can be fed out of phase or fed all in the same phase so that they act like a center feed. Note that the upper sides of the triangular patch have associated single tuning strips and while two tuning strips and are provided at the lower edge This configuration would be used if low frequencies are only required with a directed antenna pattern. The antenna shown in FIG. Substrate can be a semiconductor or other material, including circuit-board material such as alumina.
Substrate is disposed over a ground plane A coaxial or microstrip feedpoint terminates on one of the plates and thereby provides a feed for RF energy to the antenna In order to not obscure the invention, the control lines and the bias lines to the switches are not shown.
With suitable means of addressing and controlling the individual MEMS switches, using techniques adapted from U. It should be noted that the drawing in FIG. Certain aspects of such fine tuning will be described hereinbelow. While the plates shown in FIG.
For example, the length of each plate may depend on its distance from the center of the segmented patch. Additionally, while only one feedpoint is shown in FIG. For example, a dual polarized antenna can be constructed with antenna that has two feed points.
It should be noted that, with appropriate control, certain of plates can be coupled to non-adjacent plates. In this regard, although FIG. From this observation, it should be appreciated that the plates can be coupled together using switches to make both a patch from a fraction of the plates and tuning strips displaced from the patch using certain of the remaining fraction of the plates. For example, plate a can be coupled to plate a and the plates in column can be connected to each other to form the outer edge of a patch or alternatively plate a and the other plates in column can be connected to each other to form the outer edge of a patch.
For example, plate b can be coupled to plate b via an appropriate connector. Further, plate c can be coupled to plate c via an appropriate connector. In this manner, plates can singly or in pairs be used for fine control.
Alternatively, various numbers of plates in column can be coupled together or various numbers of plates in column can be coupled together.
While in the description provided above, the patch and the tuning strips have straight edges, it should be appreciated that patches and tuning strips that are roughly arcuate in shape are encompassed by the teachings of this invention. For example, a patch can be in the general shape of a circle or an ellipse or some other curved shape.
A tuning strip can be in the general shape of a ring or arcuate segments. For example, as shown in FIG. It should be appreciated that the patches connected to the feed point are distributed more along the x-axis, resulting in a corresponding polarization in the x direction for the dominant mode. The operating frequency and input impedance are the same as in the configuration described in connection with FIG. Consequently, an elliptical polarization results.
It should be appreciated that a circular polarization is also possible and that many other possible configurations are possible. By selectively disconnecting patches so as to create a gap or slot within a patch network, the operating frequency can be raised or lowered relative to the original network.
Further, fine tuning of polarization in the y direction is also achieved. This technique can be used with any of the preceding FIGS.
RF energy is fed into antenna through feed The direction of the dominant mode electric field is from ground plane up to PIFA lid , and standing waves run the length of the lid , between shorting wall and radiating aperture One of ordinary skill in the art would understand that the PIFA lid, shorting wall and feed can be together considered a radiating element, but a PIFA is typically used with a truncated ground plane, not much larger than the lid, in which case, the whole combination is the radiating element.
It should be noted that FIG. However, other alternatives to the shorting wall shown in FIG. For example, the wall need not be the same length as the edge of the lid to which it is coupled. As another example, the shorting element may be comprised of a plated through hole or via through the antenna dielectric layer that acts as a shorting pin between the lid and the ground plane.
Referring back to FIG. While in the description provided in connection with FIG. In a further alternative using patch segments, in place of a shorting wall, a shorting pin comprised of a via or plated through hole can be coupled between the ground plane and an arbitrary one of the patch segments. It should be further noted that, although the tuning strips in FIG. For example, 3 patches of relative areas 1 , 2 , and 4 as shown in FIG. For this, the smallest patch is selected to create a first small frequency shift, the next larger patch creates a larger shift, and the combination of these two results in an even larger shift, and so on.
This arrangement provides certain additional advantages over the previously described tuning strips, such as simplified tuning and control.
Thus, there has been shown and described novel antennas which fulfill all of the objects and advantages sought therefor. Many changes, alterations, modifications and other uses and application of the subject antennas will become apparent to those skilled in the art after considering the specification together with the accompanying drawings.
All such changes, alterations and modifications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow. What is claimed is: 1. An antenna including:. The antenna as defined in claim 1 wherein the at least two patch segments are disposed along an axis with certain other of the patch segments in between them.
The antenna as defined in claim 1 , wherein the patch segments are coupled to achieve a desired resonant frequency for the antenna. The antenna as defined in claim 1 , wherein the patch segments are coupled to achieve a desired input impedance to the antenna.
The antenna as defined in claim 1 , wherein the patch segments are coupled to achieve a desired polarization for the antenna. The antenna as defined in claim 7 wherein the patch segments are spaced from each other by distances that increase in accordance with increasing distances of said patch segments from a point within the segmented patch, and wherein said first and second side surfaces of said dielectric layer are parallel.
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