Design of compact reconfigurable ultra‐wideband slot antenna with switchable single/dual band notch functions
2014; Institution of Engineering and Technology; Volume: 8; Issue: 8 Linguagem: Inglês
10.1049/iet-map.2013.0311
ISSN1751-8733
AutoresBahareh Badamchi, Javad Nourinia, Changiz Ghobadi, A. Valizade,
Tópico(s)Microwave Engineering and Waveguides
ResumoIET Microwaves, Antennas & PropagationVolume 8, Issue 8 p. 541-548 ArticleFree Access Design of compact reconfigurable ultra-wideband slot antenna with switchable single/dual band notch functions Bahareh Badamchi, Bahareh Badamchi Department of Electrical Engineering, Urmia University, Urmia, IranSearch for more papers by this authorJavad Nourinia, Javad Nourinia Department of Electrical Engineering, Urmia University, Urmia, IranSearch for more papers by this authorChangiz Ghobadi, Changiz Ghobadi Department of Electrical Engineering, Urmia University, Urmia, IranSearch for more papers by this authorArash Valizade Shahmirzadi, Corresponding Author Arash Valizade Shahmirzadi [email protected] Young Researchers Club, Qaemshahr Branch, Islamic Azad University, Qaemshahr, IranSearch for more papers by this author Bahareh Badamchi, Bahareh Badamchi Department of Electrical Engineering, Urmia University, Urmia, IranSearch for more papers by this authorJavad Nourinia, Javad Nourinia Department of Electrical Engineering, Urmia University, Urmia, IranSearch for more papers by this authorChangiz Ghobadi, Changiz Ghobadi Department of Electrical Engineering, Urmia University, Urmia, IranSearch for more papers by this authorArash Valizade Shahmirzadi, Corresponding Author Arash Valizade Shahmirzadi [email protected] Young Researchers Club, Qaemshahr Branch, Islamic Azad University, Qaemshahr, IranSearch for more papers by this author First published: 01 June 2014 https://doi.org/10.1049/iet-map.2013.0311Citations: 71AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Abstract A compact reconfigurable microstrip slot antenna with switchable single and dual band notch functions for ultra-wideband (UWB) applications is presented in this study. In the proposed structure, an additional resonance is excited by etching two symmetrical notches on the feed-line and thereby a UWB characteristic is obtained. Then, by cutting two slots on the radiating patch and embedding two positive-intrinsic-negative (PIN) diodes along these slots, switchable single and dual band notch performances are added to the antenna performance. By changing the bias states of the PIN diodes, the antenna is capable of exhibiting four different performances of UWB spectrum coverage, UWB coverage with single rejection of the wireless local area network (WLAN) band, UWB coverage with single rejection of the WiMAX and C-band spectrum, and UWB coverage with dual band notch function at the WLAN, the WiMAX and the C-band frequencies. Good agreement between the simulated and the measured results is achieved at different performances of the antenna. The designed antenna has a small size of 20 × 20 mm2 and the measured results reveal that the fabricated antenna has good radiation behaviour in the UWB frequency spectrum with switchable band notch functions at 3.15–3.85 and 5.43–6.1 GHz which can eliminate the UWB frequency band interference with the WiMAX, the C-band and the WLAN systems. 1 Introduction The development of wireless communications and the increasing demand for operating frequency bands have made the radio spectrum congested and different radio systems overlap because of their standard frequency band allocations. The wide frequency range of the ultra-wideband (UWB) systems which because of the FCC's allocations is spread between 3.1 and 10.6 GHz will cause interference in the existing wireless communication systems, such as the wireless local area network (WLAN) for IEEE 802.11a operating in the 5.15–5.35 and the 5.725–5.825 GHz bands, WiMAX operating in 3.3–3.6 GHz and C-band operating in 3.7–4.2 GHz, hence, the UWB antenna with single and dual band-stop performances is required [1-3]. Consequently, recently, several planar microstrip monopole and slot antennas with single and multiple band notch performances have been presented [4-9]. However, these antennas have fixed band notch characteristics and in cases where there is no interference, they are unable to utilise the whole UWB frequency band. Hence, in order to improve the performance of the UWB system, antennas with reconfigurable structures which exhibit switchable band notch performances are desirable [10-13]. The main advantage of this kind of antennas is that they are able to utilise the whole UWB spectrum and when an interfering signal appears the antenna can change its configuration in such a way as to produce a band-notch function which eliminates the interference with the coexistent system. Different kind of RF switches such as metal semiconductor field effect transistor (MESFET), RF MEMS and PIN diodes can be used to create the reconfiguration of the antenna structure. Any of these switches has their own advantages and disadvantages [14]. In [15], RF microelectromechanical system (MEMS) are used to form a reconfigurable microstrip monopole antenna with switchable single band notch performance, whereas in [16], a PIN diode is used for the same reason on a microstrip slot antenna. The reconfigurable antennas with switchable band-notched functions can be used in cognitive and intelligent radio systems [3]. In this paper, a novel design of a compact microstrip slot antenna with switchable single and dual band notch performances for UWB applications is presented in which two PIN diodes are used to form a reconfigurable structure. In the proposed design, in order to achieve a full coverage of the UWB spectrum, two symmetrical modified notches are etched on the feed-line which creates an additional resonance and gives a multi-resonance performance to the antenna [6]. Then, by cutting two slots with modified dimensions on the square radiating patch the antenna is able to exhibit a dual band notch function in the frequency bands of interest. The slots on the radiating stub create additional surface current paths and change the current flow direction and as a result the desired attenuations at the notched frequencies can be achieved [15]. Finally, by adding the PIN diodes to the design and embedding them along the slots on the radiating patch leads to a reconfigurable antenna which is able to switch between the UWB, the single band notch and the dual band notch performances which can notch the frequency bands of interference between the UWB systems with the WiMAX, the C-band and also the WLAN systems [16]. Switching the PIN diodes on and off gives different functionalities to the proposed antenna. Good voltage standing wave ratio (VSWR) and radiation characteristics are obtained in the frequency band of interest. Simulated and measured results are presented to validate the usefulness of the proposed antenna structure for UWB applications. 2 Antenna design and configuration The proposed reconfigurable microstrip slot antenna configuration with its design parameters is shown in Fig. 1, which is printed on an FR4 substrate with a thickness of 0.8 mm, a permittivity of 4.4 and a loss tangent of 0.018. As observed in Fig. 1, the basic antenna structure consists of a simple square slotted ground plane, a microstrip feed-line and a square radiating patch. In the design procedure of the UWB microstrip antennas, the basic antenna structure must be designed so as to have a multi-resonance performance in the UWB spectrum and then by modification of the antenna structure such as cutting slots or notches with suitable dimensions on the metallic parts of the antenna additional resonances can be excited in order to improve the bandwidth of the antenna. Also, addend characteristics such as band-notch function can be introduced to the performance of the antenna through etching slots with proper dimensions on the metallic sections of the antenna. In this work, in order to design a basic antenna structure, we started by choosing the aperture length (the length of the slot on the ground plane, y-direction in Fig. 1a). We have a lot of flexibility in choosing this parameter. The length of the aperture mostly affects the antenna bandwidth, as the length of the aperture decreases so does the antenna bandwidth and vice versa. At the next step, we have to determine the aperture width W11. The aperture width is approximately λs/2, where λs is the slot wavelength. λs depends on a number of parameters such as the slot width as well as the thickness and the dielectric constant of the substrate on which the slot is fabricated. The next step in the design of the basic structure is to choose the length and the width of the radiating patch, L1 and W1 in Fig. 1. A good starting point is to choose them to be equal to L1 = W1 = λm/4, where λm is the guided wavelength in the microstrip line. Fig 1Open in figure viewerPowerPoint Geometry of the proposed reconfigurable microstrip slot antenna a Transparent view from top b Top view To design a novel reconfigurable UWB antenna, first of all, two notches with modified dimensions were etched on the feed-line. The notches on the feed-line play an important role in the wideband characteristics of the proposed antenna as it perturbs the current distribution on the feed-line and changes the coupling between the feed-line and the ground plane and as a result an additional resonance is created which can be adjusted towards the desired frequency band by tuning the notches dimensions [9]. At the next step of the design process, two inverted U-shaped slots with folded arms were etched on the square radiating stub, as shown in Fig. 1. These slots create additional current paths which change the direction of the surface current flows along the radiating stub and act as a half wavelength resonator at the notched frequencies which perturb the resonant response [8]. The place of the attenuations can be adjusted by tuning the dimensions of the slots on the radiating stub. At the notched frequencies, the current flows which are more dominant around these slots, change their direction along the edges of the slots and as a result high attenuation at the desired frequency bands occurs [6-9]. Each slot adds a notch band performance to the antenna functionality and consequently a UWB microstrip antenna with dual band notch function is produced. Finally, in order to achieve a switchable band notch function and form a reconfigurable structure, two PIN diodes were embedded in the slots on the radiating stub, as shown in Fig. 1. The role of the PIN diodes is to switch the performance of the antenna between full UWB coverage, single band notch and dual band notch functions. The upper PIN diode (D1 in Fig. 1a) controls the lower band notch (WiMAX and the C-band) whereas the lower PIN diode (D2 in Fig. 1a) controls the upper band notch function (WLAN). When each of the PIN diodes is biased forwardly the rejection effect of the corresponding slot is eliminated and as a result the corresponding band notch function is omitted from the frequency response of the antenna [13, 15, 16]. In the selection of the PIN diode switches, the main factors which should be taken into consideration are forward resistance and reverse bias capacitance. BAR64-3 W PIN diodes which have low capacitance at zero volt reverse bias (typically 0.17 pF at frequencies above 1 GHz) and low forward resistance (typically 2.1 Ω at 10 mA) were used as switches. To avoid DC short circuit in the PIN diodes biasing circuits, four 100 pF DC blocking capacitors were utilised, as shown in Fig. 1a. 3 Results and discussions A prototype of the proposed microstrip reconfigurable slot antenna with its final modified parameters, based on the aforementioned design approach is designed, fabricated and tested and in this section the numerical and the experimental results of its VSWR and the radiation characteristics are presented and discussed. The simulated results are obtained by using Ansoft Simulation Software High Frequency Structure Simulator (HFSS) [17]. Various antenna structures which were compared with the proposed structure in the simulation studies are shown in Fig. 2 and their VSWR characteristics are compared in Figs. 3 and 4. Fig 2Open in figure viewerPowerPoint Various antenna structures which were used in the simulation studies a Ordinary slot antenna b Slot antenna with notches on the feed-line c Proposed antenna when both diodes on d Proposed antenna when both diodes off e Proposed antenna when D1 is on and D2 is off f Proposed antenna when D1 is off and D2 is on Fig 3Open in figure viewerPowerPoint Simulated VSWR characteristics for three of the antennas shown in Fig. 2 Fig 4Open in figure viewerPowerPoint Simulated VSWR characteristics for three of the antennas shown in Fig. 2 The frequency responses of the ordinary square microstrip slot antenna (Fig. 2a), the antenna with the notches on the feed-line (Fig. 2b) and the proposed reconfigurable slot antenna at its UWB performance (Fig. 2c) are compared in Fig. 3. As depicted in this figure, the ordinary square microstrip slot antenna has two resonances within the UWB spectrum and then by cutting the modified notches on the feed-line, the antenna is capable to excite an additional resonance (third resonance) at 9.5 GHz which leads to a full and improved coverage of the UWB bandwidth (2.7–10.7 GHz). Another important result which can be observed in Fig. 3 is that for the proposed structure when both the PIN diodes on the radiating stub are biased forwardly, the antenna keeps its full UWB performance and there is no notched frequency band in the frequency response of the antenna. The frequency responses of the proposed antenna for its dual notch (Fig. 2d), upper single notch (Fig. 2e) and lower single notch (Fig. 2f) performances are compared in Fig. 4. As depicted in this figure, when both the PIN diodes are not biased forwardly the antenna exhibits a UWB with dual notch band performance at 3.2–4.2 and 5.5–6.15 GHz and when each of the PIN diodes is biased forwardly the corresponding notch band function vanishes. To give a more clear and illustrated insight about the phenomenon behind the various switchable functions of the presented reconfigurable antenna the surface current distribution on the feed-line and the radiating stub at particular frequencies is presented in Fig. 5. As observed in this figure, at the third resonance frequency (9.5 GHz), the current flows are more dominant and concentrated near the notches on the feed-line which perturbs the frequency response and as a result an additional resonance is excited. Moreover, as depicted in Figs. 5b and c, at the upper and the lower centre notched frequencies, 3.7 and 5.7 GHz, respectively, the current flows are mainly dominant around the slots on the radiating stub and also change their direction along the interior and the exterior edges of the slots which consequently leads to the desired high attenuation at these frequencies [6, 15, 16]. Fig 5Open in figure viewerPowerPoint Simulated surface current distributions on the radiating stub for a the square slot antenna with the notches on the feed-line at (9.5 GHz) b Proposed antenna at the first notched frequency (3.7 GHz) c Proposed antenna at the second notched frequency (5.7 GHz) To obtain the modified and the final values for the different design parameters of the proposed antenna, a parametric study was performed in which a parameter was changed at a time, whereas the others were kept fixed. The final modified values of the design parameters are listed in Table 1, and also Fig. 6 shows an example of this parametric study. In Fig. 6, the effect of the variation in the dimensions of the slot on the radiating stub which creates the lower notch band function, for the different cases in Table 2, is shown. As can be seen in this figure, by changing the dimensions of the corresponding slot, the attenuation can be properly adjusted towards the preferred frequency band. Table 1. Final dimensions of the designed antenna Param. mm Param. mm Param. mm Wsub 20 W10 1.5 L8 2.95 W1 9 W11 19 L9 2.5 W2 8 Lsub 20 L10 2.3 W3 7.2 L1 7.7 L11 5.3 W4 6 L2 5 L12 5.8 W5 5 L3 4.7 L13 1.5 W6 3.6 L4 4.3 L14 2.5 W7 2.8 L5 2.2 L15 5 W8 1.9 L6 2.9 L16 11.5 W9 0.8 L7 3.3 L17 4 Fig 6Open in figure viewerPowerPoint Effect of variation in the design parameters values for the various cases in Table 2 Table 2. Different cases for the dimensions of the slot on the radiating stub corresponding to the lower band notch performance Case W2, mm W3, mm 1 8 7.2 2 7.1 6 3 8 6.8 4 7.6 6.8 The proposed microstrip antenna with its final design parameters is fabricated and tested. Fig. 7 shows the realised antenna and its measured VSWR characteristics for different on and off statuses of the PIN diodes are presented in Fig. 8. The measured results reveal that the fabricated antenna can satisfy the requirements for UWB performance in the frequency band of 2.5–10.6 GHz with the dual band notch function at 3.1–3.85 and 5.43–6.1 GHz. Also, it is found out that by changing the biasing statuses of the PIN diodes, the fabricated antenna is capable of exhibiting two separate single band notch performances at the frequency bands of 3.3–4.1 and 5.2–5.9 GHz, respectively, as illustrated in Fig. 8. Moreover, there is a discrepancy between the measured results and the simulation data which can be because of a number of reasons such as the accuracy of the substrate on which the antenna is fabricated or the effect of the biasing circuits of the PIN diodes, but totally, they are in good agreement. The measured radiation pattern of the fabricated antenna including the co-polarisation and cross-polarisation in the H-plane (X−Z plane) and E-plane (Y−Z plane), respectively, for its dual band notch performance at three various frequencies is depicted in Fig. 9. As observed in this figure, the antenna has suitable radiation in a wide range of frequencies and also the radiation patterns in the X−Z plane are almost omni-directional. Moreover, a comparison of the measured maximum gain for the dual band notch performance and the UWB full coverage performance of the fabricated antenna is presented in Fig. 10. As observed in this figure, for the dual band-notch performance of the antenna, the gain drops dramatically at the notched frequency bands. Fig 7Open in figure viewerPowerPoint Photograph of the realised reconfigurable microstrip slot antenna Fig 8Open in figure viewerPowerPoint Measured VSWR of the proposed reconfigurable UWB antenna for different biasing statuses of the PIN diodes Fig 9Open in figure viewerPowerPoint Measured radiation patterns for the dual notch band performance of the proposed antenna at a 4.3 GHz b 7.5 GHz and c 9.5 GHz Fig 10Open in figure viewerPowerPoint Measured maximum gain comparisons for the UWB full coverage and the dual band notch performances at the direction perpendicular to the planar structure of the proposed antenna In the design of antennas for the UWB communication systems, an important characteristic which should be considered is the group delay variation with respect to the frequency. Constant and stable group delay is desired and vital; otherwise, temporal smearing of the signal will occur in the system. The measured group delay and the phase delay of the proposed antenna at its dual band notch performance is presented in Figs. 11 and 12, respectively. Except for the notched bands in which the group delay behaviour changes dramatically, a group delay of less than 1 ns is achieved and the phase variation is almost linear. Fig 11Open in figure viewerPowerPoint Measured group delay for the dual notch band performance of the proposed antenna Fig 12Open in figure viewerPowerPoint Measured phase delay for the dual notch band performance of the proposed antenna 4 Conclusion In this paper, a novel compact reconfigurable printed slot antenna with switchable single band notch and dual band notch performances has been proposed for the UWB applications. In the proposed antenna, wider and improved impedance bandwidth especially at the higher frequency band is obtained by cutting two modified notches on the feed-line. Switchable single and dual band notch functions are obtained by cutting the modified slots on the feed-line and embedding two PIN diodes along the slots. By changing the bias statuses of the PIN diodes, the antenna is able to switch between its various frequency responses. The fabricated antenna satisfies the VSWR < 2 requirement for 2.5–10.6 GHz with a band rejection performance in the frequency band of 3.15–3.85 GHz and also 5.43–6.1 GHz and the proposed antenna has a simple configuration and is easy to fabricate. 5 Acknowledgment The authors are thankful to the Microwave Technology (MWT) Company staff for their beneficial and professional help (http://www.microwave-technology.com), and special thanks to Arash Valizade for his endless support and help. 6 References 1Schantz, H.: ' The art and science of ultra wideband antennas' (Artech House, 2005) 2Kumar, G., Ray, K.P.: ' Broadband microstrip antennas' (Artech House, 2003) 3Erfani, E., Nourinia, J., Ghobadi, C., Niroo-Jazi, M., Denidni, T.A.: 'Design and implementation of an integrated UWB/reconfigurable-slot antenna for cognitive radio applications', IEEE Antenna Wirel. Propag. 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