Regular paperWideband SIW Self-Diplexing antenna with simultaneous control of bandwidth and band position
Introduction
In modern wireless systems, dual-band antennas are becoming increasingly popular for its ability to operate at two frequencies [1], [2], [3]. However, since a dual-band antenna is usually a one-port device, one must use a diplexing filter to separate the two frequency components. Thus, overall size of the system increases [4], [5]. A self-diplexing antenna directly separates two signals into two different ports. Thus, it does not require any external filter.
A traditional antenna can be modified to obtain self-diplexing characteristics. For example, self-diplexing antennas are designed using unequal radiating patches at different layers [6], [7], planar-inverted F-antenna using a shorting pin in between two ports [8], rectangular aperture antenna with two asymmetrical T-stubs [9] and patch antenna with two different U-shape slots [10]. However, the antennas in [6], [7], [8], [9], [10] show poor radiation performances in terms of both broadside gain and front-to-back ratio (FTBR).
Recently, self-diplexing antennas are proposed in substrate integrated waveguide (SIW) to obtain higher gain and FTBR. In SIW technology, self-diplexing antennas are usually designed by using different shapes of slot [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. However, a common problem with all of these SIW self-diplexing antennas is their narrow impedance bandwidth, typical 10 dB bandwidth being always<6%.
This paper presents an SIW based self-diplexing slot antenna with greatly improved effective bandwidth. Bandwidth is improved by using linear superposition of two radiating modes of a single stepped impedance slot. The resonant frequencies and hence the bandwidth of each band is controlled by the stepped impedance parameters. Further, a stepped SIW cavity resonator and a third slot is used to improve both impedance matching and isolation between the ports. The antenna offers a measured gain of at least 7 dBi over its entire range of operation. The bandwidth has been improved to 286%-1400% compared to SIW self-diplexing antennas in [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. Moreover, this antenna has facility to control of bandwidth and band position simultaneously. The present antenna can be directly integrated with microwave circuits because it does not use any ground plane perturbation.
Section snippets
Antenna configuration
Fig. 1 shows the layout of the wideband self-diplexing antenna. Top and bottom stepped impedance slots near the ports are used for radiation. The middle slot helps to obtain wideband impedance matching. A 0.787 mm thick Roger RT/Duroid 5880 substrate with ɛr = 2.2 and tan δ = 0.0009 is used for implementation. Analysis of the proposed antenna is carried out by Ansoft’s HFSS. Final antenna dimensions are shown in the figure caption.
Antenna Design and Analysis
Fig. 2 shows the electric field distributions inside the SIW cavity for both port 1 and 2 excitations. The TE110 and TE130 resonant modes appear inside the cavity at 9.55 and 10.3 GHz, respectively, when excited from port 1. The slot field distributions follow the cavity mode. Each radiating slot almost stops any electromagnetic leakage to other side when its length is comparable to cavity length. A perfectly magnetic plane can placed along the mid-line of the slot [22]. Thus, the part of the
Experimental results and discussions
Above wideband self-diplexing antenna shown in Fig. 1 is fabricated in the 0.787 mm thick single layer Roger RT/duriod 5880 substrate. A photograph of the fabricated antenna is shown in Fig. 6. Scattering (|S|)-parameters are measured with help of two port vector network analyser Keysight N5221A. The simulated and measured |S|-parameters are shown in Fig. 7.
Measured |S11| is below −10 dB over 9.25–10.5 GHz and it is over 10.6–12.6 GHz for |S22|. The proposed configuration allows close spacing
Conclusion
A wideband self-diplexing SIW slot antenna is presented here. Other than wide impedance bandwidth, the antenna provides high gain, high FTBR, high cross polarization suppression and small gain variation. Moreover, the bands can be tuned independently. Wideband characteristics is obtained by combining radiation from the TE110 and TE130 modes in a half-mode cavity. A prototype antenna is fabricated. Design steps are provided for other specifications. The self-diplexing antenna can be used in any
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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