Abstract
A co-design consisting of a filtering antenna integrating a cavity-backed patch antenna and a low-pass coaxial filter is proposed for size reduction of the RF front-end. The cavity-backed patch antenna is developed to exhibit a broad impedance bandwidth and a unidirectional radiation pattern. The low-pass coaxial filter is implemented to suppress harmonic resonances and gain in the stop-band of the antenna and is embedded directly inside the antenna cavity to realize a compact small-footprint co-designed filtering antenna structure. Two prototypes of the proposed filtering antennas, which integrate cavity-backed patch antennas with $4^{\textit {th}}$ and $5^{\textit {th}}$ order low-pass coaxial filters and with the overall dimensions of $0.697\lambda _{0} \times 0.585\lambda _{0} \times 0.236\lambda _{0}$ and $0.697\lambda _{0} \times 0.585\lambda _{0} \times 0.320\lambda _{0}$ (where $\lambda _{0}$ is the free space wavelength at 3.15 GHz), respectively, are fabricated and measured. The experimental results show fractional bandwidths of 25% and 23.8% and gain suppression levels exceeding 11 dB and 22 dB in the stop-bands for the filtering antennas with the $4^{\textit {th}}$ and $5^{\textit {th}}$ order filters, respectively. The measured gain is more than 6.5 dBi in the pass-band for both filtering antennas. In addition, excellent agreement is obtained between the simulated and measured results.
Highlights
I N recent years, there has been an increasing level of demand for multifunction, multipurpose RF front-end components with miniaturization designs for use in wireless communication systems [1]–[6]
There have been numerous studies that aimed to miniaturize the overall size of RF front ends by integrating an antenna and a filter into a single module, referred to as a co-designed filtering antenna [7]–[12]
In some of the reported designs, the antenna acted as a dispersive complex load for the filter, including coupled planar resonator filters connected to microstrip patch antennas [7] and a coupled substrate-integrated waveguide (SIW) resonator filter connected to a planar coaxial collinear antenna [10]
Summary
I N recent years, there has been an increasing level of demand for multifunction, multipurpose RF front-end components with miniaturization designs for use in wireless communication systems [1]–[6]. In recent work [17], a broadband duplex-filtenna using a 3-D metallic cavity structure was presented In this design, the antenna and filter are cascaded through a small section of a 50-Ω coaxial cable, resulting in a large footprint. The antenna and filter are cascaded through a small section of a 50-Ω coaxial cable, resulting in a large footprint In this communication, we present a compact smallfootprint cavity-backed filtering antenna. The 4th and 5th order low-pass coaxial filters are designed and integrated with wideband cavity-backed patch antennas effectively to suppress the harmonic resonances and gains in the stop-bands of the antennas. Because harmonic resonance transmits and receives signals in the unwanted frequency range, it is necessary to suppress the harmonic resonances with a low-pass filter
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