Compact filtering antenna using CRLH resonator and defected ground structure

Abstract

A compact filtering antenna with high band-edge gain selectivity using a composite right-/left-handed (CRLH) resonator and a defected ground structure is presented. The CRLH resonator resonates at the zeroth-order mode and acts as the first stage of the corresponding filter; an octagonal patch acts as a radiator as well as the last stage of the filter. The design procedure follows the circuit approach -synthesis of bandpass filters. The filtering antenna has two poles in the passband and two radiation nulls (zeros) at the band edges. Compared to the conventional patch antenna, the proposed filtering antenna, with little extra circuit area, has flat gain response within the passband, good selectivity at the passband edge and wider bandwidth. Measurement results show that the filtering antenna can operate at 5.29 GHz, has a 430 MHz bandwidth and a 2.5 dBi antenna gain in the broadside (+Z ) direction within the passband.Introduction: In modern wireless communication technology, one of the issues is integrating multiple functional circuitries into one device to achieve miniaturisation and improved performance. The filtering antenna is a new concept that could realise both filtering and radiation functions, which avoids designing the antenna and the bandpass filter separately, and achieves the more compact devices and improves the performance of microwave front ends. Different from direct connection of the filter and the antenna by an extra impedance transformation structure, several studies on filtering antenna design which follow the filter synthesis that the antenna acts as one of the resonators have been presented in [1][2][3][4][5], such as a fan-shaped patch antenna with a circular openloop resonator [1], a U-shaped patch antenna with a T-shaped resonator [2], an Γ-shaped antenna with a coupled line resonator [3], an Γ-shaped antenna with two square open-loop resonators [4] and an inverted-L antenna with parallel coupled microstrip line sections [5].In this Letter, using a miniaturised composite right/left-handed (CRLH) resonator and an octagonal patch antenna with a defected ground structure (DGS), a new compact two-pole filtering antenna is proposed (Fig. 1). The CRLH resonator consists of an inter-digital capacitor and four metallic vias, resonating at zeroth-order mode, so that the size of the structure could be more flexible and compact than the conventional half-wavelength resonator. The octagonal patch antenna with the DGS acts as a radiator as well as the second resonator. The filtering antenna has a flat gain response within the passband and good selectivity at the passband edge. The measured results are in good agreement with the simulated ones.

Experimentally Validated, Planar, Wideband, Electrically Small, Monopole Filtennas Based on Capacitively Loaded Loop Resonators

“…Efforts to miniaturize and compactify filtennas have employed composite right/left handed transmission lines (CRLH-TLs) [14], [15] and multiple electrically small resonators in series [16], [17]. Unfortunately, the relatively large radiation patch / long meander-line strip above the ground required in those CRLH-TL-based filtenna designs prohibits any further miniaturization [14], [15].…”

“…Unfortunately, the relatively large radiation patch / long meander-line strip above the ground required in those CRLH-TL-based filtenna designs prohibits any further miniaturization [14], [15]. Similarly, multi-resonator filtenna makes use of multi-pole filter design principles, exploiting the presence of more transmission poles to achieve broader operational bandwidths.…”

Compact Filtering Antenna Based on Dumbbell-Shaped Resonator

“…The function of the antenna is receiving and transmitting signal, and the bandpass filter is used to filter spurious signals. In general, these two components are designed separately [1][2][3], but many scholars start to study the co-design method and other methods to realize filtering antennas [4][5][6][7][8][9][10][11][12][13][14][15]. Filtering antennas not only improve the performance of communications systems, but also minimize the total size.…”

“…Transmission zero is induced by the coupled line resonator, but the antenna size is 73 mm ×50 mm. In [5], based on a composite right-/left-handed (CRLH) resonator and a defected ground structure, a compact filtering antenna with two poles in the passband and two radiation zeros at the band edges is presented. An octagonal patch acts as a radiator as well as the last stage of the filter.…”

Integrated Filtering Antenna Based on D-CRLH Transmission Lines for Ultra-Compact Wireless Applications

“…Based on CRLH TL, many ultra-compact multi-band antennas [10][11][12][13][14][15][16] and bandstop filters [17,18] have been reported. Also, some different design integrated filtering antennas have been presented in [19][20][21][22]. However, realizing CRLH TL requires shunt connection for inductive load which becomes not simple in practical configurations.…”