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A compact dual-band, differentially fed filtenna with wide bandwidth, high selectivity, and low cross-polarization is presented. It is composed of a slot-loaded rectangular patch, two pairs of shorting pins, a pair of novel differential coupling feedlines, and a defected ground structure (DGS). Good broadside radiation patterns with an adjustable frequency ratio (FR) between its two bands are realized. A pair of U-shaped slots is loaded on the patch to enhance the bandwidth of the lower passband. The DGS and its compact differential feedlines produce five out-of-band radiation nulls to improve the frequency selectivity of the two passbands. Simultaneously, extra in-band resonances are introduced that broaden the impedance bandwidth while maintaining a compact $0.155\lambda _{0}^{2}$ aperture size and a relatively low profile ($0.065\lambda _{0}$ height). Prototypes were fabricated, assembled, and tested. The measured results, in agreement with their simulated values, demonstrate that it exhibits −10 dB fractional impedance bandwidths of 17.5% and 8.2%, peak realized gain values of 8.4 and 9.5 dBi, and cross-polarization levels smaller than −44 and −40 dB, in its lower and upper passbands, respectively. Its dual-band quasi-elliptic responses have sharp roll-off rates and high stopband suppression levels. [ABSTRACT FROM AUTHOR]

Vertically polarized, omnidirectional- and endfire-radiating, bandwidth-enhanced, high efficiency, electrically small monopole filtennas are developed. Both designs are attained by organically combining a coax-fed top-hat loaded monopole with two hybrid quarter-wavelength open-end stubs and a shorting post. The hybrid stubs serve two functions. They produce two radiation nulls at both the lower and upper band edges to sharpen the roll-off rate. Moreover, they facilitate the appearance of an additional resonance without affecting the original resonant mode. The shorting post is introduced to engineer the overlap of two resonant modes to yield an enhanced bandwidth. Prototypes of both filtennas were fabricated, assembled, and tested. The measured results are in good agreement with their simulated values, validating their efficacy. The omnidirectional filtenna has an electrically small size (ka = 0.73), a fractional bandwidth (FBW) of 11.3%, and a maximum realized gain of 3.01 dBi. The endfire-radiating filtenna has an electrically small size (ka = 0.93), an operating FBW of 12.8%, and a peak realized gain of 6.09 dBi. Both filtennas exhibit a flat realized gain response and high radiation efficiencies over their entire passbands, as well as very good selectivity with high out-of-band suppression levels. [ABSTRACT FROM AUTHOR]

A compact, differential diplex filtenna (DDF) with common-mode (CM) suppression is presented. A rectangular dual-mode patch is developed that operates in both its TM10 mode and a reshaped TM30 mode to realize two passbands. Two capacitively loaded loop (CLL) resonators that work at different frequencies are combined with the dual-mode patch to enhance its operational bandwidth and to provide a second-order Chebyshev filter response for both passbands. A slot-coupled differential feed is adopted to suppress the harmonic and CM noise and to obtain symmetrical radiation patterns with low cross-polarization levels. The design process, which is based on filter synthesis theory, is detailed. A prototype operating over the 2.4G and 5.8G WLAN bands was fabricated, assembled, and tested. The measured results, in good agreement with their simulated values, confirm that it attains maximum broadside realized gains of 5.45 and 8.5 dBi and −10 dB fractional impedance bandwidths of 2.4% (2.42–2.48 GHz) and 5.2% (5.65–5.95 GHz) for the lower and upper passbands, respectively. Moreover, it exhibits good out-of-band rejection levels of 18 and 29 dB for the lower and upper stopbands, respectively. [ABSTRACT FROM AUTHOR]

In this communication, a compact vertically integrated full-duplex filtenna is developed by using common feeding and radiating substrate integrated waveguide (SIW) cavities. A rectangular dual-mode SIW cavity, operating at its two orthogonal TE120 and TE210 modes, is first employed as the common feeding cavity to realize two passbands. And then, a common radiating square slot-loaded SIW cavity is vertically integrated with the common feeding cavity so as to enhance the operational bandwidth and improve the frequency selectivity for both two passbands. Two metallic posts are utilized to achieve the desired coupling strength between the feeding and radiating cavities for the two passbands, respectively. By properly arranging the locations of two input ports and coupling regions, high isolation between the two input ports is realized. The detailed design process based on the coupling matrix is presented. To verify the proposed concept, a prototype is fabricated and measured. The measurement results agree well with the simulated values, showing the maximum broadside realized gains of 4.36 and 4.83 dBi, and the impedance bandwidths of 3.2% (4.03–4.16 GHz) and 3.9% (4.81–5 GHz) for the lower and upper passbands, respectively. The proposed antenna also exhibits good performance in terms of port isolation, flat in-band gain response, and out-of-band frequency selectivity. [ABSTRACT FROM AUTHOR]

Compact, low-profile, linearly polarized (LP), and circularly polarized (CP) patch-based filtennas are realized with a custom-designed coupling probe. It introduces a deep null at both the lower and upper band edges of the filter response. These two nulls facilitate a quasi-elliptic bandpass behavior and can be independently controlled to achieve sharp band-edge skirts and high out-of-band suppression levels. The CP version evolves from the LP design by introducing a T-shaped near-field resonant parasitic (NFRP) element near the probe to create two transmission paths with an inherent 90° phase difference. Its presence facilitates the simultaneous excitation of the TM10 and TM01 modes of the patch without the need for any power divider or phase delay line, reducing the design complexity and lowering the insertion loss. Prototypes were fabricated, assembled, and tested. The measured results agree well with their simulated values. They are low profile (0.03 $\lambda _{0}$ height) and compact in size ($0.04~\lambda _{0}^{2}$ footprint). The LP and CP prototypes exhibit, respectively, a −10-dB fractional impedance bandwidth of 7% and an overlapping axial ratio fractional bandwidth of 4.5%. Excellent measured performance characteristics are demonstrated, including flat passband realized gain values and filter responses with sharp roll-off rates and high out-of-band suppression levels. [ABSTRACT FROM AUTHOR]

A compact, single-layered substrate-integrated waveguide (SIW) filtenna with parasitic patch is synthesized and designed. A half-mode substrate-integrated rectangular cavity (HMSIRC) is adopted as the first stage resonator to reduce the circuit size. A parasitic patch functioning as the last stage resonator as well as the radiator is arranged closely to the HMSIRC so as to enhance the operational bandwidth and facilitate the filtering performance. Two broadside radiation nulls are realized at both the upper and lower band-edges to sharpen the band-edge roll-off rate: one is generated by the interaction between the HMSIRC and the parasitic patch, and the other is introduced by placing two pairs of shorting posts under the parasitic patch. The standard filter synthesis technology is utilized to guide the filtenna design. The optimized prototype was fabricated and measured. The measured results, in good agreement with simulated values, indicated the proposed filtenna provides a 5.1% fractional bandwidth, a maximum realized gain of 6.3 dBi, and a flat passband gain response along with excellent out-of-band selectivity, even with ultralow profile $0.015~\lambda _{0}$ and small volume $0.005~\lambda _{0}^{3}$. [ABSTRACT FROM AUTHOR]