A microstrip line fed rectangular patch antenna with slots in the patch radiator is designed to realise triple resonant frequencies with satisfactory impedance matching (| S ₁₁ |≤−10 dB) at 3.36, 5.96, and 9.09 GHz. Current distribution analysis is presented to provide an insight to the mechanism of triple resonance generation. A triple‐band artificial magnetic conductor (AMC) is designed and analysed based on resonance phenomenon of stepped impedance resonators. The resonant frequencies of the AMC coincide with the antenna. A rectangular split‐ring slot is embedded in the metallic ground of the antenna. The designed AMC is placed beneath the antenna maintaining an air gap between the structures. The slot in the ground plane enables the surface waves to interact with the AMC. The proposed arrangement enhances the gain from 1.38 to 3.77 dBi at 3.36 GHz, 3.22 to 6.29 dBi at 5.96 GHz, and 7.58 to 11.16 dBi at 9.09 GHz. The proposed structure exhibits good radiation patterns with low cross‐polarisation and high front to back ratio at all the three resonant frequencies. A prototype of the proposed structure is fabricated and the measured results are in good agreement with the simulated results.

In this paper, a novel microstrip line-fed meander-line-based four-elements quad band Multiple Input and Multiple Output (MIMO) antenna is proposed with a gain enhancement technique. The proposed structure resonates at four bands simultaneously, that is, 1.23, 2.45, 3.5 and 4.9 GHz, which resemble GPS L2, Wi-Fi, Wi-MAX and WLAN wireless application bands, respectively. The unit element is extended to four elements MIMO antenna structure exhibiting isolation of more than 22 dB between the adjacent elements without disturbing the resonant frequencies. In order to enhance the gain, two orthogonal microstrip lines are incorporated between the antenna elements which result in significant gain improvement over all the four resonances. Furthermore, the diversity performance of the MIMO structure is analyzed. The Envelope Co-Relation Coefficient (ECC), Diversity Gain (DG), Channel Capacity Loss (CCL), Mean Effective Gain (MEG) and Multiplexing Efficiency are obtained as 0.003, 10 dB, 0.0025 bps/Hz, −3 dB (almost) and 0.64 (min.), respectively, which are competent and compatible with practical wireless applications. The Total Active Reflection Coefficient (TARC) resembles the characteristic of the individual antenna elements. The layout area of the overall MIMO antenna is 0.33 λ × 0.29 λ, where λ is the free-space wavelength corresponding to the lowest resonance. The advantage of the proposed structure has been assessed by comparing it with previously reported MIMO structures based on number of antenna elements, isolation, gain, CCL and compactness. A prototype of the proposed MIMO structure is fabricated, and the measured results are found to be aligned with the simulated results.

Device-to-device communication in the Internet of Things (IoT) enables seamless data exchange, aiding automation, monitoring, and control. Yet, sustainability challenges arise due to energy-limited devices. This paper presents a novel method for Indoor IoT sensors to function without batteries. A broadband rectenna on low-cost FR4 substrate is proposed, mitigating battery constraints. It integrates a circularly polarized (CP) antenna with an Artificial Magnetic Conductor (AMC) and a RF-to-DC rectifier. A coplanar waveguide fed CP (CPW-CP) antenna achieves a broad axial ratio bandwidth (ARBW) of 19.6% (AR <3 dB) spanning from 2.3 GHz to 2.8 GHz, boosting gain from 0.5-0.8 dBic to 5-6.5 dBic within the ARBW, courtesy of the AMC integration. A stable RF-DC rectifier, using a modified wideband resistance compression network (WRCN), attains a power conversion efficiency (PCE) exceeding 30% for input powers ranging from -10 dBm to 12 dBm, peaking at 65% for 7 dBm input power for a 2 k $\Omega $ load. PCE variation within ARBW is only 5-8%. The RF-DC rectifier is integrated with the enhanced gain CPW-CP antenna to form a rectenna which is fabricated and measured. The experimental results comply with the simulated results, and the experimental validation demonstrates the rectenna’s effectiveness in charging a 0.1 pF capacitor within 2 ms in an indoor environment equipped with a Wi-Fi router. This innovative design marks a promising step towards addressing energy constraints in IoT devices, facilitating their long-term operation and deployment in diverse settings.

In this letter, a wide band Circularly polarized four element multiple input multiple output (MIMO) antenna is reported. The impedance and the axial ratio bandwidth (ARBW) of wide-band CP MIMO antenna are 82% and 81.5% respectively. The axial ratio bandwidth of single element is controlled by modifying the ground plane. The design steps are illustrated with characteristics mode analysis. The four elements are arranged orthogonal in MIMO configuration and also the plus shaped decoupling structure (PSDS) is placed to reduce inter element coupling. The measured results are presented and compared with simulated results which shows both are in good agreement. According to measured S-Parameter and axial ratio, the operating frequency of fabricated quad port MIMO antenna is 3.4GHz to 8.25GHz. The MIMO diversity performances are investigated using measured S-Parameter. The diversity gain (DG), channel capacity loss (CCL), envelope correction coefficient (ECC) and total active reflection coefficients (TARC) are reported to provide MIMO performance. The linear phase characteristics are confirmed with the group delay performances of fabricated antenna.It is found that the almost constant group delay within 2.3ns variation. The high overlapping factor (OF) of 0.99, wider ARBW of 81.5% without using additional feeding network makes the wide band CP MIMO antenna compact in size.