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Radiation efficiency of electrically small antennas largely depends on antenna geometry. However, the actual mechanism that governs the antenna radiation efficiency remains unclear, although various models have been developed since the 1940s. Extant circuit models are either intuition-based or mathematic representations of input impedance/far-field spherical mode functions for structurally simple antennas with limited uses and physical insight. In this article, a recently developed physical micromodeling circuit (MMC) model is utilized to explain the nature of radiation of an electrically small antenna of arbitrary configuration. It is theoretically discovered and experimentally validated for the first time that the radiation efficiency decisively depends on mutual radiated power associated with partial segments of the antenna. A circuital figure of merit for describing the total mutual radiated power is introduced to quantify the measure. The graphical representation of the figure of merit called the holographic radiation diagram is also proposed for illustrating the correspondence of the positive and negative radiated power and the antenna structure. The applications of the proposed theory to antenna design is demonstrated by designing a highly efficient loop antenna. The physical circuit model paves a new way of understanding electromagnetic (EM) radiation problems. [ABSTRACT FROM AUTHOR]

A generalized mesh-network equivalent model for a microstrip rectangular patch antenna (RPA), which is simple yet efficient is proposed, studied, and demonstrated in this article. The mesh-network equivalent model is established through the segmentation of RPA width and radiation parameters into $M$ sections, as well as the segmentation of RPA length into $N$ sections. A general design procedure to realize the mesh-network equivalent model is addressed and described for any number of RPA segmentations, as desired by specific applications. Subsequently, the proposed mesh-network equivalent model is used to accurately evaluate the input impedance responses at various feed positions along the length of RPA. In addition, to include the effects of a slot etched inside the RPA geometry, a generalized microstrip coupled line equivalent model is proposed, analyzed, and discussed in detail. Eventually, the microstrip coupled line model in conjunction with the proposed mesh-network equivalent model can accurately estimate the input impedance response of a slotted RPA, and has been verified for RPA with center slot, edge slot, and multiple slots as examples in this work. Two cases with multiport excitation of RPA are also analyzed and presented as a part of this work. For demonstration purposes, all these prototypes are designed, fabricated, and measured at 28 GHz. The proposed equivalent model-based results are validated by measured and simulated counterparts. Furthermore, the extension of the proposed mesh-network model to accommodate slots of smaller size inside RPA, RPA loaded with via, inverted-F antenna, and multimode operation are demonstrated and discussed through a comparison between mesh-network modeling results and simulation results. [ABSTRACT FROM AUTHOR]

The concept of a self-decoupled antenna array using the cancellation of two opposite couplings is proposed in this article. A pair of such antennas can be closely placed with inherent high isolation without using an extra decoupling structure between the antennas. A pertinent equivalent circuit model is presented to illustrate the physical mechanism of this new concept. It is found that the inductive and capacitive couplings between the antennas can be well canceled out with each other by properly adjusting the antenna dimensions. A demonstrating antenna array with a spacing of $0.024\lambda _{0}$ at the working frequency of 3.5 GHz and its counterpart array are first studied. The measured results show that although the proposed antenna array occupies a slightly larger size than its counterpart array, it presents better performance compared with its counterpart antenna array in port isolation (from 10 to 20 dB), total efficiency (from 68% to 80%), and envelope correlation coefficient (ECC) (from 0.14 to 0.04) throughout the desired frequency band of 3.3–3.8 GHz. A 3-D self-decoupled antenna array is designed to show that the proposed antenna can be in a compact form factor. Another self-decoupled array and its counterpart working at 2.14 GHz (long-term evolution (LTE) band 1) are studied through multi-input multi-output (MIMO) over-the-air (OTA) test when the arrays are integrated with an LTE module, showing significant improvement on the data throughput. [ABSTRACT FROM AUTHOR]

Substrate integrated waveguide (SIW) cavity backed dual-band triangular-ring slot (TRS) antennas are proposed for planar integration. First, a low profile dual band 45^\circ linearly polarized (LP) antenna is designed and analyzed. The dual-mode TRS is proposed and developed by simultaneously exciting the mode of the slot and the mode of the patch inside the slot. To minimize the antenna size, the lowest mode (TE110 mode) of the SIW cavity is adopted to excite the TRS. The -10 dB impedance bandwidth at the higher band is 5.9%, 58.3% wider than that of the conventional SIW cavity backed slot antenna. The interactions of the SIW cavity, the slot mode and the patch mode are analyzed with circuit models and verified by full wave simulations, which provides a new insight into the SIW cavity backed antennas. Then, by exciting a pair of the 45^\circ LP antennas with an SIW coupler, a circularly polarized (CP) dual band antenna with a small frequency ratio of 1.26 is developed. The two antennas are fabricated and tested, and the measured and simulated results agree well. [ABSTRACT FROM PUBLISHER]

This paper presents and demonstrates a class of 3-D integration platforms of substrate-integrated waveguide (SIW). The proposed right angle E-plane corner based on SIW technology enables the implementation of various 3-D architectures of planar circuits with the printed circuit board and other similar processes. This design scheme brings up attractive advantages in terms of cost, flexibility, and integration. Two circuit prototypes with both 0- and 45^\circ vertical rotated arms are demonstrated. The straight version of the prototypes shows 0.5 dB of insertion loss from 30 to 40 GHz, while the rotated version gives 0.7 dB over the same frequency range. With this H-to-E-plane interconnect, a T-junction is studied and designed. Simulated results show 20-dB return loss over 19.25% of bandwidth. Measured results suggest an excellent performance within the experimental frequency range of 32–37.4 GHz, with 10-dB return loss and less than \pm4^\circ phase imbalance. An optimized wideband magic-T structure is demonstrated and fabricated. Both simulated and measured results show a very promising performance with very good isolation and power equality. With two 45^\circ vertical rotated arm bends, two antennas are used to build up a dual polarization system. An isolation of 20 dB is shown over 32–40 GHz and the radiation patterns of the antenna are also given. [ABSTRACT FROM PUBLISHER]