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A four‐port MIMO antenna design focused on the sub‐6 GHz fifth generation wireless communication application is presented. The design does not need any other decoupling structure for achieving isolation between multiple ports. A combination of four single wideband antenna units results in the formation of a circular‐shaped metallic disc in the ground plane of the proposed antenna. This disc acts as a pool of current with 180° phase difference leading to isolation between various ports. Diversity performance of the antenna is shown with the help of an envelope correlation coefficient using both S‐parameter and far‐field data. The radiation pattern of the proposed antenna has four lobes in four quadrants for proper reception of signals from different directions. A prototype of the designed antenna is fabricated and measured successfully.

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In this work, two configurations (Config.-A and Config.-B) of planar four-port dual circularlypolarized (CP) multiple-input-multiple-output (MIMO) antenna are proposed for sub-6 GHz (3.4-3.8 GHz) applications. The MIMO antennas are designed on the FR-4 substrate with size of 60×60×1.6 mm 3. Each radiating element (unit cell) of the MIMO antenna is comprised of a microstrip feed line and an open slot ground plane integrated with two rectangular arms for realizing circular polarization. An I-shaped metallic strip is used in the proposed four-port MIMO Config.-A and Config.-B antennas for obtaining common voltage level in the ground plane. Both MIMO antenna configurations exhibit good impedance matching in the band of interest. In the MIMO Config.-A antenna, all ports provide the same CP band, while in the Config.-B antenna the ports-1/-2 and-3/-4 radiate at different CP bands. The proposed MIMO Config.-A and Config.-B antennas support both types of polarization (left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP)). With the Config.-B antenna, the maximum 3-dB axial-ratio (AR) beamwidths of 118.9 • and 92.7 • are obtained at 3.536 GHz in the xz-and yz-planes, respectively. Furthermore, the Ishaped strip helps in improving 3-dB AR beamwidth in the MIMO Config.-B antenna. Inter-element isolation greater than 19 dB and envelope correlation coefficient (ECC) less than 0.12 (far-field) are achieved between the ports of the fabricated MIMO antenna prototype. INDEX TERMS Connected ground, dual circular polarization, four-port, MIMO antenna, planar.

A trajectory correction flight control system is small and durable, and consists of a lateral pulsejet ring mounted on the rocket body. The pulsejet ring consists of a finite number of individual pulsejets. Each pulsejet on the ring imparts a single, short-duration, large force to the rocket in the plane normal to the rocket axis of symmetry. Lateral pulsejets are used by flight control system to assist the rocket to follow a pre-specified (command) trajectory. The trajectory-tracking flight control system computes the position error by comparing the measured position of the rocket with the pre-specified trajectory. In actual application, the position of the rocket could be measured using in-house inertial measurement unit (IMU) or by ground-based-tracking radar system located at the firing site. A study has been undertaken to explore the feasibility of reducing the impact point dispersion of a routinely-used artillery rocket using lateral pulsejets coupled to a trajectory correction flight control system. Simulation studies have been conducted to arrive at tuning parameters, namely the tracking error window size, the required elapsed time between the pulsejet firings and the angle of tolerance between the tracking error and the individual pulsejet force. Further, the robustness of the methodology wrt measurement noise has also been evaluated.