Abstract-In this paper, a new antenna is designed in order to use in the wireless capsule endoscopy (WCE) system. This antenna consists of two parts; the small monopole part and the small spiral. Having the omnidirectional radiation pattern for covering the stochastic motions of the capsule into gastrointestinal and also, appropriate gain and wide bandwidth to achieve high resolution images must be considered in designing procedure. In this design, a good radiation pattern is obtained from small monopole, and using the spiral structure leads to an appropriate wide bandwidth and a miniaturized antenna. By simulating this antenna in the human body environment and considering four different body tissues and their results, the antenna has the bandwidth of 360 MHz (39.3% relative bandwidth) at 928 MHz center frequency which covers the ISM band (868.0-868.6 MHz and 902.8 to 928.0 MHz). The radiation pattern of the antenna is omnidirectional. The maximum gain of the designed antenna is −23 dB, over the frequency band that is suitable for using as a transmitter antenna in the WCEs.

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In this paper, a Decoupling Nearfield Surface (DNS) is designed above the antenna, to reduce the mutual coupling of closely two or more patch array. In this way, the electrical and magnetic distributions are utilized to demonstrate the mechanism of isolation. The proposed DNS element creates the electric field distributions with an orthogonal mode and the magnetic field distributions with excitation in substrate such that the effective suppression of antenna mutual coupling is obtained. The DNS element can be easily applied to the Multiple-Input Multiple-Output (MIMO) antennas that having multiple patch elements. Moreover, the proposed structure is implemented practically and simulated for a patched antenna. The measurement and simulation results verifies that the isolation is more than 20 dB and the isolated impedance bandwidth is about 7%.