A compact navigation receiver comprising a decoupled and matched four-element L1-band antenna array with an inter-element separation of a quarter of the free-space wavelength is presented in this paper. We investigate the impact of the decoupling and matching network on the robustness of the navigation receiver. It is observed that in order to achieve high robustness with a compact antenna array, it is necessary to employ a decoupling and matching network, particularly in case of three spatially separated interferers. Furthermore, we study the influence of the polarization impurity of the compact planar antenna array on the equivalent carrier-to-interference-plus-noise ratio (CINR) of the receiver when impinged with different numbers of diametrically polarized interference signals. It is shown that the higher-order modes possess strong polarization impurity, which may halve the available degrees-of-freedom for nulling in the presence of linear-polarized interferers, using a conventional null-steering algorithm. We verify the robustness of the designed compact receiver by means of a complete global-navigation-satellite-system demonstrator. It is shown that the maximum jammer power that is allowed us to maintain the CINR above 38 dBHz with three interferers can be improved by more than 10 dB if a decoupling and matching network is employed.

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At L-band (1-2GHz) due to significantly large freespace wavelengths, compact antenna arrays with small interelement separation i.e., d < λ/2, are a suitable choice for overall size reduction. However, mutual coupling becoming prominent in compact arrays results in a degradation of the diversity degreesof-freedom, which are required for beamforming capabilities in modern receivers. In this paper we discuss a potential approach to mitigate this limitation. We present empirical results for an eigenmode analysis applied to the radiation matrices of compact planar arrays, derived from the far-field integration of complex realised-gain matrices. Furthermore, optimal arrangements for compact planar arrays with respect to the highest possible value of minimum eigenmode efficiency are discussed. It could be shown that planar arrays have higher efficiencies and lower radiation correlation, hence better diversity degrees-of-freedom than linear arrays, particularly in a compact configuration.

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