An effective method to reduce the radar cross‐section (RCS) of an ultra‐wideband multiple‐input multiple‐output (MIMO) antenna is proposed. In order to reduce the RCS of the antenna, the antenna patch is divided into two parts, each of which contains a half of the antenna patch. That half which is not connected to the feed line is omitted with its substrate. A perfect electric conductor wall is used in front of the minimized structure to compensate for the effect of the omitted part. An equivalent circuit model for the MIMO antenna is proposed. The equivalent circuit model is simulated and optimized using advanced design system (ADS). The ADS results of the equivalent circuit model exhibit a reasonable agreement with the full wave results of the antenna. According to the results, the antenna shows a noticeable RCS reduction, a low mutual coupling of < −17.5 dB and a proper impedance bandwidth of 8.8 GHz in the range of 3 to 11.8 GHz. The diversity performance of the proposed antenna for example, diversity gain, envelope correlation coefficient (ECC), and the total active reflection coefficient is analyzed as well and an ECC of <0.11 is achieved.

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A novel dual‐band waveguide slot array antenna with low cross‐polarisation is proposed. The main structure of the proposed antenna consists of two waveguides in which the top broad wall of the smaller waveguide, a WR‐28 Ka‐band waveguide, is connected to the top broad wall of the larger waveguide, a WR‐90 X‐band waveguide. The WR‐28 waveguide operating in the higher frequency band of the proposed antenna acts as a ridge inside the WR‐90 waveguide operating in the lower frequency band. For achieving a suitable side lobe level (SLL) and cross‐polarisation in the lower frequency band, the slots are placed close to the higher frequency waveguide and side ridges are placed beside each slot. A 2D graph is presented in which the normalised resonance conductance versus the offset of a side ridge from the outer edge of the lower frequency waveguide is shown, while the slot is located between the higher frequency waveguide and the side ridge. By applying proper coefficients to this graph, appropriate offsets from the outer edge of the lower frequency waveguide for the side ridges are obtained so that a low SLL can be realised.

This paper presents a design method for a multi-octave, high-efficiency power amplifier (PA) with a novel low-pass filtering matching network. Both extended continuous Class-F and continuous Class-F À1 are engaged to expand the design space for the ultra-broad operating band. A wideband vertex coupled radial stubs (VCRS) low-pass filter alongside a transmission line network (TLN) is proposed as an output impedance matching network of the PA. The wide rejection band and sharp transition band of this filter make it suitable for harmonic tuning PAs. To verify the feasibility of the proposed structure, the PA is fabricated and its performance is measured. The fractional bandwidth of 155% across 150 to 1200 MHz with a drain efficiency of 61%-73% and output power of 38.9-39.5 dBm is achieved.