onionstring.com

Q-par Angus Limited

 

 

 

We design antennas and positioners. We have standard products and we also design specials.

PRINTED CIRCUIT BOARD ANTENNAS, including: Spiral antennas, Patch antennas, Sinuous antennas, Dipole antennas

• Cavity Backed Spiral Antennas covering frequency bands from 1 to 40 GHz, these are available in RHCP or LHCP models.
• Patch Antennas, 1 to 18 GHz, in beam forming arrays and providing linear, circular or dual circular polarisation. These antennas can be very rugged due to their low profile. They are inheritantly narrow band devices.
• Cavity Backed Sinuous Antennas, operating from 0.4 to 18 GHz. Giving a very wide bandwidth of up to 9:1. They can be supplied in linear, circular or dual circular polarisation.
• Printed Circuit Dipole Antennas display up to an octave bandwidth. They are an ideal array device, having many applications including feeds for reflectors and beamformed arrays in their own right.

 BESPOKE HORN ANTENNAS

 

As well as the standard horns that we offer, we offer many unusual and unique designs including dielectric filled horns, sectoral horns & conical horns. We also offer horns to your requirements, i.e. frequency range, gain, beamwidth, material, weight can all be tailored to suit.

Dielectric filled horns have the advantage of being smaller, at a given frequency, for a similar performance compared with a horn in free space. This can make them ideally suited for inclusion in arrays where space may be a problem. They can come in a number of forms, in the same manner as standard horns. These include: sectoral horns, conical horns, hog horns and double ridged horns.

MISCELLANEOUS ANTENNAS

 

• Miniature radars for measuring depth of liquids in tanks.

• Antennas for detecting and timing 3-phase switching in electricity sub-stations from the RF emissions during the switching arc.
• Wooden Reflector Antennas (Dual Wooden Reflector prototype shown above).
• Outside Broadcast antennas.
• Dual-frequency, dual-circularly-polarised communications antennas.
• Millimetric passive-imaging antennas.
• Wide-band illuminating and detecting antennas for Electromagnetic Compatibility (EMC) measurements.
• Antennas for Identification Friend or Foe (IFF).
• Jamming antennas.
• Mortar-locating radars.
• Antenna probes for measuring moisture content of commercial substances.
• An electric field generator for inductively coupling to a small ingested capsule, for the internal dispensing of drugs within the body for medical research.

HIGH POWER/ HIRF EMC TEST SYSTEMS

• We have produced a set of antenna and amplifier solutions that provide unrivalled field strengths in EMC tests, exceeding the latest aerospace requirements.
  The horn antennas have been specially developed to focus the RF energy at short distances from the aperture, and thus overcome the near field limitations of traditional designs.
  Various mounting options are available for these antennas, depending on the budget or test requirements, ranging from a fixed mount to fully variable geometry.  The Mounting Systems brochure shows the most sophisticated version.  This is based on a common mobile mounting frame serving the entire antenna range and has variable height, inclination and polarisation controls.  All our mounting options are designed to make adjustments as quick and easy as possible with the minimum of downtime.
  Focussing is achieved either by using dielectric lenses or by dividing the aperture up into four cophased smaller horn antennas.  In the latter case the horns are also squinted in towards the target.  The squint angle is adjustable:  this allows the spot size to be traded off against field intensity to suit test conditions.
  Features

• Nine specialised antennas cover the frequency range 0.4 – 18 GHz.

• Six broadband amplifiers cover the range 1 to 18 GHz, each having output powers in excess of 4 kW.

• In excess of 3 kV / m at one metre is now achievable in free field tests.

• 3 dB spot sizes are 150 mm or greater.

• All exceed Latest Category K specification.

 

SOME DEFINITIONS

Gain – This is a measure of the Directivity or Directionality of the antenna. The higher the gain, the narrower its beam. The vast majority of antennas have gain in the region 0 to 50 dBi (decibels with respect to isotropic). An antenna having a gain of 0 dBi (or unity ratio) radiates equally in all directions and is called Isotropic. An antenna with a gain of 50 dBi (or a ratio of 100,000) has a very narrow beam, of the order of half a degree. The gain (as a ratio) is inversely proportional to the beamwidth.
Beamwidth – This is a measure of the Directivity or Directionality of the antenna and is usually measured at the –3 dB or half-power points. The tenth-power or –10 dBi point is also useful for assessing how well a horn feed illuminates a reflector.
Horn Antenna – A horn is possibly the simplest type of microwave antenna, acting rather like a funnel. However, the larger the horn aperture, the narrower the beamwidth and the higher the gain. The beamwidth is inversely proportional to the gain (as a ratio). The slant length of a horn is longer than the axial length, and this gives rise to an aperture phase error which degrades the beam shape and reduces the gain. It is thus important to minimise the phase error by making the horn as long as practicable. As the aperture gets wider, the length must increase as the square of the increase in aperture width, in order to maintain a given aperture phase error. In most cases, horns cannot have gain much higher than 20 dBi, or the horn becomes impracticably long (except in the case of millimetric horns, which are quite small). A simple horn will generally have –13 dB sidelobes in the E-plane. These can be reduced by adding chokes around the aperture, or creating extra modes in the horn, or by corrugating the walls of the horn.
Reflector Antenna – The reflector antenna takes over where the horn leaves off, at gains of about 20 dBi. A small horn feeds the reflector, and the gain/beamwidth is determined by the width of the reflector aperture. A reflector antenna generally has lower sidelobes than a horn antenna, because the radiation distribution on the reflector is tapered towards the edge of the reflector, rather than being cut off abruptly. A reflector with a long focal length has a relatively flat surface and a narrower subtended angle, requiring a relatively large feed horn and consequently higher aperture blockage. A reflector with a short focal length is relatively steeply curved, and has a larger subtended angle, requiring a relatively small feed horn, but it can be difficult to achieve very wide beamwidths from feed horns.
Space Attenuation – Because reflectors are paraboloidal and not spherical, the radiation from the feed spreads out more towards the edges of the reflector, resulting in lower power density and a more tapered distribution. This edge illumination is a function of the feed beamwidth, and the space attenuation, itself a function of the focal length to diameter ratio (f/D). The greater the taper, the lower the sidelobes and the lower the gain. A flattish reflector (long focal length) has very low space attenuation. Thus for a given reflector edge illumination (e.g. –10 dB gives a good compromise between high gain and low sidelobes), the feed horn’s –10 dB beamwidth has to match the reflector’s subtended angle. Any feed radiation below –10 dB is wasted as spillover. On the other hand, a steeply curved reflector has high space attenuation, e.g. 3 dB. Thus for the same –10 dB reflector edge illumination, the feed horn’s –7 dB beamwidth has to match the reflector’s subtended angle. Thus now any feed radiation below –7 dB is wasted as spillover, and this is less efficient.
Spillover – This appears as sidelobes in the rear hemisphere of the antenna’s radiation pattern, but does not acquire any gain from the reflector, so is relatively low with respect to the antenna beam nose.
Far Field Range – This is the range at which the antenna behaves more or less properly, according to an arbitrary but reasonable level of phase error. The formula for this range is   2D2/ ?, where D is the diameter or maximum width of the antenna aperture, and ? is the wavelength. Most antennas will operate quite well at half this range, and even at a quarter with some loss of performance, but below that serious distortion can occur.
Field Strength – For EMC applications, it is often necessary to produce a given field strength at a given distance (usually one metre). Field strength is a function only of power, gain and range, and is independent of frequency. However, the gain depends on frequency at distances less than the far field range. The formula for this range is 2D2/ ? (see above), of which D / ? is proportional to the gain. Thus for a given gain (necessary to produce a given field from a given power at a given range), the far field range is proportional to D. Thus for that given gain, the lower the frequency, the bigger is D, and the longer is the far field range. So there is a low frequency limit, below which the antenna will not develop the required gain at the required range. The only solution is to increase the power – increasing the gain will make matters worse!